The Sway Reference Manual/Primitives

Sway works by figuring out the meaning or value of some code.
This is true for the tiniest pieces of code to the largest
programs. The process of finding out the meaning of code
is known as "evaluation".
The things whose values are the things themselves are known as
primitives. The primitives of Sway can be categorized by the following
types: integers, real numbers, strings, and symbols.
Sway (or more correctly, the Sway interpreter) responds to primitives
by giving the type of the value plus the value itself.
Here are examples of each of the types:
 sway&gt; 3
 INTEGER: 3
 sway&gt; -4.9
 REAL_NUMBER: -4.9
 sway&gt; "hello"
 STRING: "hello"
 sway&gt; :age
 SYMBOL: :age
Let's examine the
four types in more detail.
Integers.
Integers are numbers without any fractional parts.
Examples of integers are:
 sway&gt; 3;
 INTEGER: 3
 sway&gt; -5;
 INTEGER: -5
 sway&gt; 0;
 INTEGER: 0
Integers must begin with a digit or a minus sign. The initial minus sign
must immediately be followed by a digit.
Real Numbers.
Reals are numbers that do have a fractional part (even if that fractional
part is zero!). Examples of real numbers are:
 sway&gt; 3.2;
 REAL: 3.20000000000
 sway&gt; 4.0;
 REAL: 4.00000000000
 sway&gt; 5.;
 REAL: 5.00000000000
 sway&gt; 0.3;
 REAL: 0.30000000000
 sway&gt; .3;
 REAL: 0.30000000000
 sway&gt; 3.0e-4;
 REAL: 0.00030000000
 sway&gt; 3.0e4;
 REAL: 30000.0000000
 sway&gt; .000000987654321
 REAL: 9.8765432e-07
Real numbers must start with a digit or a minus sign or a decimal
point. An initial minus sign must immediately be followed by a digit or a
decimal point. An initial decimal point must immediately be followed by
a digit. Sway accepts real numbers in scientific notation. For example,
formula_1 would be entered as 3.0e-11. The 'e' stands for exponent and
the 10 is understood, so e-11 means multiply whatever precedes the e by formula_2.
The Sway interpreter only displays between six and eleven significant
digits, depending on the size of the number,
so 1.234567898765432 would display as:
 sway&gt; 1.234567898765432;
 REAL: 1.2345678988
Don't be fooled. Although the result looks like 1.2345678988,
it is not. The following code tests if the two numbers are equal:
 sway&gt; 1.234567898765432 == 1.2345678988;
 SYMBOL: :false
Numbers greater than formula_3 and
less than formula_4 are displayed in
scientific notation.
To display more (or less) significant digits, the
"fmt" function can be found. Here's how to display 15
digits after the decimal point:
 sway&gt; fmt("%.15f",1.234567898765432);
 STRING: 1.234567898765432
The "fmt" function uses the same format codes as the C printf
function.
Don't try and display more than 16 significant digits; the
least significant digits will not be accurate.
Strings.
Strings are sequences of characters delineated by double quotation marks:
 sway&gt; "hello, world!";
 STRING: "hello, world!"
 sway&gt; "x\nx";
 STRING: "x\nx"
 sway&gt; "\"z\"";
 STRING: "\"z\" 
 sway&gt; ";
 STRING: ""
Characters in a string can be "escaped" with the backslash character,
which changes the meaning of some characters. For example, the character
'n', in a string refers to the letter 'n' while the character sequence
'\n' refers
to the "newline" character. A backslash also changes the meaning of the
letter 't',
converting it into a tab character '\t'.
When other characters are escaped,
their meanings are not changed. Thus '\z' is equivalent to 'z'.
To include a backslash
character in a string, escaped it with a backslash, '\\'.
Note that Sway, when asked
the value of strings that contain newline and tab characters, displays
them as escaped characters. When newline and tab characters in a string
are printed in a program, however, they are displayed as actual newline
and tab characters, respectively.
Double quotes can be embedded in a
string by escaping them with backslashes. A string with no characters
between the double quotes is known as an empty string.
Unlike some languages, there is no character type in Sway. A single
character 'a', for example, is entered as the string "a".
Symbols.
Sway symbols are collections of certain characters beginning with a colon:
 sway&gt; :abc;
 SYMBOL: :abc
 sway&gt; :a+b;
 SYMBOL: :a+b
When symbols are printed in a program,
the colon is omitted from the
output. Symbols may contain any of the printable characters except
parentheses, braces, semicolons, and commas. The colon marks the
beginning of the symbol while whitespace (newlines, tabs, and spaces)
and the prohibited characters signal the end of the symbol. As we shall
see later, symbols are useful for setting up symbolic constants and for
passing messages.
There are a few special symbols in Sway, two of which
are :true and :false.
These symbols are known as the "Boolean" values
and are used to guide the flow of a program.
The term Boolean is derived from the last name of George Boole, who,
in his 1854 paper "An Investigation of the Laws of Thought, on which are
founded the Mathematical Theories of Logic and Probabilities", laid one
of the cornerstones of the modern digital computer. The so-called Boolean
logic or Boolean algebra is concerned with the rules of combining truth
values (i.e., true or false). As we will see, knowledge of such rules will
be important for making Sway programs behave properly. In particular,
Boolean expressions will be used to control conditionals and loops.
Another special symbol is :null. This symbol is used to
indicate the end of lists and arrays; it also indicates an
'not yet created' object.,