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Let DEF take structure parameters, and give call scopes back

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DEF AREA(S@ AS RECT) = S@.W# * S@.H#
    DEF POKEIT(P@ AS PTR TO RECT)

A parameter names its type, exactly as DIM does. A bare `DEF F(S@)` is refused:
@ says "a structure" without saying which, so it does not state a contract the
way S$ does, and accepting it would mean checking fields at the call rather than
at the declaration -- which is the hole naming the type closes. The cost is that
there are no generic functions, and that is a real loss rather than an oversight.

Passing is by value, because a parameter is bound by assignment and assignment
copies; a pointer parameter copies its reference and lets a function change its
caller's record on purpose. Neither is a special rule. What a structure
parameter does need is its storage prepared before the copy, since a structure
variable is a run of slots and there is nothing to copy into until the run
exists.

A DEF parameter list is no longer parsed as an argument list, because a
parameter is a declaration rather than an expression: `S@ AS RECT` stopped that
parser dead with "Unbalanced parenthesis".

akbasic_value_is_truthy() learned that a pointer is true when it points at
something, which had to come with this. Without it there is no way to test for
the end of a list at all -- comparing a pointer to 0 reads a numeric field it
does not carry and answers whatever that field held. A structure is deliberately
given no truth value: it always exists, so the question has no answer worth
guessing at.

And a regression I introduced last commit, plus the older one underneath it.
prev_environment() released a scope but not the variables the scope created, so
a call leaked one slot per parameter and two hundred calls exhausted the
128-slot pool. Giving each DEF call its own scope made that reachable; it was
there for GOSUB all along, measured on a stashed build -- a subroutine with a
local of its own failed after about 128 calls before any of this work. The
release is safe because a scope's table holds only what it created, and it is
the variable slot that comes back rather than its storage, so a pointer into a
record DIMmed in that scope stays sound.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Andrew Kesterson
2026-08-01 13:05:32 -04:00
parent 00daa17a47
commit c1d06ee4b8
8 changed files with 452 additions and 40 deletions
Download Patch File Download Diff File Expand all files Collapse all files

47
tests/language/structures/parameters.bas Normal file
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@@ -0,0 +1,47 @@
10 REM A structure parameter must name its type: @ says "a structure" without
20 REM saying which, so B@ does not state a contract the way B$ does.
30 TYPE CRATE
40 W#
50 H#
60 END TYPE
70 DIM A@ AS CRATE
80 A@.W# = 5
90 A@.H# = 3
100 DEF AREA(B@ AS CRATE) = B@.W# * B@.H#
110 PRINT AREA(A@)
120 REM Passing is BY VALUE, because a parameter is bound by assignment and
130 REM assignment copies. A function cannot change its caller's record by
140 REM accident.
150 DEF WIDEN(B@ AS CRATE)
160 B@.W# = 99
170 RETURN B@.W#
180 PRINT WIDEN(A@)
190 PRINT A@.W#
200 REM To change one on purpose, pass a pointer. Assignment copies a pointer's
210 REM reference, so the callee is looking at the caller's own record.
220 DIM Q@ AS PTR TO CRATE
230 POINT Q@ AT A@
240 DEF POKEIT(P@ AS PTR TO CRATE)
250 P@->W# = 42
260 RETURN P@->W#
270 PRINT POKEIT(Q@)
280 PRINT A@.W#
290 REM And a recursive function can carry a record down with it.
300 TYPE NODE
310 COUNT#
320 TAIL@ AS PTR TO NODE
330 END TYPE
340 DIM N1@ AS NODE
350 DIM N2@ AS NODE
360 N1@.COUNT# = 10
370 N2@.COUNT# = 20
380 POINT N1@.TAIL@ AT N2@
390 DEF TOTAL(P@ AS PTR TO NODE)
395 REM A pointer is true when it points at something, which is how a walk knows
396 REM where the list ends. NOT is the bitwise operator here, so the test is
397 REM written the positive way round.
400 IF P@->TAIL@ THEN RETURN P@->COUNT# + TOTAL(P@->TAIL@)
410 RETURN P@->COUNT#
420 DIM W@ AS PTR TO NODE
430 POINT W@ AT N1@
440 PRINT TOTAL(W@)

6
tests/language/structures/parameters.txt Normal file
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@@ -0,0 +1,6 @@
15
99
5
42
42
30

109
tests/user_functions.c
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@@ -128,36 +128,107 @@ static void test_single_expression_form(void)
}
/**
* @brief A function reaches a structure through the caller's scope.
* @brief A structure parameter is passed by value, and a pointer one is not.
*
* **Not through a parameter**: `DEF F(B@ AS CRATE)` is not implemented, and a
* bare `DEF F(B@)` is refused because `@` alone does not say *which* type. So
* the way a function works with a record today is by name, which the dynamic
* scoping already allows -- a call's environment has the caller's as its parent.
*
* Pinned rather than left implicit, because it is the only route there is and a
* reader would otherwise reasonably assume the parameter form works.
* Neither is a special rule: a parameter is bound by assignment like any other
* variable, and assignment copies a structure and copies a pointer's reference.
* The two halves of the feature seen from a function's side.
*/
static void test_structures_reached_through_scope(void)
static void test_structure_parameters(void)
{
TEST_REQUIRE_OK(run_program("10 TYPE CRATE\n"
"20 W#\n"
"30 END TYPE\n"
"40 DIM A@ AS CRATE\n"
"50 A@.W# = 5\n"
"60 DEF SCALED(N#) = A@.W# * N#\n"
"70 PRINT SCALED(3)\n"));
TEST_REQUIRE_STR(HARNESS_OUTPUT, "15\n");
"60 DEF WIDEN(B@ AS CRATE)\n"
"70 B@.W# = 99\n"
"80 RETURN B@.W#\n"
"90 PRINT WIDEN(A@)\n"
"100 PRINT A@.W#\n"));
/* The callee saw 99; the caller still has 5, because it was a copy. */
TEST_REQUIRE_STR(HARNESS_OUTPUT, "99\n5\n");
harness_stop();
/* And a structure parameter is refused rather than silently misbehaving. */
TEST_REQUIRE_OK(run_program("10 TYPE CRATE\n"
"20 W#\n"
"30 END TYPE\n"
"40 DEF WID(B@) = B@.W#\n"
"50 PRINT 1\n"));
TEST_REQUIRE(strstr(HARNESS_OUTPUT, "ERROR") != NULL,
"a structure parameter should be refused for now, got \"%s\"", HARNESS_OUTPUT);
"40 DIM A@ AS CRATE\n"
"50 A@.W# = 5\n"
"60 DIM Q@ AS PTR TO CRATE\n"
"70 POINT Q@ AT A@\n"
"80 DEF POKEIT(P@ AS PTR TO CRATE)\n"
"90 P@->W# = 42\n"
"100 RETURN P@->W#\n"
"110 PRINT POKEIT(Q@)\n"
"120 PRINT A@.W#\n"));
/* And through a pointer the caller's record does change. */
TEST_REQUIRE_STR(HARNESS_OUTPUT, "42\n42\n");
harness_stop();
}
/**
* @brief A structure parameter must name its type, and the type is checked.
*
* `@` says "a structure" without saying which, so `X@` does not state a contract
* the way `X$` does. Naming the type is what closes that, and refusing a bare
* `X@` rather than treating it as "any structure" is what keeps the rule to one
* -- duck typing there would put the hole straight back.
*/
static void test_structure_parameter_types_are_checked(void)
{
static const struct { const char *tail; const char *expect; } CASES[] = {
{ "90 DEF F(B@) = B@.W#\n100 PRINT 1\n", "must name its type" },
{ "90 DEF F(B@ AS CRATE) = B@.W#\n100 PRINT F(O@)\n", "cannot take a OTHERT" },
{ "90 DEF F(B@ AS NOSUCH) = B@.W#\n100 PRINT F(A@)\n", "which is not a type" },
{ "90 DEF F(B@ AS PTR TO CRATE) = B@->W#\n100 PRINT F(A@)\n", "expects a pointer to" },
{ "90 DEF F(B@ AS) = 1\n100 PRINT 1\n", "Expected a type name" }
};
char source[2048];
size_t i = 0;
for ( i = 0; i < sizeof(CASES) / sizeof(CASES[0]); i++ ) {
snprintf(source, sizeof(source),
"10 TYPE CRATE\n20 W#\n30 END TYPE\n"
"40 TYPE OTHERT\n50 N#\n60 END TYPE\n"
"70 DIM A@ AS CRATE\n80 DIM O@ AS OTHERT\n%s", CASES[i].tail);
TEST_REQUIRE_OK(run_program(source));
TEST_REQUIRE(strstr(HARNESS_OUTPUT, CASES[i].expect) != NULL,
"case %zu should say \"%s\", got \"%s\"",
i, CASES[i].expect, HARNESS_OUTPUT);
harness_stop();
}
}
/**
* @brief A call gives its parameter variables back when it returns.
*
* One variable leaked per call before this, so a function called two hundred
* times exhausted the 128-slot pool and reported "Maximum runtime variables
* reached" on a four-line program. It was there for `GOSUB` all along --
* measured on a stashed build -- and giving each `DEF` call its own scope simply
* made it reachable a second way.
*/
static void test_call_scopes_are_reclaimed(void)
{
TEST_REQUIRE_OK(run_program("10 DEF DBL(N#) = N# * 2\n"
"20 T# = 0\n"
"30 FOR I# = 1 TO 200\n"
"40 T# = T# + DBL(I#)\n"
"50 NEXT I#\n"
"60 PRINT T#\n"));
TEST_REQUIRE_STR(HARNESS_OUTPUT, "40200\n");
harness_stop();
/* The GOSUB half, which is where the leak actually started. */
TEST_REQUIRE_OK(run_program("10 FOR I# = 1 TO 300\n"
"20 GOSUB 100\n"
"30 NEXT I#\n"
"40 PRINT \"OK\"\n"
"50 END\n"
"100 LOCALV# = I# * 2\n"
"110 RETURN\n"));
TEST_REQUIRE_STR(HARNESS_OUTPUT, "OK\n");
harness_stop();
}
@@ -170,7 +241,9 @@ int main(void)
test_arguments_are_per_call();
test_runaway_recursion_is_diagnosed();
test_single_expression_form();
test_structures_reached_through_scope();
test_structure_parameters();
test_structure_parameter_types_are_checked();
test_call_scopes_are_reclaimed();
return akbasic_test_failures;
}