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Architecture

The structure of the ZORKERB I ERB implementation. File names refer to ZORKERB-I/ERB/.

Overview

The game is entered through Emuera's system functions: @SYSTEM_TITLE, @EVENTFIRST, @SHOW_SHOP and @EVENTLOAD. One move of the original MAIN-LOOP is handled by Z_READ_TURN, which @SHOW_SHOP calls.

@SYSTEM_TITLE (02_Flow)     title screen; new game, restore, quit; reinitialisation after RESTART
  └ @SHOW_SHOP (02_Flow)    input for each move; performs SAVE, RESTORE, RESTART and QUIT
      └ Z_READ_TURN (42_CommandStream)
          ├ reads input, splits sentences, handles quotations and orders to characters
          ├ parser (37–43, 49)
          ├ Z_PERFORM (50_Actions)     calls the ACTIONs in the original PERFORM order
          └ clock (90_Clock)          interrupts at the end of the move
@EVENTLOAD (02_Flow)         checks the save format and the restored state

State and saves

• Game state lives in the variables declared in 01_State.ERH. That covers object locations, flags, timers, random state and the parser's pending state.
• Only variables marked SAVEDATA are saved. Saving and loading use Emuera's SAVEDATA, CHKDATA and LOADDATA.
• @EVENTLOAD checks the save format (Z_SCHEMA) and the restored values. It abandons a load that fails these checks and returns to the title screen.

World definition

Rooms and objects (110 rooms, 141 objects) are in two files generated from the development definitions:

• 00_Ids.ERH (room and object numbers);
• 10_World.ERB (initial placement and attributes).

21_ObjectTree.ERB maintains the object tree with the same ordering rules as the Z-machine's INSERT_OBJ and REMOVE_OBJ.

Parser

File	Role
42_CommandStream.ERB	Reading the input line (120 characters), sentence breaks (period, THEN), quotations, orders, AGAIN, OOPS
37_SourceParser.ERB	gparser.zil word scan, CLAUSE, SYNTAX-CHECK
38_ParserTables.ERB	Dictionary (684 words) and syntax table (267 lines) read from the original story; generated file
39_Dictionary.ERB	V3 dictionary matching (first six letters)
40_Parser.ERB, 41_Grammar.ERB	Object resolution, verbs and prepositions
43_SyntaxChecks.ERB	TAKE-CHECK, ITAKE-CHECK and other syntax flags
49_Inference.ERB	GWIM (guessing objects) and narrowing candidates
44_Speech.ERB	SAY, TELL and orders to characters
58_PseudoObjects.ERB	GLOBAL-CHECK and pseudo-objects

Actions

Z_PERFORM in 50_Actions.ERB follows the original PERFORM order:

1. objects that are not here;
2. the actor (WINNER);
3. the room's M-BEG;
4. the pre-action (PRE-);
5. the indirect object's ACTION;
6. the direct object's ACTION;
7. the verb's default routine.

Files	Role
46_ObjectOverrides, 53_SceneryActions, 54_GlobalActions	Object ACTIONs
45_MiscActions, 48_SimpleVerbs, 52_SelfActions, 55_GenericActions, 57_AdditionalActions, 59_SourceVerbs	Default verb routines (gverbs.zil)
47_Water	Water and containers
56_Leap	Jumping and falling
60_Puzzles, 72_Maze, 80_Dam–85_EggEnd, 91_Forest	Regional puzzles: house, maze, dam, temple, river, mine, egg and ending, forest
70_Combat–74_ThiefText, 86_Thief	Combat and the thief
87_Death	Death, scattering of possessions, actions while dead (DEAD-FUNCTION)
90_Clock	gclock.zil interrupt table and end of move
30_Display, 31_OracleResponses	Room and object descriptions, inventory listings, shared responses

Random numbers

03_Random.ERB implements ZIL's RANDOM as the Z-machine does.

• Normally: values come from the engine's random generator.
• After #random N (1–999): the Z-machine standard's predictable sequential mode is used.

Draws happen at the same points and in the same order as in the original, so the sequential mode yields the original's random sequence.

Generation and run time

Stage	What is used
Generation	00_Ids.ERH, 10_World.ERB and 38_ParserTables.ERB were generated from definition data by Python tools in the development environment. All other ERB and ERH files are hand-written source.
Run time	ERB, ERH and CSV only. No Python code, story file or Z-machine interpreter.