bdd0e96d78
A block's value is now its last statement ONLY when that statement is a trailing expression with no `;`. A trailing `;` discards the value, leaving the block void. This makes value-vs-statement explicit and lets the compiler reject "this block was supposed to produce a value". Compiler: - Parser records `Block.produces_value` (last stmt is a no-`;` trailing expression) + `Block.discarded_semi` (the `;` that discarded a value), via `expectSemicolonAfter`. A trailing expression before `}` may now omit its `;` (previously a parse error). Match-arm and else-arm bodies are built value-producing regardless of the arm `;` (arms are exempt — the `;` is an arm terminator). - Lowering: `lowerBlockValue` / the block-expr path / `inferExprType` respect `produces_value`. A value-position block that discards its value is a hard error (`lowerValueBody` for function bodies; the value-context `.block` path for if/else branches, `catch` bodies, value bindings, match arms). Pure-failable `-> !` bodies (value rides the error channel) and a value-if whose branches are void are handled without false errors. - `defer`/`onfail` cleanup bodies lower as statements (void), so a trailing `;` there is fine. Migration (behavior-preserving — output unchanged): - stdlib + ~210 examples: dropped the trailing `;` on value-position last expressions. `format` now ends with an explicit `#insert "return result;"` (it relied on `#insert`-as-block-value, which `;` discards). - Two `main :: () -> s32` examples that relied on the old silent default-return got an explicit trailing `0`. - Rejection snapshots 0412 / 1013 regenerated (their quoted source lines lost a `;`); the diagnostics themselves are unchanged. Docs/tests: specs.md "Block values" section; examples 0040 (rules) + 0041 (rejection); 3 parser unit tests. Filed issue 0066 (pre-existing match-arm negated-literal phi-width quirk, surfaced not caused here). Gates: zig build, zig build test, run_examples.sh -> 343 passed, cross_compile.sh -> 7 passed (also refreshed its stale example names).
39 lines
1.3 KiB
Plaintext
39 lines
1.3 KiB
Plaintext
// Feature 1 — TYPE-position pack projection `xs.T`. The per-element protocol
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// type-arg `T` projects into a Pack of types, usable in type/signature
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// positions: a tuple type `(..xs.T)` and a closure signature
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// `Closure(..xs.T) -> R`. (`T` of each element comes from its
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// `impl Box(T) for <elem>`.)
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#import "modules/std.sx";
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Box :: protocol(T: Type) {
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get :: () -> T;
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}
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IntCell :: struct { v: s64; }
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StrCell :: struct { s: string; }
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Dbl :: struct { n: s64; }
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impl Box(s64) for IntCell { get :: (self: *IntCell) -> s64 => self.v; }
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impl Box(string) for StrCell { get :: (self: *StrCell) -> string => self.s; }
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impl Box(s64) for Dbl { get :: (self: *Dbl) -> s64 => self.n * 2; }
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// Tuple type `(..xs.T)` — heterogeneous (s64, string), matched by the
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// value-projection `(..xs.get)`.
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snap :: (..xs: Box) -> void {
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t : (..xs.T) = (..xs.get);
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print("0={} 1={}\n", t.0, t.1);
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}
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// Closure signature `Closure(..xs.T) -> s64` — here `Closure(s64, s64) -> s64`.
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// The closure literal's params are contextually typed from the projection.
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fold :: (..xs: Box) -> s64 {
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cb : Closure(..xs.T) -> s64 = (a, b) => a + b;
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return cb(xs[0].get(), xs[1].get());
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}
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main :: () -> s32 {
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snap(IntCell.{ v = 42 }, StrCell.{ s = "hi" }); // (s64, string)
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print("fold={}\n", fold(IntCell.{ v = 10 }, Dbl.{ n = 5 })); // 10 + 10 = 20
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0
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}
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