0.6.0 and 0.7.0 break nothing here: 0.6.0 is three arcade-physics fixes and a
physics.max_timestep property this port does not use, and 0.7.0 reports failures
libakstdlib's wrappers were already catching and takes libakerror 2.0.1 so it
can drop the exit-status trap its own suites needed. That is the same defect
include/akbasic/error.h guards for this band, now fixed at the source rather
than worked around in two places.
The floor moves to 0.7.0 anyway. The soname carries MAJOR.MINOR while the major
is 0, so deciding for ourselves which of libakgl's minor releases were really
compatible is exactly the judgement it exists to take away.
0.7.0 is largely about a defect class worth checking for here rather than
assuming past: ten unterminated strncpy calls into fixed-width name fields. Ours
are clean -- every one is bounded to size - 1 and every buffer is either
explicitly terminated afterwards or memset first, checked site by site. But two
of them, both written last week in src/structtype.c, truncated an over-long name
silently, and truncation is an error everywhere else in this interpreter. It
matters more for a name than for a value: two long type names trimmed to the
same 31 characters collide, and the second is then reported as redeclaring a
type the program never wrote.
Both are refused now, showing the name as written. The check was unreachable as
first drafted, because the prescan read words into a buffer the size of the
limit and so trimmed them before anything could look -- the scratch is twice the
limit now, which is what makes the two cases distinguishable at all.
tests/struct_types.c pins that it stays reachable.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
A BASIC TYPE and a host C struct are the same thing seen from two sides, so both
go in one type table and everything the language already does with a structure
works across the boundary with no second set of rules. The host describes its
struct once as a table of field descriptors and binds an instance:
akbasic_host_bind(&SCRIPT, "FOE@", "ENEMY", &GOBLIN);
after which `FOE@.HP# = FOE@.HP# - 10` decrements GOBLIN.hp in place, with no
marshalling step the host has to remember to run.
The sharing is done with shadow slots: a binding takes a run from the same value
pool a DIMmed record uses, a field read refreshes its slot from host memory
first, and a write converts back and stores. So the script always sees current
values and its writes always land, while the rest of the interpreter goes on
seeing one storage model instead of two.
AKBASIC_HOST_FIELD takes the offset and the width from the same member, which is
the only reason it is a macro: writing offsetof and sizeof out by hand is two
chances to name the wrong member and no way to notice. A field name's suffix
must agree with the C type it describes, refused at registration -- a host
writing "HP%" over an int32_t has said two different things about one field and
the script would believe the suffix.
Conversion refuses rather than truncates. 200 into an int8_t, 70000 into an
int16_t, -1 into a uint8_t and thirteen characters into a char[8] are each an
error naming the field, because a silent wrap is found three frames later in
code that did nothing wrong. Each width is tested separately, since a range
check is exactly the thing that is right for int32_t and wrong for int8_t when
only one of them is covered.
The language's own distinction turns out to be the one a host needs, so there is
one API rather than two: assignment copies and gives a script a private
snapshot, POINT shares and lets it change the game, and which one happened is
visible in the listing.
Two things the work required. The prescan runs again on every RUN and used to
wipe the whole type table, unregistering the host's types the first time a
script ran; it now keeps what the host registered and drops only what the script
declared. And akbasic_runtime_start() did not rewind, which cost nothing while a
host started a script once and cost everything to a host running one per enemy
-- the second start began past the end and silently did nothing.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
A pointer is a distinct declared kind rather than a mode a structure can be in,
which is what "strict" means here: `.` requires a structure on its left and `->`
requires a pointer, neither stands in for the other, and both refusals name the
operator the program should have used. So a reader always knows from the
spelling whether the thing on the left is their own copy or somebody else's
data.
Assignment still copies. POINT is the only way to share, so a program that never
writes it can never be surprised by aliasing -- and `P@ = A@` is refused with a
message saying to POINT it instead, rather than quietly becoming the one
assignment in the language that does not copy.
PTR TO is also the only way a TYPE may refer to itself, since by value it would
have no finite size. That is what makes a linked list possible, and
tests/language/structures/pointers.bas builds one, walks it and renders it.
Rendering follows pointers, so it needs a depth bound where copying does not:
copy stops at a pointer by construction, but two nodes pointing at each other is
easy to write and PRINT would not come back. Four levels, chosen so the bound
bites before the 256-byte render buffer does -- otherwise a cycle would stop
because it ran out of room rather than because it was told to.
Three things the work turned up, all now pinned by tests:
A freshly DIMmed record printed `(UNDEFINED STRING REPRESENTATION FOR 0)` for
every field. Slots now take the type their field declared, so it reads as zeros.
Adding POINT as a verb makes POINT unusable as a type name, and the parser
reported that as "Expected expression or literal" pointing at the line rather
than the problem. The prescan now refuses a reserved word as a type name and
says so.
Field names follow the same reserved-word rule as variable names, enforced by
the loader's own scan -- `TO@` is a bad field name for exactly the reason `TO#`
is a bad variable name. Recorded rather than worked around.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
BASIC 7.0 has no records at all, so none of this is a port. The `@` suffix was
not invented either: the Go reference reserved IDENTIFIER_STRUCT and never used
it, and src/grammar.c rendered such a leaf as "NOT IMPLEMENTED" until now.
Declaring the type is what buys the storage model. A TYPE states its fields, so
an instance has a known slot count and is laid out exactly as an array is -- one
contiguous run from the same value pool DIM already draws from, with field access
as offset arithmetic. No new pool holds data; the only new table holds
descriptors. A nested value flattens into its container's run, which is why
LINE with two POINTs and a string is five slots rather than three.
Each field takes its type from its own suffix, the same rule every other name
here follows, so a field list needs no type column. An `@` field is the
exception and has to name its type, because three primitive types fit in three
suffix characters and N declared types do not fit in one.
The declaration is prescanned before the program runs, like labels and DATA and
for the same reason: it has to be in effect wherever control goes. Three passes,
each for a case the one before cannot do -- names first so a field can refer to
a type declared later, then field lists, then sizes by repeated resolution. What
never resolves is a cycle of by-value containment, so "a TYPE cannot contain
itself by value" is a diagnosis rather than an assumption, and the message says
to use PTR TO instead.
Assignment copies. That interception is the whole feature and it cannot live in
akbasic_value_clone(), which copies one slot -- and one slot holds a *reference*
to an instance rather than the instance, so going through it would alias. A
structure is intercepted before that path and its slots are copied one at a
time, walking the descriptor rather than memcpy-ing the run, because a pointer
field must copy its reference where a value field must copy its slots.
Two smaller things the work required. All three prescans now sit inside one
ATTEMPT: a malformed declaration is the program's mistake, and it was printing a
stack trace and taking the driver with it, which is the boundary goal 3 exists
to draw. And a fresh variable's structtype is -1 rather than the 0 a memset
leaves, because 0 is a valid type index and every new variable was claiming to
be the first type declared.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
