Andrew Kesterson
a01554d304
Chapter 18 still taught the machinery the listing lost when it moved onto SOLID and the persistent drawing layer: the frame-boundary PACE routine, the flattened live list, the SSHAPE pool accounting, and the sixty lines of BALLBRICKS/TESTCELL that computed a minimum translation axis by hand. Step 8 now registers each brick with SOLID, arms COLLISION 2 and reads the contact back with RCOLLISION, including the point that costs an evening if it is missed: the BUMP mask is by sprite, and the balls are sprites 5, 6 and 7, so their bits are 16, 32 and 64. The FOR-with-equal-bounds rule that every one-item case in the chapter depends on is now stated where it is first used rather than referred to from a step that no longer exists. The listing loses six declarations orphaned by the conversion and the comment blocks that still described the captures. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01EwxGB6TdoVvZ11KQQME9cL
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
| 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 |
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.