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).
23 lines
875 B
Plaintext
23 lines
875 B
Plaintext
// Phase 4.2 — parameterized protocol as a runtime VALUE type. `VL(s64)` is a
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// 16-byte protocol value {ctx, vtable} (a plain protocol was already, but a
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// parameterized one used to resolve to a 0-field stub). A conforming struct
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// `xx`-erases into it, and method dispatch uses the bound type-arg
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// (`get -> T` becomes `get -> s64` for `VL(s64)`).
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#import "modules/std.sx";
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VL :: protocol(T: Type) { get :: () -> T; }
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IntCell :: struct { v: s64; }
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StrCell :: struct { s: string; }
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impl VL(s64) for IntCell { get :: (self: *IntCell) -> s64 => self.v; }
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impl VL(string) for StrCell { get :: (self: *StrCell) -> string => self.s; }
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main :: () -> s32 {
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a : VL(s64) = xx IntCell.{ v = 42 };
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print("a.get={}\n", a.get()); // 42 (T = s64)
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b : VL(string) = xx StrCell.{ s = "hi" };
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print("b.get={}\n", b.get()); // hi (T = string)
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0
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}
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