Tachikoma
f7e8d4b82b
Adds generator support per the plan in issue 57: - environment.h: isGenerator/generatorFn on a GEN call's own environment, isEachLoop and forGeneratorEnv on a FOR EACH/DO EACH loop's own environment. - runtime.c: splits akbasic_runtime_prev_environment() into akbasic_runtime_detach_environment() (return to parent without releasing) and akbasic_runtime_release_environment() (give variables and the pool slot back, on any environment); prev_environment() is now the two in sequence. akbasic_runtime_call_function() refuses to call a GEN like an ordinary function. - verbs.c/verbs.h/scanner: new keywords GEN, EMIT, EACH, IN and the compound verb "END GEN" (built by a new akbasic_parse_end(), the same trick akbasic_parse_print() uses for PRINT #). - parser_commands.c: akbasic_parse_gen() (modelled on multi-line DEF), akbasic_parse_end(), and EACH branches in akbasic_parse_for()/ akbasic_parse_do(). - runtime_generator.c (new): akbasic_cmd_gen, akbasic_cmd_emit, akbasic_cmd_end_gen, and the invoke/pump/release machinery FOR EACH, DO EACH, NEXT and LOOP share. EMIT walks up to the nearest isGenerator ancestor rather than assuming it is standing directly in the GEN's own call frame, because a GEN body may nest its own FOR/DO/GOSUB around an EMIT -- the issue's own ROOMOBJECTS example does exactly that. - runtime_commands.c/runtime_structure.c: EACH branches in cmd_for/cmd_do, matching EACH branches in cmd_next/cmd_loop, and forGeneratorEnv release on every path that can abandon a live generator (EXIT, a NEXT that pops for a mismatched loop variable). Deviates from the plan in one place: FunctionDef gained an isGenerator flag (not in the plan's field list) because refusing a GEN called like a function has to happen before anything is pushed. Relying on EMIT's own isGenerator check for that case doesn't work: akbasic_runtime_call_function() drives its own step loop the same way akbasic_runtime_pump_generator() does, and a BASIC-level error inside that loop is swallowed by process_line_run() as reported-but-not-propagated, so the call would silently "succeed" with a meaningless return value instead of failing. Also: a zero-argument parameter list is not supported by the DEF/GEN parameter parser this reuses (a pre-existing limitation, not generator-specific); every generator in the tests takes at least one parameter as a result. Tests: tests/generators.c (pool exhaustion under repeated EXIT, calling a GEN like a function, EMIT outside a GEN, self-recursion, sibling/nested invocations) and tests/language/flowcontrol/generators_*.bas -- the issue's own ROOMOBJECTS example in both loop shapes, an empty generator, non-numeric EMIT, nested/interleaved invocations, and three error-path golden cases. Docs: control-flow chapter 4 gets a GEN/EMIT/FOR EACH/DO EACH section, the verb reference gets GEN/EMIT/END GEN entries and updated FOR/DO/NEXT/LOOP/EXIT rows, and architecture chapter 14 documents the detach/release split and the two-environment generator invocation. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
The akbasic guide
akbasic is a BASIC interpreter in the style of Commodore BASIC 7.0 — the dialect the C128 shipped with — and Dartmouth BASIC. It runs programs from a file or from an interactive prompt, and it is also a C library you can link into a game so that players can script it.
These chapters follow the shape of the C128 Programmer's Reference Guide: the language first, then each hardware area, then the reference sections. If you know BASIC 7.0 you can skip to Chapter 13, which is the list of everything that behaves differently here and why. Chapter 14 is the odd one out: it is about the interpreter rather than the language, for anyone embedding it, debugging it or changing it.
Chapters 17 and 18 are tutorials rather than reference: they build one complete game twice, two different ways, in numbered steps you can type in one at a time. Start with 17 — it needs nothing but the earlier chapters, and 18 assumes it. Chapters 20 and 21 are the third tutorial, from the other side of the boundary: a C game on libakgl that embeds the interpreter as its enemy-behavior engine, for anyone whose question is "how do I put this in my game".
Chapters
| 1. Introduction | What akbasic is, what it is not, and how to build it |
| 2. Getting started | The prompt, your first program, saving and loading |
| 3. The language | Variables, types, arrays, operators, expressions |
| 4. Control flow | IF, FOR, DO, GOSUB, labels, ON, error trapping |
| 5. Strings and formatting | String functions, PRINT USING, PUDEF |
| 6. Graphics | GRAPHIC, DRAW, BOX, CIRCLE, PAINT, shapes |
| 7. Sound | SOUND, PLAY, ENVELOPE, VOL, TEMPO |
| 8. Sprites | SPRITE, SPRSAV, MOVSPR, collision |
| 9. Files and disk | Channels, DOPEN, program storage |
| 10. Embedding | Driving the interpreter from C |
| 11. Verb reference | Every statement, alphabetically |
| 12. Function reference | Every function, alphabetically |
| 13. Differences from BASIC 7.0 | What a C128 programmer needs to know |
| 14. Architecture | How the interpreter is put together, how to debug it, how to change it |
| 15. Error codes | Appendix: every value ER# can hold and every error line the interpreter prints |
| 16. Structures | TYPE, records, strict pointers, and sharing a C struct with an embedding host |
| 17. Tutorial: Breakout | Build a whole game out of the text grid and two DATA sprites, in sixteen steps |
| 18. Tutorial: Breakout with artwork | Build it again out of loaded artwork, powerups and a drawn colour HUD, in thirteen |
| 19. Menus and dialogs | MENU, DIALOG, HUD and UISTYLE — the widgets, and who owns the keyboard |
| 20. Tutorial: GALAGA | Build a C engine on libakgl that embeds the interpreter, boots a script and hands it an actor |
| 21. Tutorial: GALAGA enemies | Share three C structs with the script, then write the wave's whole brain in BASIC |
The shortest possible start
$ cmake -S . -B build && cmake --build build
$ ./build/basic
10 FOR I# = 1 TO 5
20 PRINT "HELLO " + I#
30 NEXT I#
RUN
HELLO 1
HELLO 2
HELLO 3
HELLO 4
HELLO 5
READY
Two things in that program are not Commodore BASIC and will catch you out
immediately: variables carry a type suffix (I# is an integer) and +
concatenates a string with a number. Chapter 3 explains both.
Every example in these chapters is executed by the test suite and its output
compared byte for byte — see MAINTENANCE.md if you are editing them.