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).
34 lines
1.2 KiB
Plaintext
34 lines
1.2 KiB
Plaintext
// Phase 6 / issue 0054 — generic-struct → parameterized-protocol erasure.
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// - A generic-struct impl method `self: *Box` now resolves `self.field` to the
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// concrete INSTANCE (the template name binds to the instance type), so
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// `self.x` works (was "field not found on type 'Box'").
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// - `xx c` erases a generic-struct instance (`Combined__s64_s64`) to a
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// parameterized protocol (`VL(s64)`) via the generic
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// `impl VL($R) for Combined($R, ..$Ts)`: the thunk monomorphizes the
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// template method for the instance and dispatch works (was a trap).
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#import "modules/std.sx";
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VL :: protocol(T: Type) { get :: () -> T; }
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IntCell :: struct { v: s64; }
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impl VL(s64) for IntCell { get :: (self: *IntCell) -> s64 => self.v; }
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Combined :: struct($R: Type, ..$Ts: []Type) {
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sources: (..VL(Ts));
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value: $R;
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}
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impl VL($R) for Combined($R, ..$Ts) { get :: (self: *Combined) -> $R => self.value; }
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make :: (..sources: VL) -> VL(s64) {
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c : Combined(s64, ..sources.T) = ---;
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c.value = 99;
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c.sources = (..sources);
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return xx c; // Combined__s64_s64 -> VL(s64)
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}
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main :: () -> s32 {
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r := make(IntCell.{ v = 1 });
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print("{}\n", r.get()); // 99 (dispatch through the erased Combined)
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0
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}
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