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
// Slice-of-protocol variadic `..xs: []P` — the RUNTIME counterpart to the
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// comptime pack `..xs: P`. Each trailing arg is `xx`-erased to a `P` protocol
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// value {ctx, vtable} and packed into a runtime `[]P`, so the elements can be
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// indexed by a RUNTIME index and dispatched through the protocol interface
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// (unlike a pack, which is comptime-only — see examples/163).
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//
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// This is the type-safe way to iterate a heterogeneous arg list at runtime:
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// concrete per-position types are erased to the constraint protocol.
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#import "modules/std.sx";
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Show :: protocol { show :: () -> string; }
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A :: struct { x: s64; }
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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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// Runtime loop over a []Show: runtime index + protocol-method dispatch.
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each :: (..xs: []Show) -> void {
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i := 0;
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while i < xs.len {
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print("[{}]={}\n", i, xs[i].show());
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i = i + 1;
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}
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}
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main :: () -> s32 {
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each(A.{ x = 1 }, B.{ s = "hi" }, A.{ x = 3 }); // heterogeneous, erased to Show
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each(); // empty is fine (len 0)
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0
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}
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