title: Interpret brainfuck

text:
# Question
Title: Interpret brainfuck
Write the shortest program in your favourite language to interpret a brainfuck program. The program is read from a file. Input and output are standard input and standard output.

1. Cell size: 8bit unsigned. Overflow is undefined.
2. Array size: 30000 bytes (not circled)
3. Bad commands are not part of the input
4. Comments begin with # and extend to the end of line Comments are everything not in `+-.,[]<>`
5. no EOF symbol

A very good test can be found here. It reads a number and then prints the prime numbers up to that number. To prevent link rot, here is a copy of the code:

```
compute prime numbers
to use type the max number then push Alt 1 0
===================================================================
======================== OUTPUT STRING ============================
===================================================================
>++++++++[<++++++++>-]<++++++++++++++++.[-]
>++++++++++[<++++++++++>-]<++++++++++++++.[-]
>++++++++++[<++++++++++>-]<+++++.[-]
>++++++++++[<++++++++++>-]<+++++++++.[-]
>++++++++++[<++++++++++>-]<+.[-]
>++++++++++[<++++++++++>-]<+++++++++++++++.[-]
>+++++[<+++++>-]<+++++++.[-]
>++++++++++[<++++++++++>-]<+++++++++++++++++.[-]
>++++++++++[<++++++++++>-]<++++++++++++.[-]
>+++++[<+++++>-]<+++++++.[-]
>++++++++++[<++++++++++>-]<++++++++++++++++.[-]
>++++++++++[<++++++++++>-]<+++++++++++.[-]
>+++++++[<+++++++>-]<+++++++++.[-]
>+++++[<+++++>-]<+++++++.[-]

===================================================================
======================== INPUT NUMBER  ============================
===================================================================
+                          cont=1
[
 -                         cont=0
 >,
 ======SUB10======
 ----------

 [                         not 10
  <+>                      cont=1
  =====SUB38======
  ----------
  ----------
  ----------
  --------

  >
  =====MUL10=======
  [>+>+<<-]>>[<<+>>-]<     dup

  >>>+++++++++
  [
   <<<
   [>+>+<<-]>>[<<+>>-]<    dup
   [<<+>>-]
   >>-
  ]
  <<<[-]<
  ======RMOVE1======
  <
  [>+<-]
 ]
 <
]
>>[<<+>>-]<<

===================================================================
======================= PROCESS NUMBER  ===========================
===================================================================

==== ==== ==== ====
numd numu teid teiu
==== ==== ==== ====

>+<-
[
 >+
 ======DUP======
 [>+>+<<-]>>[<<+>>-]<

 >+<--

 >>>>>>>>+<<<<<<<<   isprime=1

 [
  >+

  <-

  =====DUP3=====
  <[>>>+>+<<<<-]>>>>[<<<<+>>>>-]<<<

  =====DUP2=====
  >[>>+>+<<<-]>>>[<<<+>>>-]<<< <

  >>>

  ====DIVIDES=======
  [>+>+<<-]>>[<<+>>-]<   DUP i=div

  <<
  [
    >>>>>+               bool=1
    <<<
    [>+>+<<-]>>[<<+>>-]< DUP
    [>>[-]<<-]           IF i THEN bool=0
    >>
    [                    IF i=0
      <<<<
      [>+>+<<-]>>[<<+>>-]< i=div
      >>>
      -                  bool=0
    ]
    <<<
    -                    DEC i
    <<
    -
  ]

  +>>[<<[-]>>-]<<
  >[-]<                  CLR div
  =====END DIVIDES====

  [>>>>>>[-]<<<<<<-]     if divides then isprime=0

  <<

  >>[-]>[-]<<<
 ]

 >>>>>>>>
 [
  -
  <<<<<<<[-]<<

  [>>+>+<<<-]>>>[<<<+>>>-]<<<

  >>

  ===================================================================
  ======================== OUTPUT NUMBER  ===========================
  ===================================================================
  [>+<-]>

  [
   ======DUP======
   [>+>+<<-]>>[<<+>>-]<

   ======MOD10====
   >+++++++++<
   [
    >>>+<<              bool= 1
    [>+>[-]<<-]         bool= ten==0
    >[<+>-]             ten = tmp
    >[<<++++++++++>>-]  if ten=0 ten=10
    <<-                 dec ten
    <-                  dec num
   ]
   +++++++++            num=9
   >[<->-]<             dec num by ten

   =======RROT======
      [>+<-]
   <  [>+<-]
   <  [>+<-]
   >>>[<<<+>>>-]
   <

   =======DIV10========
   >+++++++++<
   [
    >>>+<<                bool= 1
    [>+>[-]<<-]           bool= ten==0
    >[<+>-]               ten = tmp
    >[<<++++++++++>>>+<-] if ten=0 ten=10  inc div
    <<-                   dec ten
    <-                    dec num
   ]
   >>>>[<<<<+>>>>-]<<<<   copy div to num
   >[-]<                  clear ten

   =======INC1=========
   <+>
  ]

  <
  [
   =======MOVER=========
   [>+<-]

   =======ADD48========
   +++++++[<+++++++>-]<->

   =======PUTC=======
   <.[-]>

   ======MOVEL2========
   >[<<+>>-]<

   <-
  ]

  >++++[<++++++++>-]<.[-]

  ===================================================================
  =========================== END FOR ===============================
  ===================================================================

  >>>>>>>
 ]
 <<<<<<<<

 >[-]<
  [-]
 <<-
]

======LF========

++++++++++.[-]
@

```

Example run:

```
$ python2 bf.py PRIME.BF
Primes up to: 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

```

# Answer
> 48 votes
## Perl, 120 ~~138~~

```
%c=qw(> $p++ < $p-- + D++ - D-- [ while(D){ ] } . print+chrD , D=ord(getc));
$/=$,;$_=<>;s/./$c{$&};/g;s[D]'$b[$p]'g;eval

```

This runs hello.bf and primes.bf flawlessly:

```
$ perl bf.pl hello.bf
Hello World!
$ perl bf.pl prime.bf
Primes up to: 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

```

Initialization: The opcode to Perl translation table is stored in `%c`. The readable form looks like this:

```
%c=(
  '>' => '$p++',
  '<' => '$p--',
  '+' => '$b[$p]++',
  '-' => '$b[$p]--',
  '[' => 'while($b[$p]){',
  ']' => '}',
  '.' => 'print chr$b[$p]',
  ',' => '$b[$p]=ord(getc)',
);

```

Step 1: Slurp program input to `$_` and transform it to Perl code using the translation table. Comments are automatically stripped (replaced with `undef`) in this step.

Step 2: Uncompress all `$b[$p]` occurrences

Step 3: Launch the program using `eval`.

# Answer
> 85 votes
# Python (no eval), 317 bytes

```
from sys import*
def f(u,c,k):
 while(c[1]>=k)*u:
  j,u='[]<>+-,.'.find(u[0]),u[1:];b=(j>=0)*(1-j%2*2);c[1]+=b*(j<2)
  while b*c[c[0]]and j<1:f(u,c,k+1);c[1]+=1
  b*=c[1]==k;c[[0,c[0],2][j/2-1]]+=b
  if(j==6)*b:c[c[0]]=ord(stdin.read(1))
  if(j>6)*b:stdout.write(chr(c[c[0]]))
f(open(argv[1]).read(),[-1]+[0]*30003,0)

```

# Answer
> 80 votes
# brainfuck, ~~843~~ 691 bytes

Edit: decided to revisit this and found a surprising number of ways to golf off bytes

```
>>>,[>++++[-<-------->]<-[>+<<]>[----------[>]>[<+<+>>>>]<<<-[>]>[<+<+>>>>]<<<-[>]>[<+<+>>>>]<<<-[>]>[<-<+++>>>>]<<<--------------[>]>[<++<+>>>>]<<<--[>]>[<-<+++++++>>+>>]<<++++[-<------>]+<+[>]>[<++<+>>>>]<<<--[>]>[<<+>>>>]<<-<[+]<[>]>,>]<]<-[<]>[-[<<]>[<+[>]>>[<+[<<[<]<<-[>>]<[>>>>[>]>+<<[<]<]<-[>>]<[>>>>[>]>-<<[<]<]<++[->>+<<]>>[>]>]]<<<[<]>-<]>-[<<]>[<++[>]>+>[<-]<[<<[<]>[-<<+>>]>--[<<]>[[>]>+<<[<]<]>+[<<]>[[>]>-<<[<]<]>+[>]>]<<[<]>--<]>-[<<]>[[>]>>.<<<[<]<]>-[<<]>[[>]>>-<<<[<]<]>-[<<]>[[>]>>,<<<[<]<]>-[<<]>[[>]>>+<<<[<]<]>-[<<]>[[>]>>>[>>]>[<<<[<<]<+>>>[>>]>-]>[-]<<+[<[->>+<<]<]<[->>+<<]<[<]<]>-[<<]>[[>]>-[+>[-<<+>>]>]+<<[-]+[-<<]<[->>>[>>]>+<<<[<<]<]<[<]<]<++++++++>>[+<<->>]>]

```

This takes input in the form `code!input` where the `!input` is optional. It also simulates negative cells without using negative cells itself and can store up to `(30000-(length of code+6))/2` cells.

Try it online!

# Answer
> 55 votes
## 16 bit 8086 machine code: 168 bytes

Here's the base64 encoded version, convert and save as 'bf.com' and run from Windows command prompt: 'bf progname'

```
gMYQUoDGEFKzgI1XAgIfiEcBtD3NIR8HcmOL2LQ/i88z0s0hcleL2DPA86sz/zP2/sU783NHrL0I
AGgyAU14DTqGmAF194qOoAH/4UfDJv4Fwyb+DcO0AiaKFc0hw7QBzSGqT8MmODV1+jPtO/NzDaw8
W3UBRTxddfJNee/DJjg1dPoz7U509YpE/zxddQFFPFt18U157sM+PCstLixbXUxjTlJWXmV+

```

**EDIT**

Here's some assembler (A86 style) to create the executable (I had to reverse engineer this as I'd misplaced the original source!)

```
    add dh,10h
    push dx
    add dh,10h
    push dx
    mov bl,80h
    lea dx,[bx+2]
    add bl,[bx]
    mov [bx+1],al
    mov ah,3dh
    int 21h
    pop ds
    pop es
    jb ret
    mov bx,ax
    mov ah,3fh
    mov cx,di
    xor dx,dx
    int 21h
    jb ret
    mov bx,ax
    xor ax,ax
    repz stosw
    xor di,di
    xor si,si
    inc ch
program_loop:
    cmp si,bx
    jnb ret
    lodsb
    mov bp,8
    push program_loop
symbol_search:
    dec bp
    js ret
    cmp al,[bp+symbols]
    jnz symbol_search
    mov cl,[bp+instructions]
    jmp cx
forward:
    inc di
    ret
increment:
    inc b es:[di]
    ret
decrement:
    dec b es:[di]
    ret
output:
    mov ah,2
    mov dl,es:[di]
    int 21h
    ret
input:
    mov ah,1
    int 21h
    stosb
backward:
    dec di
    ret
jumpforwardifzero:
    cmp es:[di],dh
    jnz ret
    xor bp,bp
l1: cmp si,bx
    jnb ret
    lodsb
    cmp al,'['
    jnz l2
    inc bp
l2: cmp al,']'
    jnz l1
    dec bp
    jns l1
    ret
jumpbackwardifnotzero:
    cmp es:[di],dh
    jz  ret
    xor bp,bp
l3: dec si
    jz  ret
    mov al,[si-1]
    cmp al,']'
    jnz l4
    inc bp
l4: cmp al,'['
    jnz l3
    dec bp
    jns l3
    ret
symbols:
    db '><+-.,[]'
instructions:
    db forward and 255
    db backward and 255
    db increment and 255
    db decrement and 255
    db output and 255
    db input and 255
    db jumpforwardifzero and 255
    db jumpbackwardifnotzero and 255

```

# Answer
> 39 votes
# Vim, <sup>~~809~~</sup> 580 bytes

*-229 bytes because shenanigans and balderdash.*

```
qq<C-v><C-v><C-v>q<Esc>^mbO<C-r>q
elsei "<C-r>q<C-r>c"=="<Esc>^"xc$<C-r>q
norm <Esc>^"zc$en<C-r>q
<Esc>^"yd$i`b"cyl:if "<C-v><C-r>c"==">"<C-r>z@f<C-r>x<"<C-r>z@b<C-r>x+"<C-r>z@i<C-r>x-"<C-r>z@d<C-r>x,"<C-r>z@p<C-r>x."<C-r>z@o<C-r>x["<C-r>z@s<C-r>x]"<C-r>z@l<C-v>
<C-r>y`blmb@e<Esc>^"ec$`b^mbjj30000ddk30000o0<C-v><Esc>jjmo`lk$d`ox`bjjmp`ljmi`b<Esc>^"rc$`p:if line(".")<30002<C-r>zj<C-v>
<C-r>ymp<Esc>^"fc$`p:if line(".")>3<C-r>zk<C-v>
<C-r>ymp<Esc>^"bc$`p<C-v><C-a>Y:if <C-v><C-r>"<C-v><C-h>>255<C-r>z<C-v><C-x><C-v>
<C-r>y<Esc>^"ic$`p<C-v><C-x>Y:if <C-v><C-r>"<C-v><C-h><0<C-r>z<C-v><C-a><C-v>
<C-r>y<Esc>^"dc$`i"qx`p:if "<C-v><C-r>""!="<C-r>q<Esc>"<C-r>z3xi<C-r>q<C-r>=char2nr("<C-r>q<C-r>q")<C-r>q
<C-r>q<Esc><C-v>
else<C-r>z`i3i<C-v><C-v><Esc>a<C-v><Esc><C-r>q<Esc><C-v>
<C-r>y<Esc>^"pc$`py$`oA<C-v><C-r>=nr2char(<C-v><C-r>")<C-v>
<C-v><Esc>$mo<Esc>^"oc$`py$`b:if <C-v><C-r>"==0<C-r>z%mb<C-v>
<C-r>y<Esc>^"sc$`py$`b:if <C-v><C-r>"!=0<C-r>z%mb<C-v>
<C-r>y<Esc>^"ld$ddo<Esc>90i-<Esc>30000o0<Esc>o<Esc>90i-<Esc>o<Esc>moo<Esc>ml90i-<Esc>o<C-v><Esc><Esc>mio<Esc>90i-<Esc>`bjjmp

```

Try it online!

More than just an interpreter, this sets up an environment for programming in brainfuck with the following format:

```
brainfuck program
-------------------------------------------------------------------
list
of
30000
memory
cells
-------------------------------------------------------------------
program output
-------------------------------------------------------------------
program input ^[
-------------------------------------------------------------------

```

It also sets up some macros:

* `@f` \- `>` moves the MP forward
* `@b` \- `<` moves the MP backward
* `@i` \- `+` increments the cell at the MP
* `@d` \- `-` decrements the cell at the MP
* `@p` \- `,` input a character and store it in the cell at the MP
* `@o` \- `.` output the signified by the cell at the MP
* `@s` \- `[` start `while` loop
* `@l` \- `]` end `while` loop
* `@e` \- Execute. Recursively get the command at the IP and call the corresponding macro if it is a valid command, then increment the IP.
* `@r` \- Reset. Clear the output, reset all memory cells, and move the IP back to the beginning of the program.

If using the TIO link, the input box is where the program goes to be executed. To pass input to the brainfuck program, add this to the footer before anything else: ``iiYour Input Here<Esc>`. Additionally, I added `gg30003dd`l3dd` to the footer to strip away everything except the brainfuck program's output, so you can remove that from the footer to see the entire result.

If using Vim, copy the TIO code and paste it into Vim to set up the environment. From there, you can use ``b` to jump to the brainfuck program, ``p` to jump to the MP, ``o` to jump to the output, and ``i` to jump to the input.

A few caveats:

* The environment does not support newlines in the program, so the brainfuck program must be a single line.
* The input must be terminated with `<Esc>`. The setup code automatically puts the `<Esc>` in the input section, so just make sure that the input goes before the `^[`.
* To "read the program from a file", as it were, you can use Vim to open a file containing the brainfuck program and paste this code to set everything up and then execute it, as long as the program is already in a single line.
* It's kinda slow. The test program for finding primes took ~2 minutes to finish with `n=2`. It took ~10 minutes with `n=7`. I didn't even bother trying anything higher. Nevertheless, it works.

Note: This is the second version, and is golfed much further than the original, but I could almost certainly get it even shorter by defining the macros as macros instead of deleting into named registers. However, that will require pretty much rewriting this entire program, which I just golfed into illegibility, so I don't feel like doing it right now, but I might do it some time later.

# Answer
> 29 votes
# Ruby 1.8.7, ~~188~~ ~~185~~ ~~149~~ 147 characters

```
eval"a=[i=0]*3e4;"+$<.bytes.map{|b|{?.,"putc a[i]",?,,"a[i]=getc",?[,"while a[i]>0",?],"end",?<,"i-=1",?>,"i+=1",?+,"a[i]+=1",?-,"a[i]-=1"}[b]}*";"

```

Somewhat readable version:

```
code = "a = [0] * 3e4; i = 0;"
more_code ARGF.bytes.map {|b|
  replacements = {
    ?. => "putc a[i]",
    ?, => "a[i] = getc",
    ?[ => "while a[i] > 0 do",
    ?] => "end",
    ?< => "i -= 1",
    ?> => "i += 1",
    ?+ =>"a[i]+=1",
    ?- =>"a[i]-=1"
  }
  replacements[b]
}.join(";")
eval code+more_code

```

As you see I shamelessly stole your idea of translating to the host language and then using eval to run it.

# Answer
> 29 votes
# Binary Lambda Calculus 112

The program shown in the hex dump below

```
00000000  44 51 a1 01 84 55 d5 02  b7 70 30 22 ff 32 f0 00  |DQ...U...p0".2..|
00000010  bf f9 85 7f 5e e1 6f 95  7f 7d ee c0 e5 54 68 00  |....^.o..}...Th.|
00000020  58 55 fd fb e0 45 57 fd  eb fb f0 b6 f0 2f d6 07  |XU...EW....../..|
00000030  e1 6f 73 d7 f1 14 bc c0  0b ff 2e 1f a1 6f 66 17  |.os..........of.|
00000040  e8 5b ef 2f cf ff 13 ff  e1 ca 34 20 0a c8 d0 0b  |.[./......4 ....|
00000050  99 ee 1f e5 ff 7f 5a 6a  1f ff 0f ff 87 9d 04 d0  |......Zj........|
00000060  ab 00 05 db 23 40 b7 3b  28 cc c0 b0 6c 0e 74 10  |....#@.;(...l.t.|
00000070

```

expects its input to consist of a Brainfuck program (looking only at bits 0,1,4 to distinguish among ,-.+\<\>\]\[ ) followed by a \], followed by the input for the Brainfuck program.

Save the above hex dump with xxd -r \> bf.Blc

Grab a blc interpreter from https://tromp.github.io/cl/cl.html

```
cc -O2 -DM=0x100000 -m32 -std=c99 uni.c -o uni
echo -n "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.]" > hw.bf
cat bf.Blc hw.bf | ./uni

```

Hello World!

# Answer
> 18 votes
# Retina 0.8.2, ~~386~~ ~~391~~ 386 bytes

Code contains unprintable NUL (`0x00`) characters. It's also not super golfed yet, because it's already really slow, and if I golf it more, I don't know how long it'd take to finish. Appears to time out on the prime-finding sample.

There may be bugs in the online interpreter or in my program (leading new lines don't show in the output?).

Takes input like `<code>│<input>`. No, that is not a pipe (`|`). It's the Unicode character `U+2502`. The code also uses the Unicode characters `ÿ▶◀├║`. Unicode characters are used in order to support input of all ASCII characters. Therefore, these characters need to be separated from the code by a non-ASCII character.

**Try it online**

```
s`^.*
▶$0├║▶
s{`(▶>.*║.*)▶(.)(.?)
$1$2▶$3
▶$
▶
║▶
║▶
(▶<.*║.*)(.)▶
$1▶$2
T`ÿ-`o`(?<=▶\+.*║.*▶).
^\+

T`-ÿ`ÿo`(?<=▶-.*║.*▶).
^-

(▶\..*├.*)(║.*▶)(.)
$1$3$2$3
(▶,.*│)(.?)(.*├.*▶).
$1$3$2
▶\[(.*║.*▶)
[▶▶${1}
{`(▶▶+)([^[\]]*)\[
$2[$1▶
}`▶(▶+)([^[\]]*)\]
$2]$1
r`([[\]]*)▶\](.*║.*▶[^])
$1◀◀]$2
r{`\[([^[\]]*)(◀+)◀
$2[$1
}`\]([^[\]]*)(◀◀+)
$2◀]$1
◀
▶
}`▶([^│])(.*║)
$1▶$2
s\`.*├|║.*

```

Note there is a trailing newline there.

### Brief Explanation:

Zeros `0x00` are used for the tape, which is infinite. The first replacement sets up the interpreter in the form `▶<code>│<input>├<output>║▶<tape>`, where the first  is the pointer for the code, and the second one is the pointer for the tape.

`ÿ` is `0xFF` (255), which is used for Transliteration (used to implement `+` and `-`) to wrap the cells back around to zero.

is only used for readability (in case the program is stopped in the middle or you want to see the program mid-execution). Otherwise, you couldn't tell which way the pointer was moving.

### Commented Code:

```
s`^.*                       # Initialize
▶$0├║▶
s{`(▶>.*║.*)▶(.)(.?)        # >
$1$2▶$3
▶$
▶
║▶                          # <
║▶
(▶<.*║.*)(.)▶
$1▶$2
T`ÿ-`o`(?<=▶\+.*║.*▶).      # +
^\+

T`-ÿ`ÿo`(?<=▶-.*║.*▶).      # -
^-

(▶\..*├.*)(║.*▶)(.)         # .
$1$3$2$3
(▶,.*│)(.?)(.*├.*▶).        # ,
$1$3$2
▶\[(.*║.*▶)                 # [
[▶▶${1}
{`(▶▶+)([^[\]]*)\[
$2[$1▶
}`▶(▶+)([^[\]]*)\]
$2]$1
r`([[\]]*)▶\](.*║.*▶[^])    # ]
$1◀◀]$2
r{`\[([^[\]]*)(◀+)◀
$2[$1
}`\]([^[\]]*)(◀◀+)
$2◀]$1
◀
▶
}`▶([^│])(.*║)              # next instruction
$1▶$2
s\`.*├|║.*                  # print output

```

Click here for the code with zeros in place of null bytes. Any occurrences of `$0` should not be replaced with nulls.

**Edit**: Now supports empty input and suppresses trailing newline.

Infinite output is now supported. (403 bytes)

# Answer
> 15 votes
## Conveyor, 953

This might be the most beautiful code you will ever see:

```
0

:I\1\@p
>#====)
^#====<
PP0
P<=======================<
00t:)01t1  a:P:P:P:P:P:P:^
>===========">">2>">2>">"^
^           +^-^5^ ^5^]^.^
^           "^"^*^"^*^"^"^
^           -^-^6^-^6^-^-^
^           #^#^*^#^*^#^#^
^           P P -^P )^P P
^           P P #^P )^P P
^t1\)t0:))t01   P   -^  1
^===========<   P   #^  0
^  t1\(t0:))t01     P   t
^=============<     P   )
^         t11(t01   0 0 )
^===============<. t P 10
^                 FT#T#=<
^=================< P
^             t11)t01
^===================< 10t))0tP00t:(01t(1a:P:
^                     >=====#=>==========">"
^                             ^          ]^[
^                           P ^          "^"
^===========================<=^#=====<   -^-
                            ^==<     ^ PP#^#=
                                     ^===PTPT<
                                     ^  )P P
                                     ^=<=< (
                                       ^===<

```

# Answer
> 15 votes
# TypeScript Types, ~~1807~~ 1771 bytes

```
//@ts-ignore
type B<X="\0\x01\x02\x03\x04\x05\x06\x07\b\t\n\v\f\r\x0E\x0F\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1A\x1B\x1C\x1D\x1E\x1F !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7F\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8A\x8B\x8C\x8D\x8E\x8F\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9A\x9B\x9C\x9D\x9E\x9F\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff",a=[]>=X extends`${infer A}${infer C}`?B<C,[...a,A]>:a;type C={[K in keyof B&`${number}`as B[K]]:D<K>};type D<T,A=[]>=T extends`${A["length"]}`?A["length"]:D<T,[0,...A]>;type E<A=[]>=255 extends A["length"]?[...A,0]:E<[...A,[...A,0]["length"]]>;type F=[255,0,...E];type G<L,D=never>=L extends[infer A,{}]?A:D;type H<L,D=never>=L extends[{},infer B]?B:D;type M<a,b,c=0,d="",e=0,f=0,g=0,h=0,i=[],>=a extends`${infer j}${infer a}`?h extends 0?j extends"+"?M<a,b,c,d,e,E<[]>[f],g>:j extends"-"?M<a,b,c,d,e,F[f],g>:j extends"<"?e extends 0?M<a,b,c,d,e,f,g>:M<a,b,c,d,H<e>,G<e>,[f,g]>:j extends">"?M<a,b,c,d,[f,e],G<g,0>,H<g,[]>>:j extends"["?f extends 0?M<a,b,c,d,e,f,g,1>:M<a,b,[a,c],d,e,f,g>:j extends"]"?f extends 0?M<a,b,H<c>,d,e,f,g>:M<G<c>,b,c,d,e,f,g>:j extends","?b extends`${infer k}${infer b}`?M<a,b,c,d,e,k extends keyof j?j[k]:0,g>:M<a,b,c,d,e,0,g>:j extends"."?M<a,b,c,`${d}${B[f]}`,e,f,g>:M<a,b,c,d,e,f,g>:j extends"]"?M<a,b,c,d,e,f,g,G<i,0>,H<i,[]>>:j extends"["?M<a,b,c,d,e,f,g,1,[1,i]>:M<a,b,c,d,e,f,g,h,i>:d

```

Try it online!

Ungolfed / Explanation

# Answer
> 14 votes
## Python 275 248 255

I decided to give it a try.

```
import sys
i=0
b=[0]*30000
t=''
for e in open(sys.argv[1]).read():
 t+=' '*i+['i+=1','i-=1','b[i]+=1','b[i]-=1','sys.stdout.write(chr(b[i]))','b[i]=ord(sys.stdin.read(1))','while b[i]:','pass','']['><+-.,['.find(e)]+'\n'
 i+=(92-ord(e))*(e in'][')
exec t

```

# Answer
> 14 votes
# C (gcc) Linux x86\_64, ~~884 621 525 487 439 383 358~~ 347 bytes

```
*z,*mmap();d[7500];h;(*p)();*j(char*a){char*t=a,*n,c,q=0;for(;read(h,&c,!q);t=c==47?n=j(t+9),z=mempcpy(t,L"\xf003e80Ƅ",5),*z=n-t-9,n:c==49?q=*t++=233,z=t,*z=a-13-t,z+1:stpcpy(t,c-18?c-16?~c?c-1?c-2?c?t:"1\xc0P_\xF\5":"RXR_\xF\5":L"໾":L"۾":L"컿":L"웿"))c-=44;return t;}main(P,g)int**g;{*j(p=mmap(0,1<<20,6,34,h=open(g[1],0),0))=195;p(0,d,1);}

```

Try it online!

This is a JIT that compiles BF code into x86\_64 machine language at runtime. This performs a straight translation so commonly occurring sequences such as `>>>`, `<<<`, `+++` and `---` aren't coalesced into faster instructions.

Less golfed version:

```
// size of data area
*z,c,*mmap();d[7500];h;(*p)();
// recursive function translates BF commands to x86_64 instructions
*j(char*a){
  char*t=a,*n,q=0;
  for(;read(h,&c,!q);)
    c-=44,
    t=c==47? // [
        // cmpb $0x0,(%rsi)
        // je n-t-9
        n=j(t+9),
        z=mempcpy(t,L"\xf003e80Ƅ",5),
        *z=n-t-9,
        n
      :
        c==49? // ]
          // jmp a-13-t
          q=*t++=233,
          z=t,
          *z=a-13-t,
          z+1
        :
          stpcpy(t,c-18? // >
                     c-16? // <
                       ~c? // +
                         c-1? // -
                           c-2? // .
                             c? // ,
                               ""
                             :
                               // xor %eax,%eax
                               // push %rax
                               // pop %rdi
                               // syscall
                               "1\xc0P_\xF\5"
                           :
                             // push %rdx
                             // pop %rax
                             // push %rdx
                             // pop %rdi
                             // syscall
                             "RXR_\xF\5"
                         :
                           // decb (%rsi)
                           L"໾"
                       :
                         // incb (%rsi)
                         L"۾"
                     :
                       // dec %esi
                       L"컿"
                   :
                     // inc %esi
                     L"웿");
  return t;
}
main(P,g)int**g;{
  // allocate text (executable) memory and mark as executable
  p=mmap(0,1<<20,6,34,h=open(g[1],0),0);
  // run JIT, set %rdx=1 and call code like a function
  p(*j(p)=195,d,1);
}

```

# Answer
> 13 votes
## Haskell, 457 413 characters

```
import IO
import System
z=return
'>'#(c,(l,d:r))=z(d,(c:l,r))
'<'#(d,(c:l,r))=z(c,(l,d:r))
'+'#(c,m)=z(succ c,m)
'-'#(c,m)=z(pred c,m)
'.'#t@(c,_)=putChar c>>hFlush stdout>>z t
','#(_,m)=getChar>>=(\c->z(c,m))
_#t=z t
_%t@('\0',_)=z t
i%t=i t>>=(i%)
b('[':r)=k$b r
b(']':r)=(z,r)
b(c:r)=f(c#)$b r
b[]=(z,[])
f j(i,r)=(\t->j t>>=i,r)
k(i,r)=f(i%)$b r
main=getArgs>>=readFile.head>>=($('\0',("",repeat '\0'))).fst.b

```

This code "compiles" the BF program into an `IO` action of the form `State -> IO State` the state is a zipper on an infinite string.

Sad that I had to expend 29 characters to turn buffering off. Without those, it works, but you don't see the prompts before you have to type input. The compiler itself (`b`, `f`, and `k`) is just 99 characters, the runtime (`#` and `%`) is 216. The driver w/initial state another 32.

```
>ghc -O3 --make BF.hs
[1 of 1] Compiling Main             ( BF.hs, BF.o )
Linking BF ...

>./BF HELLO.BF
Hello World!

>./BF PRIME.BF
Primes up to: 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

```

*update 2011-02-15:* Incorporated J B's suggestions, did a little renaming, and tightened up `main`

# Answer
> 11 votes
# Brainfuck, 948 bytes

Well, that took a while. I golfed a Brainfuck self-interpreter by ... not me.

```
->->>>-[,+>+<[->-]>[->]<+<-------------------------------------[+++++++++++++++++++++++++++++++++++++>-]>[->]<<[>++++++++[-<----->]<---[-[-[-[--------------[--[>+++++++[-<---->]<-[--[[+]->]<+[->++>]->]<+[->+>]->]<+[->+++++>]->]<+[->++++++>]->]<+[->+++++++>]->]<+[->++++>]->]<+[->++++++++>]->]<+[->+++>]->]+<+[->->]>[-<->]<]>>->>-<<<<<+++[<]>[-[-[-[-[-[-[-[-<<++++++++>>>[>]>>>>+[->>+]->,<<<+[-<<+]-<<<[<]<]>[<<<+++++++>>>[>]>>>>+[->>+]->.<<<+[-<<+]-<<<[<]]<]>[<<<++++++>>>[>]>>>>+[->>+]<<-<<+[-<<+]-<<<[<]]<]>[<<<+++++>>>[>]>>>>+[->>+]+>>-<<[-<<+]-<<<[<]]<]>[<<<++++>>>[>]>>>>+[->>+]->-<<<+[-<<+]-<<<[<]]<]>[<<<+++>>>[>]>>>>+[->>+]->+<<<+[-<<+]-<<<[<]]<]>[<++[>]>>>>+[->>+]->[<<<+[-<<+]-<<<[<]-[<<-[>->-[<+]]<+[->>[<]]<-[>-->+[<++]]<++[-->>[<]]<++>>[[-<+>]<<[->>+<<]]<[>]>]]<[<<+[-<<+]-<<<[<]>--<<++>]>]<]>[<<<+>>>[>]>>>>+[->>+]->[<<<+[-<<+]-<<<[<]]<[<<+[-<<+]-<<<[<]+[>-[<-<]<<[>>]>>-[<+<]<<[>>]>>++<[>[-<<+>>]<[->+<]]<[>]>]]>[[-<<+>>]<[->+<]>]]>]

```

# Answer
> 11 votes
# Vyxal, ~~150~~ ~~149~~ 148 bytes

```
k2T0ẋ→_0→0?£{D¥L<|¥i:‛+-$c[:‛ +ḟ←_:_←›Ǔṫ∇∇+J←›ǔ→_|:‛<>$c[:‛ >ḟ←+→|:\.=[←_← iC₴|:\,=[←_:_←?CȦ→_|:\[=[←_← i¬[Ȯ¥$ȯ\]ḟ∇∇+$]|:\]=[Ȯ¥$Ẏf\[=TG‹∇$_]]]]]]]_›

```

Try it Online!

"But there's already a Vyxal answer that's ~~100~~ ~~99~~ 98 bytes shorter bro what is this cringe" I hear you say. Well this version doesn't use `eval`, and instead runs it manually. Note that it can be slow because it's doing things like rotating a 30000 item list quite frequently, so here's a version with only 100 cells for testing

Some assumptions this program makes:

* Closed brackets
* EOF handled manually
* Program on first line, each input character on a new line

## Explained

### Quick Overview

```
k2T0ẋ→_                                                                                # Tape
       0→                                                                                # Cell pointer
         0                                                                                # Instruction pointer
          ?£                                                                                # Prog
            {D¥L<|                                                                                # While the instruction pointer is less than program length
                  :,←_,¥i                                                                                # Get command
                         :‛+-$c[:‛ +ḟ←_:_←›Ǔṫ∇∇+J←›ǔ→_|                                                                                # Handle addition and subtraction in the same place
                                                       :‛<>$c[:‛ >ḟ←+→|                                                                                # Handle moving the pointer left and right
                                                                       :\.=[←_← iC,|                                                                         # Output
                                                                                :\,=[←_:_←?CȦ→_|                                                         # Input
                                                                                :\[=[                                                    # jump to next `]` if tape[cell] == 0
                                                                                ←_← i¬[Ȯ¥$ȯ:,\]ḟ›∇+$]|
                                                                                :\]=[Ȯ¥$Ẏf\[=TG›∇$_]          # Jump back to the previous `[`
                                                                                ]]]]]]
                                                                                _   # Remove the char from the stack
                                                                                ›  # Next command
                                                                                }

```

### Detailed Explanation

```
k2T0ẋ→_

```

This is the tape. It consists of 30000 0s in a list. It's stored in a global variable called `_`.

```
0→

```

This is the cell pointer. It tracks which cell is being pointed to. It's stored in the ghost variable. The ghost variable is another name for the variable with no name (as in, its name is literally `""` \- the empty string.)

```
0

```

This is the instruction pointer. It tracks which character of the program is being executed. It's stored on the stack as the bottom of the stack. Throughout this answer, the stack is `[instruction pointer, current character, ...]` where `...` is whatever processing is happening in each command.

This gets the program to execute and stores it in the register.

```
{D¥L<|

```

This is the main program execution loop. It calls its code while the instruction pointer is less than the length of the program. Before performing the comparison, the instruction pointer is triplicated (i.e. three copies of it are pushed to the stack). This is so that there is a copy for the comparison, for getting the current character in the program and for maintaining the value of the pointer.

```
¥i

```

This gets the character at the index of the instruction pointer and puts it on the stack. The stack is now `[instruction pointer, command]`. We now move on to handling the commands

#### Addition and Subtraction

```
:‛+-$c[:‛ +ḟ←_:_←›Ǔṫ∇∇+J←›ǔ→_

```

The above snippet is the entirety of the section that handles the `+` and `-` commands.

```
:‛+-$c

```

This checks if the command is in the string `"+-"`, while leaving a copy of the command on the stack for further comparison if needed.

```
[:‛ +ḟ

```

If the command *is* one of `+` or `-`, then the command is duplicated yet again, and its index in the string `" +"` is returned. This returns `1` for `+` and `-1` for `-`, as `-1` is returned for characters not in the string. The `1` or `-1` acts as an offset for the current cell, and saves having to check for `+` and `-` individually. It also means `+` can be used for both commands instead of  for addition and  for subtraction.

```
←_:_←›Ǔ

```

This pushes the tape (stored in the global variable called `_`), the value of the cell pointer + 1 (stored in the ghost variable and then incremented) and then rotates the tape left that many times. The `:_` after `←_` is needed because there seems to be a bug with list mutability when rotating. (TODO: Fix)

After the rotation, the cell that is to be incremented or decremented is at the tail of the tape.

```
ṫ∇∇+J

```

This separates the tail and the rest of the list - first it pushes `tape[:-1]` and then it pushes `tape[-1]`. It then rotates the top three items on the stack so that the order is `[tape[:-1], tape[-1], offset]`. The offset is then added to the tail, and the tail is then appended back to the rest of the tape.

```
←›ǔ→_

```

The tape is then rotated `cell pointer + 1` times to the right to "undo" the left rotation and then placed back into the global variable called `_`.

#### Moving the Cell Pointer

```
|:‛<>$c[:‛ >ḟ←+→

```

The above snippet is the entirety of the section that handles the `<` and `>` commands.

```
|:‛<>$c

```

Just like with the `+` and `-` commands, a check is done to see if the command is in the string `"<>"`.

```
[:‛ >ḟ

```

And also just like with the `+` and `-` commands, if the command *is* one of `<` or `>`, then the command is duplicated yet again, and its index in the string `" >"` is returned. This returns `1` for `>` and `-1` for `<`. The `1` or `-1` acts as an offset for the current cell location, and saves having to check for `<` and `>` individually. It also means `+` can be used for both commands instead of  for moving right and  for moving left.

```
←+→

```

This adds the offset to the cell pointer and updates the value stored in the ghost variable. It also acts as a weird face.

#### Output

```
|:\.=[←_← iC₴

```

The above snippet is the entirety of the section that handles the `.` command.

```
|:\.=

```

This checks if the command is equal to the string `"."`. Unlike addition/subtraction and cell pointer movement, input and output cannot be handled in the same if-statement, as their functions are different at a fundamental level.

```
[←_← i

```

If the command is `.`, the tape is pushed, as well as the cell pointer's value. The item at the location of the cell pointer is then retrieved. The space after the second  is needed to avoid it being interpreted as `←i`

```
C₴

```

This prints that item after converting it to its ASCII equivalent (think `chr` in python)

#### Input

```
|:\,=[←_:_←?CȦ→_

```

The above snippet is the entirety of the section that handles the `,` command.

```
|:\,=

```

This checks if the command is equal to the string `","`.

```
[←_:_←?C

```

If the command *is* `,`, the tape and current cell pointer are pushed to the stack, as well as the ordinal value (think `ord` in python) of the next input.

```
Ȧ→_

```

This sets the `cell pointer`th item of `tape` to the input. Basically `tape[cell_pointer] = ord(input())`.

#### Looping

```
|:\[=[←_← i0=[Ȯ¥$ȯ\]ḟ∇∇+$]

```

The above snippet is the entirety of the section that handles the `[` command.

```
|:\[=

```

The usual check for a certain character. `[` this time.

```
[←_← i

```

If the command is `[`, get the `cell pointer`th item of `tape`.

```
¬[

```

If the cell is not a truthy value (i.e. not `0`), then:

```
Ȯ¥$ȯ\]ḟ

```

Push `program[instruction_pointer:]` and find the first `]` in that string. The stack is now `[instruction pointer, command, position of "]"]`.

```
∇∇+$

```

Rotate the stack so that its order is `[command, position of "]", instruction pointer]` and add the position of the `]` to the instruction pointer. This has the effect of iterating through the program until the next `]` is found without having to have lengthy while loops.

```
|:\]=[Ȯ¥$Ẏf\[=TG‹∇$_

```

The above snippet is the entirety of the section that handles the `]` command.

```
|:\]=

```

Check if the command is `]`

```
[Ȯ¥$Ẏf\[=TG

```

And if it is, get the greatest index of all `[`s in the string `program[0:instruction_pointer]`. This has the effect of backtracking to the matching `[` without having to have a lengthy while loop.

```
‹∇$_

```

Decrement that so that the instruction pointer will be re-incremented to the position of the matching `[` and rotate the stack so that the stack order is once again `[instruction pointer, command]`

#### Final bits

```
]]]]]]] # Close all the if statements
_       # Remove the command from the stack
›       # Move the instruction pointer forward 1
}       # Close the main while loop

```

# Answer
> 10 votes
# CJam, 75 bytes

```
lq3e4Vc*@{"-<[],.+>"#"T1$T=(t T(:T; { _T=}g \0+(@T@t _T=o "_'(')er+S/=}%s~@

```

Try it online: string reverser, Hello World.

## Explanation

Takes code on the first line of STDIN and input on all lines below it.

```
l            Read a line from STDIN (the program) and push it.
 q           Read the rest of STDIN (the input) and push it.
  3e4Vc*     Push a list of 30000 '\0' characters.
        @    Rotate the stack so the program is on top.

{               }%   Apply this to each character in prog:
 "-<[],.+>"#         Map '-' to 0, '<' to 1, ... and everything else to -1.
            ...=     Push a magical list and index from it.

s~       Concatenate the results and evaluate the resulting string as CJam code.
  @      Rotate the top three elements again -- but there are only two, so the
         program terminates.

```

What about that magical list?

```
"T1$T=(t T(:T; { _T=}g \0+(@T@t _T=o "  Space-separated CJam snippets.
                                        (Note the final space! We want an empty
                                        string at the end of the list.)
_'(')er+                                Duplicate, change (s to )s, append.
        S/                              Split over spaces.

```

The resulting list is as follows:

```
T1$T=(t    (-)
T(:T;      (<)
{          ([)
_T=}g      (])
\0+(@T@t   (,)
_T=o       (.)
T1$T=)t    (+)
T):T;      (>)
{          (unused)
_T=}g      (unused)
\0+(@T@t   (unused)
_T=o       (unused)
           (all other characters)

```

We generate the snippets for `+` and `>` from those for `-` and `<`, simply by changing left parens (CJam’s “decrement”) into right parens (CJam’s “increment”).

# Answer
> 9 votes
## C 284 362 (From a file)

```
#include <stdio.h>
char b[30000],z[9999],*p=b,c,*a,i;f(char*r,int s){while(c=*a++){if(!s){(c-62)?(c-60)?(c-43)?(c-45)?(c-46)?(c-44)?0:(*p=getchar()):putchar(*p):--*p:++*p:--p:++p;if(c==91)f(a,!*p);else if(c==93){if(!*p)return;else a=r;}}else{if(c==93){--s;if(!*p&&!s)return;}else if(c==91){s++;}}}}main(int c,char**v){fread(z,1,9999,fopen(*++v,"r"));a=z;f(0,0);}

```

**Primes:**

```
Primes up to: 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
Press any key to continue . . .

```

Compiled and ran successfully VS2008

Original solution failed to recognize loops that were initially set to zero. Still some room to golf. But finally solves the Prime Number program.

**Ungolfed:**

```
#include <stdio.h>
char b[30000],z[9999],*p=b,c,*a,i;
f(char*r,int s)
{
    while(c=*a++)
    {
        if(!s)
        {
            (c-62)?(c-60)?(c-43)?(c-45)?(c-46)?(c-44)?0:(*p=getchar()):putchar(*p):--*p:++*p:--p:++p;
            if(c==91)f(a,!*p);
            else if(c==93){if(!*p)return;else a=r;}
        }
        else
        {
            if(c==93)
            {
                --s;
                if(!*p&&!s)return;
            }
            else if(c==91)
            {
                s++;
            }
        }
    }
}

main(int c,char**v){
    fread(z,1,9999,fopen(*++v,"r"));
    a=z;
    f(0,0);
}

```

**Tests:**

Hello World

Rot13

# Answer
> 9 votes
## PHP 5.4, ~~296~~ ~~294~~ ~~273~~ ~~263~~ ~~261~~ ~~209~~ ~~191~~ ~~183~~ ~~178~~ 166 characters:

I gave it a shot without using eval, but I eventually had to use it

```
<?$b=0;eval(strtr(`cat $argv[1]`,["]"=>'}',"["=>'while($$b){',"."=>'echo chr($$b);',","=>'$$b=fgetc(STDIN);',"+"=>'$$b++;',"-"=>'$$b--;',">"=>'$b++;',"<"=>'$b--;']));

```

All commands are working. This heavily abuses variable variables, and spews warnings. However, if one changes their php.ini to squelch warnings (or pipes stderr to /dev/null), this works great.

Verification (It's the "Hello World!" example from Wikipedia): http://codepad.viper-7.com/O9lYjl

**Ungolfed, ~~367~~ ~~365~~ ~~335~~ ~~296~~ 267 characters:**

```
<?php
$a[] = $b = 0;
$p = implode("",file($argv[1])); // Shorter than file_get_contents by one char
$m = array("]" => '}', "[" => 'while($a[$b]){',"." => 'echo chr($a[$b]);', "," => '$a[$b]=fgetc(STDIN);', "+" => '$a[$b]++;', "-" => '$a[$b]--;', ">" => '$b++;', "<" => '$b--;');
$p = strtr($p,$m);
@eval($p);

```

This should be run via the command line: `php bf.php hello.bf`

# Answer
> 8 votes
## F#: 489 chars

The following program doesn't jump at '\[' / '\]' instructions, but scans the source code for the next matching token. This of course makes it kind of slow, but it can still find the primes under 100. F# integer types don't overflow but wrap.

Here's the short version:

```
[<EntryPoint>]
let M a=
 let A,B,i,p,w=Array.create 30000 0uy,[|yield!System.IO.File.ReadAllText a.[0]|],ref 0,ref 0,char>>printf"%c"
 let rec g n c f a b=if c then f i;if B.[!i]=a then g(n+1)c f a b elif B.[!i]=b then(if n>0 then g(n-1)c f a b)else g n c f a b
 while !i<B.Length do(let x=A.[!p]in match B.[!i]with|'>'->incr p|'<'->decr p|'+'->A.[!p]<-x+1uy|'-'->A.[!p]<-x-1uy|'.'->w x|','->A.[!p]<-byte<|stdin.Read()|'['->g 0(x=0uy)incr '['']'|']'->g 0(x>0uy)decr ']''['|_->());incr i
 0

```

A nasty gotcha was that the primes.bf program chokes on windows newlines. In order to run it I had to save the input number to a UNIX formatted text document and feed it to the program with a pipe:

```
interpret.exe prime.bf < number.txt

```

*Edit: entering Alt+010 followed by Enter also works in Windows* cmd.exe

Here's the longer version:

```
[<EntryPoint>]
let Main args =
    let memory = Array.create 30000 0uy
    let source = [| yield! System.IO.File.ReadAllText args.[0] |]
    let memoryPointer = ref 0
    let sourcePointer = ref 0
    let outputByte b = printf "%c" (char b)
    let rec scan numBraces mustScan adjustFunc pushToken popToken =
        if mustScan then
            adjustFunc sourcePointer
            if source.[!sourcePointer] = pushToken then
                scan (numBraces + 1) mustScan adjustFunc pushToken popToken
            elif source.[!sourcePointer] = popToken then
                if numBraces > 0 then scan (numBraces - 1) mustScan adjustFunc pushToken popToken
            else
                scan numBraces mustScan adjustFunc pushToken popToken

    while !sourcePointer < source.Length do
        let currentValue = memory.[!memoryPointer]
        match source.[!sourcePointer] with
            | '>' -> incr memoryPointer
            | '<' -> decr memoryPointer
            | '+' -> memory.[!memoryPointer] <- currentValue + 1uy
            | '-' -> memory.[!memoryPointer] <- currentValue - 1uy
            | '.' -> outputByte currentValue
            | ',' -> memory.[!memoryPointer] <- byte <| stdin.Read()
            | '[' -> scan 0 (currentValue = 0uy) incr '[' ']'
            | ']' -> scan 0 (currentValue > 0uy) decr ']' '['
            |  _  -> ()
        incr sourcePointer
    0

```

# Answer
> 8 votes
## Windows PowerShell, 204

```
'$c=,0*3e4;'+@{62='$i++
';60='$i--
';43='$c[$i]++
';45='$c[$i]--
';44='$c[$i]=+[console]::ReadKey().keychar
';46='write-host -n([char]$c[$i])
';91='for(;$c[$i]){';93='}'}[[int[]][char[]]"$(gc $args)"]|iex

```

Fairly straightforward conversion of the instructions and then `Invoke-Expression`.

History:

* 2011-02-13 22:24 (220) First attempt.
* 2011-02-13 22:25 (218) `3e4` is shorter than `30000`.
* 2011-02-13 22:28 (216) Unnecessary line breaks. Matching on integers instead of characters is shorter.
* 2011-02-13 22:34 (207) Used indexes into a hash table instead of the `switch`.
* 2011-02-13 22:40 (205) Better cast to string removes two parentheses.
* 2011-02-13 22:42 (204) No need for a space after the argument to `Write-Host`.

# Answer
> 8 votes
# C, 260 + 23 = 283 bytes

I created a C program which can be found here.

```
main(int a,char*s[]){int b[atoi(s[2])],*z=b,p;char*c=s[1],v,w;while(p=1,
*c){q('>',++z)q('<',--z)q('+',++*z)q('-',--*z)q('.',putchar(*z))q(',',*z
=getchar())if(*c=='['||*c==']'){v=*c,w=184-v;if(v<w?*z==0:*z!=0)while(p)
v<w?c++:c--,p+=*c==v?1:*c==w?-1:0;}c++;}}

```

Has to be compiled via `gcc -D"q(a,b)"="*c-a||(b);" -o pmmbf pmmbf.c` and can be called as follows: `pmmbf ",[.-]" 30000` whereby the first argument (quoted) contains the bf-program to run, the second determines how large the tape should be.

# Answer
> 8 votes
## C, 333 characters

This is my first BF interpreter and the first golf I actually had to debug.

This runs the prime number generator on Mac OS X/GCC, but an additional `#include<string.h>` may be necessary at a cost of 19 more characters if the implicit definition of `strchr` doesn't happen to work on another platform. Also, it assumes `O_RDONLY == 0`. Aside from that, leaving `int` out of the declaration of `M` saves 3 characters but that doesn't seem to be C99 compliant. Same with the third `*` in `b()`.

This depends on the particulars of ASCII encoding. The Brainfuck operators are all complementary pairs separated by a distance of 2 in the ASCII code space. Each function in this program implements a pair of operators.

```
#include<unistd.h>
char C[30000],*c=C,o,P[9000],*p=P,*S[9999],**s=S,*O="=,-\\",*t;
m(){c+=o;}
i(){*c-=o;}
w(){o<0?*c=getchar():putchar(*c);}
b(){if(o>0)*c?p=*s:*--s;else if(*c)*++s=p;else while(*p++!=93)*p==91&&b();}
int(*M[])()={m,i,w,b};
main(int N,char**V){
read(open(V[1],0),P,9e3);
while(o=*p++)
if(t=strchr(O,++o&~2))
o-=*t+1,
M[t-O]();
}

```

# Answer
> 8 votes
## C, 267

```
#define J break;case
char*p,a[40000],*q=a;w(n){for(;*q-93;q++){if(n)switch(*q){J'>':++p;J'<':--p;J'+':++*p;J'-':--*p;J'.':putchar(*p);J',':*p=getchar();}if(*q==91){char*r=*p&&n?q-1:0;q++;w(r);q=r?r:q;}}}main(int n,char**v){p=a+read(open(v[1],0),a,9999);*p++=93;w(1);}

```

Run as ./a.out primes.bf

## Ungolfed Version:

```
#define J break;case

char*p,a[40000],*q=a; // packed so program immediately followed by data

w(n){
    for(;*q-93;q++){ // until ']'
        if(n)switch(*q){ // n = flagged whether loop evaluate or skip(0)
                J'>':++p;
                J'<':--p;
                J'+':++*p;
                J'-':--*p;
                J'.':putchar(*p);
                J',':*p=getchar();
        }
        if(*q==91){char*r=*p&&n?q-1:0;q++;w(r);q=r?r:q;} // recurse on '[', record loop start
    }
}

main(int n,char**v){
    p=a+read(open(v[1],0),a,9999);
    *p++=93; // mark EOF with extra ']' and set data pointer to next
    w(1); // begin as a loop evaluate
}

```

# Answer
> 7 votes
## Delphi, 397 382 378 371 366 364 328 characters

Eat this Delphi!

```
328 var p,d:PByte;f:File;z:Word=30000;x:Int8;begin p:=AllocMem(z+z);d:=p+z;Assign(F,ParamStr(1));Reset(F,1);BlockRead(F,p^,z);repeat z:=1;x:=p^;case x-43of 1:Read(PChar(d)^);3:Write(Char(d^));0,2:d^:=d^+44-x;17,19:d:=d+x-61;48,50:if(d^=0)=(x=91)then repeat p:=p+92-x;z:=z+Ord(p^=x)-Ord(p^=x xor 6);until z=0;end;Inc(p)until x=0;end.

```

Here the same code, indented and commented :

```
var
  d,p:PByte;
  x:Int8;
  f:File;
  z:Word=30000;
begin
  // Allocate 30000 bytes for the program and the same amount for the data :
  p:=AllocMem(z+z);
  d:=p+z;
  // Read the file (which path must be specified on the command line) :
  Assign(F,ParamStr(1));
  Reset(F,1);
  BlockRead(F,p^,z);
  // Handle all input, terminating at #0 (better than the spec requires) :
  repeat
    // Prevent a begin+end block by preparing beforehand (values are only usable in '[' and ']' cases) :
    z:=1;                       // Start stack at 1
    x:=p^;                      // Starting at '[' or ']'
    // Choose a handler for this token (the offset saves 1 character in later use) :
    case x-43of
      1:Read(PChar(d)^);        // ','     : Read 1 character from input into data-pointer
      3:Write(Char(d^));        // '.'     : Write 1 character from data-pointer to output
      0,2:d^:=d^+44-x;          // '+','-' : Increase or decrease data
      17,19:d:=d+x-61;          // '<','>' : Increase or decrease data pointer
      48,50:                    // '[',']' : Start or end program block, the most complex part :
        if(d^=0)=(x=91)then     // When (data = 0 and forward), or when (data <> 0 and backward)
        repeat                  //
          p:=p+92-x;            // Step program 1 byte back or forward
          z:=z+Ord(p^=x)        // Increase stack counter when at another bracket
              -Ord(p^=x xor 6); // Decrease stack counter when at the mirror char
        until z=0;              // Stop when stack reaches 0
    end;
    Inc(p)
  until x=0;
end.

```

This one took me a few hours, as it's not the kind of code I normally write, but enjoy!

Note : The prime test works, but doesn't stop at 100, because it reads #13 (CR) before #10 (LF)... do other submissions suffer this problem too when running on CRLF OSes?

# Answer
> 7 votes
# Python 2, 223

I admit that I recycled an old program of mine (but had to change it quite a bit, because the old version didn't have input, but error checking...).

```
P="";i,a=0,[0]*30000
import os,sys
for c in open(sys.argv[1]).read():x="><+-.[,]".find(c);P+=" "*i+"i+=1 i-=1 a[i]+=1 a[i]-=1 os.write(1,chr(a[i])) while+a[i]: a[i]=ord(os.read(0,1)) 0".split()[x]+"\n";i+=(x>4)*(6-x)
exec P

```

Runs the primes calculator fine.

I see now that Alexandru has an answer that has some similarities. I'll post mny answer anyways, because I think there are some new ideas in it.

# Answer
> 7 votes
## X86\_64/Linux Machine Code, 104 101 100 99 98 97 96 95 93 92 91 89

**Usage:**

```
$> gcc -s -static -nostartfiles -nodefaultlibs -nostdlib -Wl,-Tbss=0x7ffe0000 -DBF_IDEAL_BSS -Wl,--build-id=none bf.S -o bf
$> ./bf <input>

```

#### Notes

* Size is measured in machine code (i.e 89 bytes of `PROGBITS`; `.text`, `.data`, etc...)
* `-9` bytes if reads input prog from stdin
* `-4` more bytes without `BF_EXITCLEANLY` (it will segfault to exit).
* `-2` more bytes with `BF_BALANCED` (assumes that over course of program data cell returns to start).
* So minimum possible size **74** bytes.
* **NOTE** Without the ideal bss setup (at address `0x7ffe0000` and `BF_IDEAL_BSS` defined as seen in compile command above) add `+2` bytes.

```
#define BF_LBRACE   91
#define BF_RBRACE   93

#define BF_DOT  46
#define BF_COMMA    44

#define BF_PLUS 43
#define BF_MINUS    45

#define BF_LSHIFT   60
#define BF_RSHIFT   62

#define BF_READFILE
#define BF_EXITCLEANLY
    // #define BF_IDEAL_BSS
    // #define BF_BALANCED

    .global _start
    .text
_start:
    /* All incoming registers at zero.  */

    /* Large read range. This may cause errors for huge programs
       (which will fail anyways).  */
    decl    %edx
#ifdef BF_READFILE
    /* open.  */
    movb    $2, %al
    /* 3rd argument in rsp is first commandline argument.  */
    pop %rdi
    pop %rdi
    pop %rdi
    /* O_RDONLY is zero.  */
    syscall
    /* Error is okay, we will eventually just exit w.o executing.  */
    xchgl   %eax, %edi

    /* Sets ESI at 2 ** 31. This is an arbitrary address > 65536
       (minimum deref address on linux) < 2 ** 32 - PROG_SPACE
       (PROG_SPACE ~= 262144). We setup bss at 2 ** 31 - 131072 via
       linker script (-Tbss=0x7ffe0000).  */
# ifdef BF_IDEAL_BSS
    bts %edx, %esi
# else
    movl    $(G_mem + 65536), %esi
# endif
    /* bss initialized memory is zero. This is cheapest way to zero
       out eax.  */
    lodsl
#else
# ifdef BF_IDEAL_BSS
    bts %edx, %esi
# else
    movl    $(G_mem + 65536), %esi
# endif
#endif

    /* eax/edi are already zero which happens to match
       SYS_read/STDIN_FILENO.  */
    syscall

    /* Usage linux' pre-allocated stack for braces.  */

    /* Program code grows up.  */
    movl    %esi, %ebx
    /* Assuming no errors, reach stores size in eax. Note errors or
       0-byte reads are okay. The ebx is readable memory and zero-
       initialized (bss), so it its zero-length, it will just be an
       invalid op and we will hit bounds check below. If its error,
       eax is negative so ebx will be negative and likewise we will
       hit bounds check below.  */

#ifdef BF_BALANCED
    addl    %eax, %esi
    xchgl   %eax, %ebp
#else
    addl    %esi, %eax
    xchgl   %eax, %ebp
    movl    %ebp, %esi
#endif

    /* We have -1 in edx, so negative to get 1. 1 is needed in a
       variety of places.  */
    negl    %edx
run_program:
    /* Need to zero eax.  */
    movb    (%rbx), %al
    incl    %ebx

    /* %al contains the program "instruction". Its unique to one of
       8 values so just test each in order. If instruction matches
       execute it then fallthrough (%al can only ever match one).
       We occasionally set al but are sure never to set it to the
       ASCII value of any of our 8 instructions.  */

    /* TODO: Brace handling could probably be smaller.  */
try_lbrace:
    cmpb    $BF_LBRACE, %al
    je  do_lbrace
try_rbrace:
    cmpb    $BF_RBRACE, %al
    jne try_cont
do_rbrace:
    /* Popping state (we might repush if we are looping back).  */
    pop %rdx
    pop %rdi
    /* Non-zero cell means loop. Note we have 1 cached in edx.  */
    cmpb    %dl, (%rsi)
    jb  next_insn
    movl    %edi, %ebx
do_lbrace:
    /* Restore loop state.  */

    push    %rbx
    push    %rdx

    /* If cell is zero, then we are skipping till RBRACE. Note we
       have 1 cached in edx.  */
    cmpb    %dl, (%rsi)
    /* -1 if we want to start skipping.  */
    sbb %dh, %dh
try_cont:
    orb %dh, %al
    /* we have set ah s.t its either zero or has a value that makes
       any further matches impossible.  */

    /* For the rest of the ops we take advantage of the fact that
       the ascii values of the pairs '<'/'>', '+'/'-', and '.',','
       are all 2 apart. This allows use to test a pair with the
       following formula: `((al - PAIR_LO) & -3) == 0`. This will
       always leave the pair as 0/2 and will match only the pair.
       It turns out 0/2 are useful and can be used to do all the
       rest of the operations w.o extra branches.  */

try_lshift:
    subb    $BF_LSHIFT, %al
    testb   $-3, %al
    jnz try_comma
    addl    %eax, %esi
    decl    %esi
try_comma:
try_dot:
    subb    $(BF_PLUS - BF_LSHIFT), %al

    /* We have 0/1/2/3 for '+'/','/'-'/'.' so check if we remaining
       valid opcode.  */
    cmpb    $3, %al
    ja  next_insn

    /* 0/2 are '+'/'-' so check low bits. TODO: There may be a way
       to just care from `shr $1, %al' which would save us an
       instruction. But it messes up the '+'/'-' case.  */
    testb   $-3, %al
    jz  try_minus

    /* al is either 3/1. Shift by 1 to get 1/0 for our syscall number.  */
    shrb    $1, %al

    // btsq    $, %rax
    /* SYS_write == STDOUT_FILENO, SYS_read == STDIN_FILENO.  */
    movl    %eax, %edi
    /* We already have 1 in rdx.  */
    syscall
    /* Assuming no io error, eax is 1. We will subtract 1 from eax
       in try_minus/try_plus so it will be +/- 0 which does
       nothing.  */
try_minus:
try_plus:
    /* If not coming from syscall eax is 0/2. 0 --> plus, 2 -->
       minus. So (rsi - eax + 1) translates.  */
    // setbe   %cl

    subb    %al, (%rsi)
    incb    (%rsi)

next_insn:
#ifdef BF_BALANCED
    /* If BF_BALANCED is set, we assume that the program will have
       shifted back columns to start before exiting.  */
    cmpl    %ebx, %esi
#else
    cmpl    %ebx, %ebp
#endif
    jg  run_program

#ifdef BF_EXITCLEANLY
    /* eax has zero upper 24 bits so we can cheat and use movb here.
       (This isn't exact correct, assuming no IO errors on last
       instruction).  */
    movb    $60, %al
    syscall
#endif

    .section .bss
    .align  32
G_mem:  .space(65536 * 4)

```

Edit: Just for fun, here a compliant **269** byte fully contained ELF file that implements brainfuck on Linux/X86\_64:

Its possible to make this smaller.

* We could take advantage of the known linux ELF impl and put code in known-unused fields.

```
00000000  7f 45 4c 46 02 01 01 00  00 00 00 00 00 00 00 00  |.ELF............|
00000010  02 00 3e 00 01 00 00 00  b0 10 40 00 00 00 00 00  |..>.......@.....|
00000020  40 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |@...............|
00000030  00 00 00 00 40 00 38 00  02 00 00 00 00 00 00 00  |....@.8.........|
00000040  01 00 00 00 05 00 00 00  00 00 00 00 00 00 00 00  |................|
00000050  00 10 40 00 00 00 00 00  00 10 40 00 00 00 00 00  |..@.......@.....|
00000060  cd 00 00 00 00 00 00 00  cd 00 00 00 00 00 00 00  |................|
00000070  00 00 00 00 00 00 00 00  01 00 00 00 06 00 00 00  |................|
00000080  00 00 00 00 00 00 00 00  00 00 fe 7f 00 00 00 00  |................|
00000090  00 00 fe 7f 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000a0  00 00 04 00 00 00 00 00  20 00 00 00 00 00 00 00  |........ .......|
000000b0  ff ca b0 02 5f 5f 5f 0f  05 97 0f ab d6 ad 0f 05  |....___.........|
000000c0  89 f4 89 f3 01 c6 89 f5  f7 da 0f b6 03 ff c3 3c  |...............<|
000000d0  5b 74 0c 3c 5d 75 0e 5a  5f 38 16 72 28 89 fb 53  |[t.<]u.Z_8.r(..S|
000000e0  52 38 16 18 f6 08 f0 2c  3c a8 fd 75 04 01 c6 ff  |R8.....,<..u....|
000000f0  ce 2c ef 3c 03 77 0e a8  fd 74 06 d0 e8 89 c7 0f  |.,.<.w...t......|
00000100  05 28 06 fe 06 39 dd 7f  c1 b0 3c 0f 05           |.(...9....<..|
0000010d

```

# Answer
> 7 votes
# Desmos, 470 bytes

Program input:

* variable \\$P\\$, containing an array of ASCII codepoints representing the brainfuck program.
* variable \\$I\\$, also containing an array of ASCII codes for stdin

You can use this program to convert your ASCII to a list of numbers. Unless you like to play the waiting game, I would also recommend that you minify your program

stdout is represented by the array \\$O\\$. Like \\$P\\$ and \\$I\\$, it is also an array of codepoints.

In addition, you can inspect the memory tape in variable \\$M\\$. The memory consists of 30000 unsigned bytes, though it will only store as many bytes as necessary because storing 30000 bytes is not great for performance.

To begin execution, run the "reset" action and then start the ticker.

---

**Ticker code**

```
\left\{j<=P.length:c,a\right\}

```

**Expression list**

```
O=[]
i=1
k=1
M=[0]
s(x)=M->[\{l=p:\mod(x,256),M[l]\}\for l=[1...M.\length]]
p=1
v=M[p]
w=P[i]
j=1
N=[]
S=[]
a=\{59<w<63:p->p+w-61,w=44:b,42<w<46:s(v+44-w),w=46:O->O.\join(v),w=91:i->\{v=0:N[i],i\}+1,w=93:i->\{v=0:i,N[i]\}+1\},\{w=62:\{30000>p>=M.\length:M->M.\join(0)\}\},\{\{w=91,w=93,0\}=0:i->i+1\}
b=s(I[k]),k->k+1
c=\{P[j]=93:d,N->N.\join(0)\},\{P[j]=91:S->\join(j,S)\},j->j+1
d=N->[\{m=S[1]:j,m=j:S[1],N[m]\}\for m=[1...j]],S->S[2...]

```

Try it on Desmos!

The program loaded in the above TioD is a "Hello, World!" program. The prime number program took around five minutes to print `2 3 5` so I decided that maybe it wasn't the best idea to run it.

---

**How it works**

The interpreter first matches up bracket pairs, then scans through the program character-by-character and executes them.

Below is the code for bracket-matching:

```
j=1
N=[]
S=[]
c=\{P[j]=93:d,N->N.\join(0)\},\{P[j]=91:S->\join(j,S)\},j->j+1
d=N->[\{m=S[1]:j,m=j:S[1],N[m]\}\for m=[1...j]],S->S[2...]

```
* \\$j\\$ is a list index, indicating that character \\$P\[j\]\\$ is currently being processed
* \\$N\\$ holds the index of the matching bracket pair, if it exists. If \\$N\[i\]\\$ is a positive integer, then \\$P\[i\]\\$ matches with \\$P\[N\[i\]\]\\$.
* \\$S\\$ is a stack containing the indices of all unmatched `[`s thus far. The top of the stack is at \\$S\[1\]\\$.

Next there are two actions, \\$c\\$ and \\$d\\$.

Every time action \\$c\\$ is run, the next character in the program is processed.

```
c=\{P[j]=93:d,N->N.\join(0)\},\{P[j]=91:S->\join(j,S)\},j->j+1
c=                                                                c is an action containing:
  \{                       \},                                     a conditional...
    P[j]=93:d,                                                      that runs d if P[j]=93 (']')
              N->N.\join(0)                                         and appends 0 to N otherwise
                              \{                     \},           a conditional...
                                P[j]=91:                            that when P[j]=91 ('[')...
                                        S->\join(j,S)                pushes j to S
                                                        j->j+1     increment j

```

\\$d\\$ is the response to when a `']'` character is detected. Because it consists of two actions, it cannot be directly placed in the conditional and thus must be defined separately.

```
d=N->[\{m=S[1]:j,m=j:S[1],N[m]\}\for m=[1...j]],S->S[2...]
d=                                                            d is an action consisting of:
  N->[\{                  N[m]\}\for m=[1...j]],               a modification to N
        m=S[1]:j,                                               in which N[S[1]] is set to j
                 m=j:S[1],                                      and N[j] is set to S[1]
                                                S->S[2...]     the topmost value is popped from S

```

Once bracket pairs are matched the expression is evaluated character-by-character:

```
i=1
k=1
M=[0]
s(x)=M->[\{l=p:\mod(x,256),M[l]\}\for l=[1...M.\length]]
p=1
v=M[p]
w=P[i]
a=\{59<w<63:p->p+w-61,w=44:b,42<w<46:s(v+44-w),w=46:O->O.\join(v),w=91:i->\{v=0:N[i],i\}+1,w=93:i->\{v=0:i,N[i]\}+1\},\{w=62:\{p=M.\length:M->M.\join(0)\}\},\{\{w=91,w=93,0\}=0:i->i+1\}
b=s(I[k]),k->k+1

```
* \\$i\\$ is the instruction pointer
* \\$k\\$ is the next character to be read in stdout
* \\$M\\$ is the memory tape
* \\$s(x)\\$ sets the value of the current cell to \\$x\\$
* \\$p\\$ points to the current memory cell
* \\$v\\$ is the value of the current cell
* \\$w\\$ is the current instruction

\\$a\\$ is an action that executes the next character. \\$b\\$ is a utility for reading from stdin - like \\$d\\$, \\$b\\$ is separated because conditional branches only support one action.

\\$a\\$ is rather long, so here it is branch-by-branch:

```
a=
\{
  59<w<63:p->p+w-61,                       ><: hack for p±±-ing; 6 bytes smaller than doing it separately
  w=44:b,                                  ,: read from stdin (do this before +- to avoid interference)
  42<w<46:s(v+44-w),                       +-: same hack
  w=46:O->O.\join(v),                      .: write to stdout
  w=91:i->\{v=0:N[i],i\}+1,                [: jump to end if v=0
  w=93:i->\{v=0:i,N[i]\}+1                 ]: jump to start if v!=0
\},
\{w=62:\{p=M.\length:M->M.\join(0)\}\},    widen memory tape if necessary
\{\{w=91,w=93,0\}=0:i->i+1\}               increment instruction pointer if not '[' or ']'

```

Essentially \\$a\\$ is a big conditional that performs different actions for different characters, then ties up some loose ends afterwards.

\\$b\\$, which reads from stdin, is relatively straightforward:

```
b=s(I[k]),k->k+1
b=                  b is an action that
  s(I[k]),          writes the next character from stdin into memory
          k->k+1    and increments the character pointer for stdin

```

Finally, the exection of all of this is controlled by a ticker:

```
\left\{j<=P.length:c,a\right\}

```

This ticker will choose between \\$a\\$ and \\$c\\$ depending on whether the bracket matching is done or not.

When the input program and stdin are set up and the ticker is run, this program should be able to interpret any brainfuck expression. Just maybe not in a reasonable time frame.

# Answer
> 6 votes
# Recall, 594 bytes

In short: Recall has no arithmetic operators in a classic sense, it only has bitwise operations. You can not just "add one" etc. Recall is also strictly stack-based.

```
DC505M22022M32032M606M42042M707M92092M4405022o032o06o042o07o092o044o1305022o06o042o092o52052q.q2305022o06o07o93093q.q5403206o07o14014q.q6403206o042o07o24024q.q74Yx34034z03MMMMMMMM034o3yY030401r3.4.101zyY040301r4.3.101zY01052gZ02Z040301052023s4.3.10zyY01023gZ02z030401023052s3.4.10zyY01093gZ02q20zyY01054gZ02u20zyY01014gZx20zyY01064gZ02X0zyY01024gZ03304302r33.43.20zyY01074gZ04303302r43.33.20zyyQ6205.8Y06208g6206208iZ08M808013izy062U7205.9Y07209g7207209iz09M909013izy072R53.63.82063MMMMMMMM053o63082013i53082KKKKKKKK82053063082S84.94.12.73.83t012073083TY083073012r83.73.12012084gzY012094gZt0zyy

```

---

### Example 1: Print something

Input:

```
-[--->+<]>-----..-[----->+<]>.++++.+[->++++<]>.---[----->++<]>.---.------------.++++++++.++++++++.+[-->+++++<]>-.

```

Output:

```
PPCG rocks!

```

---

### Example 2: Output square numbers up to 100

Input:

```
+[>++<-]>[<+++++>-]+<+[>[>+>+<<-]++>>[<<+>>-]>>>[-]++>[-]+>>>+[[-]++++++>>>]<<<[[<++++++++<++>>-]+<.<[>----<-]<]<<[>>>>>[>>>[-]+++++++++<[>-<-]+++++++++>[-[<->-]+[<<<]]<[>+<-]>]<<-]<<-]

```

Output:

```
0
1
4
9
16
25
36
49
64
81
100

```

This example might take a few minuted to execute and might cause a "this tab is frozen" message. Ignore that and wait.

# Answer
> 6 votes
# C (gcc), ~~273~~ 268 bytes

```
main(_,a){_=fopen("w.c","w");fputs("main(){char a[30000],*p=a;",_);x:a=getchar();fputs(a-62?a-60?a-43?a-45?a-46?a-44?a-91?a-93?~a?"":"}":"}":"while(*p){":"*p=getchar();":"putchar(*p);":"--*p;":"++*p;":"--p;":"++p;",_);if(~a)goto x;fclose(_);system("cc w.c;./a.out");};

```

Try it online!

-5 thanks to ceilingcat

Takes input from stdin.

This relies a little bit on the environment, but is pretty consistent. This is effectively the eval solution for c. It writes an appropriate C program to the file w.c, compiles it, and runs it as the desired executable. Thus as a bonus effect this actually compiles the bf code and leaves `a.out` as a binary for it. Note that depending on the system you may need to modify the last string. In particular most windows c compilers call the default executable "a.exe". Luckily as far as I can tell, they all have the same length so the bytecount is the same. (though if you don't have a cc defined you may need to add a letter such as gcc to the compile command, adding 1 byte).

*I am aware that this thread is a bit old, but I didn't see this style of C solution yet, so I thought I'd add it.*

# Answer
> 6 votes
# Vyxal `DOb`, ~~54~~ ~~53~~ 50 bytes

```
`><+-][.,`£¥↔¥`‟„›‹}`f`{:|:C₴_¼`²JĿ?ṘƛC⅛;k23*(0)„Ė

```

Try it Online!

-4 thanks to Aaron Miller.

The basic idea is that a stack is a wrapping tape if you can rotate the whole thing. So it's really just setting up the input, pushing 0s, and transpiling:

* `>` \-  \- rotate stack right
* `<` \-  \- rotate stack left
* `+` \-  \- increment the current item
* `-` \-  \- decrement the current item
* `[` \- `{:|` \- set a while loop without popping the top
* `]` \- `}` \- close a while loop
* `.` \- `:C₴` \- Duplicate, make a char and output without a trailing newline
* `,` \-  \- pop, then take a character from input

`?ṘƛC⅛;` takes the input and pushes each character to the global array. Then `k23*(0)` pushes 30k zeroes, then `„Ė` runs the code!

# Answer
> 5 votes
# Lua, 285

```
loadstring("m,p={0},1 "..io.open(arg[1]):read"*a":gsub("[^.,<>[%]+-]",""):gsub(".",{["."]="io.write(string.char(@)) ",[","]="@=io.read(1):byte() ",["<"]="p=p-1 ",[">"]="p=p+1 @=@or 0 ",["["]="while @~=0 do ",["]"]="end ",["+"]="@=(@+1)%256 ",["-"]="@=(@-1)%256 "}):gsub("@","m[p]"))()

```

Somewhat readable version:

```
loadstring( --execute
    "m,p={0},1 ".. --initialize memory and pointer
    io.open(arg[1]) --open file
        :read"*a" --read all
            :gsub("[^.,<>[%]+-]","") --strip non-brainfuck
                :gsub(".", --for each character left
                    {["."]="io.write(string.char(@)) ", -- '@' is shortcut for 'm[p]', see below
                    [","]="@=io.read(1):byte() ",
                    ["<"]="p=p-1 ",
                    [">"]="p=p+1 @=@or 0 ", --if a before unexplored memory cell, set to 0
                    ["["]="while @~=0 do ",
                    ["]"]="end ",
                    ["+"]="@=(@+1)%256 ", --i like it overflowing
                    ["-"]="@=(@-1)%256 "
                    }
                )
                    :gsub("@","m[p]") --replace the '@' shortcut
    ) --loadstring returns a function
() --call it

```

Works perfectly

# Lua, 478, w/o loadstring

```
local m,p,i,r,c={0},1,1,{},io.open(arg[1]):read"*a"while i<=#c do(({[43]=function()m[p]=(m[p]+1)%256 end,[45]=function()m[p]=(m[p]-1)%256 end,[62]=function()p=p+1 m[p]=m[p]or 0 end,[60]=function()p=p-1 end,[46]=function()io.write(string.char(m[p]))end,[44]=function()m[p]=io.read(1):byte()end,[91]=function()if m[p]==0 then i=select(2,c:find("%b[]",i))else r[#r+1]=i end end,[93]=function()if m[p]==0 then r[#r]=nil else i=r[#r] end end})[c:byte(i)]or function()end)()i=i+1 end

```

Readable version:

```
local m,   p, i, r,  c= --memory, pointer, brackets stack, code
      {0}, 1, 1, {}, io.open(arg[1]) --open file
              :read"*a" --read it
while i<=#c do --while there's code
    (
        (
            {
                [43]=function() -- +
                    m[p]=(m[p]+1)%256
                end,
                [45]=function() -- -
                    m[p]=(m[p]-1)%256
                end,
                [62]=function() -- >
                    p=p+1 m[p]=m[p]or 0 --if new memory cell, set it to 0
                end,
                [60]=function() -- <
                    p=p-1
                end,
                [46]=function() -- .
                    io.write(string.char(m[p]))
                end,
                [44]=function() -- ,
                    m[p]=io.read(1):byte()
                end,
                [91]=function() -- [
                    if m[p]==0 then
                        i=select(2,c:find("%b[]",i)) --find matching ]
                    else
                        r[#r+1]=i --push position to the stack
                    end
                end,
                [93]=function() -- ]
                    if m[p]==0 then
                        r[#r]=nil --pop from stack
                    else
                        i=r[#r] --go to position on the top of stack
                    end
                end
            }
        )[c:byte(i)] --transform character into code
        or function()end --do nothing on non-brainfuck
    )() --run the resulting function
    i=i+1 --go to the next opcode
end

```

# Answer
> 5 votes
# Exceptionally, 294 bytes

```
{0C}r{c?!1!14G}cG+r}i{0}p}q}fR}t}s{""}o{1F}u{t:29999?{t;~0;}t{t:q}k{c:p?{o;P;/A}d{f>0?!11{d=91?!3{f+1}f=93?!3{f-1}f{0}d{q}l{d=43?!3{k+1}k{d=44?!7{i:0A}k{i[1}i=45?!3{k-1}k{d=46?!6{kC}y{o+y}o{d=62?!3{q+1}q{d=91?!8{k=0?!3{1}f!3{s~p}s=93?!7{s:u-1}p{s]u}s=60?!3{q-1}q{k%256}k{t[l[1}u{t]l~k+u}t{p+1}p

```

Attempt This Online! This took ages to write.

Input is terminated with a null byte (and going past this crashes it), wrapping the tape is undefined behaviour for reasons explained below.

Ungolfed version (ish). Also, here's a modified version that appends a trailing newline to the input running the example primes code. This is so slow that it times out for n=10, so this is n=5.

## Explanation

Exceptionally is a language created by DLosc where the program runs in an infinite loop, and the only form of control flow is throwing and catching exceptions.

A few quirks of this answer:

* Rather than initialising the tape as an array of 30000 0s, which couldn't be done in one cycle, I start with \[\] and append a 0 before each iteration, up to a length of 30000. This only causes issues if the program attempts to go to the left of the tape, so that's undefined behaviour and will result in the IP pointing to the constantly-updating end of the tape.
* Exceptionally only allows printing strings with a leading newline, so I store the output in a buffer and print it upon termination.
* I can't easily change the value of one item in an array, so instead I take `tape[:ip-1] + [new_value] + tape[ip+1:]`.
* To deal with loops, I store a stack of previous `[` bracket positions, jump back to the last `]` on a `[`, and if the current cell is 0 on a `[` I move forward until I find the matching bracket.

**Setup**

```
{0C}r{c?!1!14G}cG+r}i{0}p}q}fR}t}s{""}o{1F}u
{0C}r                                        ' r = "\0"
     {c?!1!14                                ' If c (code) is not defined (to only run once)
             G}c                             ' c = input()
                G+r}i                        ' i (input) = input() + "\0"
                     {0}p}q}f                ' p (IP) = q (tape pointer) = f (skip counter) = 0
                             R}t}s           ' t (tape) = s (bracket stack) = []
                                  {""}o      ' o (output)
                                       {1F}u ' u = -1

```

```
{t:29999?{t;~0;}t{t:q}k{c:p?{o;P;/A}d{f>0?!11{d=91?!3{f+1}f=93?!3{f-1}f{0}d{q}l
{t:29999?                                                                       ' If tape length < 30000
         {t;~0;}t                                                               ' Append a zero to the tape
                 {t:q}k                                                         ' k (current cell) = tape[tp]
                       {c:p       A}d                                           ' d (current char) = ord(code[ip])
                           ?{o;P;/                                              ' If that crashes because IP's gone out of bounds, print output and terminate
                                     {f>0?!11------------------------------     ' If skip > 0 (currently skipping a loop)
                                             {d=91?!3{f+1}f                     ' If d is 91 ("[") increment skip counter
                                                           =93?!3{f-1}f         ' If d is 93 ("]") decrement skip counter
                                                                       {0}d     ' Nullify current char (currently skipping chars)
                                                                           {q}l ' Make a copy of IP for tape-shifting purposes

```

**Commands**

```
{d=43?!3{k+1}k{d=44?!7{i:0A}k{i[1}i=45?!3{k-1}k{d=46?!6{kC}y{o+y}o
{d=43?!3                                                           ' If current char is 43 (+)
        {k+1}k                                                     ' Increment current cell
              {d=44?!7                                             ' If 44 (,)
                      {i:0A}k                                      ' current cell = ord(input[0])
                             {i[1}i                                ' remove first char of input buffer
                                   =45?!3                          ' If 45 (-)
                                         {k-1}k                    ' Decrement current cell
                                               {d=46?!6            ' If 46 (.)
                                                       {kC}y{o+y}o ' Append chr(current cell) to output buffer

```

```
{d=62?!3{q+1}q{d=91?!8{k=0?!3{1}f!3{s~p}s=93?!7{s:u-1}p{s]u}s=60?!3{q-1}q
{d=62?!3                                                                  ' If current char is 62 (>)
        {q+1}q                                                            ' Increment tape pointer
              {d=91?!8                                                    ' If 91 ([)
                      {k=0?!3                                             ' If current cell is 0
                             {1}f                                         ' Start skipping chars
                                 !3{s~p}s                                 ' Else (nonzero) continue normal execution and push current IP to call stack
                                         =93?!7                           ' If 93 (])
                                               {s:u-1}p{s]u}s             ' Jump to before last item of call stack, pop call stack
                                                             =60?!3       ' If 60 (<)
                                                                   {q-1}q ' Decrement tape pointer

```

**Final stuff**

```
{k%256}k{t[l[1}u{t]l~k+u}t{p+1}p
{k%256}k                         ' Modulo current cell by 256
        {t[l[1}u                 ' u = all tape cells past IP
                {t]l             ' All tape cells before IP
                    ~k+u         ' Append new current cell value and concatenate rest of tape
                        }t       ' Store into tape
                          {p+1}p ' Increment IP

```

# Answer
> 4 votes
## C, 374 368

Reads from a file. Passes PRIME.BF test.

**Usage: ./a.out PRIME.BF**

```
#include <stdio.h>
main(int c,char**v){int m[30000],s[99],p=0,i=0,n=0;char l[9999],d;FILE*f=fopen(v[1],"r");for(l[i]=0;i<9999&&l[i]!=EOF;l[i]=getc(f))i++;for(i=1;d=l[i];i++){if(!n){p+=d-62?0:1;p-=d-60?0:1;m[p]+=d-43?0:1;m[p]-=d-45?0:1;if(d==46)putchar(m[p]);if(d==44){m[p]=getchar();}if(d==93){i=s[c]-1;c--;n++;}}if(d==91){if(m[p]){c++;s[c]=i;}else{n++;}}n-=d-93?0:1;}}

```

**Reformatted:**

```
#include <stdio.h>
main(int c,char**v){
    int m[3000],s[99],p=0,i=0,n=0;
    char l[9999],d;
    FILE*f=fopen(v[1],"r");
    for(l[i]=0;i<9999&&l[i]!=EOF;l[i]=getc(f))i++;
    for(i=1;d=l[i];i++){
        if(!n){ // > < + - . , ] \n [ ]
            p+=d-62?0:1;
            p-=d-60?0:1;
            m[p]+=d-43?0:1;
            m[p]-=d-45?0:1;
            if(d==46)putchar(m[p]);
            if(d==44){m[p]=getchar();}
            if(d==93){i=s[c]-1;c--;n++;}
        }
        if(d==91){if(m[p]){c++;s[c]=i;}else{n++;}}
        n-=d-93?0:1;
    }
}

```

# Answer
> 4 votes
## 16-bit x86 assembler code, 104 bytes

Assembles with YASM. It wants the file piped from stdin, though.

```
;compliant version, non-commands are ignored, but 104 bytes long

[bits 16]
[org 0x100]
; assume bp=091e used
; assume di=fffe
; assume si=0100
; assume dx=cs (see here)
; assume cx=00ff
; assume bx=0000
; assume ax=0000 used (ah)
; assume sp=fffe
start:
        mov al, code_nothing - start
code_start:
        mov ch, 0x7f ; allow bigger programs
        mov bx, cx
        mov di, cx
        rep stosb
        mov bp, find_right + start - code_start ;cache loop head for smaller compiled programs
        jmp code_start_end
find_right:
        pop si
        dec si
        dec si ;point to loop head
        cmp [bx], cl
        jne loop_right_end
loop_right:
        lodsb
        cmp al, 0xD5 ; the "bp" part of "call bp" (because 0xFF is not unique, watch for additional '[')
        jne loop_left
        inc cx
loop_left:
        cmp al, 0xC3 ; ret (watch for ']')
        jne loop_right
        loop loop_right ;all brackets matched when cx==0
        db 0x3c ;cmp al, xx (mask push)
loop_right_end:
        push si
        lodsw ; skip "call" or dummy "dec" instruction, depending on context
        push si
code_sqright:
        ret
code_dec:
        dec byte [bx]
code_start_end:
        db '$' ;end DOS string, also "and al, xx"
code_inc:
        inc byte [bx]
        db '$'
code_right:
        inc bx ;al -> 2
code_nothing:
        db '$'
code_left:
        dec bx
        db '$'
code_sqleft:
        call bp
        db '$'
; create lookup table
real_start:
        inc byte [bx+''] ;point to code_right
        mov byte [bx+'['], code_sqleft - start
        mov byte [bx+']'], code_sqright - start
        lea sp, [bx+45+2] ;'+' + 4 (2b='+', 2c=',', 2d='-', 2e='.')
        push (code_dec - start) + (code_dot - start) * 256
        push (code_inc - start) + (code_comma - start) * 256
pre_write:
        mov ah, code_start >> 8
        xchg dx, ax
; write
        mov ah, 9
        int 0x21
; read
code_comma:
        mov dl, 0xff
        db 0x3d ; cmp ax, xxxx (mask mov)
code_dot:
        mov dl, [bx]
        mov ah, 6
        int 0x21
        mov [bx], al
        db '$'
        db 0xff ; parameter for '$', doubles as test for zero
; switch
        xlatb
        jne pre_write
  ; next two lines can also be removed
  ; if the program ends with extra ']'
  ; and then we are at 100 bytes... :-)
the_end:
        mov dl, 0xC3
        int 0x21
        int 0x20
```

# Answer
> 4 votes
# Gol\>\<\>, 111 bytes

```
/2ds2e111`!a0im*aF+:ZB|0L.
^9R~`;r"0RXf2"WL0p|m0.
^8R~`P
^7R~"~iE0"
^6R~`M
^5R~":o"
^4R~`{
^3R~`}
^~~`W
^~`|
^~

```

Try Hello World online! or Try String Reverser online!

### How it works

```
The first row is the main loop.

/2ds2e111`!a0im*aF+:ZB|0L.

 2ds2e111`!a0               Push [2,29,2,14,1,1,1,33,10,0]
                            (the differences of all valid chars)
             im*            Take input and negate it
                aF... |     Repeat 10 times...
                  +:ZB      Add, and break if the sum is 0
                       0L.  Jump to another row based on loop count

Other rows share the structure:

^xR~...

 xR~     Discard unneeded numbers x times
    ...  Push relevant code
^        Return to the main loop

Newline is the delimiter between code and input.

^9R~`;r"0RXf2"WL0p|m0.

    `;r"0RXf2"          Add "2fXR0" to the start and ";" to the end
                        "2fXR0" pushes 2**15 zeros to the stack
                        ";" finishes the program
              W...|     While there is some code on the stack...
               L0p      Write the code on the row 0
                   m0.  Jump to row 0

Other lines are for command translation.

^8R~`P      "+" => "P"    Increment
^7R~"~iE0"  "," => "~iE0" Erase current cell, take input and
                          change to 0 if EOF
^6R~`M      "-" => "M"    Decrement
^5R~":o"    "." => ":o"   Duplicate current cell and print
^4R~`{      "<" => "{"    Rotate to the left
^3R~`}      ">" => "}"    Rotate to the right
^~~`W       "[" => "W"    While (non-popping)
^~`|        "]" => "|"    End while
^~       Others => ""     Ignore

```

Inlining the switch-case turned out to be a nightmare (simply because there is no explicit `if...else` structure in `Gol><>`), so I used an index-jump method instead.

# Answer
> 4 votes
# dirt, 489

```
'@[^@]*"# @00000000 "(#[^#]*|"#")'#|[^R]*(('<R+`<|'>R+`>|'-R+`-|'+R+`+|'.R+`.|',R+`,|'['RR+`[|']`RR+`])|`R\]'@).*|.*((`<L+'<|`>L+'>|`-L+'-|`+L+'+|`.L+'.|`,L+',|`[`LL+'[|`]'LL+'])|'@\[`L)[^L]*|[^x]*(`x('0[^#]*#`0|'1[^#]*#`1)|(`x'0)+ .*##).*|.*`I",@"[^x]*|.*`o(0'o.*'0|1'o.*'1| .*)|.*`O".@"[^o]*|.*`@(-'@.*@([^ ]*`1'0|)(`0'1)* |\+'@.*@([^ ]*`0'1|)(`1'0)* |<'@.*#( @"00000000 "|.* '@[^ ]+ `@)|>'@.*`@[^ ]+ '@("00000000 "|[^#]+)#|\['@.*@([^ ]*1)|'L\]|\['R.*@0* |`,'I.*@({0|1}'x)* |`.'O.*@'o).*

```

Has unbounded tape but doesn't work with comment characters.

To run, save as `brainfuck.dirt` and run `dirt brainfuck.dirt -i "[bf_program]#[binary_input]"` (`#` can be omitted if there's no input). It will print `[bf_program]#[memory]#[unread_input]#[output]`.

e.g.

```
> dirt brainfuck.dirt -i ",[.,]#0100100001001001"
,[.,]@# @00000000 ##0100100001001001

```

Use the `-v` flag to watch it as it runs:

```
    > dirt brainfuck.dirt -v -i "+++++++[>+++++++<-]>.+.+."
+++++++[>+++++++<-]>.+.+.
@+++++++[>+++++++<-]>.+.+.# @00000000 ##
+@++++++[>+++++++<-]>.+.+.# @00000001 ##
++@+++++[>+++++++<-]>.+.+.# @00000010 ##
+++@++++[>+++++++<-]>.+.+.# @00000011 ##
++++@+++[>+++++++<-]>.+.+.# @00000100 ##
+++++@++[>+++++++<-]>.+.+.# @00000101 ##
++++++@+[>+++++++<-]>.+.+.# @00000110 ##
+++++++@[>+++++++<-]>.+.+.# @00000111 ##
+++++++[@>+++++++<-]>.+.+.# @00000111 ##
+++++++[>@+++++++<-]>.+.+.# 00000111 @00000000 ##
+++++++[>+@++++++<-]>.+.+.# 00000111 @00000001 ##
+++++++[>++@+++++<-]>.+.+.# 00000111 @00000010 ##
+++++++[>+++@++++<-]>.+.+.# 00000111 @00000011 ##
+++++++[>++++@+++<-]>.+.+.# 00000111 @00000100 ##
+++++++[>+++++@++<-]>.+.+.# 00000111 @00000101 ##
+++++++[>++++++@+<-]>.+.+.# 00000111 @00000110 ##
+++++++[>+++++++@<-]>.+.+.# 00000111 @00000111 ##
+++++++[>+++++++<@-]>.+.+.# @00000111 00000111 ##
+++++++[>+++++++<-@]>.+.+.# @00000110 00000111 ##
+++++++[>+++++++<-L]>.+.+.# @00000110 00000111 ##
+++++++[>+++++++<L-]>.+.+.# @00000110 00000111 ##
+++++++[>+++++++L<-]>.+.+.# @00000110 00000111 ##
+++++++[>++++++L+<-]>.+.+.# @00000110 00000111 ##
+++++++[>+++++L++<-]>.+.+.# @00000110 00000111 ##
+++++++[>++++L+++<-]>.+.+.# @00000110 00000111 ##
+++++++[>+++L++++<-]>.+.+.# @00000110 00000111 ##
+++++++[>++L+++++<-]>.+.+.# @00000110 00000111 ##
+++++++[>+L++++++<-]>.+.+.# @00000110 00000111 ##
+++++++[>L+++++++<-]>.+.+.# @00000110 00000111 ##
+++++++[L>+++++++<-]>.+.+.# @00000110 00000111 ##
+++++++@[>+++++++<-]>.+.+.# @00000110 00000111 ##
+++++++[@>+++++++<-]>.+.+.# @00000110 00000111 ##
+++++++[>@+++++++<-]>.+.+.# 00000110 @00000111 ##
+++++++[>+@++++++<-]>.+.+.# 00000110 @00001000 ##
+++++++[>++@+++++<-]>.+.+.# 00000110 @00001001 ##
+++++++[>+++@++++<-]>.+.+.# 00000110 @00001010 ##
+++++++[>++++@+++<-]>.+.+.# 00000110 @00001011 ##
+++++++[>+++++@++<-]>.+.+.# 00000110 @00001100 ##
+++++++[>++++++@+<-]>.+.+.# 00000110 @00001101 ##
+++++++[>+++++++@<-]>.+.+.# 00000110 @00001110 ##
+++++++[>+++++++<@-]>.+.+.# @00000110 00001110 ##
+++++++[>+++++++<-@]>.+.+.# @00000101 00001110 ##
+++++++[>+++++++<-L]>.+.+.# @00000101 00001110 ##
+++++++[>+++++++<L-]>.+.+.# @00000101 00001110 ##
+++++++[>+++++++L<-]>.+.+.# @00000101 00001110 ##
+++++++[>++++++L+<-]>.+.+.# @00000101 00001110 ##
+++++++[>+++++L++<-]>.+.+.# @00000101 00001110 ##
+++++++[>++++L+++<-]>.+.+.# @00000101 00001110 ##
+++++++[>+++L++++<-]>.+.+.# @00000101 00001110 ##
+++++++[>++L+++++<-]>.+.+.# @00000101 00001110 ##
+++++++[>+L++++++<-]>.+.+.# @00000101 00001110 ##
+++++++[>L+++++++<-]>.+.+.# @00000101 00001110 ##
+++++++[L>+++++++<-]>.+.+.# @00000101 00001110 ##
+++++++@[>+++++++<-]>.+.+.# @00000101 00001110 ##
+++++++[@>+++++++<-]>.+.+.# @00000101 00001110 ##
+++++++[>@+++++++<-]>.+.+.# 00000101 @00001110 ##
+++++++[>+@++++++<-]>.+.+.# 00000101 @00001111 ##
+++++++[>++@+++++<-]>.+.+.# 00000101 @00010000 ##
+++++++[>+++@++++<-]>.+.+.# 00000101 @00010001 ##
+++++++[>++++@+++<-]>.+.+.# 00000101 @00010010 ##
+++++++[>+++++@++<-]>.+.+.# 00000101 @00010011 ##
+++++++[>++++++@+<-]>.+.+.# 00000101 @00010100 ##
+++++++[>+++++++@<-]>.+.+.# 00000101 @00010101 ##
+++++++[>+++++++<@-]>.+.+.# @00000101 00010101 ##
+++++++[>+++++++<-@]>.+.+.# @00000100 00010101 ##
+++++++[>+++++++<-L]>.+.+.# @00000100 00010101 ##
+++++++[>+++++++<L-]>.+.+.# @00000100 00010101 ##
+++++++[>+++++++L<-]>.+.+.# @00000100 00010101 ##
+++++++[>++++++L+<-]>.+.+.# @00000100 00010101 ##
+++++++[>+++++L++<-]>.+.+.# @00000100 00010101 ##
+++++++[>++++L+++<-]>.+.+.# @00000100 00010101 ##
+++++++[>+++L++++<-]>.+.+.# @00000100 00010101 ##
+++++++[>++L+++++<-]>.+.+.# @00000100 00010101 ##
+++++++[>+L++++++<-]>.+.+.# @00000100 00010101 ##
+++++++[>L+++++++<-]>.+.+.# @00000100 00010101 ##
+++++++[L>+++++++<-]>.+.+.# @00000100 00010101 ##
+++++++@[>+++++++<-]>.+.+.# @00000100 00010101 ##
+++++++[@>+++++++<-]>.+.+.# @00000100 00010101 ##
+++++++[>@+++++++<-]>.+.+.# 00000100 @00010101 ##
+++++++[>+@++++++<-]>.+.+.# 00000100 @00010110 ##
+++++++[>++@+++++<-]>.+.+.# 00000100 @00010111 ##
+++++++[>+++@++++<-]>.+.+.# 00000100 @00011000 ##
+++++++[>++++@+++<-]>.+.+.# 00000100 @00011001 ##
+++++++[>+++++@++<-]>.+.+.# 00000100 @00011010 ##
+++++++[>++++++@+<-]>.+.+.# 00000100 @00011011 ##
+++++++[>+++++++@<-]>.+.+.# 00000100 @00011100 ##
+++++++[>+++++++<@-]>.+.+.# @00000100 00011100 ##
+++++++[>+++++++<-@]>.+.+.# @00000011 00011100 ##
+++++++[>+++++++<-L]>.+.+.# @00000011 00011100 ##
+++++++[>+++++++<L-]>.+.+.# @00000011 00011100 ##
+++++++[>+++++++L<-]>.+.+.# @00000011 00011100 ##
+++++++[>++++++L+<-]>.+.+.# @00000011 00011100 ##
+++++++[>+++++L++<-]>.+.+.# @00000011 00011100 ##
+++++++[>++++L+++<-]>.+.+.# @00000011 00011100 ##
+++++++[>+++L++++<-]>.+.+.# @00000011 00011100 ##
+++++++[>++L+++++<-]>.+.+.# @00000011 00011100 ##
+++++++[>+L++++++<-]>.+.+.# @00000011 00011100 ##
+++++++[>L+++++++<-]>.+.+.# @00000011 00011100 ##
+++++++[L>+++++++<-]>.+.+.# @00000011 00011100 ##
+++++++@[>+++++++<-]>.+.+.# @00000011 00011100 ##
+++++++[@>+++++++<-]>.+.+.# @00000011 00011100 ##
+++++++[>@+++++++<-]>.+.+.# 00000011 @00011100 ##
+++++++[>+@++++++<-]>.+.+.# 00000011 @00011101 ##
+++++++[>++@+++++<-]>.+.+.# 00000011 @00011110 ##
+++++++[>+++@++++<-]>.+.+.# 00000011 @00011111 ##
+++++++[>++++@+++<-]>.+.+.# 00000011 @00100000 ##
+++++++[>+++++@++<-]>.+.+.# 00000011 @00100001 ##
+++++++[>++++++@+<-]>.+.+.# 00000011 @00100010 ##
+++++++[>+++++++@<-]>.+.+.# 00000011 @00100011 ##
+++++++[>+++++++<@-]>.+.+.# @00000011 00100011 ##
+++++++[>+++++++<-@]>.+.+.# @00000010 00100011 ##
+++++++[>+++++++<-L]>.+.+.# @00000010 00100011 ##
+++++++[>+++++++<L-]>.+.+.# @00000010 00100011 ##
+++++++[>+++++++L<-]>.+.+.# @00000010 00100011 ##
+++++++[>++++++L+<-]>.+.+.# @00000010 00100011 ##
+++++++[>+++++L++<-]>.+.+.# @00000010 00100011 ##
+++++++[>++++L+++<-]>.+.+.# @00000010 00100011 ##
+++++++[>+++L++++<-]>.+.+.# @00000010 00100011 ##
+++++++[>++L+++++<-]>.+.+.# @00000010 00100011 ##
+++++++[>+L++++++<-]>.+.+.# @00000010 00100011 ##
+++++++[>L+++++++<-]>.+.+.# @00000010 00100011 ##
+++++++[L>+++++++<-]>.+.+.# @00000010 00100011 ##
+++++++@[>+++++++<-]>.+.+.# @00000010 00100011 ##
+++++++[@>+++++++<-]>.+.+.# @00000010 00100011 ##
+++++++[>@+++++++<-]>.+.+.# 00000010 @00100011 ##
+++++++[>+@++++++<-]>.+.+.# 00000010 @00100100 ##
+++++++[>++@+++++<-]>.+.+.# 00000010 @00100101 ##
+++++++[>+++@++++<-]>.+.+.# 00000010 @00100110 ##
+++++++[>++++@+++<-]>.+.+.# 00000010 @00100111 ##
+++++++[>+++++@++<-]>.+.+.# 00000010 @00101000 ##
+++++++[>++++++@+<-]>.+.+.# 00000010 @00101001 ##
+++++++[>+++++++@<-]>.+.+.# 00000010 @00101010 ##
+++++++[>+++++++<@-]>.+.+.# @00000010 00101010 ##
+++++++[>+++++++<-@]>.+.+.# @00000001 00101010 ##
+++++++[>+++++++<-L]>.+.+.# @00000001 00101010 ##
+++++++[>+++++++<L-]>.+.+.# @00000001 00101010 ##
+++++++[>+++++++L<-]>.+.+.# @00000001 00101010 ##
+++++++[>++++++L+<-]>.+.+.# @00000001 00101010 ##
+++++++[>+++++L++<-]>.+.+.# @00000001 00101010 ##
+++++++[>++++L+++<-]>.+.+.# @00000001 00101010 ##
+++++++[>+++L++++<-]>.+.+.# @00000001 00101010 ##
+++++++[>++L+++++<-]>.+.+.# @00000001 00101010 ##
+++++++[>+L++++++<-]>.+.+.# @00000001 00101010 ##
+++++++[>L+++++++<-]>.+.+.# @00000001 00101010 ##
+++++++[L>+++++++<-]>.+.+.# @00000001 00101010 ##
+++++++@[>+++++++<-]>.+.+.# @00000001 00101010 ##
+++++++[@>+++++++<-]>.+.+.# @00000001 00101010 ##
+++++++[>@+++++++<-]>.+.+.# 00000001 @00101010 ##
+++++++[>+@++++++<-]>.+.+.# 00000001 @00101011 ##
+++++++[>++@+++++<-]>.+.+.# 00000001 @00101100 ##
+++++++[>+++@++++<-]>.+.+.# 00000001 @00101101 ##
+++++++[>++++@+++<-]>.+.+.# 00000001 @00101110 ##
+++++++[>+++++@++<-]>.+.+.# 00000001 @00101111 ##
+++++++[>++++++@+<-]>.+.+.# 00000001 @00110000 ##
+++++++[>+++++++@<-]>.+.+.# 00000001 @00110001 ##
+++++++[>+++++++<@-]>.+.+.# @00000001 00110001 ##
+++++++[>+++++++<-@]>.+.+.# @00000000 00110001 ##
+++++++[>+++++++<-L]>.+.+.# @00000000 00110001 ##
+++++++[>+++++++<L-]>.+.+.# @00000000 00110001 ##
+++++++[>+++++++L<-]>.+.+.# @00000000 00110001 ##
+++++++[>++++++L+<-]>.+.+.# @00000000 00110001 ##
+++++++[>+++++L++<-]>.+.+.# @00000000 00110001 ##
+++++++[>++++L+++<-]>.+.+.# @00000000 00110001 ##
+++++++[>+++L++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>++L+++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>+L++++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>L+++++++<-]>.+.+.# @00000000 00110001 ##
+++++++[L>+++++++<-]>.+.+.# @00000000 00110001 ##
+++++++@[>+++++++<-]>.+.+.# @00000000 00110001 ##
+++++++[R>+++++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>R+++++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>+R++++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>++R+++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>+++R++++<-]>.+.+.# @00000000 00110001 ##
+++++++[>++++R+++<-]>.+.+.# @00000000 00110001 ##
+++++++[>+++++R++<-]>.+.+.# @00000000 00110001 ##
+++++++[>++++++R+<-]>.+.+.# @00000000 00110001 ##
+++++++[>+++++++R<-]>.+.+.# @00000000 00110001 ##
+++++++[>+++++++<R-]>.+.+.# @00000000 00110001 ##
+++++++[>+++++++<-R]>.+.+.# @00000000 00110001 ##
+++++++[>+++++++<-]@>.+.+.# @00000000 00110001 ##
+++++++[>+++++++<-]>@.+.+.# 00000000 @00110001 ##
+++++++[>+++++++<-]>O+.+.# 00000000 @o00110001 ##
+++++++[>+++++++<-]>O+.+.# 00000000 @0o0110001 ##0
+++++++[>+++++++<-]>O+.+.# 00000000 @00o110001 ##00
+++++++[>+++++++<-]>O+.+.# 00000000 @001o10001 ##001
+++++++[>+++++++<-]>O+.+.# 00000000 @0011o0001 ##0011
+++++++[>+++++++<-]>O+.+.# 00000000 @00110o001 ##00110
+++++++[>+++++++<-]>O+.+.# 00000000 @001100o01 ##001100
+++++++[>+++++++<-]>O+.+.# 00000000 @0011000o1 ##0011000
+++++++[>+++++++<-]>O+.+.# 00000000 @00110001o ##00110001
+++++++[>+++++++<-]>O+.+.# 00000000 @00110001 ##00110001
+++++++[>+++++++<-]>.@+.+.# 00000000 @00110001 ##00110001
+++++++[>+++++++<-]>.+@.+.# 00000000 @00110010 ##00110001
+++++++[>+++++++<-]>.+O+.# 00000000 @o00110010 ##00110001
+++++++[>+++++++<-]>.+O+.# 00000000 @0o0110010 ##001100010
+++++++[>+++++++<-]>.+O+.# 00000000 @00o110010 ##0011000100
+++++++[>+++++++<-]>.+O+.# 00000000 @001o10010 ##00110001001
+++++++[>+++++++<-]>.+O+.# 00000000 @0011o0010 ##001100010011
+++++++[>+++++++<-]>.+O+.# 00000000 @00110o010 ##0011000100110
+++++++[>+++++++<-]>.+O+.# 00000000 @001100o10 ##00110001001100
+++++++[>+++++++<-]>.+O+.# 00000000 @0011001o0 ##001100010011001
+++++++[>+++++++<-]>.+O+.# 00000000 @00110010o ##0011000100110010
+++++++[>+++++++<-]>.+O+.# 00000000 @00110010 ##0011000100110010
+++++++[>+++++++<-]>.+.@+.# 00000000 @00110010 ##0011000100110010
+++++++[>+++++++<-]>.+.+@.# 00000000 @00110011 ##0011000100110010
+++++++[>+++++++<-]>.+.+O# 00000000 @o00110011 ##0011000100110010
+++++++[>+++++++<-]>.+.+O# 00000000 @0o0110011 ##00110001001100100
+++++++[>+++++++<-]>.+.+O# 00000000 @00o110011 ##001100010011001000
+++++++[>+++++++<-]>.+.+O# 00000000 @001o10011 ##0011000100110010001
+++++++[>+++++++<-]>.+.+O# 00000000 @0011o0011 ##00110001001100100011
+++++++[>+++++++<-]>.+.+O# 00000000 @00110o011 ##001100010011001000110
+++++++[>+++++++<-]>.+.+O# 00000000 @001100o11 ##0011000100110010001100
+++++++[>+++++++<-]>.+.+O# 00000000 @0011001o1 ##00110001001100100011001
+++++++[>+++++++<-]>.+.+O# 00000000 @00110011o ##001100010011001000110011
+++++++[>+++++++<-]>.+.+O# 00000000 @00110011 ##001100010011001000110011
+++++++[>+++++++<-]>.+.+.@# 00000000 @00110011 ##001100010011001000110011

```

# Answer
> 4 votes
## Python 3.8 (single expression, no eval), 711 bytes

```
(g:=lambda s,a,b,p,c:None if p>=len(s)else g(s,a,b,p+1,c+1)if a==s[p]else(p if c==1 else g(s,a,b,p+1,c-1))if b==s[p]else g(s,a,b,p+1,c),x:=lambda f:None if f is None else x(f()),f:=lambda s,p,m,c:[None,(lambda:f(s,*{"+":lambda:(p,m[:p]+[m[p]+1]+m[p+1:],c+1),"-":lambda:(p,m[:p]+[m[p]-1]+m[p+1:],c+1),">":lambda:(p+1,m+[0]*(p+1>=len(m)),c+1),"<":lambda:(max(p-1,0),[0]*(p-1<0)+m,c+1),".":lambda:print(chr(m[p]),end="") or(p,m,c+1),",":lambda:(p,m[:p]+[ord(input())]+m[p+1:],c+1),"[":lambda:(p,m,(g(s,"[","]",c,0)if 0==m[p]else c)+1),"]":lambda:(p,m,len(s)-g(s[::-1],"]","[",len(s)-c-1,0)if m[p]!=0 else 1+c)}.get(s[c],lambda:(p,m,c+1))()))][c<len(s)],x(lambda:f(open(__import__("sys").argv[-1]).read(),0,[0],0)))

```

I've provided a hello world example here: Try it online!

### *single expression*?

I've seen multiple fun python implementations already, but I thought that another hurdle beside just golfing would be fun. As the *single expression* part implies the whole solution is packed into a **single** python expression, through the use of things like assignment expressions (`:=`).

### Explanation

This solution, as it stands, consists of 3 distinct functions:

* `g`: facilitates find the index of a matching bracket
* `x`: describes the main loop, i.e. drives the state transitions
* `f`: implements the state transition of one "machine state" to another, i.e. the meat of the interpreter

```
g = lambda s, a, b, p, c: (
    None
    if p >= len(s)
    else g(s, a, b, p + 1, c + 1)
    if s[p] == a
    else (p if c == 1 else g(s, a, b, p + 1, c - 1))
    if s[p] == b
    else g(s, a, b, p + 1, c)
)

```

```
x = lambda f: None if f is None else x(f())

```

```
f = lambda s, p, m, c: [
    None,
    (
        lambda: f(
            s,
            *{
                "+": lambda: (p, m[:p] + [m[p] + 1] + m[p + 1 :], c + 1),
                "-": lambda: (p, m[:p] + [m[p] - 1] + m[p + 1 :], c + 1),
                ">": lambda: (p + 1, m + [0] * (p + 1 >= len(m)), c + 1),
                "<": lambda: (max(p - 1, 0), [0] * (p - 1 < 0) + m, c + 1),
                ".": lambda: print(chr(m[p]), end="") or (p, m, c + 1),
                ",": lambda: (p, m[:p] + [ord(input())] + m[p + 1 :], c + 1),
                "[": lambda: (p, m, (g(s, "[", "]", c, 0) if m[p] == 0 else c) + 1),
                "]": lambda: (
                    p,
                    m,
                    len(s) - g(s[::-1], "]", "[", len(s) - c - 1, 0)
                    if m[p] != 0
                    else 1 + c,
                ),
            }.get(s[c], lambda: (p, m, c + 1))(),
        )
    ),
][c < len(s)]

```

Finally all of this gets stuffed together using a "simple" call to `x` with a curried `f`, already preloaded with the initial state:

```
x(lambda: f(open(__import__("sys").argv[-1]).read(), 0, [0], 0))

```

And voilà it works and is a true python one-liner.

Sadly this interpreter is limited in the amount of characters it can read in as it is driven by recursion and python doesn't like "very" deep recursion...

## Python 3.8 (single expression, no recursion, no eval), 702 bytes

```
(i:=__import__,k:=i("itertools"),g:=lambda s,a,b,p:p+next(i for i,d in enumerate(k.accumulate({a:1,b:-1}.get(c,0)for c in s[p:]))if 0==d),f:=lambda s,p,m,c:(s,*{"+":lambda:(p,m[:p]+[m[p]+1]+m[p+1:],c+1),"-":lambda:(p,m[:p]+[m[p]-1]+m[p+1:],c+1),">":lambda:(p+1,m+[0]*(p+1>=len(m)),c+1),"<":lambda:(max(p-1,0),[0]*(p-1<0)+m,c+1),".":lambda:print(chr(m[p]),end="") or(p,m,c+1),",":lambda:(p,m[:p]+[ord(input()[0])]+m[p+1:],c+1),"[":lambda:(p,m,(g(s,"[","]",c)if 0==m[p]else c)+1),"]":lambda:(p,m,len(s)-g(s[::-1],"]","[",len(s)-c-1)if 0!=m[p]else 1+c)}.get(s[c],lambda:(p,m,c+1))()),i("functools").reduce(lambda s,_:exit(0)if len(s[0])<=s[3]else f(*s),k.count(1),(open(i("sys").argv[1]).read(),0,[0],0)))

```

To get around the nasty recursion depth in python I rewrote some parts, and it even turned out shorter than before...

Here is the hello world example for this version: Try it online!

# Answer
> 4 votes
# **C** \- **~~306~~ ~~243~~ ~~237~~ 235** bytes

This was actually my second ever code golf, and is from a while ago

```
char m[30000],*p=m,o[30000];i,c;k(v){return v==o[i];}main(x,y)int**y;{for(read(open(y[1],0),o,30000);o[i];i++)if(*(p+=k(62)-k(60))+=k(43)-k(45),x=k(91)-k(93),read(write(1,p,k(46)),p,k(44)),x&&!!*p^!~-x)for(i+=c=x;c+=k(91)-k(93);)i+=x;}

```

**235** by ceilingcat

# Answer
> 4 votes
# Scala, 459 bytes

## I'd love to see other scala solutions!

The golfed version:

```
@main def a(n:String)={val t=io.Source.fromFile(n).mkString;var r=t;var p=0;var q=0;val b=Array.fill(30000){0};def f(c:Int)={var l=1;p=r.indexWhere(x=>{l+=Map('['->c,']'-> -c).getOrElse(x,0);l==0},p+1);1<0};def a=p=t.size-1-p;while(t.size!=p){t(p)match{case'+'=>b(q)+=1case'-'=>b(q)-=1case'>'=>q+=1case'<'=>q-=1case'['=>r=t;b(q)==0&&f(1)case']'=>r=t.reverse;a;b(q)!= 0&&f(-1);a case'.'=>print((b(q)&255).toChar)case','=>b(q)=Console.in.read()case _=>0};p+=1}}

```

The ungolfed version:

```
@main def evalFromFile(fileName: String) =
  val code = io.Source.fromFile(fileName).mkString
  val size = code.size
  var tempCode = code
  var codePtr = 0
  var cellPtr = 0
  val cells = Array.fill(30_000){0}

  def moveLoopPtr(direction: Int) =
    var count = 1;
    codePtr = tempCode.indexWhere(x => {
      count += Map('[' -> direction, ']' -> -direction).getOrElse(x, 0)
      count == 0
    }, codePtr + 1)
    1 > 1

  while (code.size != codePtr) {
    code(codePtr) match
      case '+' => cells(cellPtr) += 1
      case '-' => cells(cellPtr) -= 1
      case '>' => cellPtr += 1
      case '<' => cellPtr -= 1
      case '[' =>
        tempCode = code;
        cells(cellPtr) == 0 && moveLoopPtr(1)
      case ']' =>
        tempCode = code.reverse
        codePtr = code.size - 1 - codePtr
        cells(cellPtr) != 0 && moveLoopPtr(-1)
        codePtr = code.size - 1 - codePtr
      case '.' => print((cells(cellPtr) & 255).toChar)
      case ',' => cells(cellPtr) = Console.in.read()
      case _ => 0
    codePtr += 1
  }

```

# Answer
> 4 votes
# ARM Thumb-2 Machine code (Linux), 116 bytes

## Hexdump (little endian)

```
9802 2705 df00 f44f 3280 ebad 0d42 4669
2703 df00 466b 1889 2201 cb20 b355 2001
2d3e bf08 3101 2d3c bf08 3901 780e 2d5b
d014 2d5d bf04 bc08 3b04 2d2b bf08 3601
2d2d bf08 3e01 700e 2d2e d101 2704 df00
2d2c d1e2 2000 2703 df00 e7de b10e b408
e7db cb20 2d5d d101 3801 d0d6 2d5b bf08
3001 e7f6

```

## Commented assembly

```
        .syntax unified
        .arch armv6t2
        .thumb
        // The BF program must be saved in UTF-32LE, not ASCII. Use iconv if you have to.
        .equ BUFSIZ, 65536 // should be movable

        .thumb_func
        .globl _start
_start:
        // Open the file
        // file = open(argv[1], O_RDONLY /* = 0 */)
        ldr     r0, [sp, #8] // argv[1] is at sp + 8
        movs    r7, #5 // open
        svc     #0

        // Create a buffer for the file and the tape (todo: improve reg shuffling)
        mov     r2, #BUFSIZ
        sub.w   sp, sp, r2, lsl #1 // doubled
        // Read into the file
        // read(file, insn_ptr, BUFSIZ)
        mov     r1, sp
        movs    r7, #3 // read
        svc     #0
        // insn_ptr = sp
        mov     r3, sp
        // tape_ptr = &insn_ptr[BUFSIZ]
        adds    r1, r2
        movs    r2, #1 // 1 byte for read/write syscalls

        // ----- Interpreter loop ------
.Linterpret:
        // insn = *insn_ptr++
        ldm     r3!, {r5}
        // Null terminator
        cbz     r5, .Lexit
        movs    r0, #1 // stdout, also loop depth
        // > -> right
        cmp     r5, #'>'
        it      eq
        addeq   r1, #1
        // < -> left
        cmp     r5, #'<'
        it      eq
        subeq   r1, #1
        // Load
        ldrb    r6, [r1]
        // [ -> start
        cmp     r5, #'['
        beq     .Ldo_loop // outlined
        // ] -> end
        cmp     r5, #']'
        // Pop insn_ptr
        itt     eq
        popeq   {r3}
        subeq   r3, #4
        // + -> inc
        cmp     r5, #'+'
        it      eq
        addeq   r6, #1
        // - -> dec
        cmp     r5, #'-'
        it      eq
        subeq   r6, #1
        // Store
        strb    r6, [r1]
        // . -> print
        cmp     r5, #'.'
        bne     .Lnot_dot
.Ldot:
        // write(STDOUT_FILENO, tape_ptr, 1)
        // r0 is already 1 for stdout.
        movs    r7, #4 // write
        svc     #0
.Lnot_dot:
        // , -> read
        cmp     r5, #','
        bne     .Linterpret
.Lcomma:
        // read(STDIN_FILENO, tape_ptr, 1)
        movs    r0, #0 // stdin
        movs    r7, #3 // read
        svc     #0
        // Loop
        b       .Linterpret

        // loop handling
.Ldo_loop:
        // depth = 1; (from above)
        // if (tape_val != 0)
        cbz     r6, .Ldo_loop.scan
.Ldo_loop.no_jump:
        // Push insn_ptr to the call stack and continue
        push    {r3}
        b       .Linterpret
        // else
        //   scan for the closing brace and jump.
.Ldo_loop.scan:
        ldm     r3!, {r5}
        // ] -> --depth
        cmp     r5, #']'
        bne     .Ldo_loop.not_rb
.Ldo_loop.rb:
        // if (--depth == 0) break;
        subs    r0, #1
        beq     .Linterpret
.Ldo_loop.not_rb:
        // [ -> ++depth
        cmp     r5, #'['
        it      eq
        addeq   r0, #1
        b       .Ldo_loop.scan
.Lexit:
        // segfault like a true chad :D

```

## Notes

* Compiled as `clang --target= arm-linux-gnueabi -nostdlib -static bfarm.s -o bfarm`.
* The filename of the BF file is passed as the first command line argument.
* **The BF file is encoded in UTF-32LE (not ASCII)**. (This saves 4 bytes thanks to `ldm`). The input and output is still through 8-bit bytes though.
    + `iconv -f UTF-8 -t UTF-32LE prog.bf > prog.bf32` if you need to convert.
* The BF file must be shorter than 65536 bytes (16384 codepoints) long and not contain null codepoints. The size can be configured, though, with some tweaking.
* You get a whopping 65536 `u8` cells, non-wrapping
* Expects the default Linux ELF startup state.
    + `argv` is an array at `sp + 4`
    + The unused stack memory is clear
    + All registers but `sp` and `pc` are zeroed
* Segfaults to exit by leaving the end of the `.text` section like a true gigachad.
* EOF leaves the cell unchanged.

# Answer
> 4 votes
# ReRegex, 12046 bytes

```
#import math
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```

Try it online!

## With Comments

```
#import math
# Santize Input
# Keeps removing characters from the code that aren't the standard BF chars
^1([^$]*?)[^\[\]<>,.+-]/1$1/
^1([\[\]<>,.+-]*)(\$[^$]*)$/2'$1\$$2/
^1([\[\]<>,.+-]*)$/2'$1\$\$/
# Pair up brackets
# Bit by bit replaces square brackets with parentheticals, counting depth by proceeding them with =, eg.
# [a[b]c] becomes [a=[b=]c]
# This is vital for loops later.
^2([^$]*)'([()<>,.+-])/2$1$2'/
^2([^()$]*)'\[/2$1'\(/
^2([^()$]*)'\]/2$1'/
^2([^$]*?)(=*)\(([^()$]*)'\[/2$1$2($3$2=('/
^2([^$]*?)(=*)\(([^()$]*)'\]/2$1$2($3$2)'/
^2([^$]*?)(=*)=\)([^()$]*)'\]/2$1$2=)$3$2)'/
^2([^$]*?)(=*)\)([^()$]*)'\[/2$1$2)$3$2('/
# Afterwards, sets up the memory in the form of:
# 3aTAPE$CODE$OUTPUT$INPUT
^2([^']*)'\$/3'\$'$1\$/
# Alternator. This increments the instruction pointer by one after an instruction is ran.
# We use the states 3a and 3b to ensure exactly one instruction is run per tick
^4([_,']*\$[^']*)'([^$])/3$1$2'/
# +
^3([_,]*)'([^$]*)\$([^']*)'\+/4$1'_$2\$$3'+/
_{256}//
# - Has to manually wrap.
^3([_,]*)'_([^$]*)\$([^']*)'-/4$1'$2\$$3'-/
^3([_,]*)'(?=[^_])([^$]*)\$([^']*)'-/4$1'u<255>$2\$$3'-/
# >
^3([_,]*)'(_*),?([_,]*)\$([^']*)'>/4$1$2,'$3\$$4'>/
# <
^3([_,]*?)(_*),?'([_,]*)\$([^']*)'</4$1'$2,$3\$$4'</
# .
^3([_,]*?)'(_*)([_,]*)\$([^']*)'\.([^$]*)\$([^$]*)/4$1'$2$3\$$4'.$5\$$6$2,/
# ,
^3([_,]*?)'(_*)([_,]*)\$([^']*)',([^$]*\$[^$]*)\$([\x00-\xFF])/5$1':$6$3\$$4',$5\$/
^3([_,]*?)'(_*)([_,]*)\$([^']*)',([^$]*\$[^$]*)\$$/4$1'$3\$$4',$5\$/
^5([_,]*)':\x00/4$1'u<$i>/
^5([_,]*)':\x01/4$1'u<$i>/
^5([_,]*)':\x02/4$1'u<$i>/
^5([_,]*)':\x03/4$1'u<$i>/
^5([_,]*)':\x04/4$1'u<$i>/
^5([_,]*)':\x05/4$1'u<$i>/
^5([_,]*)':\x06/4$1'u<$i>/
^5([_,]*)':\x07/4$1'u<$i>/
^5([_,]*)':\x08/4$1'u<$i>/
^5([_,]*)':\x09/4$1'u<$i>/
^5([_,]*)':\x0A/4$1'u<$i>/
^5([_,]*)':\x0B/4$1'u<$i>/
^5([_,]*)':\x0C/4$1'u<$i>/
^5([_,]*)':\x0D/4$1'u<$i>/
^5([_,]*)':\x0E/4$1'u<$i>/
^5([_,]*)':\x0F/4$1'u<$i>/
^5([_,]*)':\x10/4$1'u<$i>/
^5([_,]*)':\x11/4$1'u<$i>/
^5([_,]*)':\x12/4$1'u<$i>/
^5([_,]*)':\x13/4$1'u<$i>/
^5([_,]*)':\x14/4$1'u<$i>/
^5([_,]*)':\x15/4$1'u<$i>/
^5([_,]*)':\x16/4$1'u<$i>/
^5([_,]*)':\x17/4$1'u<$i>/
^5([_,]*)':\x18/4$1'u<$i>/
^5([_,]*)':\x19/4$1'u<$i>/
^5([_,]*)':\x1A/4$1'u<$i>/
^5([_,]*)':\x1B/4$1'u<$i>/
^5([_,]*)':\x1C/4$1'u<$i>/
^5([_,]*)':\x1D/4$1'u<$i>/
^5([_,]*)':\x1E/4$1'u<$i>/
^5([_,]*)':\x1F/4$1'u<$i>/
^5([_,]*)':\x20/4$1'u<$i>/
^5([_,]*)':\x21/4$1'u<$i>/
^5([_,]*)':\x22/4$1'u<$i>/
^5([_,]*)':\x23/4$1'u<$i>/
^5([_,]*)':\x24/4$1'u<$i>/
^5([_,]*)':\x25/4$1'u<$i>/
^5([_,]*)':\x26/4$1'u<$i>/
^5([_,]*)':\x27/4$1'u<$i>/
^5([_,]*)':\x28/4$1'u<$i>/
^5([_,]*)':\x29/4$1'u<$i>/
^5([_,]*)':\x2A/4$1'u<$i>/
^5([_,]*)':\x2B/4$1'u<$i>/
^5([_,]*)':\x2C/4$1'u<$i>/
^5([_,]*)':\x2D/4$1'u<$i>/
^5([_,]*)':\x2E/4$1'u<$i>/
^5([_,]*)':\x2F/4$1'u<$i>/
^5([_,]*)':\x30/4$1'u<$i>/
^5([_,]*)':\x31/4$1'u<$i>/
^5([_,]*)':\x32/4$1'u<$i>/
^5([_,]*)':\x33/4$1'u<$i>/
^5([_,]*)':\x34/4$1'u<$i>/
^5([_,]*)':\x35/4$1'u<$i>/
^5([_,]*)':\x36/4$1'u<$i>/
^5([_,]*)':\x37/4$1'u<$i>/
^5([_,]*)':\x38/4$1'u<$i>/
^5([_,]*)':\x39/4$1'u<$i>/
^5([_,]*)':\x3A/4$1'u<$i>/
^5([_,]*)':\x3B/4$1'u<$i>/
^5([_,]*)':\x3C/4$1'u<$i>/
^5([_,]*)':\x3D/4$1'u<$i>/
^5([_,]*)':\x3E/4$1'u<$i>/
^5([_,]*)':\x3F/4$1'u<$i>/
^5([_,]*)':\x40/4$1'u<$i>/
^5([_,]*)':\x41/4$1'u<$i>/
^5([_,]*)':\x42/4$1'u<$i>/
^5([_,]*)':\x43/4$1'u<$i>/
^5([_,]*)':\x44/4$1'u<$i>/
^5([_,]*)':\x45/4$1'u<$i>/
^5([_,]*)':\x46/4$1'u<$i>/
^5([_,]*)':\x47/4$1'u<$i>/
^5([_,]*)':\x48/4$1'u<$i>/
^5([_,]*)':\x49/4$1'u<$i>/
^5([_,]*)':\x4A/4$1'u<$i>/
^5([_,]*)':\x4B/4$1'u<$i>/
^5([_,]*)':\x4C/4$1'u<$i>/
^5([_,]*)':\x4D/4$1'u<$i>/
^5([_,]*)':\x4E/4$1'u<$i>/
^5([_,]*)':\x4F/4$1'u<$i>/
^5([_,]*)':\x50/4$1'u<$i>/
^5([_,]*)':\x51/4$1'u<$i>/
^5([_,]*)':\x52/4$1'u<$i>/
^5([_,]*)':\x53/4$1'u<$i>/
^5([_,]*)':\x54/4$1'u<$i>/
^5([_,]*)':\x55/4$1'u<$i>/
^5([_,]*)':\x56/4$1'u<$i>/
^5([_,]*)':\x57/4$1'u<$i>/
^5([_,]*)':\x58/4$1'u<$i>/
^5([_,]*)':\x59/4$1'u<$i>/
^5([_,]*)':\x5A/4$1'u<$i>/
^5([_,]*)':\x5B/4$1'u<$i>/
^5([_,]*)':\x5C/4$1'u<$i>/
^5([_,]*)':\x5D/4$1'u<$i>/
^5([_,]*)':\x5E/4$1'u<$i>/
^5([_,]*)':\x5F/4$1'u<$i>/
^5([_,]*)':\x60/4$1'u<$i>/
^5([_,]*)':\x61/4$1'u<$i>/
^5([_,]*)':\x62/4$1'u<$i>/
^5([_,]*)':\x63/4$1'u<$i>/
^5([_,]*)':\x64/4$1'u<$i>/
^5([_,]*)':\x65/4$1'u<$i>/
^5([_,]*)':\x66/4$1'u<$i>/
^5([_,]*)':\x67/4$1'u<$i>/
^5([_,]*)':\x68/4$1'u<$i>/
^5([_,]*)':\x69/4$1'u<$i>/
^5([_,]*)':\x6A/4$1'u<$i>/
^5([_,]*)':\x6B/4$1'u<$i>/
^5([_,]*)':\x6C/4$1'u<$i>/
^5([_,]*)':\x6D/4$1'u<$i>/
^5([_,]*)':\x6E/4$1'u<$i>/
^5([_,]*)':\x6F/4$1'u<$i>/
^5([_,]*)':\x70/4$1'u<$i>/
^5([_,]*)':\x71/4$1'u<$i>/
^5([_,]*)':\x72/4$1'u<$i>/
^5([_,]*)':\x73/4$1'u<$i>/
^5([_,]*)':\x74/4$1'u<$i>/
^5([_,]*)':\x75/4$1'u<$i>/
^5([_,]*)':\x76/4$1'u<$i>/
^5([_,]*)':\x77/4$1'u<$i>/
^5([_,]*)':\x78/4$1'u<$i>/
^5([_,]*)':\x79/4$1'u<$i>/
^5([_,]*)':\x7A/4$1'u<$i>/
^5([_,]*)':\x7B/4$1'u<$i>/
^5([_,]*)':\x7C/4$1'u<$i>/
^5([_,]*)':\x7D/4$1'u<$i>/
^5([_,]*)':\x7E/4$1'u<$i>/
^5([_,]*)':\x7F/4$1'u<$i>/
^5([_,]*)':\x80/4$1'u<$i>/
^5([_,]*)':\x81/4$1'u<$i>/
^5([_,]*)':\x82/4$1'u<$i>/
^5([_,]*)':\x83/4$1'u<$i>/
^5([_,]*)':\x84/4$1'u<$i>/
^5([_,]*)':\x85/4$1'u<$i>/
^5([_,]*)':\x86/4$1'u<$i>/
^5([_,]*)':\x87/4$1'u<$i>/
^5([_,]*)':\x88/4$1'u<$i>/
^5([_,]*)':\x89/4$1'u<$i>/
^5([_,]*)':\x8A/4$1'u<$i>/
^5([_,]*)':\x8B/4$1'u<$i>/
^5([_,]*)':\x8C/4$1'u<$i>/
^5([_,]*)':\x8D/4$1'u<$i>/
^5([_,]*)':\x8E/4$1'u<$i>/
^5([_,]*)':\x8F/4$1'u<$i>/
^5([_,]*)':\x90/4$1'u<$i>/
^5([_,]*)':\x91/4$1'u<$i>/
^5([_,]*)':\x92/4$1'u<$i>/
^5([_,]*)':\x93/4$1'u<$i>/
^5([_,]*)':\x94/4$1'u<$i>/
^5([_,]*)':\x95/4$1'u<$i>/
^5([_,]*)':\x96/4$1'u<$i>/
^5([_,]*)':\x97/4$1'u<$i>/
^5([_,]*)':\x98/4$1'u<$i>/
^5([_,]*)':\x99/4$1'u<$i>/
^5([_,]*)':\x9A/4$1'u<$i>/
^5([_,]*)':\x9B/4$1'u<$i>/
^5([_,]*)':\x9C/4$1'u<$i>/
^5([_,]*)':\x9D/4$1'u<$i>/
^5([_,]*)':\x9E/4$1'u<$i>/
^5([_,]*)':\x9F/4$1'u<$i>/
^5([_,]*)':\xA0/4$1'u<$i>/
^5([_,]*)':\xA1/4$1'u<$i>/
^5([_,]*)':\xA2/4$1'u<$i>/
^5([_,]*)':\xA3/4$1'u<$i>/
^5([_,]*)':\xA4/4$1'u<$i>/
^5([_,]*)':\xA5/4$1'u<$i>/
^5([_,]*)':\xA6/4$1'u<$i>/
^5([_,]*)':\xA7/4$1'u<$i>/
^5([_,]*)':\xA8/4$1'u<$i>/
^5([_,]*)':\xA9/4$1'u<$i>/
^5([_,]*)':\xAA/4$1'u<$i>/
^5([_,]*)':\xAB/4$1'u<$i>/
^5([_,]*)':\xAC/4$1'u<$i>/
^5([_,]*)':\xAD/4$1'u<$i>/
^5([_,]*)':\xAE/4$1'u<$i>/
^5([_,]*)':\xAF/4$1'u<$i>/
^5([_,]*)':\xB0/4$1'u<$i>/
^5([_,]*)':\xB1/4$1'u<$i>/
^5([_,]*)':\xB2/4$1'u<$i>/
^5([_,]*)':\xB3/4$1'u<$i>/
^5([_,]*)':\xB4/4$1'u<$i>/
^5([_,]*)':\xB5/4$1'u<$i>/
^5([_,]*)':\xB6/4$1'u<$i>/
^5([_,]*)':\xB7/4$1'u<$i>/
^5([_,]*)':\xB8/4$1'u<$i>/
^5([_,]*)':\xB9/4$1'u<$i>/
^5([_,]*)':\xBA/4$1'u<$i>/
^5([_,]*)':\xBB/4$1'u<$i>/
^5([_,]*)':\xBC/4$1'u<$i>/
^5([_,]*)':\xBD/4$1'u<$i>/
^5([_,]*)':\xBE/4$1'u<$i>/
^5([_,]*)':\xBF/4$1'u<$i>/
^5([_,]*)':\xC0/4$1'u<$i>/
^5([_,]*)':\xC1/4$1'u<$i>/
^5([_,]*)':\xC2/4$1'u<$i>/
^5([_,]*)':\xC3/4$1'u<$i>/
^5([_,]*)':\xC4/4$1'u<$i>/
^5([_,]*)':\xC5/4$1'u<$i>/
^5([_,]*)':\xC6/4$1'u<$i>/
^5([_,]*)':\xC7/4$1'u<$i>/
^5([_,]*)':\xC8/4$1'u<$i>/
^5([_,]*)':\xC9/4$1'u<$i>/
^5([_,]*)':\xCA/4$1'u<$i>/
^5([_,]*)':\xCB/4$1'u<$i>/
^5([_,]*)':\xCC/4$1'u<$i>/
^5([_,]*)':\xCD/4$1'u<$i>/
^5([_,]*)':\xCE/4$1'u<$i>/
^5([_,]*)':\xCF/4$1'u<$i>/
^5([_,]*)':\xD0/4$1'u<$i>/
^5([_,]*)':\xD1/4$1'u<$i>/
^5([_,]*)':\xD2/4$1'u<$i>/
^5([_,]*)':\xD3/4$1'u<$i>/
^5([_,]*)':\xD4/4$1'u<$i>/
^5([_,]*)':\xD5/4$1'u<$i>/
^5([_,]*)':\xD6/4$1'u<$i>/
^5([_,]*)':\xD7/4$1'u<$i>/
^5([_,]*)':\xD8/4$1'u<$i>/
^5([_,]*)':\xD9/4$1'u<$i>/
^5([_,]*)':\xDA/4$1'u<$i>/
^5([_,]*)':\xDB/4$1'u<$i>/
^5([_,]*)':\xDC/4$1'u<$i>/
^5([_,]*)':\xDD/4$1'u<$i>/
^5([_,]*)':\xDE/4$1'u<$i>/
^5([_,]*)':\xDF/4$1'u<$i>/
^5([_,]*)':\xE0/4$1'u<$i>/
^5([_,]*)':\xE1/4$1'u<$i>/
^5([_,]*)':\xE2/4$1'u<$i>/
^5([_,]*)':\xE3/4$1'u<$i>/
^5([_,]*)':\xE4/4$1'u<$i>/
^5([_,]*)':\xE5/4$1'u<$i>/
^5([_,]*)':\xE6/4$1'u<$i>/
^5([_,]*)':\xE7/4$1'u<$i>/
^5([_,]*)':\xE8/4$1'u<$i>/
^5([_,]*)':\xE9/4$1'u<$i>/
^5([_,]*)':\xEA/4$1'u<$i>/
^5([_,]*)':\xEB/4$1'u<$i>/
^5([_,]*)':\xEC/4$1'u<$i>/
^5([_,]*)':\xED/4$1'u<$i>/
^5([_,]*)':\xEE/4$1'u<$i>/
^5([_,]*)':\xEF/4$1'u<$i>/
^5([_,]*)':\xF0/4$1'u<$i>/
^5([_,]*)':\xF1/4$1'u<$i>/
^5([_,]*)':\xF2/4$1'u<$i>/
^5([_,]*)':\xF3/4$1'u<$i>/
^5([_,]*)':\xF4/4$1'u<$i>/
^5([_,]*)':\xF5/4$1'u<$i>/
^5([_,]*)':\xF6/4$1'u<$i>/
^5([_,]*)':\xF7/4$1'u<$i>/
^5([_,]*)':\xF8/4$1'u<$i>/
^5([_,]*)':\xF9/4$1'u<$i>/
^5([_,]*)':\xFA/4$1'u<$i>/
^5([_,]*)':\xFB/4$1'u<$i>/
^5([_,]*)':\xFC/4$1'u<$i>/
^5([_,]*)':\xFD/4$1'u<$i>/
^5([_,]*)':\xFE/4$1'u<$i>/
^5([_,]*)':\xFF/4$1'u<$i>/
# [
^3([_,]*)'(_+)([,_]*)\$([^']*)'(=*)\(/4$1'$2$3\$$4$5'(/
^3([_,]*)'(?!_)([,_]*)\$([^']*)'(=*)\(([^$]*?)(?<!=)\4\)/4$1'$2\$$3$4($5$4')/
# ]
^3([_,]*)'(_+)([,_]*)\$([^']*)(?<!=)(=*)\(([^']*?)'\5\)/4$1'$2$3\$$4$5'($6$5)/
^3([_,]*)'(?!_)([,_]*)\$([^']*)(?<!=)(=*)\(([^']*?)'\4\)/4$1'$2\$$3$4($5$4')/
# Move to output finalization
^3['_,]*\$[^$]*'\$([_,]*)\$[^\x00-\xFF]*$/6$1\$/
^6_{0,31},([_,]*)\$([\x00-\xff]*)/6$1\$$2/
^6_{32},([_,]*)\$([\x00-\xff]*)/6$1\$$2 /
^6_{33},([_,]*)\$([\x00-\xff]*)/6$1\$$2!/
^6_{34},([_,]*)\$([\x00-\xff]*)/6$1\$$2"/
^6_{35},([_,]*)\$([\x00-\xff]*)/6$1\$$2\#/
^6_{36},([_,]*)\$([\x00-\xff]*)/6$1\$$2\$/
^6_{37},([_,]*)\$([\x00-\xff]*)/6$1\$$2%/
^6_{38},([_,]*)\$([\x00-\xff]*)/6$1\$$2&/
^6_{39},([_,]*)\$([\x00-\xff]*)/6$1\$$2'/
^6_{40},([_,]*)\$([\x00-\xff]*)/6$1\$$2(/
^6_{41},([_,]*)\$([\x00-\xff]*)/6$1\$$2)/
^6_{42},([_,]*)\$([\x00-\xff]*)/6$1\$$2*/
^6_{43},([_,]*)\$([\x00-\xff]*)/6$1\$$2+/
^6_{44},([_,]*)\$([\x00-\xff]*)/6$1\$$2,/
^6_{45},([_,]*)\$([\x00-\xff]*)/6$1\$$2-/
^6_{46},([_,]*)\$([\x00-\xff]*)/6$1\$$2./
^6_{47},([_,]*)\$([\x00-\xff]*)/6$1\$$2\//
^6_{48},([_,]*)\$([\x00-\xff]*)/6$1\$$20/
^6_{49},([_,]*)\$([\x00-\xff]*)/6$1\$$21/
^6_{50},([_,]*)\$([\x00-\xff]*)/6$1\$$22/
^6_{51},([_,]*)\$([\x00-\xff]*)/6$1\$$23/
^6_{52},([_,]*)\$([\x00-\xff]*)/6$1\$$24/
^6_{53},([_,]*)\$([\x00-\xff]*)/6$1\$$25/
^6_{54},([_,]*)\$([\x00-\xff]*)/6$1\$$26/
^6_{55},([_,]*)\$([\x00-\xff]*)/6$1\$$27/
^6_{56},([_,]*)\$([\x00-\xff]*)/6$1\$$28/
^6_{57},([_,]*)\$([\x00-\xff]*)/6$1\$$29/
^6_{58},([_,]*)\$([\x00-\xff]*)/6$1\$$2:/
^6_{59},([_,]*)\$([\x00-\xff]*)/6$1\$$2;/
^6_{60},([_,]*)\$([\x00-\xff]*)/6$1\$$2</
^6_{61},([_,]*)\$([\x00-\xff]*)/6$1\$$2=/
^6_{62},([_,]*)\$([\x00-\xff]*)/6$1\$$2>/
^6_{63},([_,]*)\$([\x00-\xff]*)/6$1\$$2?/
^6_{64},([_,]*)\$([\x00-\xff]*)/6$1\$$2@/
^6_{65},([_,]*)\$([\x00-\xff]*)/6$1\$$2A/
^6_{66},([_,]*)\$([\x00-\xff]*)/6$1\$$2B/
^6_{67},([_,]*)\$([\x00-\xff]*)/6$1\$$2C/
^6_{68},([_,]*)\$([\x00-\xff]*)/6$1\$$2D/
^6_{69},([_,]*)\$([\x00-\xff]*)/6$1\$$2E/
^6_{70},([_,]*)\$([\x00-\xff]*)/6$1\$$2F/
^6_{71},([_,]*)\$([\x00-\xff]*)/6$1\$$2G/
^6_{72},([_,]*)\$([\x00-\xff]*)/6$1\$$2H/
^6_{73},([_,]*)\$([\x00-\xff]*)/6$1\$$2I/
^6_{74},([_,]*)\$([\x00-\xff]*)/6$1\$$2J/
^6_{75},([_,]*)\$([\x00-\xff]*)/6$1\$$2K/
^6_{76},([_,]*)\$([\x00-\xff]*)/6$1\$$2L/
^6_{77},([_,]*)\$([\x00-\xff]*)/6$1\$$2M/
^6_{78},([_,]*)\$([\x00-\xff]*)/6$1\$$2N/
^6_{79},([_,]*)\$([\x00-\xff]*)/6$1\$$2O/
^6_{80},([_,]*)\$([\x00-\xff]*)/6$1\$$2P/
^6_{81},([_,]*)\$([\x00-\xff]*)/6$1\$$2Q/
^6_{82},([_,]*)\$([\x00-\xff]*)/6$1\$$2R/
^6_{83},([_,]*)\$([\x00-\xff]*)/6$1\$$2S/
^6_{84},([_,]*)\$([\x00-\xff]*)/6$1\$$2T/
^6_{85},([_,]*)\$([\x00-\xff]*)/6$1\$$2U/
^6_{86},([_,]*)\$([\x00-\xff]*)/6$1\$$2V/
^6_{87},([_,]*)\$([\x00-\xff]*)/6$1\$$2W/
^6_{88},([_,]*)\$([\x00-\xff]*)/6$1\$$2X/
^6_{89},([_,]*)\$([\x00-\xff]*)/6$1\$$2Y/
^6_{90},([_,]*)\$([\x00-\xff]*)/6$1\$$2Z/
^6_{91},([_,]*)\$([\x00-\xff]*)/6$1\$$2[/
^6_{92},([_,]*)\$([\x00-\xff]*)/6$1\$$2\\/
^6_{93},([_,]*)\$([\x00-\xff]*)/6$1\$$2]/
^6_{94},([_,]*)\$([\x00-\xff]*)/6$1\$$2^/
^6_{95},([_,]*)\$([\x00-\xff]*)/6$1\$$2_/
^6_{96},([_,]*)\$([\x00-\xff]*)/6$1\$$2`/
^6_{97},([_,]*)\$([\x00-\xff]*)/6$1\$$2a/
^6_{98},([_,]*)\$([\x00-\xff]*)/6$1\$$2b/
^6_{99},([_,]*)\$([\x00-\xff]*)/6$1\$$2c/
^6_{100},([_,]*)\$([\x00-\xff]*)/6$1\$$2d/
^6_{101},([_,]*)\$([\x00-\xff]*)/6$1\$$2e/
^6_{102},([_,]*)\$([\x00-\xff]*)/6$1\$$2f/
^6_{103},([_,]*)\$([\x00-\xff]*)/6$1\$$2g/
^6_{104},([_,]*)\$([\x00-\xff]*)/6$1\$$2h/
^6_{105},([_,]*)\$([\x00-\xff]*)/6$1\$$2i/
^6_{106},([_,]*)\$([\x00-\xff]*)/6$1\$$2j/
^6_{107},([_,]*)\$([\x00-\xff]*)/6$1\$$2k/
^6_{108},([_,]*)\$([\x00-\xff]*)/6$1\$$2l/
^6_{109},([_,]*)\$([\x00-\xff]*)/6$1\$$2m/
^6_{110},([_,]*)\$([\x00-\xff]*)/6$1\$$2n/
^6_{111},([_,]*)\$([\x00-\xff]*)/6$1\$$2o/
^6_{112},([_,]*)\$([\x00-\xff]*)/6$1\$$2p/
^6_{113},([_,]*)\$([\x00-\xff]*)/6$1\$$2q/
^6_{114},([_,]*)\$([\x00-\xff]*)/6$1\$$2r/
^6_{115},([_,]*)\$([\x00-\xff]*)/6$1\$$2s/
^6_{116},([_,]*)\$([\x00-\xff]*)/6$1\$$2t/
^6_{117},([_,]*)\$([\x00-\xff]*)/6$1\$$2u/
^6_{118},([_,]*)\$([\x00-\xff]*)/6$1\$$2v/
^6_{119},([_,]*)\$([\x00-\xff]*)/6$1\$$2w/
^6_{120},([_,]*)\$([\x00-\xff]*)/6$1\$$2x/
^6_{121},([_,]*)\$([\x00-\xff]*)/6$1\$$2y/
^6_{122},([_,]*)\$([\x00-\xff]*)/6$1\$$2z/
^6_{123},([_,]*)\$([\x00-\xff]*)/6$1\$$2{/
^6_{124},([_,]*)\$([\x00-\xff]*)/6$1\$$2|/
^6_{125},([_,]*)\$([\x00-\xff]*)/6$1\$$2}/
^6_{126},([_,]*)\$([\x00-\xff]*)/6$1\$$2~/
^6_{127}_*,([_,]*)\$([\x00-\xff]*)/6$1\$$2/
# Finalize output. For reasonable outputs, this can be blanked. To prevent re-interpreting, intentionally prepends a =
^6\$/=/
1#input

```

This behemoth of ReRegex code is a true torture test for the language.

Takes input after the `$` character, Supports the full byte range on inputs, though is limited to printable ascii for outputs due to a limitation of the Java version used to run ReRegex.

Takes a couple seconds to run the simple Hello World, over a minute to run the golfed version, and primes to 15 is still running...

# Answer
> 3 votes
## PHP, 208 bytes

```
<?$a=array_fill(0,3e4,$b=0);$A='$a[$b]';$c=explode('|',"|while($A){|}|echo chr($A);|$A=ord(fgetc(STDIN));|++$A;|--$A;".'|++$b;|--$b;');eval(preg_replace('~.~e','$c[strpos(" [].,+-><","\0")]',`cat $argv[1]`));

```

Tested with PRIME.BF

```
php ./bf.php PRIME.BF
Primes up to: 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

```

# Answer
> 3 votes
**OCaml(lex), 497 chars**

OCamllex is part of the standard distribution of OCaml.

```
{let a=Array.create 30000 0
let(%)f g h=f(g h)
let s v i=a.(i)<-v;i
let o d i=s(a.(i)+d)i
let p i=print_char(Char.chr a.(i));flush stdout;i
let r i=s(Char.code(input_char stdin))i
let rec w g i=if 0=a.(i)then i else w g(g i)
let n x=x}
rule t f=parse
|'>'{t(succ%f)lexbuf}
|'<'{t(pred%f)lexbuf}
|'+'{t((o 1)%f)lexbuf}
|'-'{t((o(-1))%f)lexbuf}
|'.'{t(p%f)lexbuf}
|','{t(r%f)lexbuf}
|'['{t((w(t n lexbuf))%f)lexbuf}
|']'|eof{f}
|_{t f lexbuf}
{let _=t n(Lexing.from_channel(open_in Sys.argv.(1)))0}

```

Save as b.mll and run with

```
ocamllex b.mll && ocaml b.ml prime.bf

```

I don't like parsing by hand, so I used the provided lexer generator. From the tokens read, we compose a function for the whole brainf\*ck program.

# Answer
> 3 votes
## \[EDIT\] C++11, 318, reads from file:

```
#include <bits/stdc++.h>
char b[99999]={0},g[99999]={0},*f=g,*p=b;std::function<void()>m[128]={[43]=[]{++*p;},[]{*p=getchar();},[]{--*p;},[]{putchar(*p);},[62]=[]{p++;},[60]=[]{p--;},[91]=[]{if(!(*p))while(*f-93)f++;f++;},[93]=[]{while(*f-91)f--;f--;}};int main(){
fread(g,99,999,stdin);for(;*f;f++)if(m[*f])m[*f]();}

```

https://godbolt.org/z/7xxbqM

# Answer
> 3 votes
# C# (2861 char, ~84 lines)

This is not the prettiest solution to the problem, and probably not all that 'Golf-ish', since I wasn't as concerned with length as I probably should have been. (I didn't remove the comments or extra white space.) I just wanted to try something in a new language, to see if I could. If I did it again, I'd drop the use of the stack for returning from '\]' and just look back. Run without command line arguments it runs the hello world program given in the problem description. It accepts one command line argument, the filename of the program to run.

```
using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            String ProgSource;
            if (args.Length > 0)
                ProgSource = System.IO.File.ReadAllText(args[0]);
            else //hello world
                ProgSource = "";

            Stack<int> stack = new Stack<int>();
            char[] bfProg = ProgSource.ToCharArray();
            char[] mem = new char[30000];
            int ptr = 0;

            for (int ip = 0; ip<bfProg.Length; ip++){
                switch (bfProg[ip])
                {
                    case ('>'): ptr++;  break;
                    case ('<'): ptr--;  break;
                    case ('+'): mem[ptr]++; break;
                    case ('-'): mem[ptr]--; break;
                    case ('.'): Console.Write(mem[ptr]); break;
                    case (','):
                        char key = Console.ReadKey(false).KeyChar;
                        if (key == '\r')
                        {
                            key = (char)10;
                            Console.WriteLine();
                        }
                        mem[ptr] = key;
                        break;
                    case ('['):
                        if (mem[ptr] == 0)
                        {
                            int openBraces = 1;
                            //find the closing brace for this expression
                            for (int x = 1; x < (bfProg.Length - ip); x++)
                            {
                                if (bfProg[ip + x] == ']') openBraces--;
                                if (bfProg[ip + x] == '[') openBraces++;
                                if (openBraces == 0)
                                {
                                    if (stack.Peek() == ip) stack.Pop();
                                    ip += x;
                                    break;
                                }
                            }
                       }
                       else
                       {
                           stack.Push(ip);
                       }
                       break;
                    case (']'):
                        if (mem[ptr] == 0)
                            stack.Pop();
                        else
                        {
                            ip = stack.Peek();
                        }
                        break;
                }
            }

            Console.WriteLine("\n\n\nExecution Completed Sucessfully. Press any key to continue...");
            Console.ReadKey();

        }
    }

}

```

Edit: Removed unused references.

# Answer
> 3 votes
# Julia 0.6, ~~427~~ 422 bytes

I know the challenge is old, but who cares... My solution feels huge, and I bet it could be a lot shorter.

```
function g(n::AbstractString) p=open(n);c=readchomp(p);close(p);b="a[k]";e=30000;j="a=zeros(UInt8,$e);k=1;";for i=1:length(c) c[i]=='<'?(j=j*"k-=1;"):c[i]=='>'?(j=j*"k+=1;"):c[i]=='+'?(j=j*"$b+=1;"):c[i]=='-'?(j=j*"$b-=1;"):c[i]=='['?(j=j*"while $b>0 "):c[i]==']'?(j=j*"end;"):c[i]=='.'?(j=j*"print(Char($b));"):c[i]==','?(j=j*"s=chomp(readline(STDIN));s==\"\"?$b=10:$b=s[1];"):nothing;end;println(j);@eval $(parse(j));end

```

Try it online!

Characters are entered one by one, no buffered input. Just hitting the `enter` key sends newline (ASCII 10).

Execution of the test case for primes up to 255, on my i5 2410 M laptop takes about 9.5 minutes:

```
julia> @time bf("primes.bf")
Primes up to: 2
5
5

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199 211 223 227 229 233 239 241 251
567.207327 seconds (301.29 k allocations: 19.484 MB)

```

Ungolfed:

```
function bf(n::AbstractString)
    p=open(n)
    c=readchomp(p)
    close(p)
    b="a[k]"
    U="UInt8(1)"
    e=30000
    j="a=zeros(UInt8,$e);k=1;"
    for i=1:length(c)
        c[i]=='<' ? (j=j*"k-=1;") :
        c[i]=='>' ? (j=j*"k+=1;") :
        c[i]=='+' ? (j=j*"$b+=$U;") :
        c[i]=='-' ? (j=j*"$b-=$U;") :
        c[i]=='[' ? (j=j*"while $b>0 ") :
        c[i]==']' ? (j=j*"end;") :
        c[i]=='.' ? (j=j*"print(Char($b));") :
        c[i]==',' ? (j=j*"s=chomp(readline(STDIN));s==\"\" ? $b=10 :  $b=s[1];") : nothing
    end
    j=parse(j)
    @eval $j
end

```

The interpreter generates julia code from the bf source and evaluates the code. For the test case, the result would look like this:

```
a=zeros(UInt8,30000);k=1;k+=1;a[k]+=1;a[k]+=1;a[k]+=1;a[k]+=1;a[k]+=1;a[k]+=1;...........

```

In a more readable version with newlines instead of semicolons, this results in 1368 SLOC:

```
a=zeros(UInt8,30000)
k=1
k+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
while a[k]>0
k-=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
k+=1
a[k]-=1
end
...
...
...
while a[k]>0
a[k]-=1
end
k-=1
while a[k]>0
a[k]-=1
end
k-=1
k-=1
a[k]-=1
end
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
a[k]+=1
print(Char(a[k]))
while a[k]>0
a[k]-=1
end

```

# Answer
> 3 votes
# Cy, ~~272~~ ~~270~~ ~~253~~ ~~233~~ 232 bytes

This is mind-numbingly slow, but I guess that's what I get for interpreting an inefficent language in an interpreted interpreted language.

Thanks to this answer, Cy is my first language to be proven Turing-complete!

```
[0 &=d] =C
{$C $d ::} =c
("+" "$C $d ::++" :
"-" "$C $d ::--" :
"<" ".d --" :
">" ".d ++ $C 0 <~" :
"[" "{c 0 >} {" :
"]" "} while" :
"." "c chr :<<" :
"," "$C $d :>c ord ::=" :
"",)=f
"" =m
:>R {=x .m $f $x :: "% " +=} each
$m exec

```

I have created a monster.

Ungolfed/"readable":

```
[0] =cells
0 =dp

{ $cells $dp :: } =cell
(
    "+" " $cells $dp ::++ " :
    "-" " $cells $dp ::-- " :
    "<" "
        .dp --
    " :
    ">" "
        .dp ++
        $dp $cells len >< {
            $cells 0 <~
        } if
    " :
    "[" "
        { cell 0 > } {
    " :
    "]" "
        } while
    " :
    "." " cell chr :<< " :
    "," " $cells $dp :>c ord  ::= " :
    "" ,
) =funcs

:>R =code
"" =cmds
$code { =x
    .cmds $funcs $x :: +=
} each
$cmds exec

```

# Answer
> 3 votes
# C, 194 bytes

```
s[99999],*p;char*c;k(h){h=*c-h;return h*h<2?h:0;}main(d,i){c=1[p=i];for(p=s;*c;++c){(*p)-=k(44);p+=k(61);*c^46?*c^44?0:(*p=getchar()):putchar(*p);d=k(92);if(*p?~d:d-1)for(i=d;i;i+=k(92))c-=d;}}

```

Expects the brainfuck program as the first command line argument.

# Answer
> 3 votes
# Python 3 (no eval), ~~288~~ ~~286~~ 280 bytes

Based on @boothby's solution, but I replaced recursion with loop+stack and made other changes.

```
from sys import*
s=[];c=open(argv[1]).read();m=[0]*8**5;k=i=0
while i<len(c):
 x='+-<>[],.'.find(c[i]);u=x>3;i+=1;d=m[1]
 if m[2]<=k:
  e=m[d]and x==4;k=m[2]+e;u=1;*s,i=s+[i-1]*e+[i]*(x!=5)
  if x==6:m[d]=ord(stdin.read(1))
  print(end=chr(m[d]*(x>6)))
 m[x%8>>1or d]+=(1-x%2*2)*u

```

Try it online!

### How it works

* `c` \- BF code to interpret
* `m` \- memory, not cyclic (32768 total cells, 3 reserved)
* `i` \- instruction pointer
* `d` \- data pointer
* `x` \- current command (-1 to 7)
* `s` \- stack of return addresses
* `k` \- depth at which execution is allowed
* `u` \- flag: is memory update required
* `e` \- flag: should loop be executed or skipped

Cells `m[1]`,`m[2]`, and `m[3]` are reserved for internal use:

* `m[1]` \- actual data pointer, `d` is just a shortcut.
* `m[2]` \- depth counter, it increases on `[` and decreases on `]`. If depth is more than `k`, instructions should be ignored: this is how interpreter reaches end of loop when condition is not met (but `[` and `]` still count depth).
* `m[3]` \- trash cell, it increases on `.` and decreases on `,` and comments, but its value is never used.

To prevent accidental rewrite, user memory is reverted: it starts at `m[0]`, next is `m[-1]`, then `m[-2]` and so on.

# Answer
> 3 votes
# C (gcc), (Try it online!) 194 187 176 175 bytes (thanks to @ceilingcat)

```
char t['u0'],*p=t;c;l;f(char*b){for(;c=*b;b++)if(c-=43,read(write(l=1,p+=c==19,c==3),p-=c==17,!~c),*p+=!c-(c==2),c-=48,!c|c==2)for(;l&&!*p^c/2;l-=*b==93-c)l+=0[b-=c-1]==91+c;}

```

# C (gcc), (Try it online!) 231 bytes

```
char t['u0'],*p=t;c;l;f(char*b){for (;c=*b;b++) {l=1;c-43||++*p;c-45||--*p;c-60||p--;c-62||p++;c-46||putchar(*p);c-44||(*p=getchar());for(;l&&!*p&&c==91;){++b;*b-91||l++;*b-93||l--;}for(;l&&*p&&c==93;){--b;*b-93||l++;*b-91||l--;}}}

```

# Answer
> 3 votes
# C (gcc) Linux AArch64, ~~483 461 449 439 424~~ 413 bytes

```
#define S(x)"(\0@9\b\5\0"#x"(\0\0\71":
*T=" \0\1J\b\xfc\0\21!@\0\xd4",c,h,*mmap(),*wcpcpy();d[7500];(*p)();*j(int*a){int*t=a,*n,q=0;for(;read(h,&c,!q);)t=c==91?n=j(t+2),*t++='9@\0(',*t=n-t<<5|8|90<<25,n:c==93?q=*t=a-t-2&33554431|22<<24,t+1:wcpcpy(t,c-60?c-62?c-45?c-43?c-46?c-44?t:T:T+1:S(\21)S(Q)"!\4\0\x91":"!\4\0\xd1");return t;}main(P,g)int**g;{*j(p=mmap(0,1<<20,6,34,h=open(g[1],0),0))=3596551104;p(1,d,1);}

```

This is a JIT that compiles BF code into AArch64 machine language at runtime. This performs a straight translation so commonly occurring sequences such as \>\>\>, \<\<\<, +++ and --- aren't coalesced into faster instructions.

This is a port of the "JIT" for x86\_64 https://codegolf.stackexchange.com/a/178298/52904

Less golfed version:

```
#include<wchar.h>
// size of data area
c,*mmap();d[7500];h;(*p)();
*j(int*a){
  int*t=a,*n,q=0;
  for(;read(h,&c,!q);){
    t=c==91?
      // ldrb w8, [x1]
      // cbz w8, n-t
      n=j(t+2),
      *t++=0x39400028,
      *t=n-t<<5|8|180<<24,
      n
    :c==93?
      // b a-t-2
      q=a-t-2,
      *t=q&0x1ffffff|22<<24,
      t+1
    :
      wcpcpy(t,c-'<'?
                 c-'>'?
                   c-'-'?
                     c-'+'?
                       c-'.'?
                         c-','?
                           L""
                         :
                           // eor w0, w1, w1
                           // add w8, w0, #0x3f ; read(0,buf,1)
                           // svc #0x201        ; Linux is not picky about the argument
                           L"\x4a010020\x1100fc08\xd4004021"
                       :
                         // add w8, w0, #0x3f ; write(1,buf,1)
                         // svc #0x201        ; w0 was 1 from last syscall
                         L"\x1100fc08\xd4004021"
                     :
                       // ldrb w8, [x1]
                       // add w8,w8, 1
                       // strb w8, [x1]
                       L"\x39400028\x11000508\x39000028"
                   :
                     // ldrb w8, [x1]
                     // sub w8,w8, 1
                     // strb w8, [x1]
                     L"\x39400028\x51000508\x39000028"
                 :
                   // add x1, x1, 1
                   L"\x91000421"
               :
                 // sub x1, x1, 1
                 L"\xd1000421"
      );
  }
  return t;
}
main(P,g)int**g;{
  // allocate text (executable) memory and mark as executable
  p=mmap(0,1<<20,6,34,h=open(g[1],0),0);
  // run JIT, exit gracefully
  *j(p)=0xd65f03c0;
  // set %x2=1 and call code like a function
  p(1,d,1);
}

```

# Answer
> 3 votes
ABPL: 303 bytes

<pre><code>{c0↓{αβ~# c↑0≠}{{"["=}{c↓1+↑}I{"]"=}{c↓1-↑}I}æ}wloop↓
"+++[->+++<]>."code↓0,30000~Am↓0p↑
{β~λα↓≠}{{βα~#"+"=}{m↓p↓~#1+m↓~^p↓~^~%m↑&}I{βα~#"-"=}{m↓p↓~#1-m↓~^p↓~^~%m↑&}I{βα~#"<"=}{p↓1-30000%}I{βα~#">"=}{p↓1+30000%}I{βα~#"["=}{wloop! αβ;}{βα~#"."=}{m↓p↓~#→}I{βα~#","=}{m↓p↓~#←m↓~^p↓~^~%m↑}I}W```
</code></pre>

# Answer
> 2 votes
## golfscript, partial solution only, 150 chars

```
:i;[0]30000*[]0 "#{File.open('f').read}"{{\(@=\''if}+['>+\\(@\\' '<@+\\)' '+1+256%' '-1- 256%' ".[0$]''+print " ',;i(\:i;' '[{.}{' ']}while']\%}%~;;;;

```

i am greatly indebted to the pattern of generating your own source and then eating it, as others have already posted.

misfeatures:

* only parses brainfuck code from the file `'f'`.
* all input you want to read with `','` must be piped in at the beginning.
* runs hello world, yet dies somewhere during prime.bf. i'm not sure why. i did read somewhere that golfscript is broken for nested while loops, so that might be it.
* stores a char=\>string map in a way that is entertainingly horrible, at least to me.

I've tried loading arbitrary files with constructions like "#{File.open(" "some\_file.bf" ").read}" + + but Ruby seems to helpfully escape the "#" for me so i dont accidentally load the file im trying to load. On the other hand, embedding "#{getc}" works okay for reading from stdin, but there's still the restriction that input is non-interactive - only stuff piped in at the start is read. Anyone know a way around one or more of these input issues?

# Answer
> 2 votes
From sepp2k solution - 148

```
eval"a=[i=0]*3e4;"+$<.bytes.map{|b|{?.,"putc a[i]",?,,"a[i]=getc",?[,"while a[i]>0",?],"end",?<,"i-=1",?>,"i+=1",?+,"a[i]+=1",?-,"a[i]-=1"}[b]}*";"

```

`eval"a=[i=0]*3e4;"+$<.bytes.map{` can be replaced with `a=[i=0]*3e4;eval$<.bytes.map{` -3 bytes

`*";"` =\> `*$/` -1 bytes

`"while a[i]>0"` and`"end"` =\> `"("` and `")while(a[i]>0)"` -1 bytes

And we get 143 (5 bytes less)

```
a=[i=0]*3e4;eval$<.bytes.map{|b|{?.,"putc a[i]",?,,"a[i]=getc",?[,"(",?],")while a[i]>0",?<,"i-=1",?>,"i+=1",?+,"a[i]+=1",?-,"a[i]-=1"}[b]}*$/

```

And what if there aren't any comments in input (only `+-<>[],.`) http://codepad.org/EihHsoJO

we can write like this:

```
a=[i=0]*3e4;eval$<.bytes.map{|b|%w{putc(a[i]) a[i]=getc ( )while(a[i]>0) i-=1 i+=1 a[i]+=1 a[i]-=1}[".,[]<>+-\n".index b]}*$/

```

And this is 126 bytes, if there wouldn't be `"\n"` at the end, we can skip it in this part `".,[]<>+-\n"` =\> `".,[]<>+-"` saving 2 bytes

And this can be shorten to:

```
a=[i=0]*3e4;eval$<.bytes.map{|b|%w{i-=1 ( i+=1 )while(0<a[i]) a[i]+=1 a[i]=getc a[i]-=1 putc(a[i])}[b%30%9]}*$/

```

which is 112 bytes

where `b%30%9` is a mapping from ascii code to array index

How to find this formula?

Very easy:

```
c="<[>]+,-."
(1..99).each do |i|
    (1..99).each do |j|
        r = c.each_byte.map {|a| a%i%j}.select {|x| x < c.size}.uniq
        puts "#{r} #{i} #{j} " if r.size==c.size
    end
end

>>>
[0, 1, 2, 3, 4, 5, 6, 7] 30 9
[4, 5, 6, 7, 0, 1, 2, 3] 43 13
[4, 3, 6, 5, 7, 0, 1, 2] 44 12
[0, 7, 2, 1, 3, 4, 5, 6] 52 8
[0, 7, 2, 1, 3, 4, 5, 6] 60 8

```

So if only we can assume, that there would be only `<>+-[],.` whe can shorten the solution to `112` bytes

# Answer
> 2 votes
## VB.net, 730 bytes

```
If P.Aggregate(Of Int32)(0,Function(s,i)If(s<0,s,If(i="["c,s+1,If(i="]"c,s-1,s))))=0 Then Dim C=0,O=0,M(30000)As Int32:Dim J As Func(Of Int32,Int32,Int32,Char,Char,Int32)=Function(x,n,l,g,t)If(P(x)=g,J(x+n,n,l+1,g,t),If(P(x)=t,If(l=1,x,J(x+n,n,l-1,g,t)),J(x+n,n,l,g,t))):Dim Q As New Dictionary(Of Char,Action)From{{"+"c,Sub()M(O)=If(M(O)=255,255,M(O)+ 1)},{"-"c,Sub()M(O)=If(M(O)=0,0,M(O)-1)},{"<"c,Sub()O=If(O=0,M.Length,O-1)},{">"c,Sub()O=If(O=M.Length-1,0,O+1)},{"["c,Sub()C=If(M(O)=0,J(C,+1,0,"["c,"]"c),C)},{"]"c,Sub()C=If(M(O)=0,C,J(C,-1,0,"]"c,"["c))},{","c,Sub()M(O)=Console.Read()},{"."c,Sub()Console.Write(Convert.ToChar(M(O)))}}:For C=0To P.Length-1:Dim a=If(Q.ContainsKey(P(C)),Sub()Q(P(C))(),Sub()Exit Sub):a():Next

```

# Answer
> 2 votes
# PynTree, 123 bytes

```
Æp+"Dw[0]Dy0"Ƭ+"æ#wy%+1#wy256"-"æ#wy%_#wy1 256"."ƤȮ#wy","æ#wy%OĊ256">";ß+y1æSwy"<"¿yß_y1æIw0 0"["¡#wy¤"]'}}JfxSėx"+-.,[]<>"

```

Try it online!

Transpiles Brainfuck to PynTree and then calls `pyntree_eval` on it. PynTree transpiles directly to Python.

# Answer
> 2 votes
# Powershell, ~~175~~ ~~195~~ ~~183~~ ~~175~~ 173 bytes, Transpiler

```
,'$p=0
$c=@{}'+(gc $args|% t*y|%{(-split'$p++
$p--
$c.$p++
$c.$p--
$c.$p=[console]::Read()
write-host([char]$c.$p)-n
for(;$c.$p){
}
#')[('><+-,.[]'|% i*f $_)]
})-join'
'|iex

```

Explanation:

The script is transpiler from a brainfuck source code to a powershell source code. Finally, the script evaulates the result powershell code by command iex.

* init commands `$p=0` and `$c=@{}`
* `gc $args|% t*y|%{` \- for each character from file
* `('><+-,.[]'|% i*f $_)+1` \- treats a current char as index in the array of code snippets. If character match no code snippet, the script uses the comment char `#`.
* and `iex` evaulates the result powershell code

Compared to Joey's answer, this script fixes a bug "Index operation failed; the array index evaluated to null" (`$p=0` in the init block)

Known issues:

* `[console]::Read()` eats first char in `VSCode`. This expression work correct in a powershell window.

Less golfed test script:

```
$f = {

'$p=0',
'$c=@{}'+
(gc $args|% t*y|%{
    $bfcmd_Idx='><+-,.[]'.IndexOf($_)     # IndexOf returns -1 if char $_ does not found.
    @(  '$p++',
        '$p--',
        '$c.$p++',
        '$c.$p--',
        '$c.$p=[console]::Read()',
        'write-host([char]$c.$p)-n',
        'for(;$c.$p){',
        '}',
        '#'
    )[$bfcmd_Idx]      # push to pipe an element. -1 means last element
})-join"`n"|Invoke-Expression

}

&$f interpret-brainf-hello.bf
&$f interpret-brainf-prime.bf

```

Output:

```
Hello World!
Primes up to: 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

```

File `interpret-brainf-prime.bf` contains a test script from the question.

File `interpret-brainf-hello.bf` (from wiki):

```
[ This program prints "Hello World!" and a newline to the screen, its
  length is 106 active command characters. [It is not the shortest.]

  This loop is an "initial comment loop", a simple way of adding a comment
  to a BF program such that you don't have to worry about any command
  characters. Any ".", ",", "+", "-", "<" and ">" characters are simply
  ignored, the "[" and "]" characters just have to be balanced. This
  loop and the commands it contains are ignored because the current cell
  defaults to a value of 0; the 0 value causes this loop to be skipped.
]

++++++++               Set Cell #0 to 8
[
    >++++               Add 4 to Cell #1; this will always set Cell #1 to 4
    [                   as the cell will be cleared by the loop
        >++             Add 2 to Cell #2
        >+++            Add 3 to Cell #3
        >+++            Add 3 to Cell #4
        >+              Add 1 to Cell #5
        <<<<-           Decrement the loop counter in Cell #1
    ]                   Loop till Cell #1 is zero; number of iterations is 4
    >+                  Add 1 to Cell #2
    >+                  Add 1 to Cell #3
    >-                  Subtract 1 from Cell #4
    >>+                 Add 1 to Cell #6
    [<]                 Move back to the first zero cell you find; this will
                        be Cell #1 which was cleared by the previous loop
    <-                  Decrement the loop Counter in Cell #0
]                       Loop till Cell #0 is zero; number of iterations is 8

The result of this is:
Cell No :   0   1   2   3   4   5   6
Contents:   0   0  72 104  88  32   8
Pointer :   ^

>>.                     Cell #2 has value 72 which is 'H'
>---.                   Subtract 3 from Cell #3 to get 101 which is 'e'
+++++++..+++.           Likewise for 'llo' from Cell #3
>>.                     Cell #5 is 32 for the space
<-.                     Subtract 1 from Cell #4 for 87 to give a 'W'
<.                      Cell #3 was set to 'o' from the end of 'Hello'
+++.------.--------.    Cell #3 for 'rl' and 'd'
>>+.                    Add 1 to Cell #5 gives us an exclamation point
>++.                    And finally a newline from Cell #6

```

# Powershell, 257 bytes, Interpreter

```
$c=@{}
$p=$i=0
$m={for(;($b+=($s[$i]-92)|?{$_-in-1,1})){$i+=$args[0]}}
for($s=gc $args -ra;$i-lt$s.Length){switch($s[$i]-40){22{$p++}20{$p--}3{$c.$p++}5{$c.$p--}4{$c.$p=[console]::Read()}6{write-host([char]$c.$p)-n}51{if(!$c.$p){.$m 1}}53{.$m -1;$i--}}$i++}

```

Less golfed test script:

```
$f = {

$c=@{}                                      # $c - hashtable
$p=$i=0                                     # $p - ptr (a key in the hashtable), $i - IC (Instruction Counter)
$m={
    for(;($b+=($s[$i]-92)|?{$_-in-1,1})){   # $b - balance of the brackets
        $i+=$args[0]                        # move IC forward or backward
    }                                       # while balance of the brackets is not 0
}
for($s=gc $args -ra;$i-lt$s.Length){        # -ra is shortcut for -raw parameter = get-content as char array
    switch($s[$i]-40){                      # '-40' needs to convert into [int] and to reduce cases 43 44 45 46 into 3 4 5 6 (-2 bytes)
        22{$p++}
        20{$p--}
        3{$c.$p++}
        5{$c.$p--}
        4{$c.$p=[console]::Read()}          # it eats a first char in a VSCode, it works correct in a Powershell terminal
        6{write-host([char]$c.$p)-n}
        51{if(!$c.$p){.$m 1}}               # dot source the script block m
        53{.$m -1;$i--}                     # dot sourcing does not create a new scope https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_scripts
    }
    $i++
}

}

&$f interpret-brainf-hello.bf
&$f interpret-brainf-prime.bf

```

Output:

```
Hello World!
Primes up to: 20
2 3 5 7 11 13 17 19

```

# Answer
> 2 votes
# Javascript - 342 bytes

This is pretty much a complete ripoff of https://codegolf.stackexchange.com/a/220/85546, but I've translated it to Javascript, which was mostly simple except for the converting of character codes, which required some extra lines of code.

```
d=l=>{i=0,b=new Array(300).fill(0),t="",q=[];r=new Response(l).text().then(q=>(q.split("").forEach(e=>{t+=["i++;","i--;","b[i]++;","b[i]--;","n=new Buffer(1);n[0]=b[i];q.push(n.toString());","b[i]=prompt().charCodeAt(0);","while (b[i]){","}"]["><+-.,[]".indexOf(e)]||"\n",i+=(92-e.charCodeAt(0))*(e.indexOf("][")>-1)});eval(t);return q))}

```

It reads input from a Blob (`l`), and returns the output as an array of numbers/strings/whatever. All other input is taken as a `prompt`, of which only the first character is stripped. As with @Alexandru's submission, it `eval`s the translated code, which is simply mapped one character at a time to corresponding JS.

# Answer
> 2 votes
# C# - ~~373~~ ~~349~~ ~~339~~ 335 chars

```
using C=System.Console;class P{static void Main(string[] z){try{for(dynamic c,p=z[0],a=new int[30000],s=new int[9],f=1>0,i=0,d=0,t=0;;i=c==51&&f&(f|=s[--t]<0)?s[t]:++i){c=p[i]-42;a[d+=(c-19)*(f&c>17&c<21?1:0)]+=(2-c)*(f&c>0&c<4?1:0);if(f&c==4)C.Write((char)a[d]);if(f&c==2)a[d]=C.Read();if(c==49)s[t++]=f?(f=a[d]!=0)?i:-1:i;}}catch{}}}

```

And more readable:

```
using C=System.Console;
class P
{
    static void Main(string[] z)
    {
        try
        {
            for(dynamic c,p=z[0],a=new int[30000],s=new int[9],f=1>0,i=0,d=0,t=0;;i=c==51&&f&(f|=s[--t]<0)?s[t]:++i)
            {
                c=p[i]-42;
                a[d+=(c-19)*(f&c>17&c<21?1:0)]+=(2-c)*(f&c>0&c<4?1:0);
                if(f&c==4)C.Write((char)a[d]);
                if(f&c==2)a[d]=C.Read();
                if(c==49)s[t++]=f?(f=a[d]!=0)?i:-1:i;
            }
        }
        catch{}
    }
}

```

Limitation is it only handles nested `[` up to 9 deep. Can make the `s` array bigger to handle more.

Edit 373 -\> 349: Removed outer loop (was for a different site), character comparisons to integers, moved `c` declaration into the for loop

Edit 349 -\> 339:

* Combined `+`/`-` and `>`/`<` into single lines.
* Reduced integer literal lengths by subtracting 42 from `c` to allow for some of the integer literals to be a single character (credit @ceilingcat).
* Moved `i=...` into the for loop iterator section (credit @ceilingcat).

Edit 339 -\> 335:

* Combined `+`/`-` and `>`/`<` into a single line (credit @ceilingcat)
* Removed unnecessary parenthesis in the `i=...` (credit @ceilingcat)

# Answer
> 2 votes
# Rust, 312 bytes

```
use std::io::*;macro_rules! b{(@+)=>{A[I]+=1;};(@-)=>{A[I]-=1;};(@>)=>{I+=1;};(@<)=>{I-=1;};(@[$($t:tt)*])=>{while A[I]>0{$(b!(@$t);)*}};(@.)=>{print!("{}",A[I]as char);};(@,)=>{stdin().read(&mut A[I..=I]);};(@$t:tt)=>{};($($t:tt)*)=>{static mut A:[u8;30000]=[0;30000];static mut I:usize=0;unsafe{$(b!(@$t);)*}}}

```

Try it online! A more readable (and expansionable) version here. A macro that takes in a list of tokens and transforms them into rust code. The code is inputted as rust tokens, so some characters need to have a separator between them, and the most common ones to avoid are the `>>`, `<<`, `->`, `<-` and `..` operators. If you would like to read the tape after the code's execution the statics generated will still be usable. Also, loops nested 31 or greater deep may run into the recursion limit.

# Answer
> 2 votes
# Duocentehexaquinquagesimal, 260 bytes

```
5„-^ñ™[fyΛÈÐ\∍ζ=¦δW€ªвƵиˆóδˆ†¦#Ûø“:#”Ù@θý9îæζJ¯иεhlÎà₂âY&т9zì*qI∍`ç∍Šñí¼GÏ0¦R˜#ðžèLÛüûK;Øî“müƶrηÝ'ç0Œ©₆V²_Δ≠tδ<üC/ï„Õ›0aÜ7H:¡°RF®Õ(:3%Yñβù½Sègæ₁„z¹*ôŒ$Ðεüõ<тD8ʒ: óǝÁ¸33ùçUηïZç†§Ëh/Wαï¹AÑÜ×ŒÞ¢Íη.ÓAËΩćUQ¯Óƒ‡`EuÈänÖÎo'²₃ĆÄHн
Á3ÞIœæÃλ≠HΛ8ˆÔ„ö|ÐÛ¸Γ>)W₃âf?ā¯®Ìмv₅—ƶζ

```

Try it online!

# Answer
> 2 votes
# JavaScript (ES6), <sub><sup>~~222~~ ~~200~~ ~~197~~</sup></sub> 196 bytes

*-19 bytes by stealing the idea of `indexOf`ing from @GezaKerecsenyi's answer.*

Takes BF code (`b`) and input (`i`) via currying, and returns the output.

```
b=>i=>eval(`m=Array(3e4).fill(k=p=0);o='';${[...b].map(c=>'m[p]++@m[p]--@p++@p--@while(m[p]){@}@m[p]=i.charCodeAt(k++)|0@o+=String.fromCharCode(m[p])'.split`@`['+-><[],.'.indexOf(c)]).join`;`};o`)

```

Try it online!

It works by generating a piece of valid JS code from the BF, then `eval`s it. (If you strip away `eval`, you can see the generated code.)

### Technical details

* Tape length: 30000 cells
* Tape left-hand-side: unusable
* Tape wrap-around: no
* Max value: `2<sup>53</sup>-1` (JS `MAX_SAFE_INTEGER`)
* Negative numbers: allowed
* EOF: `0` (solution with -2 bytes possible by letting EOF corrupt the tape with a `NaN`)

# Answer
> 2 votes
# Python 3.8 (pre-release), 245 237 247 bytes

*-8 bytes thanks to Jo King*

*+10 bytes because input wasn't handled correctly*

```
from sys import*
i,n,*a=[0]*30002
exec('\n'.join([((i:=i+(v:=s=='[')-(s==']'))-v)*' '+'while(a[n]): 0 n-=1 n+=1 a[n]+=1 a[n]-=1 a[n]=ord(stdin.read(1)) print(end=chr(a[n]))'.split()[u.index(s)]for s in open(argv[1]).read()if s in(u:='[]<>+-,.')]))

```

Try it online!

Compiles `bf` source code to `python` and execs.

# Answer
> 2 votes
# Rattle, 234 bytes

```
\&[0]*199&99&\|!I[g0P4I~n[62P2g+s][60P2g-s][43f6+f5][45f6-f5][46f6,][91f6[0f0]]
[93f6[^0f1]][44g3P5I~nP2f5P5g+s]P4g+sg0I^[~q]g]0;P6g=+s[P4g+f2[91f3]g8[93f4[0f]]]0
;P6g=+s[P4g-f2[93f3]g8[91f4[0f]]]0;sg0I~ns8;P6g+s;P6g-s;r`g1l(~,\);g1P2I~

```

(without the line breaks)

Try it Online!

This is by far Rattle's most complicated program yet.

This takes Brainf\*** code as the first line of input and input for the Brainf\*** code as the second line of input. Note that Rattle expects the second line to exist even if there is no input for Brainf\***.

Here's a similar example except instead of the classic Hello World!, I've modified it to take `!` as input but otherwise still output the same thing.

# Explanation

This program is a little lengthy to do a full explanation for but here's a much more human-readable version of the program:

```
\&[0]*199&99&\|!I

[
  g0 P4 I~n

  [62 g2 + s2]
  [60 g2 - s2]
  [43 g1 P2 I~ + r` g1 l(~,\)]
  [45 g1 P2 I~ - r` g1 l(~,\)]
  [46 g1 P2 I~ ,]
  [91 g1 P2 I~ [0 f0]]
  [93 g1 P2 I~ [^0 f1]]
  [44 g3 P5 I~ n r` g1 P2 l(~,\) g5 + s5]

  g4 + s4
  g0 I^ P4 [~q]
  P4g
]0

;g6 =+ s6 [g4 + s4 g0 P4 I~ n s8 [91 g6 + s6] g8 [93 g6 - s6 [0 f]]]0
;g7 =+ s7 [g4 - s4 g0 P4 I~ n s8 [93 g7 + s7] g8 [91 g7 - s7 [0 f]]]0

:(this line and below is just a comment)
data tape values:
0 - code
1 - code data tape
2 - code pointer
3 - input
4 - code command index
5 - input character index
6 - open loop counter
7 - close loop counter
8 - temp

```

# Answer
> 2 votes
# nice-expr, 660 bytes

```
var f is func(str)none func(var C is str)none{var T is list[int]repeat(0,30001);var p is int;var B is map[int]int;var b is list[int];for var i is int0{var c is str C_i;if c="["then{set b+[i];}else if c="]"then{set B@b_-1is i;set B@i is b_-1;set b is b_0..-1;};set i+1;if i>=len(C)then{break;};};for var i is int0{var c is str C_i;if c=">"then{set p+1;}else if c="<"then{set p-1;}else if c="+"then{set T@p is(T_p)+1;}else if c="-"then{set T@p is(T_p)-1;}else if c="."then{print(char(T_p));}else if c=","then{set T@p is ord(inputchar());}else if c="["and(T_p)=0then{set i is B_i;}else if c="]"and(T_p)!=0then{set i is B_i;};set i+1;if i>=len(C)then{break;};};};

```

This is a function that takes takes in the brainfuck code as a string.

This certainly can be golfed down; half the code in the solution is only dedicated to pairing up brackets to each other.

## Ungolfed Explanation

```
var interpret is func(str)none func(var code is str)none {
    // there are neither 8-bit, nor unsigned, types in nice-expr.
    // a list of ints will have to do.
    var tape is list[int] repeat(0,30000);
    var ptr is int 0; // start on the start of the tape.

    var brackets is map[int]int <||>; // keys and values are indexes of brackets.

    var bracketStack is list[int] []; // stack that holds left bracket indexes
    for var i is int 0 { // first pass: match up brackets
        var c is str code_i;
        if c = "[" then {
            set bracketStack + [i]; // push a left bracket
        } else if c = "]" then {
            // pop a left bracket
            var left is int bracketStack_-1;
            set bracketStack is bracketStack_0..-1;
            var right is int i;
            set brackets@left is right;
            set brackets@right is left;
        };
        set i + 1;
        if i >= len(code) then { break; };
    };

    for var i is int 0 {
        var c is str code_i;
        if c = ">" then {
            set ptr + 1;
        } else if c = "<" then {
            set ptr - 1;
        } else if c = "+" then {
            set tape@ptr is (tape_ptr) + 1;
        } else if c = "-" then {
            set tape@ptr is (tape_ptr) - 1;
        } else if c = "." then {
            print(char(tape_ptr));
        } else if c = "," then {
            set tape@ptr is ord(inputchar());
        } else if c = "[" and (tape_ptr) = 0 then {
            set i is brackets_i; // jump to the matching right bracket
        } else if c = "]" and (tape_ptr) != 0 then {
            set i is brackets_i; // jump to matching left bracket
        };

        set i + 1;
        if i >= len(code) then { break; };
    };
};

```

# Answer
> 2 votes
# ASCII FALSE, 365 bytes

Takes Brainfuck program and input separated by `$` ("end of Brainfuck"); very slow (replacing a cell is a linear time operation with bad constant factors; loops search for the matching bracket each time they are executed). Could be optimized by (1) doing peephole optimizations on most commands, most notably stripping loops, memorizing loop targets and compressing sequences of `+`/`-` into single instructions (2) using binary trees as the array representation, giving better O(log n) modification time (much more complex; requires managing binary trees, and basic GC if no memory is to be leaked).

EOF is all ones (255; it's unclear what "no EOF symbol" is supposed to mean). Overflow being undefined behavior is taken advantage of. The pointer not over/underflowing is taken advantage of as well.

Runs "hello world" correctly as well as the prime finder, though it is very inefficient (as expected). I recommend first stripping the prime finder of comments, then appending `$<small number>`:

```
>++++++++[<++++++++>-]<++++++++++++++++.[-]>++++++++++[<++++++++++>-]<++++++++++++++.[-]>++++++++++[<++++++++++>-]<+++++.[-]>++++++++++[<++++++++++>-]<+++++++++.[-]>++++++++++[<++++++++++>-]<+.[-]>++++++++++[<++++++++++>-]<+++++++++++++++.[-]>+++++[<+++++>-]<+++++++.[-]>++++++++++[<++++++++++>-]<+++++++++++++++++.[-]>++++++++++[<++++++++++>-]<++++++++++++.[-]>+++++[<+++++>-]<+++++++.[-]>++++++++++[<++++++++++>-]<++++++++++++++++.[-]>++++++++++[<++++++++++>-]<+++++++++++.[-]>+++++++[<+++++++>-]<+++++++++.[-]>+++++[<+++++>-]<+++++++.[-]+[->,----------[<+>-------------------------------------->[>+>+<<-]>>[<<+>>-]<>>>+++++++++[<<<[>+>+<<-]>>[<<+>>-]<[<<+>>-]>>-]<<<[-]<<[>+<-]]<]>>[<<+>>-]<<>+<-[>+[>+>+<<-]>>[<<+>>-]<>+<-->>>>>>>>+<<<<<<<<[>+<-<[>>>+>+<<<<-]>>>>[<<<<+>>>>-]<<<>[>>+>+<<<-]>>>[<<<+>>>-]<<<<>>>[>+>+<<-]>>[<<+>>-]<<<[>>>>>+<<<[>+>+<<-]>>[<<+>>-]<[>>[-]<<-]>>[<<<<[>+>+<<-]>>[<<+>>-]<>>>-]<<<-<<-]+>>[<<[-]>>-]<<>[-]<[>>>>>>[-]<<<<<<-]<<>>[-]>[-]<<<]>>>>>>>>[-<<<<<<<[-]<<[>>+>+<<<-]>>>[<<<+>>>-]<<<>>[>+<-]>[[>+>+<<-]>>[<<+>>-]<>+++++++++<[>>>+<<[>+>[-]<<-]>[<+>-]>[<<++++++++++>>-]<<-<-]+++++++++>[<->-]<[>+<-]<[>+<-]<[>+<-]>>>[<<<+>>>-]<>+++++++++<[>>>+<<[>+>[-]<<-]>[<+>-]>[<<++++++++++>>>+<-]<<-<-]>>>>[<<<<+>>>>-]<<<<>[-]<<+>]<[[>+<-]+++++++[<+++++++>-]<-><.[-]>>[<<+>>-]<<-]>++++[<++++++++>-]<.[-]>>>>>>>]<<<<<<<<>[-]<[-]<<-]++++++++++.[-]
$20

```

This runs in about 1s for me, producing

```
Primes up to: 2 3 5 7 11 13 17 19

```

(Since input is given after the program in stdin, the number "up to" which primes are printed is of course missing from the output; this could be addressed by outputting all read characters (insert `$,` after `^`), if desired.)

Note: This is ASCII FALSE, using `O` instead of `ø` (if `ø` were to be used instead, it would be a couple bytes longer) and `B` instead of `ß` (buffering is not relevant here however). Interpreters for ASCII FALSE can be found here.

## Golfed

```
[n;0=$[%%x;0~]?~[$0=$[% % n;1-n:q;!0 0~]?~[$1&\2/\ $[% q;!2*1|0~]?~[q;!2*]?]?]?]q:0c:[^$'$=~][c;1+c:]#%30000$t:[1-$][0\]#0i:0p:[t;c;+i;-1-O]o:[x:p;n:q;!]s:[o;!$'[=[b;1+b:]?']=[b;1-b:]?]j:[c;i;>][o;!k:k;'.=[p;O,]?k;',=[^255&s;!]?k;'>=[p;1+p:]?k;'<=[p;1-p:]?k;'+=[p;O1+s;!]?k;'-=[p;O1-s;!]?k;'[=[p;O0=[1b:[b;][i;1+i:j;!]#]?]?k;']=[p;O[1_b:[b;][i;1-i:j;!]#]?]?i;1+i:]#

```

There are most probably quite a few more easy golfs possible.

## Ungolfed

The core function is `q` ("shove/splice"), which allows fully using the stack like an array by remembering items on the call stack, then mutating the stack by replacing an element, and then restoring the elements remembered on the call stack. Once we can use the stack as an array, the rest is straightforward.

<pre><code>{
    shove/splice (q):
    pop n elements, remembering them on the call stack,
    then mutate the stack, dropping an item and replacing it with x,
    then restore the popped elements

    invocation: 101x: 42n: q;!
}
[
    n;0=
    $[% %x; 0~]?
    ~[
        $0=
        $[
            % {kill cond}
            % {kill dup'd zero on stack}
            n; 1- n:
            q;!
            0 {this is to be left on the stack}
            0~
        ]?
        ~[
            $ 1& {extract lowest bit}
            \ 2/ \ {>> 1 thing on stack}
            $[
                % q;! 2* 1| 0~
            ]?
            ~[
                q;! 2*
            ]?
        ]?
    ]?
]q:

0c: {# commands}
[^$ '$=~][c;1+c:]# {loop until `$` is encountered, leaves chars on stack}
% {drop '$}

30000$t:[1-$][0\]# {leave 30k 0's on the stack (note: final iteration will leave zeroed counter itself on stack)}

0i: {instruction pointer}
0p: {data pointer (0-based)}
[t;c;+ {depth of stack} i;- 1- O]o: {get (o)p}

[x: p;n: q;!]s: {set item}

[
    o;!
    $'[=[b;1+b:]?
    ']=[b;1-b:]?
]j: {count bracket balance}

[c;i;>][
    o;! k:
    k;'.=[p;O ,]?
    k;',=[^ 255& s;!]?
    k;'>=[
        p;1+p:
    ]?
    k;'<=[
        p;1-p:
    ]?
    k;'+=[p;O 1+ s;!]?
    k;'-=[p;O 1- s;!]?
    k;'[=[
        p;O 0=[
            1b: {balance}
            [b;][
                i;1+i:
                j;!
            ]#
        ]?
    ]?
    k;']=[
        p;O [
            {analogeous with two small changes}
            1_ b: {balance}
            [b;][
                i;1-i:
                j;!
            ]#
        ]?
    ]?
    i;1+i:
]#
```
</code></pre>

# Answer
> 1 votes
### Lua (to long)

I made some Lua implementation, but I can't get the bracket stuff right. Here it is anyway:

```
-- >    increment the data pointer (to point to the next cell to the right).
-- <    decrement the data pointer (to point to the next cell to the left).
-- +    increment (increase by one) the byte at the data pointer.
-- -    decrement (decrease by one) the byte at the data pointer.
-- .    output a character, the ASCII value of which being the byte at the data pointer.
-- ,    accept one byte of input, storing its value in the byte at the data pointer.
-- [    if the byte at the data pointer is zero, then instead of moving the instruction pointer forward to the next command, jump it forward to the
--      command after the matching ] command*.
-- ]    if the byte at the data pointer is nonzero, then instead of moving the instruction pointer forward to the next command, jump it back to the
--      command after the matching [ command*.
s=setmetatable({0},{__index=function() return 0 end})

i=1 -- index array
j=1 -- index input
l=loadstring
t="><+-.,[]"
o=0
fh=arg[1] and io.open(arg[1]) or io.stdin
I=fh:read"*a":gsub("[^><%+%-%.,%[%]]","")
fh:close()
print(I)
for k=1,#I do io.write(k%5==1 and"+"or"-") end
io.write"\n"
for k=1,math.ceil(#I/5) do local n=5*(k-1)+1 local s=(" "):rep(4-math.floor(math.log10(n))) io.write(n,s) end
io.write"\n"
dbg=true
f={
"i=i+1 ",   -- array index ++
"i=i-1 ",   -- array index --
"s[i]=(s[i]+1)%256 ",   -- byte + 1
"s[i]=(s[i]-1)%256 ",   -- byte - 1
"io.write(string.char(s[i])) ", -- put byte
"local c=io.read(1):byte()s[i]=c==10 and s[i] or c",        -- read byte "Newline required!"
[=[if s[i]==0 then
    o=0
    repeat
        if dbg then print(j,"Forward!",o,b) end
        b=I:sub(j,j):match'[%[%]]'
        o= b=='['and o+1 or b==']' and o-1 or o;
        j=j+1
    until b==']' and o == 0
end
]=],    -- jump to matching ]
[=[
if s[i]~=0 then
    o=0
    count=0
    repeat
        if dbg then print(j,"Backwards",o,b) end
        b=I:sub(j,j):match"[%[%]]"
        o= b=='['and o-1 or b==']' and o+1 or o;
        j=j-1
    until b=='[' and o == 0
end
]=],    -- jump to matching ]
}
for k,v in ipairs(f) do f[t:sub(k,k)],e=l(v) if e then error(e)end end
function run()
j=1
while j<=#I do
    f[I:sub(j,j)]()
    j=j+1
end
end
res,err = pcall(run)
if not res then
    print('error=',err)
    print('Dumping state')
    print('','stack')
    for k,v in pairs(s) do print("",k,v) end
end
if debug then
    print("stack")
    for k,v in pairs(s) do print(k,v) end
end

```

It doesn't pass the prime test, but acts nicely with Hello World and all echo and reverse examples I tried. So if anyone sees the bug, feel free to catch it.

# Answer
> 1 votes
**Smalltalk**, Squeak 4.x flavour **414** chars

Here is an interpreter which works exclusively with streams and block closures:

```
b:=[:c :i :o :n |
| v |
v := 1 to: n.
v := (v collect: [:x| | t |
    t := 0.
    Dictionary newFrom: {
        $+ -> [t:=t+1\\256].
        $- -> [t:=t-1\\256].
        $. -> [o nextPut:t].
        $, -> [t:=i next].
        $< -> [v back].
        $> -> [v next].
        $[ -> [t=0 and: [
            [c next=$[
                ifTrue: [(v peek at: $[) value].
             c peek=$]] whileFalse.
            c next]].
        $] -> [t=0 or: [c back.
            [c back=$]
                ifTrue: [(v peek at: c next) value. c back;back].
             c peek=$[] whileFalse.
            c next]].
        }]) readStream.
[c atEnd] whileFalse: [(v peek at: c next ifAbsent: [[]]) value]]

```
* c is a readStream on code
* i is a readStream on input (a ByteArray)
* o is a writeStream on output (a ByteArray)
* v is a readStream on interpreters (an Array)
* n is number of cells

For each cell, we create an interpreter - that is a Dictionary which associate a Block to each BF command (a Character).
Those blocks close over a value t, initialized at zero.
The jump instructions are implemented recursively.
The pointers (code and data) are hidden in streams state.

To use the interpreter, we just have to feed this block with proper streams:

```
c := 'http://esoteric.sange.fi/brainfuck/bf-source/prog/PRIME.BF' asUrl retrieveContents contents readStream.
i := '15\' withCRs withUnixLineEndings asByteArray readStream.
o := #[] writeStream.
n := 30000.
b valueWithArguments: {c.i.o.n}.
^'',o contents

```

The interpreter can be golfed to 414 chars, using as:Dictionary which is shorter and by removing overflow and underflow protections (the cell value is then unbound).

```
b:=[:c :i :o :n||v|v:=1to:n.v:=(v collect:[:x||t|t:=0.{$+->[t:=t+1].$-->[t:=t-1].$.->[o nextPut:t].$,->[t:=i next].$<->[v back].$>->[v next].$[->[t=0and:[[c next=$[ifTrue:[(v peek at:$[)value].c peek=$]]whileFalse.c next]].$]->[t=0or:[c back.[c back=$]ifTrue:[(v peek at:c next)value.c back;back].c peek=$[]whileFalse.c next]]}as:Dictionary])readStream.[c atEnd]whileFalse:[(v peek at:c next ifAbsent:[[]])value]].

```

# Answer
> 1 votes
# C: 317 characters (reads from a file)

```
#include <stdio.h>
char t[30000],*p=t,b[30000],c;void r(char*a){while((c=*a++)&&c-93){p+=c==62;p-=c==60;*p+=c==43;*p-=c==45;c^46||putchar(*p);c^44||(*p=getchar());if(c==91){while(*p)r(a);c=1;while(c+=(*a==91)-(*a++==93));}}}int main(int n,char**a){FILE*f;f=fopen(a[1],"r");fread(b,1,30000,f);fclose(f);r(b);return 0;}

```

This is my brainfuck interpreter that I wrote for a couple of months ago, it's quite a bit longer than it needs to be, but that is because I didn't focus on size when I wrote it, I focused on readability (just the fact that it compiles without error and even includes a library suggest that it is heavily shrinkable).

And expanded:

```
#include <stdio.h>
char t[30000],*p=t,b[30000],c;
void r(char*a){
    while((c=*a++)&&c-93){
        p+=c==62;
        p-=c==60;
        *p+=c==43;
        *p-=c==45;
        c^46||putchar(*p);
        c^44||(*p=getchar());
        if(c==91){
            while(*p)r(a);
            c=1;
            while(c+=(*a==91)-(*a++==93));
        }
    }
}
int main(int n,char**a){
    FILE*f;
    f=fopen(a[1],"r");
    fread(b,1,30000,f);
    fclose(f);
    r(b);
    return 0;
}

```

I might return with an actually golfed version.

# Answer
> 1 votes
# Binary Lambda Calculus 104 bytes (829 bits)

I didn't come up with this solution. Go credit whoever put it on wikipedia. However it is amazing.

( λ 11 ) ( λ ( λ λ λ 1 ( λ ( λ 2111 ( λ λ 133 ( λ λ 1 ( λ λ ( λ 7 ( 1 ( 3 ( λ λ λ λ λ 10 ̲ ( 1 ( λ 6143 ) ) ( λ 15 ( 65432 ) ) ) ( λ λ 2 ( ( λ 11 ) ( λ λ λ 2 ( λ λ λ 662 ( λ λ 6 ( λ 1 ( 26 ) 3 ) ( 15 ̲ ( 51 ( λ 1 ) ) ( 5 ( λ 1 ) 1 ) ) ) ) ( 12 ( λ λ λ 312 ) ) ) 1 ( λ λ 2 ) ) ) ) ) ( 3 ( 1 ( λ λ λ λ 9 ( 1 ( λ 51 ( λ 154 ) ) ) ( 24 ( λ 142 ) ) ) ) ( 5 ( 11 ̲ ( λ 1 ) ) ( 12 ̲ ( λ 2 ( ( λ 11 ) ( λ λ λ 1 ( ( λ 11 ) ( λ λ λ 2 ( 1 ( 33 ) ) ( λ 8 ( 771 ) ) ) ) 21 ) ) ) ) ) ) ) ( λ 12 ̲ ( λ 12 ̲ ( λ 3 ( 21 ) ) ) ) ) ) ) ) ( λ λ 1 ) ) ) ( 11 ) ) ( λ ( λ 11 ) ( λ λ 1 ( ( λ 1 ( 1 ( 1 ( λ λ 1 ( λ λ 2 ) 2 ) ) ) ) ( λ λ 2 ( 21 ) ) ( λ λ 1 ) ) ( 22 ) ) ( 1 ( λ λ λ λ λ λ 1 ) ) 1)

# Answer
> 1 votes
# LiveScript `eval`ing JavaScript: 263

Note that this is currently untested.

```
p='process.std';g=p+'in.read';f='function(x){return';eval "eval('var i=0,m=[#{[0]*3e4*\,}];'+#g().map(#f'[]+-<>,.'.indexOf(x)).filter(#f~-x).map(#f['#{"while(8){,},i++,i--,8++,8--,#{p}out.write(String.fromCharCode(8)),#g(1)"/','*"','"/'8'*'m[i]'}'][x]).join(''))"

```

Ungolfed:

```
p='process.std'
g=p+'in.read'
f='function(x){return'
eval """
  eval('
      var i = 0,
          m=[#{[0]*3e4*\,}];' +
    #{g}()
      .map(#{f} '[]+-<>,.'.indexOf(x))
      .filter(#{f} ~-x)
      .map(#{f} ['#{
        "while( 8 ){ 0
         } 0
         i++ 0
         i-- 0
         8++ 0
         8-- 0
         #{p}out.write(String.fromCharCode( 8 )) 0
         #{g}(1)" / '0' * "','" / '8' * 'm[i]'
       }'][x])
       .join(''))
"""

```

# Answer
> 1 votes
# SmileBASIC, 258 bytes

```
C=0DEF B S,K
DIM M[3E4]FOR I=0TO LEN(S)-1C=ASC(S[I])N=M[P]ON!F GOTO@C?CHR$(N)*(C==46);
O=C==91F=!N*O
K=K+CHR$(I)*O*!F
IF C==93THEN I=ASC(POP(K))-1
M[P]=N-N(42)P=P+N(59)IF C==44THEN M[P]=ASC(SHIFT(K))@C:F=F-N(90)
NEXT
END
DEF N(L)RETURN(C-L-2)*(C<L&&C<L+4)END

```

Call the function as `B code,input`

# Answer
> 1 votes
# Python 3, 306 bytes (no eval)

```
from sys import*
s=open(argv[1]).read()
d=[0]*30000
i=p=a=0
k=[]
j=k+d
for o in s:
 if o==']':j[a]=k.pop();j[j[a]]=a
 k+=[a]*(o=='[');a+=1
while i<a:x,r='[]<>,.+-'.find(s[i]),d[p];d[p],p=(r+(x==6)-(x>6))%256if 4!=x else ord(stdin.read(1)),p+(x==3)-(x==2);i=j[i] if x==(r>0)else 1+i;print(end=chr(r)*(5==x))

```

Outputs null (0x00) characters though, and times out on prime example but should theoretically finish.
Can still be improved a bit.

# Answer
> 1 votes
# Go, 377 bytes

I just had to **Go**lf this. Straightforward implementation; leverages constraints (no overflows, no bad instructions), prime finder works as expected. Takes path to Brainfuck program as first argument and input over stdin.

```
package main
import."os"
func main(){
var t[30000]uint8
d,i,s:=0,0,[]byte{0}
c,_:=ReadFile(Args[1])
for;i<len(c);i++{m:=func(j int){b:=j
for b!=0{i+=j
switch c[i]{case'[':b++
case']':b--}}}
switch c[i]{case',':Stdin.Read(s);t[d]=s[0]
case'.':s[0]=t[d];Stdout.Write(s)
case'<':d--
case'>':d++
case'+':t[d]++
case'-':t[d]--
case '[':if t[d]==0{m(1)}
case ']':if t[d]!=0{m(-1)}}}}

```

# Answer
> 1 votes
# Lua, 353 bytes

Doesn't beat the other working Lua solution which transpiles the entire source to Lua, then runs that rather than doing the mish-mash this one does; very inefficient due to the use of heavy pattern matching for finding matching brackets concisely.

```
s=io.open(...):read"*a"f="if(d[p]or 0)%s0 then i=%s end"d={}p=1 i=1 while#s>i do load(({[43]="d[p]=(d[p]or 0)+1",[45]="d[p]=(d[p]or 0)-1",[60]="p=p-1",[62]="p=p+1",[46]="io.write(string.char(d[p]or 0))",[44]="d[p]=io.read(1):byte()",[91]=f:format("==","s:find('^%b[]()',i)-1"),[93]=f:format(">","s:sub(1,i):find('()%b[]$')")})[s:byte(i)]or"")()i=i+1 end

```

Or with some formatting:

```
s=io.open(...):read"*a"
f="if(d[p]or 0)%s0 then i=%s end"
g=""d={}p=1
i=1
while#s>i do
    load(({
        [43]="d[p]=(d[p]or 0)+1",
        [45]="d[p]=(d[p]or 0)-1",
        [60]="p=p-1",
        [62]="p=p+1",
        [46]="io.write(string.char(d[p]or 0))",
        [44]="d[p]=io.read(1):byte()",
        [91]=f:format("==","s:find('^%b[]()',i)-1"),
        [93]=f:format(">","s:sub(1,i):find('()%b[]$')")
    })[s:byte(i)]or"")()i=i+1
end

```

# Answer
> 1 votes
# Atto-8\*, 0 bytes

*\*with brainfuck frontend*

Unfortunately couldn't manage to golf off additional bytes. Open to suggestions if anyone has pointers.

## Explanation

The Atto-8 microprocessor, when built with its brainfuck frontend, begins executing ASCII-encoded brainfuck directly from RAM, on bare metal. The microprocessor's machine code is brainfuck source code, and so no interpreter is required.

# Answer
> 1 votes
# Julia 1.7, 193 bytes

```
!x="let a=fill(0,8^5),i=1
"*replace(x*"]",(["><+-.,[]"...].=>[["i" "a[i]"].*["+=1";"-=1"]...
"print('\0'+a[i])"
"a[i:i]=read(stdin,1)"
"while a[i]>0"
"end"].*";")...,r"."s=>"")|>Meta.parse|>eval

```

Attempt This Online!

Julia 1.7 is needed for replace with multiple patterns

**ungolfed code:**

```
!x="let a=fill(0,8^5),i=1
"*replace(x*"]",	# add `end` to close the `let` block
'>' => "i+=1;",
'<' => "i-=1;",
'+' => "a[i]+=1;",
'-' => "a[i]-=1;",
'.' => "print('\0'+a[i]);",
',' => "a[i:i]=read(stdin,1);",
'[' => "while a[i]>0;",
']' => "end;",
r"."s => ""		# remove all other characters
)|>Meta.parse|>eval

```

Attempt This Online!

This function takes the program as parameter.
Program with the stricter IO (as a file given as argument): 206 bytes

# Answer
> 0 votes
# JavaScript - Partial Solution (241 235)

Does not read from file - does not manage PRIMES.BF, but works for `Hello World!`

```
// not included in 235 count, the hello world code from wikipedia
var p="++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.",

// partial solution - dies on primes
a=[0,0,0,0,0],b=0
eval(p.replace(/[^\][.,+><-]/g,'').replace(/(.)/g,function(e){return "0while(a[b]){0}0console.log(String.fromCharCode(a[b]))0a[b]=prompt()0++a[b]0--a[b]0++b0--b".split(0)[" [].,+-><".search(new RegExp("\\"+e))]+";"}))

```

Just copy and paste it into javascript console to see it in action. Works in node.js, or broswer.

I was hoping to get PRIMES.BF to work in node.js, but not been able to emulate STDIN in a synchronous way yet.

---

## With comments

```
// should read from file - easy with node.js
// this is the `Hello World! ` program from wikipedia
var p="++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.",

// declare a and b. If a needs to be longer, can use:
//     a=[];for(0;a.length<30000;a.push(0))b=0
a=[0,0,0,0,0],b=0

// evaluate
eval(
  // the brainfuck code
  p
  // replacing all the non brainfuck commands with nothing
  .replace(/[^\][.,+><-]/g,'')
  // replacing all commands (captured in parenthesis) with callback
  .replace(/(.)/g,function(e){
     // return swapped commands
     return "0while(a[b]){0}0console.log(String.fromCharCode(a[b]))0a[b]=prompt()0++a[b]0--a[b]0++b0--b"
     // split into array on the 0 (used as seperator - shorter than "|" when
     // called in .split(0) function)
     .split(0)[
       // matching brainfuck commands
       " [].,+-><"
       // searched with escaped, captured command
       .search(new RegExp("\\"+e))
       // add a semicolon to all statements - extra semicolons do not interfere
       // with execution of javascript
     ]+";"
  })
)

```

# Answer
> 0 votes
# Simplex v.0.5, 103 bytes

```
br{j'>=?[v'R;Ru]'<=?[v'L;Ru]'+=?[v'I;Ru]'-=?[v'M;Ru]'.=?[v's;Ru]',=?[v'G;Ru]'[=?[v'{;Ru]']=?[v'};Ru]LL}
b                     ~~ Takes a string input (BF prgm)
 r                    ~~ Reverses the string (pointer is at end)
  {               LL} ~~ Loop until empty cell is found
   j                  ~~ Inserts an empty cell at pointer
    '>                ~~ Sets empty cell to character (>)
      =               ~~ Sets cell to 1 if > is the current character
       ?[      ]      ~~ Evaluate inside if cell is 1
         v    u       ~~ Goes down, then up
          'R          ~~ Puts the character (R) to the byte
            ;         ~~ Adds the current cell to the outer program
             R        ~~ Goes right (frees up next cell)
    '< =? [v'L;Ru]    ~~ …etc
    '+ =? [v'I;Ru]
    '- =? [v'M;Ru]
    '. =? [v's;Ru]
    ', =? [v'G;Ru]
    '[ =? [v'{;Ru]
    '] =? [v'};Ru]

```

I used this program to prove that Simplex is Turing-complete, it being reducible to a Turing-complete language. It's simple enough; after evaluation of this program, a second program is evaluated, which contains the BF "transcript". Yeah, it really just compiled BF to Simplex. But hey! I think this is the shortest answer thus posted.

(Note that I implemented a theoretically infinite (unbound) version, as Simplex is thus.)

---
Tags: code-golf, interpreter, brainfuck
---