# Beginner's guide to NetHack sources
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	 BEGINNER'S GUIDE TO NETHACK SOURCES
        ---------------------- by German Martin --
                                        german@spain.hp.com

                  		   version 1.0  March '95

Contents
--------

   1. About this document.
   2. Hey, I want to modify the game!
   3. Starting point.
   4. The wizard mode.
   5. Creating a new level.
   6. Creating a new monster.
   7. Refining your monster.
	   7.0. The 'monst' struct.
	   7.1. Adding a new attack type.
	   7.2. Adding new monster's abilities.
	   7.3. Adding a 'mextra' struct.
   8. Creating a new object.
	   8.0. The 'objects' array.
	   8.1. Adding a tool.
	   8.2. Adding a wand.
	   8.3. Adding a potion.
	   8.4. Adding armor/weapon.
	   8.5. Adding a ring.
	   8.6. Adding an amulet.
	   8.7. Adding a spellbook.
	   8.8. Adding food.
   9. Creating a new room type.
  10. Creating a new shop type.
  11. Goodbye.
  Apendix A. Reference Function listing

1. About this document
----------------------

   Have you played - and enjoyed - nethack for several [ months | years ]&nbsp;?
  Do you have some cool new ideas for the game but nobody seems to hear you?
  Do you have access to a machine with a C compiler? Have you ever programmed
  before?

   If you answered yes to the above questions then this paper can be of your
  interest.

   Around middle '94 I started to look around in the nethack sources; loving
  the game I really wanted to add some new monsters &amp; features, but the task
  was quite painful. I'm not a C newbie, but 100 (actually more) source
  files was more than I could manage: even trying to find the main() entry
  to the code proved to be difficult. The help provided by the inlined 
  comments is useless for the newcomer. Now, nine months later, I've learned
  a lot about the main structures in the code: I've been able to add new
  monsters, objects, rooms, levels and behaviours. I - not being a member of
  the Dev Team, in case you were wondered - don't pretend to have a full
  knowledge of the huge beast, but my objective here is to help new ideas
  to be added to the game, not being a complete guide to the code.

   So, it is quite possible that you found many things incorrect here; more
  than possible - that is, sure - that you found many things incomplete.
  OK, send the bug/comment/addition to me and I'd modify/add it.

   Please, USE THIS AT YOUR OWN RISK. If you get nothing but frustration don't
  flame me: I was only trying to help.

   All the documentation here refers to Nethack 3.1.3 (the current official
  version at the date this is written).

2. Hey, I want to modify the game!
----------------------------------

   OK. You have started to play nethack last week; got an account in a Unix
  machine and thought "Hey, I have a great idea! I'll learn C while modifying
  this game! All I have to do is follow this cookbook!". Forget it. Unless you
  are a reincarnation of Leonardo da Vinci you'll get nothing but a headache.

   In other words, to use this info you need at last:

     - Few knowledge about the OS you are running in. That is, how to edit,
      move, create and remove files basically.

     - Good knowledge of the C programming language. That is, more than the
      printf("Hello world\n") program. This includes the C preprocessor.

     - A C compiler and feel comfortable with it.

     - A blessed potion of gain ability.

3. Starting point
-----------------

   The first thing you have to do is compile the sources by yourself. You
   don't have to understand the whole process, but surely you need to be
   able to compile the official code and get it running before you add any-
   thing to the game. Refer to the README file in the top directory and to
   the Install.XXX  (XXX depending of your operating system) in /sys/XXX
   directory.

   Once you have compiled the sources suddenly you are now aware of what
   to expect.

4. The wizard mode
------------------
   As you probably know, the wizard mode is a way to start nethack with a
   few extra commands:

		^E  ==  detect secret doors and traps.
		^F  ==  do magic mapping.
		^G  ==  create monster.
		^I  ==  identify items in pack.
		^O  ==  tell locations of special levels.
		^T  ==  do intra-level teleport.
		^V  ==  do trans-level teleport.
		^W  ==  make wish.
		^X  ==  show intrinsic attributes.

     plus some changes for known actions: i.e. read a scroll of create
   monster allows to specify the type of monster.

   That allows you to quickly try out the new feature/change you just added.
   To start it, just type:

                nethack -u wizard -D

   It should work, but take present:

   - If in a unix machine you should be the correct user-id.
   - have a look in include/config.h and search for the #define WIZARD lines;
    maybe you need to put another name after the -u.

   Throughout your process of modifying nethack you should make extensible
   usage of this mode so better make sure it works. (As an alternative you
   can always play a complete game to try out your new monster in the astral
   level&nbsp;:-) )

5. Creating a new level
-----------------------

   To create a new level is easy. In fact, it doesn't require any knowledge
   of C: the dev team prepared it for us.

   Under the "util" directory the process of creating a nethack executable
   should have left a program called 'lev_comp' (lev_comp.exe if in MS-DOS).
   That binary is capable of create a new special level for nethack: give it
   a description file (named 

<something>.des) and it gives you a level file
   (named <something>.lev) suitable for the nethack binary:

            mylevel.des -----------
                                   |
                                __ | __
                                \  V  /
                              ___\___/___
                              |         | _
                              |lev_comp |/
                              |         |  -----&gt; mylevel.lev
                              -------------

   The lev_comp compiler has a manual page (have a look in the "doc" directory)
   called 'lev_comp.6'. If you are in a unix machine a command like 
                          nroff -man lev_comp.6 | more
   should give you a standard formatted man page. If not... well, you should
   have to get used to the .SH .PP etc... garbage in the file. This man page
   shows (quite obtusely) how to create a .des file; but better than starting
   from scratch is starting trying to understand a predefined file.
   For example, let's view the begining of "dat/castle.des" file:

	MAZE:"castle",random
	FLAGS: noteleport
	GEOMETRY:center,center
	MAP
	}}}}}}}}}.............................................}}}}}}}}}
	}-------}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}-------}
	}|.....|-----------------------------------------------|.....|}
	}|.....+...............................................+.....|}
	}-------------------------------+-----------------------------}
	}}}}}}|........|..........+...........|.......S.S.......|}}}}}}
	.....}|........|..........|...........|.......|.|.......|}.....
	.....}|........------------...........---------S---------}.....
	.....}|...{....+..........+.........\.S.................+......
	.....}|........------------...........---------S---------}.....
	.....}|........|..........|...........|.......|.|.......|}.....
	}}}}}}|........|..........+...........|.......S.S.......|}}}}}}
	}-------------------------------+-----------------------------}
	}|.....+...............................................+.....|}
	}|.....|-----------------------------------------------|.....|}
	}-------}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}-------}
	}}}}}}}}}.............................................}}}}}}}}}
	ENDMAP

   Sounds familiar? This file is the description from where the castle
   level is created. The part showed here just sets the level aspect: a
   drawed castle centered between mazes (note the MAZE line). 

   The rest of the file puts doors, traps, objects and monsters in a random
   or specific position (with coordinates relative to the previous map).

   The man page describes the exact syntax, so if you dare you can now start
   modifying the whole file; but let's make a very easy change and see how it
   works: suppose you feel the soldiers at the castle are too wimpy and think
   changing them to more difficult monsters, say minotaurs for example. So,
   just change the lines:

   MONSTER:'@',"soldier",(08,06) and subsequents

   with

   MONSTER:'H',"minotaur",(08,06) etc...

   (Note that with this change we are chosing a specific monster. We could have
   chosen to create monsters of a certain class, like

   MONSTER:'D',RANDOM,(08,06)   # Create a random type dragon )

   Save the new castle.des file and run: (from the dat directory)

      ../util/lev_comp castle.des      (change the /'s with \'s if in MS-DOS)

   That creates a new 'castle.lev' file in the 'dat' directory. To try it,
   copy it to the playing directory (something like games/nethack) and start
   a game in wizard mode. Teleport to the castle, wish for a floating eye
   corpse and a blindfold and have a look: you should have lots of brown H's!

   But now it is time to deal with the original subject: we wanted to added
   a NEW level to nethack, not just modifying one. Let the castle.des alone
   and create a newlevel.des!

   For that, we have to introduce a new compiler: dgn_comp, the dungeon
   compiler. As the lev_comp it has a manual page: dgn_comp.6. Its purpose
   is a step ahead: it takes a file describing the complete dungeon (as a
   collection of levels) and creates a "dungeon" file suitable for the
   nethack binary.

   The description file in question is called "dungeon.def":

	DUNGEON:        "The Dungeons of Doom" "D" (25, 5)
	ALIGNMENT:      unaligned
	%MULDGN BRANCH: "The Gnomish Mines" @ (2, 3)
	%REINCARNATION LEVEL:           "rogue" "R" @ (15, 4)
	LEVEL:          "oracle" "O" @ (5, 5)
	LEVALIGN:       neutral
	LEVEL:          "bigroom" "B" @ (10, 3) 15
	%MULDGN CHAINBRANCH:    "The Quest" "oracle" + (6, 2) portal
	%MULDGN BRANCH:         "Fort Ludios" @ (18, 4) portal
	RNDLEVEL:       "medusa" "none" @ (-5, 4) 2
	LEVALIGN:       chaotic
	LEVEL:          "castle" "none" @ (-1, 0)
	CHAINBRANCH:    "Gehennom" "castle" + (0, 0) no_down
	BRANCH:         "The Elemental Planes" @ (1, 0) no_down up

   As you probably knew, there are 'levels' and branches of the main dungeon,
   being composed of levels. The easiest thing is to add a simple level inside
   the main dungeon: 

   Suppose you created a new mylevel.des file where you define a 'mylevel' 
   level:

   MAZE:"mylevel",' '

   (IMPORTANT note here: usually the file is named the same as the MAZE it
   defines, as in castle.des, but the name for the .lev file is taken from
   the MAZE line&nbsp;!!)

   To add it to the main dungeon we can add a line after the bigroom one:

   LEVEL:	"mylevel" "none" @ (15,2)

   That is, create the 'mylevel' level randomly at 15 +-2 level deep. The 
   level won't left bones files (the 'none' part).

   And run ../util/dgn_comp dungeon.def  to get the 'dungeon' file. Copy it
   to the game directory and try it out (wizard mode command Ctrl-O is quite
   useful here).

   If there is any error loading the new level, nethack will create a random
   maze instead.

   Finally, if we wanted to add a whole new branch to the dungeon, we will
   put a line like:

   %MULDGN BRANCH: "newbranch" @ (18, 1)
   
   and later on, the lines defining the levels in this new branch:

   DUNGEON:        "newbranch" "S" (4,0)
   DESCRIPTION:    mazelike
   LEVEL:          "mylevel1" "none" @ (1, 0)
   LEVEL:          "mylevel2" "none" @ (2, 0)
   LEVEL:          "mylevel3" "none" @ (3, 0)
   LEVEL:          "mylevel4" "none" @ (4, 0)

   Now you should take a while and play around with the existing .des files
   and become familiar with the syntax. Creating new levels and dungeon wasn't
   difficult, was it?

   Maybe this chapter covers all your needs; but if you really want 
   exciting new emotions, read on.

6. Creating a new monster
-------------------------

      "Beware, there will be no return! Still read? (y/n)"
      
   Welcome to Darkness of Mordor... This is going to be painful but the
   reward is great: some modification could be blessed by the dev team and
   you will reach inmortality! And anyway, modifying nethack will give you
   even happier hours than playing it.

   So, let's cope with it:

   For start, you should know that there are two HUGE arrays: one defining the
   possible monsters and the other defining the possible objects. The first
   one is called 'mons': it's an array of 'permonst' structs defined in the
   file monst.c, under the src directory (by the way, after this point, I'll
   stop saying where the files are located: you should be familiar with the
   directory structure by now). The 'permonst' struct is defined in the
   file permonst.h, and giving it a look should give you an idea of what 
   element of the struct is for, but, for your convenience here is an expla-
   nation of what to put in a new entry for the mons array, i.e:

        {"myself", S_HUMAN, 1, 10, 10, 0, 0, G_GENO | G_NOGEN,
        { { AT_WEAP, AD_PHYS, 1, 6 }, NO_ATTK, NO_ATTK,
          NO_ATTK, NO_ATTK, NO_ATTK },
        WT_HUMAN, 400, PL_NSIZ, MS_HUMANOID, MZ_HUMAN, 0, 0,
        M1_NEEDPICK | M1_HUMANOID | M1_OMNIVORE,
        M2_HUMAN | M2_STRONG | M2_COLLECT, 0, C(HI_DOMESTIC)}

   -name: ("myself") is the name for the monster.

   -symbol: (S_HUMAN) is the letter used for it. The complete list is defined
	  in the file monsym.h

   -level: (1). The monster is initially created with this level.

   -move rate: (10). Ranges from 0 -don't move- to 30 -really fast-.

   -AC: (10). Come on! you now quite well what this is.

   -magic resistance: (0). Ranges from 0 -none- to 127 -full-.

   -alignment: (0). negative value means chaotic, positive lawful.

   -creation/geno flags: (G_GENO | G_NOGEN) 
	these are flags or'ded, with this meaning:

        G_UNIQ          /* generated only once */
        G_NOHELL        /* not generated in "hell" */
        G_HELL          /* generated only in "hell" */
        G_NOGEN         /* generated only specially */
        G_NOCORPSE      /* no corpse left ever */
        G_SGROUP        /* appear in small groups normally */
        G_LGROUP        /* appear in large groups normally */
        G_GENO          /* can be genocided */
        G_GENOD         /* have been genocided */
        G_EXTINCT       /* have been extinguished as
                           population control */
        G_FREQ          /* creation frequency mask */

                 (from monsym.h)

   -attack: ({ { AT_WEAP, AD_PHYS, 1, 6 }, NO_ATTK, NO_ATTK,
           NO_ATTK, NO_ATTK, NO_ATTK },)
      This defines how the monster attacks. This element is composed of six 
      'attack' struct, each one being the form:

	  ( attack_type, damage_type, # of dice, # of sides of each )

      where attack_type is one of:

        AT_NONE         /* passive monster (ex. acid blob) */
        AT_CLAW         /* claw (punch, hit, etc.) */
        AT_BITE         /* bite */
        AT_KICK         /* kick */
        AT_BUTT         /* head butt (ex. a unicorn) */
        AT_TUCH         /* touches */
        AT_STNG         /* sting */
        AT_HUGS         /* crushing bearhug */
        AT_SPIT         /* spits substance - ranged */
        AT_ENGL         /* engulf (swallow or by a butt) */
        AT_BREA         /* breath - ranged */
        AT_EXPL         /* explodes - proximity */
        AT_GAZE         /* gaze - ranged */
        AT_TENT         /* tentacles */
        AT_WEAP         /* uses weapon */
        AT_MAGC         /* uses magic spell(s) */

      damage_type is one of:

        AD_PHYS         /* ordinary physical */
        AD_MAGM         /* magic missiles */
        AD_FIRE         /* fire damage */
        AD_COLD         /* frost damage */
        AD_SLEE         /* sleep ray */
        AD_DISN         /* disintegration (death ray) */
        AD_ELEC         /* shock damage */
        AD_DRST         /* drains str (poison) */
        AD_ACID         /* acid damage */
        AD_SPC1         /* for extension of buzz() */
        AD_SPC2         /* for extension of buzz() */
        AD_BLND         /* blinds (glowing eye) */
        AD_STUN         /* stuns */
        AD_SLOW         /* slows */
        AD_PLYS         /* paralyses */
        AD_DRLI         /* drains life levels (Vampire) */
        AD_DREN         /* drains magic energy */
        AD_LEGS         /* damages legs (xan) */
        AD_STON         /* petrifies (Medusa, Cockatrice) */
        AD_STCK         /* sticks to you (Mimic) */
        AD_SGLD         /* steals gold (Leppie) */
        AD_SITM         /* steals item (Nymphs) */
        AD_SEDU         /* seduces &amp; steals multiple items */
        AD_TLPT         /* teleports you (Quantum Mech.) */
        AD_RUST         /* rusts armour (Rust Monster)*/
        AD_CONF         /* confuses (Umber Hulk) */
        AD_DGST         /* digests opponent (trapper, etc.) */
        AD_HEAL         /* heals opponent's wounds (nurse) */
        AD_WRAP         /* special "stick" for eels */
        AD_WERE         /* confers lycanthropy */
        AD_DRDX         /* drains dexterity (Quasit) */
        AD_DRCO         /* drains constitution */
        AD_DRIN         /* drains intelligence (mind flayer) */
        AD_DISE         /* confers diseases */
        AD_DCAY         /* decays organics (Brown pudding) */
        AD_SSEX         /* Succubus seduction (extended) */
        AD_DETH         /* for Death only */
        AD_PEST         /* for Pestilence only */
        AD_FAMN         /* for Famine only */
        AD_CLRC         /* random clerical spell */
        AD_SPEL         /* random magic spell */
        AD_RBRE         /* random breath weapon */
        AD_SAMU         /* hits, may steal Amulet (Wizard) */
        AD_CURS         /* random curse (ex. gremlin) */

      and the # dice/faces sets a range of damage:

           i.e:   1,6     means a possible damage between 1 and 6,
              but 3,7     means a possible damage between 3 and 21.

      So, a monster can attack six times per turn at maximum. To attack less
      times use the 'NO_ATTACK' entry.

   -weight: (WT_HUMAN). Can be one of several defines like WT_DRAGON, WT_HUMAN,
      WT_ELF, but also a direct number can be used.

   -nutritional value: (400). The title says it all.

   -extension length: (PL_NSIZ). Here comes a problem...This is the size of an
      extra struct added to the normal permonst if the monster has any. For
      example, shopkeepers have an extra struct used to manage the shop
      code, dogs an extra to manage taming levels, etc... For the moment
      forget about this part.

   -sounds made: (MS_HUMAN). It is one of: (from monflag.h)

        MS_SILENT       /* makes no sound */
        MS_BARK         /* if full moon, may howl */
        MS_MEW          /* mews or hisses */
        MS_ROAR         /* roars */
        MS_GROWL        /* growls */
        MS_SQEEK        /* squeaks, as a rodent */
        MS_SQAWK        /* squawks, as a bird */
        MS_HISS         /* hisses */
        MS_BUZZ         /* buzzes (killer bee) */
        MS_GRUNT        /* grunts (or speaks own language) */
        MS_NEIGH        /* neighs, as an equine */
        MS_WAIL         /* wails, as a tortured soul */
        MS_GURGLE       /* gurgles, as liquid or through saliva */
        MS_BURBLE       /* burbles (jabberwock) */
        MS_ANIMAL       /* up to here are animal noises */
        MS_SHRIEK       /* wakes up others */
        MS_BONES        /* rattles bones (skeleton) */
        MS_LAUGH        /* grins, smiles, giggles, and laughs */
        MS_MUMBLE       /* says something or other */
        MS_IMITATE      /* imitates others (leocrotta) */
        MS_ORC          /* intelligent brutes */
        MS_HUMANOID     /* generic traveling companion */
        MS_ARREST       /* "Stop in the name of the law!" (Kops) */
        MS_SOLDIER      /* army and watchmen expressions */
        MS_GUARD        /* "Please drop that gold and follow me." */
        MS_DJINNI       /* "Thank you for freeing me!" */
        MS_NURSE        /* "Take off your shirt, please." */
        MS_SEDUCE       /* "Hello, sailor." (Nymphs) */
        MS_VAMPIRE      /* vampiric seduction, Vlad's exclamations */
        MS_BRIBE        /* asks for money, or berates you */
        MS_CUSS         /* berates (demons) or intimidates (Wiz) */
        MS_RIDER        /* astral level special monsters */
        MS_LEADER       /* your class leader */
        MS_NEMESIS      /* your nemesis */
        MS_GUARDIAN     /* your leader's guards */
        MS_SELL         /* demand payment, complain about shoplifters */
        MS_ORACLE       /* do a consultation */
        MS_PRIEST       /* ask for contribution; do cleansing */

   -physical size: (MZ_HUMAN). Is one of:

        MZ_TINY         0               /* &lt; 2' */
        MZ_SMALL        1               /* 2-4' */
        MZ_MEDIUM       2               /* 4-7' */
        MZ_HUMAN        MZ_MEDIUM       /* human-sized */
        MZ_LARGE        3               /* 7-12' */
        MZ_HUGE         4               /* 12-25' */
        MZ_GIGANTIC     7               /* off the scale */

   -resistance conferred (randomly) when eaten: (0)

        MR_FIRE         /* resists fire */
        MR_COLD         /* resists cold */
        MR_SLEEP        /* resists sleep */
        MR_DISINT       /* resists disintegration */
        MR_ELEC         /* resists atomicity */
        MR_POISON       /* resists poison */
        MR_ACID         /* resists acid */
        MR_STONE        /* resists petrification */

   -First group of flags: (specify the monster behaviour)
          (M1_NEEDPICK | M1_HUMANOID | M1_OMNIVORE)

        M1_FLY          /* can fly or float */
        M1_SWIM         /* can traverse water */
        M1_AMORPHOUS    /* can flow under doors */
        M1_WALLWALK     /* can phase thru rock */
        M1_CLING        /* can cling to ceiling */
        M1_TUNNEL       /* can tunnel thru rock */
        M1_NEEDPICK     /* needs pick to tunnel */
        M1_CONCEAL      /* hides under objects */
        M1_HIDE         /* mimics, blends in with ceiling */
        M1_AMPHIBIOUS   /* can survive underwater */
        M1_BREATHLESS   /* doesn't need to breathe */
        M1_NOEYES       /* no eyes to gaze into or blind */
        M1_NOHANDS      /* no hands to handle things */
        M1_NOLIMBS      /* no arms/legs to kick/wear on */
        M1_NOHEAD       /* no head to behead */
        M1_MINDLESS     /* has no mind--golem, zombie, mold */
        M1_HUMANOID     /* has humanoid head/arms/torso */
        M1_ANIMAL       /* has animal body */
        M1_SLITHY       /* has serpent body */
        M1_UNSOLID      /* has no solid or liquid body */
        M1_THICK_HIDE   /* has thick hide or scales */
        M1_OVIPAROUS    /* can lay eggs */
        M1_REGEN        /* regenerates hit points */
        M1_SEE_INVIS    /* can see invisible creatures */
        M1_TPORT        /* can teleport */
        M1_TPORT_CNTRL  /* controls where it teleports to */
        M1_ACID         /* acidic to eat */
        M1_POIS         /* poisonous to eat */
        M1_CARNIVORE    /* eats corpses */
        M1_HERBIVORE    /* eats fruits */
        M1_OMNIVORE     /* eats both */
        M1_METALLIVORE  /* eats metal */

   -Second group of flags: (specify more monster behaviour)
        (M2_HUMAN | M2_STRONG | M2_COLLECT)

        M2_NOPOLY       /* players mayn't poly into one */
        M2_UNDEAD       /* is walking dead */
        M2_WERE         /* is a lycanthrope */
        M2_ELF          /* is an elf */
        M2_DWARF        /* is a dwarf */
        M2_GIANT        /* is a giant */
        M2_ORC          /* is an orc */
        M2_HUMAN        /* is a human */
        M2_DEMON        /* is a demon */
        M2_MERC         /* is a guard or soldier */
        M2_LORD         /* is a lord to its kind */
        M2_PRINCE       /* is an overlord to its kind */
        M2_MINION       /* is a minion of a deity */
        M2_MALE         /* always male */
        M2_FEMALE       /* always female */
        M2_NEUTER       /* neither male nor female */
        M2_PNAME        /* monster name is a proper name */
        M2_HOSTILE      /* always starts hostile */
        M2_PEACEFUL     /* always starts peaceful */
        M2_DOMESTIC     /* can be tamed by feeding */
        M2_WANDER       /* wanders randomly */
        M2_STALK        /* follows you to other levels */
        M2_NASTY        /* extra-nasty monster (more xp) */
        M2_STRONG       /* strong (or big) monster */
        M2_ROCKTHROW    /* throws boulders */
        M2_GREEDY       /* likes gold */
        M2_JEWELS       /* likes gems */
        M2_COLLECT      /* picks up weapons and food */
        M2_MAGIC        /* picks up magic items */

   -Third group of flags: (0) (specify even more monster behaviour)

        M3_WANTSAMUL    /* would like to steal the amulet */
        M3_WANTSBELL    /* wants the bell */
        M3_WANTSBOOK    /* wants the book */
        M3_WANTSCAND    /* wants the candelabrum */
        M3_WANTSARTI    /* wants the quest artifact */
        M3_WANTSALL     /* wants any major artifact */
        M3_WANTSALL     /* wants any major artifact */
        M3_WAITFORU     /* waits to see you or get attacked */
        M3_CLOSE        /* lets you close unless attacked */
        M3_COVETOUS     /* wants something */
        M3_WAITMASK     /* waiting... */

   -symbol color: (C(HI_DOMESTIC))

        C(RED), C(BROWN), C(HI_DOMESTIC), etc...

            (HI_DOMESTIC is the color for a peaceful monster).

   You should also follow this rules, as the glorious dev team says:

  
        Rule #1:        monsters of a given class are contiguous in the
                        mons[] array.
  
        Rule #2:        monsters of a given class are presented in ascending
                        order of strength.
  
        Rule #3:        monster frequency is included in the geno mask;
                        the frequency can be from 0 to 7.  0's will also
                        be skipped during generation.
  
        Rule #4:        monster subclasses (e.g. giants) should be kept
                        together, unless it violates Rule 2.  NOGEN monsters
                        won't violate Rule 2.
  
  

   And that's all. As usual it is easier to begin copying an existing monster.
   For example if you want to create a stronger centaur, get the plain one
   and change the AC and attack part.

   Now you need to recompile the whole code. Yes, you read right: the WHOLE
   CODE. The reason is this: the mons array sets a unique number for each
   monster used later for reference it in the array. Did you saw a 'makedefs'
   command while compiling? It is a vital part: generates #define for each
   monster &amp; object. So if you look at the pm.h file:

	/* This source file is generated by 'makedefs'.  Do not edit. */
	#ifndef PM_H
	#define PM_H

	#define PM_GIANT_ANT    0
	#define PM_KILLER_BEE   1
	#define PM_SOLDIER_ANT  2
	#define PM_FIRE_ANT     3

   you understand now how it works: the sources can use the PM_SOMETHING
   define to access the permonst struct of a 'something' monster without
   knowing previously its location.

   If you did set up make or ndmake correctly, make itself will take care of
   the process of recompiling the code. Note that the *.des files are also
   recompiled.

   Now, to try out the new monster start nethack in wizard mode and wish for
   a scroll of create monster. Read it and answer to create a 'your monster'
   one. Voila! You now have your own monster.

   IMPORTANT NOTE:
      It is quite important to separate your own code with the appropriate
   #ifdef, #ifndef statements. Just add the necessary #define SOMETHING 
   line at the end of include/config.h file.

7. Refining your monster
-------------------------

   7.0. The 'monst' struct.

   From the chapter 5 you now have a monster of your own wandering through
   the dungeons. But surely you want more action: specific objects, armor
   or weapon for him; concrete chatting sentences, etc... How can you
   accomplish this? read on.

   Now is the moment to introduce the 'monst' structure. This struct is what
   defines a 'concrete' monster: hps, taming status, etc... very different
   from the 'permonst' structure, where the capabilities of all monsters of
   a type are defined. The elements in 'monst' are defined in monst.h:

   -nmon: All monsters in current level are organized in a chained list. 
   Starting with a first monster descriptor ('fmon') you can navigate through
   all of them, thanks to this pointer to the next monster:

                    --------    --------   --------   --------
            fmon -&gt; | nmon ---&gt; | nmon ---&gt;| nmon ---&gt;| nmon ---&gt; NULL
                    |      |    |      |   |      |   |      |
                    | MONST|    | MONST|   | MONST|   | MONST|
                    |  #1  |    |  #2  |   |  #3  |   |  #4  |
                    --------    --------   --------   --------

   -data: Is a pointer to the permonst structure for this monster. Obviously,
   as the weight of a newt is permanent it doesn't make sense to keep it for
   each concrete newt.

   -m_id: unique number for a monster, asigned at creation time.

   -mnum: Permanent monster index number. Number asigned by makedefs. That is,
    the PM_NAME_OF_MONSTER #define in include file pm.h.  It is unique to this
    type of monster.

   -m_lev: Adjusted difficulty level of monster; that is, the level of a 
   monster can have changed from the default one (experience, potions,etc...)

   -malign: Alignment of this monster, relative to the player. A positive
   number means is good to kill it.

   -mx, my: Position of the monster in the level map (x,y coordinates).

   -mux,muy: Position in the map where the monster thinks player is. May be
   different from actual one due to cloack of displacement, invisibility, etc.

   -mtrack: Monster track???. Used in the movement routines, but I've no clear
    idea of what it is.

   -mappearance: For mimics &amp; the wizard. How it looks to the player.

   -m_ap_type: What mappearance is describing. Is one of:
	M_AP_NOTHING    0/*mappearance is unused --monster appears as itself */
	M_AP_FURNITURE  1/* stairs, a door, an altar, etc. */
	M_AP_OBJECT     2/* an object */
	M_AP_MONSTER    3/* a monster */

   -mtame: Level of tameness. If greater than 0 monster is tamed, and also
    implies peacefulness (as it doesn't make sense a tamed monster aggresive
    to the player).

   -mspec_used: Monster's special ability attack timeout. That is, monster 
   won't use its special ability -like dragon's breath- until this counter 
   reaches 0.

   -female: 1 = yes, 0 = no.
   -minvis: Monster is invisible. 1 = yes, 0 = no.
   -cham: Monster is actually a chamaleon. 1 = yes, 0 = no.
   -mundetected: Monster is hidden (as snakes) and hasn't been detected by
   the player. 1 = yes, 0 = no.
   -mcan: Monster has been zapped by a wand of cancellation (or spell).
   -mspeed: Monster extra speed. 2 bits allow 4 possibilities.
   -mflee: Monster is currently fleeing.
   -mfleetim: (7 bits) timeout for that fleeing.
   -mcansee/mblinded: monster can see / timeout for blinded.
   -mcanmove/mfrozen: monster can move / timeout for frozen.
   -msleep: monster is sleeping.
   -mstun: monster is stunned.
   -mconf: monster is confused.
   -mpeaceful: monster is peaceful.
   -mtrapped: monster is now trapped.
   -mleashed: leashed is applied to it.
   -isshk: This monster is a shopkeeper. 
   -isminion: Is a minion.
   -isgd: is a guard.
   -ispriest: is a priest.
   -iswiz: is the wizard of Yendor.
   -wormno: If a worm, this sets the number this one makes. (there can't be
    more than 31 per level).
   -mstrategy: Strategy to follow. (just applies to very special monsters).
   -mtrapseen: bitmap of traps we've been trapped in.
   -mlstmv: flag to prevent two moves at once (?). 
   -mgold: How rich this monster is.
   -minvent: It points to a 'obj' struct. The objects a monster has are 
    organized in a chained list, the same as the 'monst' struct. This is
    the beginning of that list. (obviously NULL if nothing being carried).
   -mw: If the monster is wielding a weapon, here it is.
   -misc_worn_check: Some obscure value for the worms code (?).
   -weapon_check: Flag to check if monster has to get a weapon.
   -mnamelth: Length of this monster PROPER name.
   -mxlth: Length of the 'extra' part of the struct. It differs from monster
    to monster. Most have any.
   -meating: Monster is eating timeout.
   -mextra: Allows access to the 'extra' part of the struct. Profusely used
    with shopkeepers, for example.

   
   Uffff! I'm sure you're impressed with this big struct. Don't worry, you
   don't have to deal with all the fields, at least at the beginning.

   First thing you should have to do is answer this question: Does this monster
   need any object or special ability not reflected in the M-FLAGS? If the 
   answer is yes, edit the file makemon.c and look for the 'm_initweap' 
   function.

   (NOTE to UNIX users:

   A few tools become invaluable in the process of looking for functions:

     The 'ctags' command allows to create an index for objects; run the line

		ctags *.c          (in the src directory)

     this will create a 'tags' file. After that the command 'vi -t m_initweap'
     will take you directly to the implementation of m_initweap function.

     Also, the 'grep' command allows searching for a string. I.e. Wants to
     have a look in the chamaleon code? Start looking the output for
    		 grep -i chamaleon | more

   End of NOTE)

   The m_initweap function is where the monster gets the objects it needs. A
   huge switch statement  (switch (mtmp-&gt;data-&gt;mlet) ) specify what it gets
   according to its type. This is done with the 'mongets' function. (See
   Apendix A for a complete listing of nearly 100 useful functions). 

   The easiest thing to do is search for a monster similar than ours and
   copy the code. That way shouldn't be difficult to add a known object to
   our monster. Note the usage of rn2() function to randomize the monsters
   armors &amp; weapon.

   Really interesting monsters will have its own armor/weapon/object or type
   of attack (if not, you will just get variations of standard monsters:
   tougher newts, wimpy dragons, etc...). For adding a new object have a look
   in the next section; Now we will see how to add new attacks or behaviours:

   7.1. Adding a new attack type.

   Edit the monattk.h file. Go after AT_TENT definition (in standard 3.1.3)
   and add a line with something like:

       #define AT_HELLO    16    /* Tries to kill you saying Hello */

   This will be your new attack type. Now you have to define a new damage:
   Put this line after the AD_FAMN definition:

       #define AD_HELLO	   39    /* You're saluted */

   Now go to the src directory and edit the mhitu.c (monster-hits-user) file.
   Inside the hitmsg() function you should add the code for your AT_HELLO
   attack type. I.e: just add a line after 

                case AT_EXPL:
                        pline("%s explodes!", Monnam(mtmp));
                        break;

   like:

                case AT_HELLO:
                        pline("%s says hello to you!", Monnam(mtmp));
                        break;

   Here we are introducing one of the most used function: pline() to show a
   message to the screen (see apendix A for more information).

   Later on look for the mattacku() function. You will have to add more code
   for your AT_HELLO attack inside the 'switch(mattk-&gt;aatyp)'. Easiest is to
   add a case to the 'hand to hand' attacks.

   Now look for hitmu() function. There we have to add the code for AD_HELLO.
   I.e., after 

            case AD_FAMN:
                pline("%s reaches out, and your body shrivels.",
                        Monnam(mtmp));
                exercise(A_CON, FALSE);
                morehungry(rn1(40,40));
                /* plus the normal damage */
                break;

   add

            case AD_HELLO:
                hitmsg(mtmp, mattk);
		make_confused(2,FALSE);
		break;

   so this new attack confuses you, a la umber hulk gaze.

   That finished the editing for the mhitu.c file. Now do the same with mhitm.c
   (monster- hits-monster), so a monster can attack another one with AT_HELLO.

   7.2. Adding new monster's abilities

   Within this chapter the method to add an action for a monster it is 
   explained. For example, let's add the code so a monster can read a
   remove curse scroll.

   Edit the muse.c file and look for the #define MUSE_WAN_SPEED_MONSTER 7
   line. Add a new posibility:

	#define MUSE_SCR_SCARE_MONSTER 8

   After that, inside the find_misc function look for:

                if(obj-&gt;otyp == WAN_POLYMORPH &amp;&amp; !mtmp-&gt;cham
                                &amp;&amp; monstr[(monsndx(mtmp-&gt;data))] &lt; 6) {
                        m.misc = obj;
                        m.has_misc = MUSE_WAN_POLYMORPH;
                }

   and add:
                if(obj-&gt;otyp == SCR_REMOVE_CURSE) {
                        m.misc =obj;
                        m.has_misc = MUSE_SCR_REMOVE_CURSE;
                        }  

   Now a monster is able to detect a remove curse scroll as a potential action.
   Inside use_misc() we'll add the code to execute that action:

   After the lines

        case MUSE_WAN_POLYMORPH:
                mzapmsg(mtmp, otmp, TRUE);
                otmp-&gt;spe--;
                (void) newcham(mtmp, rndmonst());
                if (oseen) makeknown(WAN_POLYMORPH);
                return 2;

   Add

        case MUSE_SCR_REMOVE_CURSE:
                {
                register struct obj *obj;
                mreadmsg(mtmp,otmp);
                pline("%s feels than someone is helping %s.",Monnam(mtmp),
                                 mtmp-&gt;female?"her":"him");
                if (!otmp-&gt;cursed) {
                   for(obj=mtmp-&gt;minvent;obj;obj=obj-&gt;nobj)
                      if (otmp-&gt;blessed || obj-&gt;owornmask ||
                         (obj-&gt;otyp == LOADSTONE)) {
                            if (mtmp-&gt;mconf) blessorcurse(obj,2);
                            else uncurse(obj);
                            }
                }
                if (oseen &amp;&amp; !objects[SCR_REMOVE_CURSE].oc_name_known
                     &amp;&amp; !objects[SCR_REMOVE_CURSE].oc_uname)
                     docall(otmp); /* not makeknown() */
                m_useup(mtmp, otmp);
                return 2;
                }

   7.3. Adding a 'mextra' struct.

   Real interesting monster behaviour needs the definition of new variables
   in the monst struct. For example, suppose you want to add the possibility
   to pray to god to your new monster; good idea would be to have a timeout
   so the monster cannot pray every two turns. So, we could just add a new
   element to the 'struct monst' in monst.h:

		long praytime;

   but that way EVERY MONSTER will have that variable defined, allocating
   four bytes although only our new monster will use it.

   Instead of that define a new struct - best in your own new include file-:

	struct onlymymonster {
		long praytime;
	};

   and in the monster's definition in monst.c put 'sizeof(struct onlymymonster)'
   as the extension length field. To refer to your new variable use this
   contruction:

		((struct onlymymonster *)&amp;(mon)-&gt;mextra[0])-&gt;praytime

		     (where mon is a pointer to a monst struct)

   To abbreviate such a beast, use a #define:

	#define MYMONSTER(mon)   ((struct onlymymonster *)&amp;(mon)-&gt;mextra[0])

   so we can use 

	MYMONSTER(mon)-&gt;praytime

   Refer to the eshk.h file for an example of using a mextra part. (the
   code for the shopkeepers).

8. Adding a new object
----------------------

   8.1 The 'objects' array.

   In chapter 6 I introduced you the mons[] array. Now it's the turn of the
   'objects' array. It is a collection of structs objclass, being composed
   of these elements: (from objclass.h)

   oc_name_idx: actual name of the object.
   oc_descr_idx: How the object is described when unknown (not identified).
   oc_uname: Description given by the user (via the Call command).
   oc_name_known: If 1, means the actual name is always showed.
   oc_merge: If 1, merge otherwise equal objects.
   oc_uses_known: Full description should be given.
   oc_magic: It is a magical object.
   oc_charged: This object may have charges.
   oc_unique: This object is unique (amulet of Yendor, etc...)
   oc_nowish: The player cannot wish for it.
   oc_big: Big object.
   oc_dir: Is it directional? Can be:
					   NODIR
					   IMMEDIATE
					   RAY
   oc_material: What is it made of? Can be one of:

	   LIQUID	WAX		VEGGY	FLESH	PAPER
	   CLOTH	LEATHER		WOOD	BONE	DRAGON_HIDE
	   IRON		METAL		COPPER	SILVER	GOLD
	   PLATINUM	MITHRIL		PLASTIC	GLASS	GEMSTONE
	   MINERAL

   oc_oprop: Properties conveyed by this object, i.e.: FIRE_RES, ANTIMAGIC,
     etc...

   oc_class: object class, i.e. WEAPON_CLASS, FOOD_CLASS, etc...
   oc_delay: Delay when using such an object.
   oc_color: Color of the object: Can be 
           BLACK	RED		GREEN		BROWN
	   BLUE		MAGENTA		CYAN		GRAY
	   NO_COLOR	ORANGE_COLORED	BRIGHT_GREEN	YELLOW
	   BRIGHT_BLUE	BRIGHT_MAGENTA	BRIGHT_CYAN	WHITE

       but also take note of this (from color.h):

		#define HI_OBJ          MAGENTA
		#define HI_METAL        CYAN
		#define HI_COPPER       YELLOW
		#define HI_SILVER       GRAY
		#define HI_GOLD         YELLOW
		#define HI_LEATHER      BROWN
		#define HI_CLOTH        BROWN
		#define HI_ORGANIC      BROWN
		#define HI_WOOD         BROWN
		#define HI_PAPER        WHITE
		#define HI_GLASS        BRIGHT_CYAN
		#define HI_MINERAL      GRAY
		#define HI_ZAP          BRIGHT_BLUE

   oc_prob: probability of the object. The total sum of same class objects 
     should be 100.
   oc_weight: its weight.
   oc_cost: Base cost in shops. Actual price depends on charisma &amp; hawaiian 
     shirts.
   oc_wsdam:
   oc_wldam: max small/large monster damage.
   oc_oc1:
   oc_oc2: Flags setting the +- something to the object. Its behaviour depends
     on the class: for a weapon oc1 is the 'to hit' bonus while oc2 is a
     negative value; for an armor, oc1 is the enchantment level &amp; oc2 is the
     - (rusting, etc...); for a spellbook oc2 is the spell level.
   oc_nutrition: food value.

   But for convenience, several "#defines" have been made so adding a certain
   class of object is more direct. i.e:

#define WEAPON(name,app,kn,mg,bi,prob,wt,cost,sdam,ldam,hitbon,metal,color) OBJE
CT( \
                OBJ(name,app), BITS(kn,mg,1,0,0,1,0,0,bi,0,metal), 0, \
                WEAPON_CLASS, prob, 0, \
                wt, cost, sdam, ldam, hitbon, 0, wt, color )

   allows to add a new weapon with the WEAPON macro, that sets several default
   values common for all weapons.

   There are macros for almost everything: WEAPON, FOOD, ARMOR, RING, etc...
   Just use the one adequate in your case, keeping in mind:

      - Put all common class objects together.
      - Check the probabilities for the class.
      - Easiest way is -as usual- copy an existing object and modify it.

   Here there are some examples of entries:

      ARMOR("Merlin's helm", "sharp-pointed cap", 0, 1, 0, POLYMORPH_CONTROL,
         0, 1, 10, 50,10, 0, CLOTH, BRIGHT_BLUE)

      ARMOR("sport t-shirt", NULL, 1, 0, 0, 0, 0, 0, 5, 3,10, 0, CLOTH, BLUE)

      TOOL("self-compatible personal computer",NULL,1, 0, 0, 0, 0,80,  200,
         PLASTIC, GR AY)

      FOOD("hamburger",            0, 1,  8, 0, VEGGY, 300, BROWN)

   That's all for the objects[] array. Now, depending of the class some files
   should be touched; but first, some general recomendations:

   a) Don't put your object as the first or last of its class: there are TONS
   of code in the form:

		if ( (object &gt; FIRST_OF_CLASS_X )
		   &amp;&amp; (object &lt; LAST_OF_CLASS_X ) )  
		   {   
			/* Assume object is of class x */
		   }
		   else 
		        /* Print some strange fatal error */

   b) Start with easy objects. Even better: add the object and put no effect
   for it ---&gt; the warning/error messages will inform you of the correct place
   to edit.
    Later put all the complicated things you have in mind, but start it simple.

   c) There are some general functions that can be applied to all classes.
   i.e: special effects when eating an object, cancelling it, dipping it, etc.
   Here is a few hints for adding that:

   - cancel_item() function, in zap.c, specifies what to do when cancelling.
   - dodip() in potion.c, for special effects when dipping an object.
   - eatspecial() in eat.c.
   - dropy() in do.c, when dropping an object (i.e: a crysknife).

   
   8.1. Adding a tool

   Your new added tool should have an effect when a)pplying it. That's defined
   in the doapply() function, inside the apply.c file.
   There is a huge switch depending on the object type (switch(obj-&gt;otyp));
   note that different objects are referenced with its name in upper case; that
   constant is generated by the makedefs command (remember?) in the onames.h
   file. 

   What a tool does when applying is defined in its 'case'; if simple the
   code is directly put there, if not a 'use_<tool-name>' function is defined
   above. Studying such functions is a very good exercise, as they provide
   lots of useful functions.

   8.2. Adding a wand

   A wand must have extra code in two ocasions: engraving with it and 
   -obviously- zapping it.

   In engrave.c file we found the doengrave() function. There you should add
   the appropiate 'case' entry and the message or code for anything you want.
   Note the differences between directional &amp; no directional wands.

   In zap.c you should edit different functions depending also in the direc-
   tional capability of your wand:

      non-directional     --------- &gt;  function zapnodir()

      directional         --------- &gt;  function bhitm() (wand hits monster).
                              |---- &gt;  function bhito() (wand hits object).
                              |---- &gt;  function zapyourself() (you, silly).

   In general adding a wand it is more difficult than any other object.
   Better start with something else.

   8.3. Adding a potion

   In this case look in file potion.c, for this functions:

   peffects():  Describes what happens when potion is quaffed.

   potionhit(): Describes what happens when potion hits a monster.

   potionbreathe(): Potion vapors effect.

   Also you'd like to edit the dodip() function where some special effects
   can be added for dipping cases.

   8.4. Adding armor/weapon

   Unless you want some special feature, there is nothing to do.

   Good place for adding code is function dmgval() in weapon.c: it adds
   special damage bonuses for a certain weapon hitting a certain monster.

   8.5. Adding a ring

   Functions to look for in this case:

   - dosinkring() in do.c. That describes the effects when dropping a ring
    in a sink.

   - Ring_on() in do_wear.c  What happens when a ring is put on.

   - Ring_off_or_gone() in do_wear.c  The opposite way.

   - eatring() in eat.c  Polymorphed player eats a ring.

   8.6. Adding an amulet 
   
   Quite similar to rings. Edit the functions Amulet_on() &amp; Amulet_off in
   do_wear.c

   8.7. Adding a spellbook 

   First, in spell.c edit two functions:

   study_book(): for learning a spell.
   spelleffects(): for casting a spell.

   As many spells behave like wands you may also have to edit the functions
   bhitm(), bhito() &amp; zapyourself() in zap.c, a la wand class.

   8.8. Adding food

   Just two functions here, both in eat.c

   fprefx(): called when first bite of food.
   fpostfx(): called when consumed food.

   You should at least add the 'case' lines for the default behaviour.

9. Creating a new room type
---------------------------

   To explain how to create a new room type, I will use an example: a clinic,
   that is, a room full of nurses.

   First of all, go to the include directory and edit the mkroom.h file. After
   the line
		#define TEMPLE 10
   add
		#define CLINIC 11

   Look than then you'll have to increment the SHOPBASE &amp; subsequents defines
   to reflect the change, so MAXRTYPE becomes 22.

   Now edit the rm.h file and after
		Bitfield(is_cavernous_lev,1);

   add
		Bitfield(has_clinic,1);

   so we can add a special message (for example an ambulance like sound) when
   being in a level that has a clinic.

   That's all for the include files. Go to the src directory and edit mkroom.c
   Look for the mkroom() function and after the line
		case BARRACKS:  mkzoo(BARRACKS); break;

   add
		case CLINIC:     mkzoo(CLINIC); break;

   Take note that we are just adding a new non-shop room type, because the
   previous mkshop() call if (roomtype &gt;= SHOPBASE). We could define a 
   complete 'mkclinic()' function (see for example mktemple) but it is quite
   simpler to use the mkzoo() code. That function will create a room and 
   fill it -function fill_zoo- with the appropiate monsters.

   After that, we should edit the mkshop() function. Why? because in wizard
   mode we could specify a room type to be created using the environment
   variable SHOPTYPE. For example, if SHOPTYPE='G' starting nethack will
   create a general shop in first level, 'Z' will create a zoo, etc... It is
   not necessary, but certainly a good idea to add a new SHOPTYPE for our
   new room, so we can test it quickly.

   So, after 
			if(*ep == 't' || *ep == 'T' || *ep == '\\'){
                                mkzoo(COURT);
                                return;
                        }

   put the following:

                        if(*ep == 'c' || *ep == 'C'){
                                mkzoo(CLINIC);
                                return;
                        }

   Now go for the fill_zoo() itself. After

	        case ZOO:
	            goldlim = 500 * level_difficulty();
		    break;

   just add
		case CLINIC
		    break;

   Now we have to select the monster to be created in our room. After

  	#ifdef ARMY
                    	(type == BARRACKS)&nbsp;? squadmon()&nbsp;:
	#endif 

   Add
			(type == CLINIC)&nbsp;? &amp;mons[PM_NURSE]:

   That is, if room type is CLINIC, monster to be created is a nurse. Several
   things to note here: you can add a more complex function -see for example,
   the courtmon() function- to select several monsters; also look how the
   central point of the room is selected in other cases to create a special
   monster -for example a queen bee in a beehive-.

   If you want to add objects to the room, several lines after, you'll see:

                    case BARRACKS:
                        if(!rn2(20))    /* the payroll and some loot */
                            (void) mksobj_at((rn2(3))&nbsp;? LARGE_BOX&nbsp;: CHEST,
                                             sx, sy, TRUE);
                        break;

   That is, 1 in 20 make a large box or a chest. We could put something like:

		    case CLINIC:
			if(!rn2(10))
			    (void) mksobj_at(ICE_BOX,sx,sy,TRUE);
			break;

   To create random ice boxes. It doesn't have to be a container, can be any
   object you like.

   Finally add a flag indicating that the level has a clinic:

              case CLINIC:
                  level.flags.has_clinic = 1;
                  break;

   You could now recompile and try out your new room using the SHOPTYPE 
   variable, but it will never generated in a normal dungeon. For that, we
   have to edit mklev.c

   First, at the beginning of the clear_level_structures() function add the
   line:
		level.flags.has_clinic = 0;

   so the flag is reset.

   Later, look for the code:

        if(depth(&amp;u.uz) &gt; 1 &amp;&amp;
           depth(&amp;u.uz) &lt; depth(&amp;medusa_level) &amp;&amp;
           rn2(depth(&amp;u.uz)) &lt; 3) mkroom(SHOPBASE);
        else if(depth(&amp;u.uz) &gt; 4 &amp;&amp; !rn2(6)) mkroom(COURT);
        else if(depth(&amp;u.uz) &gt; 6 &amp;&amp; !rn2(7)) mkroom(ZOO);
        else if(depth(&amp;u.uz) &gt; 8 &amp;&amp; !rn2(5)) mkroom(TEMPLE);
        else if(depth(&amp;u.uz) &gt; 9 &amp;&amp; !rn2(5) &amp;&amp;
           !(mons[PM_KILLER_BEE].geno &amp; (G_GENOD | G_EXTINCT))) mkroom(BEEHIVE);
        else if(depth(&amp;u.uz) &gt; 11 &amp;&amp; !rn2(6)) mkroom(MORGUE);
        else

   As you can see, here is where is defined when a certain room can be genera-
   ted: i.e. zoo's after level 6 one in 7 times, etc... So adding a line like
   
        if (depth(&amp;u.uz) &gt; 10 &amp;&amp; !rn2(4)) mkroom(CLINIC)

   will generate a clinic quite frecuently over dungeon level 10.

   Next, edit the sounds.c file. Look for dosounds() and after

	#ifdef ARMY
	    if (level.flags.has_barracks &amp;&amp; !rn2(200)) {
		static const char *barracks_msg[4] = {
			"hear blades being honed.",
			"hear loud snoring.",
			"hear dice being thrown.",
			"hear General MacArthur!",
		};
		You(barracks_msg[rn2(3)+hallu]);
		return;
	    }
	#endif /* ARMY */

   add
	#ifdef CLINIC
	    if (level.flags.has_hospital &amp;&amp; !rn2(200)) {
		static const char *hospital_msg[4] = {
			"hear something about streptococus.",
			"smell chloroform nearby.",
			"hear someone cursing viruses.",
			"seem to hear Doctor Frankenstein.",
		};
		You(hospital_msg[rn2(3)+hallu]);
		return;
	    }
	#endif /* CLINIC */

   so we get a funny message randomly when having a clinic in level.

   Last, edit hack.c and see check_special_room(), to add a salute to the
   player entering a clinic:

	        case CLINIC:
                    You("enter a modern hospital.");
                    break;

   Also after
	#ifdef ARMY
                            case BARRACKS:
                                level.flags.has_barracks = 0;
                                break;
	#endif

   add
	#ifdef CLINIC
                            case CLINIC:
                                level.flags.has_clinic = 0;
                                break;
	#endif

   Last of all, edit sp_lev.c and after
	#ifdef ARMY
		    case BARRACKS:
			level.flags.has_barracks = TRUE;
			break;
	#endif
   add
	#ifdef CLINIC
		    case CLINIC:
			level.flags.has_clinic = TRUE;
			break;
	#endif

   inside the fill_room() function.

   Recompile your code. Congratulations. You just added a new room.

10. Creating a new shop type
----------------------------

   Along this chapter we will work to add a 'pet shop' as an example.

   Adding a new shop is similar to adding a new room: we have to start with
   the mkroom.h file. After the
	
		#define BOOKSHOP 20

   line add 
		#define PETSHOP 21

   and increase the numbers for UNIQUESHOP, CANDLESHOP &amp; MAXRTYPE. (of course
   if you already added other rooms in chapter 9 put the correct number
   accordingly).

   Now edit the file shknam.c, where most of the shop code is located. First
   thing you'll note is several 'static const char *shksomething[]' arrays;
   those are the shopkeeper names for each type of shop. So, after the 
   definition of shkgeneral[], add a new array with the names for our petshops:

   static const char *shkpetshop[] = {
	   "Valoo","Tisney","Jakuna",
	   ""
	   };

   Note the array ends with a "" string. Also you should put more than 3 names,
   but for our example is enough.

   Later on the 'const struct shclass shtypes[]' array is defined. It sets
   the shop types, with these fields:

   - Name of the shop (i.e:"general store").
   
   - Letter that identifies this type of shop. (i.e: SCROLL_CLASS). It is
    later used for the SHOPTYPE environment variable in wizard mode.

   -&nbsp;% probability. Note that the total of all types should be 100, so for
   adding a new one you'll have to low the probability of other(s).

   - Object placement type:
		D_SCATTER = normal placement.
		D_SHOP    = shop-like placement.
		D_TEMPLE  = temple-like placement.

   - Objects sold there, prefixed with the probability of each. i.e:
	 {{85, RING_CLASS}, {10, GEM_CLASS}, {5, AMULET_CLASS}, {0, 0}}

      means: rings (85% stock), gems(10%), amulets(5%). Note the NULL pair
      at the end.
      Also if defining a concrete object (instead of a class) a minus sign
      is needed, as in:
	 {{90, WAND_CLASS}, {5, -LEATHER_GLOVES}, {5, -ELVEN_CLOAK}, {0, 0}}

      Note also that the array is defined (in mkroom.h) as 5 elements long,
      so a shop cannot stock more than 5 classes/concrete objects. (You can
      always increase that value as an alternative, of course).

   - Names array -the shksomething array-.

   So, in our case put something like:

   {"pet shop", VENOM_CLASS, 5, D_SHOP,
	{{70, -FIGURINE},{20,-TRIPE_RATION},{10,-LEASH}}, shkpetshop}

   meaning: create FIGURINES 70% of the time, 20% tripe rations &amp; 10% leash.
   Also this shop will be created if setting SHOPTYPE="." or 5% of the time
   a shop is created. The probability of the general store should be changed
   from 44 to 39.

   And that's all. Easy, isn't it?.

   Just recompile the code and check it out setting:

   export SHOPTYPE=.   (or set SHOPTYPE=. depending in your OS, or unix SHELL).
   nethack -u wizard -D

11. Goodbye
-----------

   Hundreds of other things can be added to the game, but this is the end;
   from here you're on your own. I hope you found this reading useful. Just 
   some last recommendations:

      1. Put lots of comments in your code. From experience, in a week or two
        you'll forget why something was that way or the other.

      2. Interchange information about new ideas in rec.games.roguelike.nethack
        newsgroup. They can help you to refine your ideas or coming up with
        new ones.

      3. Send your modifications to the dev team (at the mail address 
        nethack-bugs@linc.cis.upenn.edu). You can possible win inmortality.

      4. Play nethack a lot.

   Good luck and happy hacking!!

		-------------------------------------
		Apendix A. REFERENCE FUNCTION LISTING
		-------------------------------------

   For your convenience here go some interesting functions: 

Monster naming functions
------------------------
		They all take a pointer to a monst structure as parameter and 
		return a string:

char *mon_nam(struct monst *)
                the rust monster  it  the invisible orc  Fido
char *l_monnam(struct monst *)
		rust monster    it  invisible orc      dog called fido
char *Monnam(struct monst *)
		The rust monster    It  The invisible orc  Fido
char *Adjmonnam(struct monst *)
		The poor rust monster  It  The poor invisible orc The poor Fido
char *Amonnam(struct monst *)
		A rust monster      It  An invisible orc   Fido
char *a_monnam(struct monst *)
		a rust monster      it  an invisible orc   Fido

Object naming functions
-----------------------

char *xname(struct obj *)
		"poisoned arrow"
char *doname(struct obj *)
		"poisoned +0 arrow"
char *an(struct obj *)
		"a poisoned arrow"
char *An(struct obj *)
		"A poisoned arrow"
char *The(struct obj *)
		"The poisoned arrow"
char *the(struct obj *)
		"the poisoned arrow"
char *makeplural(char *) 
		Takes a string an pluralizes it. It is quite smart, 
		so the "homunculus" plural becomes "humunculi", etc...
char *makesingular(char *) 
		Just the opposite.

Display functions
-----------------
		(Please refer to the doc/window.doc file for more information).

pline(char *, ...)
		Takes the same arguments as the standard printf() function,
		and displays the result in the screen. It is massively used
		throughout the code.
You(char *, ...)
		A shorter way to display the "You do something" messages.
		pline("You sit") is equivalent to You("sit").
Your(char *, ...)
		A shorter way to display the "Your something" messages.
		pline("Your hands glow") is equivalent to Your("hands glow").
verbalize(char *, ...)
		It also behaves as printf(), but displays the resulting string
		between "". It is used for sounds made by other monsters.
impossible(char *, ...)
		Display an error message with the "impossible:" before it.

Several object related functions
--------------------------------

struct obj *readobjnam(char *)
		It creates an object from a string. Mainly used in the
		wishing routines.
int weight(obj)
		Returns the weight of an object. (not obvious: it can be
		a container).
void docall(struct obj *)
		Ask the player to call an object.
makeknown(obj-&gt;otyp)
		It's not a real function, just a macro. Marks an object type
		as identified.
void curse(struct obj *)
		Curses an object.
void uncurse(struct obj *)
		Uncurses an object.
void bless(struct obj *)
		Blesses an object.
void unbless(struct obj *)
		Unblesses an object.
void move_object(struct obj *,int,int)
		Move object to x,y position.
void remove_object(struct obj *)
		Remove object.
void place_object(struct obj *,int,int)
		Put object in x,y position.
int bhito(struct obj *, struct obj *)
		Object was hit by the effect of wand indicated in second 
		parameter.
void cancel_item(struct obj *)
		Object has been hit by cancellation ray.

Several monster related functions
---------------------------------
struct monst *newmonst(struct permonst *)
		Allocs a new 'monst' struct. It doesn't add it to the chained
		list of monsters. Tipically the process will be:
			mtmp = newmonst(ptr-&gt;pxlth);
			*mtmp = zeromonst; /* clear all entries in structure */
			mtmp-&gt;nmon = fmon;
			fmon = mtmp;
		Shouldn't be used directly. Better use makemon().
struct monst *makemon(struct permonst, int, int)
		Creates a new monster in the position determined by the two
		other parameters (x,y). It returns the newly created monst
		struct if success, NULL otherwise.
		The first parameter can be null; in that case a random monster
		will be created.
		The (x,y) position can also be 0 to indicate a random location.
void relmon(struct monst *mon)
		Release monster from display and monster list.
boolean mnearto(struct monst *,xchar, xchar, boolean)
		Put monster near (or at) location if possible. The boolean
		parameter is for forcing another one to move. Returns 
		1 - if a monster was moved from x, y to put mtmp at x, y
		0 - in most cases.
struct permonst *grow_up(struct monst *, struct monst *)
		Monster grows up to a bigger version. The last monst struct
		parameter is the victim, if any. If there is none it implies
		a gain level potion.
void mongone(struct monst *)
		Monster dissapears. The struct is released.
void setmangry(struct monst *)
		Monster gets angry. If already was it, does nothing.
boolean angry_guards(register boolean)
		Function used to angry guards in town. The parameter just indi-
		cate to display messages if true. Returns TRUE if any guard
		was there.
void pacify_guards()
		The name says it all.
void wake_up(struct monst *)
		Wake up -and angry- a monster.
void wake_nearby()
		Wake up nearby monsters.
void mon_to_stone(struct monst *)
		Changes the monster into a stone monster of the same type.
boolean monnear(struct monst *, x, y)
		Is the square close enough for the monster to move or 
		attack into?
int minwater(struct monst *)
		Check monster and water for compatibility, 0 (survived), 
		1 (drowned)
int rndmonnum()
		Select a random, common monster type.
Sounds functions
----------------

void dosounds()
		Make a sound, depending of what is in current level (shop,
		thrones, etc...)
void growl(struct monst *)
		Monster is happy.
void yelp(struct monst *)
		Monster is not so happy.
void whimper(struct monst *)
		Monster is about to die.
void beg(struct monst *)
		Monster begs for food.
int domonnoise(struct monst *)
		Do whatever sound a monster does.
int dotalk()
		The #chat command.

		
Monsters&lt;-&gt;objects functions
----------------------------

int mongets(struct monst *, int)
		It creates an object and gives it to a monster. The int is
		the identifier of the object as defined in onames.h (created
		by makedefs). i.e. BLUE_DRAGON_SCALE_MAIL
void m_useup(struct monst *, struct obj *)
		An object is consumed by a monster. The obj struct is freed.
void mpickobj(struct monst *, struct obj *)
		An object is picked by a monster.
void mpickgems(struct monst *)
		A monster picks up the gems under him.
void mpickgold(struct monst *)
		A monster picks up the gold under him.
void mpickstuff(struct monst *)
		A monster picks up things under him. What it takes it depend
		on the M-FLAGS defined for this type of monster.
void meatobj(struct monst *)
		Monster eats whatever in his position. Used for gelatinous
		cubes.
void meatgold(struct monst *)
		A expensive meal&nbsp;:-)
boolean can_carry(struct monst *, struct obj *)
		Returns TRUE if the monster can carry that object
struct obj *make_corpse(struct monst *)
		Creates a monster corpse, a "special" corpse, or nothing 
		if it doesn't leave corpses.

Shop related functions
----------------------

struct monst *shop_keeper(char rmno)
		Returns the shopkeeper given the room number. Example of usage:
			struct monst *shkp;
			shkp=shop_keeper(*in_rooms(u.ux,u.uy,SHOPBASE));
int inhishop(struct monst *)
		Returns true if shopkeeper is in his shop.
void mkshobj_at(const struct shclass *,int,int)
		Make an object of the appropriate type in a shop square.
int shkinit(const struct shclass *,struct mkroom *sroom)
		Create a new shopkeeper in the given room.
boolean saleable(int,struct obj *)
		Returns TRUE if the shop -indicated by the index - stocks that
		type of objects.

Other interesting functions
---------------------------

int rn2(int x)
		Returns a random number between 0 &amp; x.
		( 0 &lt;= rn2(x) &lt; x )
int rnl(int x)
		Returns a random number between 0 &amp; x, just as rn2(), but
		this time the player's luck affects the result: good luck
		approaches 0, bad luck approaches x-1.
char *getrumor(int)
		Returns a "rumor" string. if int = 1 rumor is always true,
		-1 means false and 0 is random.
void exercise(int, boolean)
		Exercise an attribute (A_INT,A_CHA,A_WIS,A_STR,A_DEX). If
		TRUE increases, FALSE decreases.
find_misc() 
use_misc()
		Both functions are used in muse.c to detect an object/action
		that a monster can do and execute it.
void mkroom(int)
		Make and stock a room of a given type.
boolean has_dnstairs(struct mkroom *)
		Returns true if room has downstairs.
boolean has_upstairs(struct mkroom *)
		Returns true if room has upstairs.
schar depth(d_level)
		Returns the depth of a level, in floors below the surface.
		(note levels in different dungeons can have the same depth).
doengrave()
		User engraves.
int bhitm(struct monst *, struct obj *)
		Monster was hit by the effect of wand or spell indicated
		in second parameter.
int zapyourself(struct obj *)
		The name says it all: player zapped himself with wand or spell.
void zapnodir(struct obj *)
		Zapping a non-directional wand.
int breaks(struct obj *, boolean)
		Object breaks. The boolean flag indicates if object is or not
		in the fobj chain.
int peffects(struct obj *)
		Function for potion quaffing effects.
void potionhit(struct monst *, struct obj *)
		Potion hits monster.
void potionbreathe(struct obj *)
		Vapors effects.
void dosinkring(struct obj *)
		Ring is dropped in a sink.
void eatring(struct obj *)
		Polymorphed player eats a ring.
void Ring_on(struct obj *)
		Ring effects when on.
void Ring_off_or_gone(struct obj *,boolean)
		Ring is removed. The boolean flag indicates if gone (stolen).
void Amulet_on()
void Amulet_off()
		Similar idea, but for amulets.
void fprefx(struct obj *)
		Called at first bite on food.
void fpostfx(struct obj *)
		Called after last bite on food.
int study_book(struct obj *)
		Study a spellbook.
int spelleffects(struct obj *, boolean)
		Cast a spell. boolean flag indicates if at player himself.

This page is based on a spoiler by German Martin, available at http://web.archive.org/web/20160802031704/http://members.shaw.ca/rob.ellwood/sources.txt

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