57d8e327cd
`onfail [e] BODY` runs cleanup only when an error LEAVES the enclosing block
(a `raise` or a propagating `try`), and is skipped on success — unlike `defer`,
which runs on every exit. On an error exit, defers and onfails run interleaved
in reverse declaration order; `onfail e` binds the in-flight error tag.
- Cleanup stack: defer_stack now holds CleanupEntry { body, is_onfail, binding }
(one declaration-ordered stack so defer/onfail interleave). lowerDefer pushes
a defer entry; lowerOnFail (new `.onfail_stmt` arm) pushes an onfail entry,
rejecting `onfail` outside a failable function.
- emitBlockDefers (success exits — return / normal block exit) now emits only
`defer` entries and discards onfails.
- emitErrorCleanup (new; wired at the error exits — lowerRaise pure +
value-carrying, lowerTry propagation) emits both kinds interleaved in reverse,
binding the in-flight tag for `onfail e`.
Block-rooted: an error propagating to the function drains all enclosing blocks'
onfails; a block that exits normally discards its onfails. Per-attempt-`try`
gating is moot for now (no compilable `or` chain can absorb a mid-block try
failure yet — E2.4b). Body restrictions beyond the parser's raise-in-onfail
ban are deferred.
Tests: examples/233-onfail.sx (interleave order on error vs success + binding;
deterministic trace), examples/234-onfail-reject.sx (onfail outside a failable
fn rejected; exit 1). Gates: zig build, zig build test, 272/272 examples.
43 lines
1.4 KiB
Plaintext
43 lines
1.4 KiB
Plaintext
// `onfail` — cleanup that runs only when an error LEAVES the enclosing block
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// (ERR step E1.7). Unlike `defer` (which runs on every exit), `onfail` fires
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// on an error exit — a `raise` or a propagating `try` — and is skipped on
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// success. On an error exit `defer` and `onfail` run interleaved in reverse
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// declaration order. `onfail e { … }` binds the in-flight error tag.
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// (Per-attempt-`try` gating and `or`-chain absorption refine this in E2.4b.)
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#import "modules/std.sx";
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E :: error { Bad }
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inner :: (n: s32) -> !E {
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if n < 0 { raise error.Bad; }
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return;
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}
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// defer + onfail interleave on the error path; only defers on success.
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run :: (n: s32) -> !E {
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defer print("defer A\n");
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onfail print("onfail B\n");
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defer print("defer C\n");
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try inner(n); // n<0 → propagates → onfail fires
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return;
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}
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// `onfail e` binds the tag.
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classify :: (n: s32) -> !E {
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onfail e { if e == error.Bad { print("cleanup: bad\n"); } }
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if n < 0 { raise error.Bad; }
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return;
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}
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main :: () -> s32 {
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print("[fail]\n");
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a := run(-1); // error → defer C, onfail B, defer A
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print("[ok]\n");
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b := run(7); // success → defer C, defer A (no onfail)
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print("[bound]\n");
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c := classify(-1); // onfail binding sees Bad
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print("[done]\n");
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return 0;
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}
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