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).
40 lines
1.5 KiB
Plaintext
40 lines
1.5 KiB
Plaintext
// Feature 1 — heterogeneous protocol-constrained variadic pack (binding).
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//
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// `..xs: Show` (no `[]`, no `$`) is a pack, not a slice: each call site
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// monomorphizes with the concrete per-position arg types (Decision 1 — a pack
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// is a comptime mechanism, no runtime pack value), and `xs.len` is a comptime
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// constant. Arity and element types vary per call; each call is a distinct
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// specialization.
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//
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// DESIGN (locked): a pack element is viewed THROUGH the protocol — only the
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// protocol's own interface (its methods, and the projections `xs.T` / `xs.value`)
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// is accessible, NOT arbitrary concrete members. So `xs[i].get()` / `xs.T` are
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// the intended interface; `xs[i].v` (a field on the concrete IntBox, not part
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// of `Show`) is an error. Those are still being implemented — this example
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// locks in only the binding + comptime `xs.len`, the protocol-agnostic part.
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#import "modules/std.sx";
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Show :: protocol(T: Type) {
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get :: (self: *Self) -> T;
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}
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IntBox :: struct { v: s64; }
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StrBox :: struct { s: string; }
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impl Show(s64) for IntBox { get :: (self: *IntBox) -> s64 => self.v; }
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impl Show(string) for StrBox { get :: (self: *StrBox) -> string => self.s; }
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howmany :: (..xs: Show) -> s64 {
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return xs.len;
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}
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main :: () -> s32 {
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a := IntBox.{ v = 42 };
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b := IntBox.{ v = 7 };
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c := StrBox.{ s = "cool" };
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print("n0={}\n", howmany()); // empty pack
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print("n2={}\n", howmany(a, b)); // two elements
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print("n3={}\n", howmany(a, b, c)); // heterogeneous: IntBox, IntBox, StrBox
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0
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}
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