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).
61 lines
2.1 KiB
Plaintext
61 lines
2.1 KiB
Plaintext
// Consuming value-carrying failables with `try` and `catch` (ERR step E2.1b —
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// the consumer side of the error-channel tuple ABI). `try f()` on a
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// `-> (T, !E)` callee binds the value slot on success and propagates the error
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// on failure (a pure-failable caller returns the tag; a value-carrying caller
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// returns `{undef, tag}`). `f() catch (e) BODY` yields the value slot on success
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// or the handler body's value on failure, merged through a block parameter.
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// The producer side is `examples/228-value-failable.sx`.
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#import "modules/std.sx";
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E :: error { Bad, Empty }
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parse :: (n: 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;
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}
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// value-carrying `try` in a value-carrying caller — propagates {undef, tag}.
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inc :: (n: i32) -> (i32, !E) {
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v := try parse(n);
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return v + 1;
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}
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// value-carrying `try` in a pure-failable caller — propagates the tag.
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relay :: (n: i32) -> !E {
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v := try parse(n);
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if v < 0 { raise error.Bad; }
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return;
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}
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// value-carrying `catch`, bare-expression fallback.
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safe :: (n: i32) -> i32 {
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return parse(n) catch (e) 0;
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}
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// value-carrying `catch`, match-body value.
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classify :: (n: i32) -> i32 {
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return parse(n) catch (e) == {
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case .Bad: 1;
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case .Empty: 2;
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else: 3
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};
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}
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main :: () -> i32 {
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r : i32 = 0;
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a, ea := inc(5); // parse(5)=10 → v=10 → 11
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if !ea { r = r + a; } // success → +11 (value live only when proven ok)
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b, eb := inc(-1); // parse(-1)=Bad → propagate {undef, Bad}
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if eb == error.Bad { r = r + 4; } // true → +4
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er := relay(3); // parse(3)=6 ok → relay ok
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if er == error.Bad { r = r + 50; } // false
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r = r + safe(7); // parse(7)=14 → +14
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r = r + safe(-1); // Bad → catch → 0
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r = r + classify(-1); // Bad → 1
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r = r + classify(0); // Empty → 2
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print("consume result: {}\n", r); // 11+4+14+0+1+2 = 32
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return r;
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}
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