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).
32 lines
1.1 KiB
Plaintext
32 lines
1.1 KiB
Plaintext
// Feature 1 — protocol-interface method calls on heterogeneous pack elements.
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//
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// `..xs: Greeter` binds per call shape; each `xs[i]` is the concrete element,
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// and calling the protocol's own method `greet()` on it dispatches to that
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// element's impl. Elements may be DIFFERENT concrete types (Dog, Cat) as long
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// as each conforms to Greeter — this is the protocol-interface access the
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// pack is for. (Protocol method decls omit the implicit `self`; impls list it.)
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#import "modules/std.sx";
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Greeter :: protocol {
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greet :: () -> s64;
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}
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Dog :: struct { age: s64; }
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Cat :: struct { lives: s64; }
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impl Greeter for Dog { greet :: (self: *Dog) -> s64 => self.age; }
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impl Greeter for Cat { greet :: (self: *Cat) -> s64 => self.lives * 100; }
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pair_sum :: (..xs: Greeter) -> s64 {
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return xs[0].greet() + xs[1].greet();
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}
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main :: () -> s32 {
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d := Dog.{ age = 3 };
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c := Cat.{ lives = 9 };
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print("dog+cat={}\n", pair_sum(d, c)); // 3 + 900 = 903 (heterogeneous)
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print("cat+dog={}\n", pair_sum(c, d)); // 900 + 3 = 903 (order swapped)
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print("dog+dog={}\n", pair_sum(d, Dog.{ age = 4 })); // 3 + 4 = 7
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0
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}
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