213cedf0b5
The trailing-`!`-after-the-value-type spelling (`-> T !`, `-> Tuple(A,B) !`) was a
redundant second way to write a failable return that the parser folded into the
same AST as the parenthesized `(T, !)` / `(A, B, !)` result list. Remove it so
there is ONE canonical spelling: the error channel always rides as the last slot
of the parenthesized list.
- parser: `parseFnReturnType` no longer folds a trailing `!` after a value type —
it rejects it with a located diagnostic ("a failable return is written `(T, !)`
… not `T !`"). This one chokepoint covers fn declarations, lambdas, fn-pointer
types `(A) -> R`, and closure types `Closure(A) -> R`. The error-ONLY `-> !` /
`-> !ErrSet` form is unaffected (parsed by parseTypeExpr as an error_type_expr).
- migrated every usage to canonical form across library/ + examples/ + issues/ +
tests/: `-> T !E` → `-> (T, !E)`; the value-carrying `-> Tuple(A, B) !` (which
FLATTENED to a multi-value failable) → `-> (A, B, !)`, preserving behavior. A
genuine single-tuple-value failable stays `-> (Tuple(A,B), !)`.
- parser unit tests: the "bare form folds" tests become "bare form is rejected";
canonical-form parse tests retained.
- docs: specs.md §12 + scattered refs and readme.md updated to the `(T, !)` form.
Behavior-preserving (the bare form was sugar for the same AST). Adversarial review
confirmed: rejection complete across all positions, every canonical form works on
both success/error paths, error-only `-> !` intact, no crashes. Full suite green
(unit tests + 850 corpus examples).
36 lines
1.1 KiB
Plaintext
36 lines
1.1 KiB
Plaintext
// Rejection counterpart to 1046 (ERR step E1.8). Reading a failable's value slot
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// where its error is NOT proven absent is a compile error. Two unproven shapes:
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//
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// (A) reading the value inside the `if err { … }` error path itself
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// (B) reading the value after a bare tag-compare (`if err == error.X`), which
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// narrows the tag but proves nothing about absence
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//
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// Each read is rejected with the E1.8 diagnostic; the program never runs (exit 1).
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#import "modules/std.sx";
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E :: error { Bad }
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parse :: (n: i32) -> (i32, !E) {
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if n < 0 { raise error.Bad; }
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return n * 10;
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}
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// (A) the read sits on the error path — `err` is present here, not absent.
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bad_a :: () -> i32 {
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v, err := parse(5);
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if err { return v; } // REJECTED: err present on this path
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return 0;
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}
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// (B) a tag-compare narrows which error, but does not prove there is none.
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bad_b :: () -> i32 {
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v, err := parse(5);
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if err == error.Bad { return 1; }
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return v; // REJECTED: err not proven absent
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}
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main :: () -> i32 {
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return bad_a() + bad_b();
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}
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