2026-07-31 21:50:50 -04:00
|
|
|
# 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](http://www.jbrain.com/pub/cbm/manuals/128/C128PRG.pdf):
|
|
|
|
|
the language first, then each hardware area, then the reference sections. If you know
|
|
|
|
|
BASIC 7.0 you can skip to **[Chapter 13](13-differences.md)**, which is the list of
|
Document the interpreter's architecture as chapter fourteen
Chapters 1 through 13 describe the language. Nothing described the machine
that runs it, and the answers were spread across header comments, TODO.md
sections written for a different purpose, and the source itself. Somebody
embedding the interpreter, debugging something it did, or adding a verb had
to reconstruct the shape from all three.
docs/14-architecture.md is that shape, and only that: the three targets and
the driver, the single akbasic_Runtime and why nothing is file-scope,
akbasic_runtime_step() unrolled with the reason each stage sits where it
does, the four modes and what set_mode() does beyond assigning, a line's
journey from text through tokens and leaves to a verb handler, the dispatch
table, the pool map with what each exhaustion actually says, environments
doubling as block state, the two kinds of error, devices, and interrupts.
It defers rather than restates. The headers are the authority on every
function's contract and the chapter says so up front; where a rule is subtle
the header comment already states it at more length than a chapter should.
MAINTENANCE.md keeps the conventions and now points here for the mechanism,
so there is still one copy of each.
Two sections are the reason it exists at all. Debugging: reading a TRON trace
as evidence about the loop rather than the lines, reading an akerror stack
trace and what it is not, four breakpoints and the expressions worth printing
at them, narrowing with ctest -R and the mock devices, and a symptom-to-cause
table. Changing it: the verb recipe end to end including the private
src/verbs.h prototype that is easy to miss, the rule that a missing
dependency capability gets filed upstream rather than worked around, and the
five constraints goal 3 puts on any change.
A `text` fence tag comes with it. Every fenced block in docs/ is executed and
an untagged one is a hard error, so six block diagrams had nowhere to live.
The tag means never executed, it is counted in the skip line like `cmake`,
and MAINTENANCE.md documents it -- the alternative was an indented block the
extractor never sees, and a picture nobody decided about is indistinguishable
from a test nobody ran.
tests/docs_examples.sh now makes --root and --basic absolute before it
starts. Both are used from inside a sandbox directory it cd's into, so the
invocation MAINTENANCE.md itself documents -- --root . --basic ./build/basic
-- failed every example with "exited 127" and every setup= with "setup
failed". CTest passes absolute paths and never saw it; running one document
by hand hits it immediately.
Writing the error section turned up a defect and TODO.md section 8 records
it. The ATTEMPT blocks that turn a script's mistake into an error line wrap
parsing and interpretation but not scanning, so a line with more than 32
tokens escapes as an interpreter error: stack trace, exit 1, and at a prompt
the REPL is gone. That is the same shape as section 8 item 2, on a path that
fix did not cover. Not fixed here -- it is a behaviour change and wants its
own tests -- but written down with the three call sites and what would cover
them.
Both configurations stay green: 95/95 and 94/94. docs_examples now runs 37
programs, 9 transcripts, 45 output comparisons, 3 C snippets, 2 excerpts and
2 shell blocks, and skips 9 text blocks.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-07-31 23:14:17 -04:00
|
|
|
everything that behaves differently here and why. **[Chapter 14](14-architecture.md)** is
|
|
|
|
|
the odd one out: it is about the interpreter rather than the language, for anyone
|
|
|
|
|
embedding it, debugging it or changing it.
|
2026-07-31 21:50:50 -04:00
|
|
|
|
|
|
|
|
## Chapters
|
|
|
|
|
|
|
|
|
|
| | |
|
|
|
|
|
|---|---|
|
|
|
|
|
| **[1. Introduction](01-introduction.md)** | What akbasic is, what it is not, and how to build it |
|
|
|
|
|
| **[2. Getting started](02-getting-started.md)** | The prompt, your first program, saving and loading |
|
|
|
|
|
| **[3. The language](03-the-language.md)** | Variables, types, arrays, operators, expressions |
|
|
|
|
|
| **[4. Control flow](04-control-flow.md)** | `IF`, `FOR`, `DO`, `GOSUB`, labels, `ON`, error trapping |
|
|
|
|
|
| **[5. Strings and formatting](05-strings-and-formatting.md)** | String functions, `PRINT USING`, `PUDEF` |
|
|
|
|
|
| **[6. Graphics](06-graphics.md)** | `GRAPHIC`, `DRAW`, `BOX`, `CIRCLE`, `PAINT`, shapes |
|
|
|
|
|
| **[7. Sound](07-sound.md)** | `SOUND`, `PLAY`, `ENVELOPE`, `VOL`, `TEMPO` |
|
|
|
|
|
| **[8. Sprites](08-sprites.md)** | `SPRITE`, `SPRSAV`, `MOVSPR`, collision |
|
|
|
|
|
| **[9. Files and disk](09-files-and-disk.md)** | Channels, `DOPEN`, program storage |
|
|
|
|
|
| **[10. Embedding](10-embedding.md)** | Driving the interpreter from C |
|
|
|
|
|
| **[11. Verb reference](11-verb-reference.md)** | Every statement, alphabetically |
|
|
|
|
|
| **[12. Function reference](12-function-reference.md)** | Every function, alphabetically |
|
|
|
|
|
| **[13. Differences from BASIC 7.0](13-differences.md)** | What a C128 programmer needs to know |
|
Document the interpreter's architecture as chapter fourteen
Chapters 1 through 13 describe the language. Nothing described the machine
that runs it, and the answers were spread across header comments, TODO.md
sections written for a different purpose, and the source itself. Somebody
embedding the interpreter, debugging something it did, or adding a verb had
to reconstruct the shape from all three.
docs/14-architecture.md is that shape, and only that: the three targets and
the driver, the single akbasic_Runtime and why nothing is file-scope,
akbasic_runtime_step() unrolled with the reason each stage sits where it
does, the four modes and what set_mode() does beyond assigning, a line's
journey from text through tokens and leaves to a verb handler, the dispatch
table, the pool map with what each exhaustion actually says, environments
doubling as block state, the two kinds of error, devices, and interrupts.
It defers rather than restates. The headers are the authority on every
function's contract and the chapter says so up front; where a rule is subtle
the header comment already states it at more length than a chapter should.
MAINTENANCE.md keeps the conventions and now points here for the mechanism,
so there is still one copy of each.
Two sections are the reason it exists at all. Debugging: reading a TRON trace
as evidence about the loop rather than the lines, reading an akerror stack
trace and what it is not, four breakpoints and the expressions worth printing
at them, narrowing with ctest -R and the mock devices, and a symptom-to-cause
table. Changing it: the verb recipe end to end including the private
src/verbs.h prototype that is easy to miss, the rule that a missing
dependency capability gets filed upstream rather than worked around, and the
five constraints goal 3 puts on any change.
A `text` fence tag comes with it. Every fenced block in docs/ is executed and
an untagged one is a hard error, so six block diagrams had nowhere to live.
The tag means never executed, it is counted in the skip line like `cmake`,
and MAINTENANCE.md documents it -- the alternative was an indented block the
extractor never sees, and a picture nobody decided about is indistinguishable
from a test nobody ran.
tests/docs_examples.sh now makes --root and --basic absolute before it
starts. Both are used from inside a sandbox directory it cd's into, so the
invocation MAINTENANCE.md itself documents -- --root . --basic ./build/basic
-- failed every example with "exited 127" and every setup= with "setup
failed". CTest passes absolute paths and never saw it; running one document
by hand hits it immediately.
Writing the error section turned up a defect and TODO.md section 8 records
it. The ATTEMPT blocks that turn a script's mistake into an error line wrap
parsing and interpretation but not scanning, so a line with more than 32
tokens escapes as an interpreter error: stack trace, exit 1, and at a prompt
the REPL is gone. That is the same shape as section 8 item 2, on a path that
fix did not cover. Not fixed here -- it is a behaviour change and wants its
own tests -- but written down with the three call sites and what would cover
them.
Both configurations stay green: 95/95 and 94/94. docs_examples now runs 37
programs, 9 transcripts, 45 output comparisons, 3 C snippets, 2 excerpts and
2 shell blocks, and skips 9 text blocks.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-07-31 23:14:17 -04:00
|
|
|
| **[14. Architecture](14-architecture.md)** | How the interpreter is put together, how to debug it, how to change it |
|
Document every error code a script can see, as chapter 15
ER# held numbers nothing explained. The appendix lists the four error classes
the interpreter prints, the eight codes it owns and what raises each, and the
codes that reach ER# from errno, libakerror and libakgl underneath it.
The table is not asserted. A program in the chapter trips seven of the eight and
prints what it got, and docs_examples byte-compares the result -- so the numbers
are checked rather than claimed. The eighth, 516, is not usefully trappable and
the chapter says why: entering a handler takes a scope, and the pool being empty
is what raised it.
Two things worth a reader's attention came out of writing it. Two codes register
the same ERR() text, so a program must compare the number and print the text.
And VAL reports libakerror's Value Error rather than the interpreter's 517,
which makes that number the platform's rather than ours -- filed as section 6
item 21, not fixed here, because deciding which libakstdlib failures to
translate is a boundary question and ENOENT out of DOPEN is the counter-case.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-01 07:36:36 -04:00
|
|
|
| **[15. Error codes](15-error-codes.md)** | Appendix: every value `ER#` can hold and every error line the interpreter prints |
|
Document structures: a chapter, the architecture, and the differences
docs/16-structures.md is the feature: records, nesting, copy-on-assign, strict
pointers, lists, what is checked and what is not, and how a host shares its own
C structs. Every example in it is executed by docs_examples and byte-compared,
including the refusals -- so a message that changes fails the suite rather than
quietly making the chapter wrong.
The chapter makes one contrast explicitly, because it is the question a reader
will actually have: a misspelled *field* is refused and a misspelled *variable*
still prints zero. The rule underneath is that what the program declared gets
checked and what it did not gets shrugged at -- a variable's name is never
declared, a TYPE's field list is. Structures end up the strictest thing in the
language, not from a higher standard but because they are the only named thing
whose valid spellings are written down.
Chapter 14 gains the layout: an instance is a contiguous run of value slots with
a diagram of where the fields sit, the three-pass prescan and why each pass
exists, why the copy cannot live in akbasic_value_clone(), and why the render
depth bound is four rather than eight. Chapter 3 gains the @ suffix, chapter 13
records that all of this is an addition BASIC 7.0 has nothing like, and the verb
reference gains TYPE, POINT and DIM ... AS.
MAINTENANCE.md gains the two rules that are on a maintainer rather than on a
test: a structure copy must not go through clone, and a field chain gets its own
leaf field. TODO.md section 5 records what was invented and the three limits
that are ours, and section 8 records the two defects the work exposed.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-01 12:03:02 -04:00
|
|
|
| **[16. Structures](16-structures.md)** | `TYPE`, records, strict pointers, and sharing a C struct with an embedding host |
|
2026-07-31 21:50:50 -04:00
|
|
|
|
|
|
|
|
## The shortest possible start
|
|
|
|
|
|
Execute every documented example as a test
docs/ and README.md carry 85 fenced blocks. Every one was checked by hand
exactly once, when it was written, which is not a standard that survives a
changing interpreter -- and four were already wrong: two transcripts showing a
leading space PRINT does not emit, akbasic_TextSink in README.md missing the
two members it had grown hours earlier, and FILTER's refusal quoted with
wording the code does not use.
tests/docs_examples.sh reads a fence-tag vocabulary and runs what it finds.
BASIC programs and transcripts run and are byte-compared against an `output`
block; C snippets compile with -fsyntax-only against the real include path,
which CMake writes out because it is transitive through akerror, akstdlib and
akgl; shell blocks run in a sandbox. Anything that would reconfigure the build
tree, hit the network or re-enter the suite is tagged norun with the reason in
MAINTENANCE.md, and the two cmake blocks stay hand-maintained by decision.
An untagged block is a failure rather than a default, and the pass line
reports what it executed by kind. Both exist because the way a harness like
this dies is by quietly matching nothing and passing -- which it duly did on
the first CTest run, where a generator expression evaluating to nothing still
contributed an empty argument that the script read as a filename. The count is
what caught it.
The excerpt check earns its own mention: a block tagged
`c excerpt=include/akbasic/sink.h` must still appear in that header, comments
and whitespace ignored. Compiling it would only redefine the type, so a
compile check could not have found the stale struct, and did not.
Registered as the CTest case docs_examples in both configurations. Fixing the
four wrong examples turned up two interpreter defects, fixed in the previous
commit and recorded in TODO.md section 8.
MAINTENANCE.md is new: the fence-tag reference, what to do when the case
fails, and the conventions that until now only existed inside source comments
-- the three test lists and how two of them invert "passed", the sorted verb
table, that a golden file is never edited to suit this interpreter, and that a
fix gets mutation-checked with a file copy rather than git checkout.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-07-31 22:41:36 -04:00
|
|
|
```sh norun
|
2026-07-31 21:50:50 -04:00
|
|
|
$ cmake -S . -B build && cmake --build build
|
|
|
|
|
$ ./build/basic
|
Execute every documented example as a test
docs/ and README.md carry 85 fenced blocks. Every one was checked by hand
exactly once, when it was written, which is not a standard that survives a
changing interpreter -- and four were already wrong: two transcripts showing a
leading space PRINT does not emit, akbasic_TextSink in README.md missing the
two members it had grown hours earlier, and FILTER's refusal quoted with
wording the code does not use.
tests/docs_examples.sh reads a fence-tag vocabulary and runs what it finds.
BASIC programs and transcripts run and are byte-compared against an `output`
block; C snippets compile with -fsyntax-only against the real include path,
which CMake writes out because it is transitive through akerror, akstdlib and
akgl; shell blocks run in a sandbox. Anything that would reconfigure the build
tree, hit the network or re-enter the suite is tagged norun with the reason in
MAINTENANCE.md, and the two cmake blocks stay hand-maintained by decision.
An untagged block is a failure rather than a default, and the pass line
reports what it executed by kind. Both exist because the way a harness like
this dies is by quietly matching nothing and passing -- which it duly did on
the first CTest run, where a generator expression evaluating to nothing still
contributed an empty argument that the script read as a filename. The count is
what caught it.
The excerpt check earns its own mention: a block tagged
`c excerpt=include/akbasic/sink.h` must still appear in that header, comments
and whitespace ignored. Compiling it would only redefine the type, so a
compile check could not have found the stale struct, and did not.
Registered as the CTest case docs_examples in both configurations. Fixing the
four wrong examples turned up two interpreter defects, fixed in the previous
commit and recorded in TODO.md section 8.
MAINTENANCE.md is new: the fence-tag reference, what to do when the case
fails, and the conventions that until now only existed inside source comments
-- the three test lists and how two of them invert "passed", the sorted verb
table, that a golden file is never edited to suit this interpreter, and that a
fix gets mutation-checked with a file copy rather than git checkout.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-07-31 22:41:36 -04:00
|
|
|
```
|
|
|
|
|
|
|
|
|
|
```basic repl
|
2026-07-31 21:50:50 -04:00
|
|
|
10 FOR I# = 1 TO 5
|
|
|
|
|
20 PRINT "HELLO " + I#
|
|
|
|
|
30 NEXT I#
|
|
|
|
|
RUN
|
|
|
|
|
```
|
|
|
|
|
|
Execute every documented example as a test
docs/ and README.md carry 85 fenced blocks. Every one was checked by hand
exactly once, when it was written, which is not a standard that survives a
changing interpreter -- and four were already wrong: two transcripts showing a
leading space PRINT does not emit, akbasic_TextSink in README.md missing the
two members it had grown hours earlier, and FILTER's refusal quoted with
wording the code does not use.
tests/docs_examples.sh reads a fence-tag vocabulary and runs what it finds.
BASIC programs and transcripts run and are byte-compared against an `output`
block; C snippets compile with -fsyntax-only against the real include path,
which CMake writes out because it is transitive through akerror, akstdlib and
akgl; shell blocks run in a sandbox. Anything that would reconfigure the build
tree, hit the network or re-enter the suite is tagged norun with the reason in
MAINTENANCE.md, and the two cmake blocks stay hand-maintained by decision.
An untagged block is a failure rather than a default, and the pass line
reports what it executed by kind. Both exist because the way a harness like
this dies is by quietly matching nothing and passing -- which it duly did on
the first CTest run, where a generator expression evaluating to nothing still
contributed an empty argument that the script read as a filename. The count is
what caught it.
The excerpt check earns its own mention: a block tagged
`c excerpt=include/akbasic/sink.h` must still appear in that header, comments
and whitespace ignored. Compiling it would only redefine the type, so a
compile check could not have found the stale struct, and did not.
Registered as the CTest case docs_examples in both configurations. Fixing the
four wrong examples turned up two interpreter defects, fixed in the previous
commit and recorded in TODO.md section 8.
MAINTENANCE.md is new: the fence-tag reference, what to do when the case
fails, and the conventions that until now only existed inside source comments
-- the three test lists and how two of them invert "passed", the sorted verb
table, that a golden file is never edited to suit this interpreter, and that a
fix gets mutation-checked with a file copy rather than git checkout.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-07-31 22:41:36 -04:00
|
|
|
```output
|
|
|
|
|
HELLO 1
|
|
|
|
|
HELLO 2
|
|
|
|
|
HELLO 3
|
|
|
|
|
HELLO 4
|
|
|
|
|
HELLO 5
|
|
|
|
|
READY
|
|
|
|
|
```
|
|
|
|
|
|
2026-07-31 21:50:50 -04:00
|
|
|
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.
|
Execute every documented example as a test
docs/ and README.md carry 85 fenced blocks. Every one was checked by hand
exactly once, when it was written, which is not a standard that survives a
changing interpreter -- and four were already wrong: two transcripts showing a
leading space PRINT does not emit, akbasic_TextSink in README.md missing the
two members it had grown hours earlier, and FILTER's refusal quoted with
wording the code does not use.
tests/docs_examples.sh reads a fence-tag vocabulary and runs what it finds.
BASIC programs and transcripts run and are byte-compared against an `output`
block; C snippets compile with -fsyntax-only against the real include path,
which CMake writes out because it is transitive through akerror, akstdlib and
akgl; shell blocks run in a sandbox. Anything that would reconfigure the build
tree, hit the network or re-enter the suite is tagged norun with the reason in
MAINTENANCE.md, and the two cmake blocks stay hand-maintained by decision.
An untagged block is a failure rather than a default, and the pass line
reports what it executed by kind. Both exist because the way a harness like
this dies is by quietly matching nothing and passing -- which it duly did on
the first CTest run, where a generator expression evaluating to nothing still
contributed an empty argument that the script read as a filename. The count is
what caught it.
The excerpt check earns its own mention: a block tagged
`c excerpt=include/akbasic/sink.h` must still appear in that header, comments
and whitespace ignored. Compiling it would only redefine the type, so a
compile check could not have found the stale struct, and did not.
Registered as the CTest case docs_examples in both configurations. Fixing the
four wrong examples turned up two interpreter defects, fixed in the previous
commit and recorded in TODO.md section 8.
MAINTENANCE.md is new: the fence-tag reference, what to do when the case
fails, and the conventions that until now only existed inside source comments
-- the three test lists and how two of them invert "passed", the sorted verb
table, that a golden file is never edited to suit this interpreter, and that a
fix gets mutation-checked with a file copy rather than git checkout.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-07-31 22:41:36 -04:00
|
|
|
|
|
|
|
|
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.
|