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Port the BASIC interpreter from Go to C

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Reproduces deps/basicinterpret in C, in the idiom of the ak* libraries. All 41
.bas files in the reference's corpus produce byte-identical stdout, including
the trailing double newline on an error line -- that comes from basicError
building a string ending in \n and handing it to Println, and
array_outofbounds.txt encodes it.

The corpus is driven in place from the submodule as 41 individual CTest cases
rather than copied, so it cannot drift from upstream. Eighteen unit tests cover
what the corpus cannot reach.

Three structural changes carry most of the work. Go's three reflection lookups
(Command*, Function*, ParseCommand*) become one sorted dispatch table in
src/verbs.c searched with bsearch; adding a verb is a row and two functions. The
five Go maps become one fixed open-addressed table over aksl_strhash_djb2. And
run(), which owned the process until MODE_QUIT, splits into step() plus a
bounded run() -- goal 3 requires a host game to be able to bound execution, and
nothing in the library now terminates the process or touches SDL.

Output goes through an akbasic_TextSink vtable. src/sink_stdio.c is what makes
the corpus runnable with no SDL present; the akgl-backed sink is still to come
and is blocked on libakgl having no text-measurement call.

src/convert.c exists because libakstdlib's aksl_ato* family cannot report a
conversion failure (its TODO.md 2.1.5). The reference checks strconv's error at
four sites and turns it into a BASIC error; routing those through aksl_atoi
would have turned four diagnosable errors into wrong answers, with VAL("garbage")
quietly returning 0. TODO.md 1.9 records which libakstdlib calls are cleared for
use here and which are not.

Reference defects are reproduced, not fixed: the golden files encode the observed
behaviour and a silent correction is a behaviour change. TODO.md section 6 lists
sixteen, and tests/known_reference_defects.c asserts the *correct* contract for
six of them under AKBASIC_KNOWN_FAILING_TESTS, so a fix shows up as
"unexpectedly passed". Five of the sixteen were found by this port and are new:
subtraction stops after one operator so 1-2-3 computes 1-2 and abandons the rest
of the line (a wrong answer, not a refused one); a unary-minus argument inflates
a function's arity so ABS(-9) is rejected; a comparison operator in a line's
final column is dropped; hex literals never survive the scanner; and the
"Reserved word in variable name" check is dead code.

Where the reference reaches undefined behaviour by a route that is defined in Go
-- an out-of-range shift, a negative string multiplier, integer division by zero
-- this raises instead of inheriting the UB. No golden case exercises any of
them.

The top-level CMakeLists shadows add_test, set_tests_properties and
add_custom_target around all three add_subdirectory calls. Without it libakerror's
tests land in our suite as Not Run, and its un-namespaced `coverage` target stops
a coverage build from configuring at all. Test targets are akbasic_test_<name>:
bare test_<name> collides with libakstdlib's, which is what broke libakgl's
configure in c2b16d3.

ctest 59/59; ASan+UBSan 59/59; 92.3% line and 96.9% function coverage; no
warnings under -Wall -Wextra. Branch coverage is not a target, for the reason
libakstdlib and libakgl both record: the akerror macros expand into large branch
trees at every call site.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>
This commit is contained in:
Tachikoma
2026-07-30 23:53:56 -04:00
commit 4e188b2794
60 changed files with 10192 additions and 0 deletions
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src/symtab.c Normal file
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/**
* @file symtab.c
* @brief Implements the fixed-capacity open-addressed symbol table.
*/
#include <string.h>
#include <akerror.h>
#include <akstdlib.h>
#include <akbasic/error.h>
#include <akbasic/symtab.h>
/*
* Probe for `key`. On success *slot points at either the slot holding the key or
* the first free slot it could occupy; *found says which. Uses
* aksl_strhash_djb2 rather than a private hash. That wrapper sign-extends char,
* so a high-bit byte hashes wrong (deps/libakstdlib/TODO.md 1.6) -- harmless
* here because BASIC identifiers are 7-bit ASCII, and it would only ever cost
* probe efficiency, never correctness, since the key comparison is a strcmp.
*/
static akerr_ErrorContext *probe(akbasic_SymbolTable *obj, const char *key, int *slot, bool *found)
{
PREPARE_ERROR(errctx);
uint32_t hashval = 0;
int index = 0;
int i = 0;
PASS(errctx, aksl_strhash_djb2((char *)key, strlen(key), &hashval));
*found = false;
index = (int)(hashval % (uint32_t)obj->capacity);
for ( i = 0; i < obj->capacity; i++ ) {
int probeidx = (index + i) % obj->capacity;
if ( !obj->slots[probeidx].used ) {
*slot = probeidx;
SUCCEED_RETURN(errctx);
}
if ( strcmp(obj->slots[probeidx].key, key) == 0 ) {
*slot = probeidx;
*found = true;
SUCCEED_RETURN(errctx);
}
}
FAIL_RETURN(errctx, AKBASIC_ERR_BOUNDS,
"Symbol table is full (%d entries), cannot place '%s'",
obj->capacity, key);
}
akerr_ErrorContext *akbasic_symtab_init(akbasic_SymbolTable *obj, int capacity)
{
PREPARE_ERROR(errctx);
FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER,
"NULL symbol table in init");
FAIL_ZERO_RETURN(errctx, (capacity > 0 && capacity <= AKBASIC_SYMTAB_MAX_SLOTS),
AKBASIC_ERR_BOUNDS,
"Symbol table capacity %d out of range 1..%d",
capacity, AKBASIC_SYMTAB_MAX_SLOTS);
memset(obj, 0, sizeof(*obj));
obj->capacity = capacity;
obj->count = 0;
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext *akbasic_symtab_set(akbasic_SymbolTable *obj, const char *key, void *value, int64_t ivalue)
{
PREPARE_ERROR(errctx);
int slot = 0;
bool found = false;
FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER,
"NULL symbol table in set");
FAIL_ZERO_RETURN(errctx, (key != NULL), AKERR_NULLPOINTER,
"NULL key in symbol table set");
FAIL_ZERO_RETURN(errctx, (strlen(key) < AKBASIC_SYMTAB_MAX_KEY),
AKBASIC_ERR_BOUNDS,
"Symbol name '%s' exceeds %d characters",
key, AKBASIC_SYMTAB_MAX_KEY - 1);
PASS(errctx, probe(obj, key, &slot, &found));
if ( !found ) {
strncpy(obj->slots[slot].key, key, AKBASIC_SYMTAB_MAX_KEY - 1);
obj->slots[slot].key[AKBASIC_SYMTAB_MAX_KEY - 1] = '\0';
obj->slots[slot].used = true;
obj->count += 1;
}
obj->slots[slot].value = value;
obj->slots[slot].ivalue = ivalue;
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext *akbasic_symtab_get(akbasic_SymbolTable *obj, const char *key, void **value, int64_t *ivalue)
{
PREPARE_ERROR(errctx);
int slot = 0;
bool found = false;
FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER,
"NULL symbol table in get");
FAIL_ZERO_RETURN(errctx, (key != NULL), AKERR_NULLPOINTER,
"NULL key in symbol table get");
FAIL_ZERO_RETURN(errctx, (strlen(key) < AKBASIC_SYMTAB_MAX_KEY),
AKERR_KEY,
"Symbol '%s' is not present", key);
PASS(errctx, probe(obj, key, &slot, &found));
FAIL_ZERO_RETURN(errctx, found, AKERR_KEY, "Symbol '%s' is not present", key);
if ( value != NULL ) {
*value = obj->slots[slot].value;
}
if ( ivalue != NULL ) {
*ivalue = obj->slots[slot].ivalue;
}
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext *akbasic_symtab_clear(akbasic_SymbolTable *obj)
{
PREPARE_ERROR(errctx);
int capacity = 0;
FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER,
"NULL symbol table in clear");
capacity = obj->capacity;
memset(obj, 0, sizeof(*obj));
obj->capacity = capacity;
SUCCEED_RETURN(errctx);
}