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).
75 lines
2.8 KiB
Plaintext
75 lines
2.8 KiB
Plaintext
// Multi-value value-carrying failables (ERR — the multi-value error-channel
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// ABI). A `-> (T1, T2, !E)` function returns EITHER a value-tuple OR an error:
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// `return (a, b)` yields the success tuple `{a, b, 0}` (the compiler appends the
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// no-error slot) and `raise error.X` yields `{undef, undef, tag}`. Every consumer
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// generalizes from the single-value shape: a destructure binds every slot
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// INCLUDING the error (dropping it is the spec'd discard error — bind it and
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// inspect); `try` binds the value-tuple on success and propagates `{undef..., tag}`
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// on failure; `catch` / `or` absorb the failure and merge the value-tuple or the
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// handler/terminator value. Single-value `-> (T, !E)` is examples/228-231.
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#import "modules/std.sx";
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E :: error { Bad, Empty }
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parse :: (n: i32) -> (i32, i32, !E) {
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if n < 0 { raise error.Bad; }
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if n == 0 { raise error.Empty; }
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return .(n * 2, n + 1); // success → {n*2, n+1, 0}
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}
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// Multi-value `try` in a multi-value caller — propagates {undef, undef, tag}.
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inc :: (n: i32) -> (i32, i32, !E) {
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v, b := try parse(n);
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return .(v + 1, b + 1);
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}
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// Multi-value `catch`, bare-expression tuple fallback (absorbs the failure).
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safe :: (n: i32) -> i32 {
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v, b := parse(n) catch (e) .(40, 50);
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return v + b;
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}
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// Multi-value `catch` match-body — per-tag dispatch, each arm a value-tuple.
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classify :: (n: i32) -> i32 {
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v, b := parse(n) catch (e) == {
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case .Bad: .(1, 1);
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case .Empty: .(2, 2);
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else: .(9, 9);
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};
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return v + b;
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}
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// Multi-value `or (tuple)` value-terminator (absorbs the failure).
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ortest :: (n: i32) -> i32 {
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v, b := parse(n) or .(7, 8);
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return v + b;
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}
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main :: () -> i32 {
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r : i32 = 0;
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// Destructure binds EVERY slot including the error tag (e1 / e2 / e3) —
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// the error is treated, never dropped.
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v1, b1, e1 := parse(5); // success → (10, 6, no-error)
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if !e1 { r = r + v1 + b1; } // success → +16 (slots live only when proven ok)
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v2, b2, e2 := parse(-1); // Bad → {undef, undef, Bad}
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if e2 == error.Bad { r = r + 4; } // +4
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a, c, ea := inc(5); // parse(5)=(10,6) → (11, 7, no-error)
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if !ea { r = r + a + c; } // success → +18
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a2, c2, e3 := inc(-1); // try parse(-1)=Bad → propagate {undef, undef, Bad}
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if e3 == error.Bad { r = r + 5; } // +5
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r = r + safe(5); // (10, 6) → 16
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r = r + safe(-1); // Bad → catch → (40, 50) → 90
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r = r + classify(-1); // Bad → match-body → (1, 1) → 2
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r = r + classify(0); // Empty → match-body → (2, 2) → 4
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r = r + ortest(0); // Empty → or → (7, 8) → 15
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print("multi-value result: {}\n", r); // 16+4+18+5+16+90+2+4+15 = 170
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return r;
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}
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