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Accept GRAPHIC CLR and a negative DATA item

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Two parse handlers refusing something the documentation promises. Landing
together because they are the same defect twice -- a verb's own argument shape
falling through to a general path that cannot see it -- in one file, found by
one program, and verified in one pass.

**`GRAPHIC CLR`** is given as `GRAPHIC mode | CLR` in both docs/06-graphics.md
and docs/11-verb-reference.md, and was refused: `CLR` is a verb of its own, so
the generic arglist path scanned it as a command token and the expression parser
answered "Expected expression or literal". `akbasic_parse_graphic()` takes it as
this verb's keyword argument and emits mode 5 -- which `akbasic_cmd_graphic()`
already treats as "drop the saved shapes and go back to text", so both spellings
are one statement and the exec handler is untouched. The documentation was right
all along; nothing in it changes.

**`DATA -5`** was refused by `akbasic_parse_data()`, and only there: `READ` scans
the source text directly (src/data.c) and always returned the -5 intact. So the
value was right and *reaching* the statement raised -- which, since section 4
settled that `DATA` at run time is a no-op, is what a program does with every
`DATA` line it walks past. A table of coordinates or velocities is full of
negative numbers, which is how a game found it.

The fix accepts a unary minus over a numeric literal and nothing else: `DATA -A#`
is still a mistake worth naming, and `akbasic_leaf_is_literal()` keeps meaning
what it says because other callers rely on it.

tests/read_data.c covers both mechanisms -- reading a negative item and reaching
the line after it -- with a mixed-sign table and a negative float, since the two
were never the same code path.

TODO.md section 9 items 7 and 8, struck.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Andrew Kesterson
2026-08-02 00:18:53 -04:00
parent a1dcfcacf3
commit d5f3c3ef5b
6 changed files with 130 additions and 3 deletions
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17
TODO.md
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@@ -2751,7 +2751,13 @@ reduced against `build/basic`, the stdio build, unless it says otherwise.
is not obvious from the failure — every brick simply comes out the colour of the last one
captured. `tests/graphics_verbs.c` is where the regression goes.
7. **`GRAPHIC CLR` is documented and refused.** `docs/06-graphics.md:65` and
7. ~~**`GRAPHIC CLR` is documented and refused.**~~ **Done** -- `akbasic_parse_graphic()`
(`src/parser_commands.c`) takes `CLR` as this verb's keyword argument and emits mode 5,
which `akbasic_cmd_graphic()` already treats as exactly this, so both spellings are one
statement and the exec handler is unchanged. The documentation was right and the parser
was not; `tests/parser_commands.c` now pins the form the two chapters give.
The original report: `docs/06-graphics.md:65` and
`docs/11-verb-reference.md:54` both give the form as `GRAPHIC mode | CLR`.
```basic
@@ -2770,7 +2776,14 @@ reduced against `build/basic`, the stdio build, unless it says otherwise.
Worth noting because `docs_examples` cannot catch it: every fenced `GRAPHIC CLR` in the
documentation is prose, not a tagged runnable block.
8. **A `DATA` line holding a negative number cannot be executed.** §4 settled that "`DATA` at
8. ~~**A `DATA` line holding a negative number cannot be executed.**~~ **Done** --
`akbasic_parse_data()` accepts a unary minus over a numeric literal, which is the only
shape that was refused. Deliberately narrow: `DATA -A#` is still a mistake worth naming,
and `akbasic_leaf_is_literal()` keeps meaning what it says because it is used elsewhere.
`tests/read_data.c` covers reading one *and* walking past the line, which were two
different mechanisms and only one of them was ever wrong.
The original report: §4 settled that "`DATA` at
run time is now a no-op: it is a declaration, and reaching the statement means walking past
it." Walking past a negative one raises instead:

60
src/parser_commands.c
View File

@@ -57,6 +57,46 @@ akerr_ErrorContext *akbasic_parse_arglist(akbasic_Parser *parser, akbasic_ASTLea
SUCCEED_RETURN(errctx);
}
/*
* GRAPHIC mode [, clear]
* GRAPHIC CLR
*
* `CLR` is a keyword argument rather than an expression, and the generic arglist
* path cannot see it as one: `CLR` is a verb of its own, so it scans as a
* command token and the expression parser refuses with "Expected expression or
* literal". Both `docs/06-graphics.md` and `docs/11-verb-reference.md` have given
* the form as `GRAPHIC mode | CLR` all along, so the documentation was right and
* the parser was not. TODO.md section 9 item 7.
*
* It becomes mode 5, which is what akbasic_cmd_graphic() already treats as "drop
* the saved shapes and go back to text" -- so `GRAPHIC CLR` and `GRAPHIC 5` are
* the same statement, and the exec handler needs no change.
*/
akerr_ErrorContext *akbasic_parse_graphic(akbasic_Parser *parser, akbasic_ASTLeaf **dest)
{
PREPARE_ERROR(errctx);
akbasic_ASTLeaf *arglist = NULL;
akbasic_ASTLeaf *expr = NULL;
akbasic_Token *peeked = NULL;
peeked = akbasic_parser_peek(parser);
if ( peeked != NULL && peeked->tokentype == AKBASIC_TOK_COMMAND &&
strcmp(peeked->lexeme, "CLR") == 0 ) {
(void)akbasic_parser_match1(parser, AKBASIC_TOK_COMMAND);
PASS(errctx, akbasic_parser_new_leaf(parser, &arglist));
arglist->leaftype = AKBASIC_LEAF_ARGUMENTLIST;
arglist->operator_ = AKBASIC_TOK_FUNCTION_ARGUMENT;
PASS(errctx, akbasic_parser_new_leaf(parser, &arglist->right));
PASS(errctx, akbasic_leaf_new_literal_int(arglist->right, "5"));
PASS(errctx, akbasic_parser_new_leaf(parser, &expr));
PASS(errctx, akbasic_leaf_new_command(expr, "GRAPHIC", arglist));
*dest = expr;
SUCCEED_RETURN(errctx);
}
PASS(errctx, akbasic_parse_arglist(parser, dest));
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext *akbasic_parse_draw(akbasic_Parser *parser, akbasic_ASTLeaf **dest)
{
PREPARE_ERROR(errctx);
@@ -942,6 +982,26 @@ akerr_ErrorContext *akbasic_parse_data(akbasic_Parser *parser, akbasic_ASTLeaf *
FAIL_ZERO_RETURN(errctx, (arglist != NULL && arglist->right != NULL), AKBASIC_ERR_SYNTAX,
"Expected literal");
for ( expr = arglist->right; expr != NULL; expr = expr->next ) {
/*
* A negated literal counts. `DATA -5` used to be refused here -- and only
* here: `READ` scans the source text directly (src/data.c) and returned
* the -5 intact, so the value was right and reaching the *statement*
* raised "Expected literal". Since section 4 settled that DATA at run
* time is a no-op, walking past one is exactly what a program does with
* it, and a table of coordinates or velocities is full of them.
* TODO.md section 9 item 8.
*
* Only over a numeric literal: `DATA -A#` is still a mistake worth
* naming, and akbasic_leaf_is_literal() keeps meaning what it says
* because it is used elsewhere.
*/
if ( expr->leaftype == AKBASIC_LEAF_UNARY &&
expr->operator_ == AKBASIC_TOK_MINUS &&
expr->left != NULL &&
(expr->left->leaftype == AKBASIC_LEAF_LITERAL_INT ||
expr->left->leaftype == AKBASIC_LEAF_LITERAL_FLOAT) ) {
continue;
}
FAIL_ZERO_RETURN(errctx, akbasic_leaf_is_literal(expr), AKBASIC_ERR_SYNTAX,
"Expected literal");
}

2
src/verbs.c
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@@ -83,7 +83,7 @@ static const akbasic_Verb VERBS[] = {
{ "GETKEY", AKBASIC_TOK_COMMAND, -1, NULL, akbasic_cmd_getkey },
{ "GOSUB", AKBASIC_TOK_COMMAND, -1, NULL, akbasic_cmd_gosub },
{ "GOTO", AKBASIC_TOK_COMMAND, -1, NULL, akbasic_cmd_goto },
{ "GRAPHIC", AKBASIC_TOK_COMMAND, -1, akbasic_parse_arglist, akbasic_cmd_graphic },
{ "GRAPHIC", AKBASIC_TOK_COMMAND, -1, akbasic_parse_graphic, akbasic_cmd_graphic },
{ "GSHAPE", AKBASIC_TOK_COMMAND, -1, akbasic_parse_arglist, akbasic_cmd_gshape },
{ "HEADER", AKBASIC_TOK_COMMAND, -1, akbasic_parse_optional_arglist, akbasic_cmd_header },
{ "HELP", AKBASIC_TOK_COMMAND_IMMEDIATE, -1, NULL, akbasic_cmd_help },

1
src/verbs.h
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@@ -17,6 +17,7 @@
/* Parse handlers -- src/parser_commands.c */
akerr_ErrorContext AKERR_NOIGNORE *akbasic_parse_arglist(struct akbasic_Parser *parser, akbasic_ASTLeaf **dest);
akerr_ErrorContext AKERR_NOIGNORE *akbasic_parse_data(struct akbasic_Parser *parser, akbasic_ASTLeaf **dest);
akerr_ErrorContext AKERR_NOIGNORE *akbasic_parse_graphic(struct akbasic_Parser *parser, akbasic_ASTLeaf **dest);
akerr_ErrorContext AKERR_NOIGNORE *akbasic_parse_draw(struct akbasic_Parser *parser, akbasic_ASTLeaf **dest);
akerr_ErrorContext AKERR_NOIGNORE *akbasic_parse_def(struct akbasic_Parser *parser, akbasic_ASTLeaf **dest);
akerr_ErrorContext AKERR_NOIGNORE *akbasic_parse_dim(struct akbasic_Parser *parser, akbasic_ASTLeaf **dest);

21
tests/parser_commands.c
View File

@@ -99,6 +99,27 @@ int main(void)
expect_command("LABEL LOOPTOP", AKBASIC_LEAF_COMMAND, "LABEL");
expect_command("DIM A#(5)", AKBASIC_LEAF_COMMAND, "DIM");
expect_command("DATA 1, 2, 3", AKBASIC_LEAF_COMMAND, "DATA");
/*
* A negated literal is one. `DATA -5` used to be refused here and only here:
* READ scans the source text directly and returned the -5 intact, so the
* value was right and reaching the *statement* raised "Expected literal" --
* which is a table of coordinates or velocities failing on the line after
* it. TODO.md section 9 item 8.
*/
expect_command("DATA -5", AKBASIC_LEAF_COMMAND, "DATA");
expect_command("DATA -1, 2, -3.5", AKBASIC_LEAF_COMMAND, "DATA");
/* Only over a literal, though: a negated variable is still a mistake. */
expect_parse_error("DATA -A#");
/*
* `GRAPHIC CLR` is documented in two chapters and used to be refused: CLR is
* a verb of its own, so the generic arglist path scanned it as a command
* token rather than as this verb's keyword argument. TODO.md section 9 item
* 7. It becomes mode 5, which the exec handler already treats as exactly
* this, so both spellings are one statement.
*/
expect_command("GRAPHIC CLR", AKBASIC_LEAF_COMMAND, "GRAPHIC");
expect_command("GRAPHIC 1, 1", AKBASIC_LEAF_COMMAND, "GRAPHIC");
expect_command("READ A#, B#", AKBASIC_LEAF_COMMAND, "READ");
expect_command("POKE 100, 1", AKBASIC_LEAF_COMMAND, "POKE");
expect_command("INPUT \"NAME? \" A$", AKBASIC_LEAF_COMMAND, "INPUT");

32
tests/read_data.c
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@@ -184,6 +184,37 @@ static void test_float_items(void)
harness_stop();
}
/**
* @brief A `DATA` line holding a negative number can be read *and* walked past.
*
* Two different mechanisms, and only one of them was ever wrong. `READ` scans
* the source text directly, so it always returned the -5 intact; the statement's
* own argument parse refused a leading minus, so reaching the line raised
* "Expected literal". Section 4 settled that `DATA` at run time is a no-op --
* reaching it means walking past it -- which is what made this reachable at all.
*
* TODO.md section 9 item 8. A table of coordinates or velocities is full of
* negative numbers, which is how a game found it.
*/
static void test_negative_items(void)
{
TEST_REQUIRE_OK(run_program("10 READ A#\n"
"20 PRINT \"READ GAVE \" + A#\n"
"30 DATA -5\n"
"40 PRINT \"PAST IT\"\n"));
TEST_REQUIRE_STR(HARNESS_OUTPUT, "READ GAVE -5\nPAST IT\n");
harness_stop();
/* Mixed signs across a real table, and a negative float. */
TEST_REQUIRE_OK(run_program("10 DATA -1, 2, -3\n"
"20 DATA -0.5\n"
"30 READ A#, B#, C#\n"
"40 READ D%\n"
"50 PRINT \"\" + A# + \" \" + B# + \" \" + C# + \" \" + D%\n"));
TEST_REQUIRE_STR(HARNESS_OUTPUT, "-1 2 -3 -0.500000\n");
harness_stop();
}
int main(void)
{
test_read_in_order();
@@ -197,5 +228,6 @@ int main(void)
test_quoted_items();
test_colon_ends_data();
test_float_items();
test_negative_items();
return akbasic_test_failures;
}