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).
47 lines
1.5 KiB
Plaintext
47 lines
1.5 KiB
Plaintext
// Block value rule: a block's value is its last statement ONLY when that
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// statement is a trailing expression with NO `;`. A trailing `;` discards the
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// value, leaving the block void. This makes value-vs-statement explicit and lets
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// the compiler reject "forgot to produce a value".
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//
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// { … expr } → value is `expr`
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// { … expr; } → void (value discarded)
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//
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// Match arms are exempt: the arm `;` is an arm terminator, so `case .x: expr;`
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// still yields `expr` (only an explicit inner braced block follows the rule).
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#import "modules/std.sx";
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// Implicit return: trailing expression, no `;`.
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double :: (n: s32) -> s32 { n * 2 }
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// if/else as a value — each branch's last expression has no `;`.
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sign :: (n: s32) -> s32 {
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if n < 0 { -1 } else if n > 0 { 1 } else { 0 }
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}
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// A value-producing block bound to a name.
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sum3 :: (a: s32, b: s32, c: s32) -> s32 {
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t := { x := a + b; x + c }; // block value is `x + c`
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t
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}
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// Match arms keep their `;` (exempt): the arm `;` is an arm terminator, so each
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// arm still yields its expression as the match value.
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classify :: (n: s32) -> s32 {
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if n == {
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case 0: 100;
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case 1: 10;
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else: 7;
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}
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}
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main :: () -> s32 {
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total : s32 = 0;
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total = total + double(10); // 20
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total = total + sign(-7); // -1
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total = total + sum3(1, 2, 3); // 6
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total = total + classify(1); // 10
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print("block-value total: {}\n", total); // 20 - 1 + 6 + 10 = 35
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total
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}
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