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).
61 lines
2.1 KiB
Plaintext
61 lines
2.1 KiB
Plaintext
// Consuming value-carrying failables with `try` and `catch` (ERR step E2.1b —
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// the consumer side of the error-channel tuple ABI). `try f()` on a
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// `-> (T, !E)` callee binds the value slot on success and propagates the error
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// on failure (a pure-failable caller returns the tag; a value-carrying caller
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// returns `{undef, tag}`). `f() catch e BODY` yields the value slot on success
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// or the handler body's value on failure, merged through a block parameter.
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// The producer side is `examples/228-value-failable.sx`.
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#import "modules/std.sx";
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E :: error { Bad, Empty }
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parse :: (n: s32) -> (s32, !E) {
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if n < 0 { raise error.Bad; }
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if n == 0 { raise error.Empty; }
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return n * 2;
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}
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// value-carrying `try` in a value-carrying caller — propagates {undef, tag}.
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inc :: (n: s32) -> (s32, !E) {
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v := try parse(n);
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return v + 1;
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}
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// value-carrying `try` in a pure-failable caller — propagates the tag.
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relay :: (n: s32) -> !E {
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v := try parse(n);
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if v < 0 { raise error.Bad; }
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return;
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}
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// value-carrying `catch`, bare-expression fallback.
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safe :: (n: s32) -> s32 {
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return parse(n) catch e 0;
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}
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// value-carrying `catch`, match-body value.
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classify :: (n: s32) -> s32 {
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return parse(n) catch e == {
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case .Bad: 1;
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case .Empty: 2;
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else: 3
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};
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}
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main :: () -> s32 {
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r : s32 = 0;
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a, ea := inc(5); // parse(5)=10 → v=10 → 11
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if !ea { r = r + a; } // success → +11 (value live only when proven ok)
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b, eb := inc(-1); // parse(-1)=Bad → propagate {undef, Bad}
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if eb == error.Bad { r = r + 4; } // true → +4
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er := relay(3); // parse(3)=6 ok → relay ok
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if er == error.Bad { r = r + 50; } // false
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r = r + safe(7); // parse(7)=14 → +14
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r = r + safe(-1); // Bad → catch → 0
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r = r + classify(-1); // Bad → 1
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r = r + classify(0); // Empty → 2
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print("consume result: {}\n", r); // 11+4+14+0+1+2 = 32
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return r;
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}
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