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).
33 lines
1.1 KiB
Plaintext
33 lines
1.1 KiB
Plaintext
// `xx <pack>` materializes a comptime pack into a runtime slice (issue 0053):
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// the explicit pack→slice bridge. With a `[]Any` target each element is boxed
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// to `Any`; with a `[]P` target each is `xx`-erased to the protocol `P`. This is
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// how you forward a pack to a runtime (`[]Any` / `[]P`) helper.
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#import "modules/std.sx";
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Show :: protocol { show :: () -> string; }
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A :: struct {}
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B :: struct { s: string; }
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impl Show for A { show :: (self: *A) -> string => "A"; }
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impl Show for B { show :: (self: *B) -> string => "B"; }
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count_any :: (items: []Any) -> s64 { return items.len; }
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show_all :: (items: []Show) -> s64 {
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i := 0;
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while i < items.len { print("{}\n", items[i].show()); i = i + 1; }
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return items.len;
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}
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// `..$args` pack → []Any via `xx`.
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fwd_any :: (..$args) -> s64 { return count_any(xx args); }
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// `..xs: Show` pack → []Show via `xx`.
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fwd_show :: (..xs: Show) -> s64 { return show_all(xx xs); }
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main :: () -> s32 {
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print("any={}\n", fwd_any(1, "hi", 2.5)); // 3
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print("show={}\n", fwd_show(A.{}, B.{ s = "x" }, A.{})); // A B A, 3
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0
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}
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