0bbff9d7fb
`expr catch [e] BODY` consumes a failable's error inline. Pure-failable slice
(value-carrying `-> (T, !)` catch deferred to E2's tuple ABI).
- lowerExpr `.catch_expr` -> lowerCatch; inferExprType `.catch_expr` ->
operand's success type (void for pure-failable).
- lowerCatch: operand must be failable (else "catch requires a failable
expression"); pure-failable LHS only (value-carrying bails to E2). Eval
operand -> err tag; condBr to handle (error) / merge (success). In handle:
child scope binds `e` to the tag (typed as the error set), lower body
(block or expr); if the body didn't diverge, br merge. Result is void.
`catch` needs no failable enclosing function — it handles the error locally.
- All four body forms work: block, no-binding `catch { }`, bare-expr, and
the match-body `catch e == { case ... }`. Re-raise (`raise e`) and diverging
bodies (`return`) rely on E1.3 / E1.4c.
Also: lowerMatch now supports error-set subjects — `case .X` resolves to the
global tag id (was the arm index, dispatching wrong), and the switch operand
is the error-set value (its u32 tag) directly rather than via enumTag. This
is what the catch match-body form (and a plain `if e == { case .X }`) needs.
Tests: examples/226-catch.sx (block / no-binding / match-body / re-raise /
diverging body / success-skip; exit 18), examples/227-catch-rejections.sx
(operand-not-failable; exit 1). Gates: zig build, zig build test,
265/265 examples.
65 lines
2.5 KiB
Plaintext
65 lines
2.5 KiB
Plaintext
// `catch` on a pure-failable LHS (ERR step E1.5). `expr catch [e] BODY`
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// consumes the error inline: on failure it binds the tag to `e` (optional)
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// and runs BODY; on success the result is void (a `-> !` LHS has no success
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// value). BODY may diverge (`return` / `raise` — typed `noreturn`, E1.4c) or
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// fall through. `catch` needs no failable *enclosing* function — it handles
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// the error locally. All four body forms appear below: block, no-binding
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// block, match-body (`== { case ... }`), and the selective handle + re-raise
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// pattern. Value-carrying `-> (T, !)` catch (binding the success value) lands
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// with the tuple ABI in E2.
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#import "modules/std.sx";
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E :: error { Bad, Empty }
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must :: (n: 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;
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}
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// Diverging body — returns from `classify` on error.
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classify :: (n: s32) -> s32 {
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must(n) catch e {
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if e == error.Bad { return 1; }
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if e == error.Empty { return 2; }
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return 9;
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};
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return 0; // must(n) succeeded
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}
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// Match-body form — sugar for `catch e { if e == { case ... } }`.
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mclassify :: (n: s32) -> s32 {
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must(n) catch e == {
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case .Bad: return 11;
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case .Empty: return 22;
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else: return 99;
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};
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return 0;
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}
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// Selective handle + re-raise (failable enclosing fn; `raise e` is the
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// variable form). Swallows Bad → success; re-raises everything else.
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handle_some :: (n: s32) -> !E {
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must(n) catch e {
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if e == error.Bad { return; } // swallow → success
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raise e; // re-raise the rest
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};
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return;
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}
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main :: () -> s32 {
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r : s32 = 0;
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must(-1) catch e { if e == error.Bad { r = r + 1; } }; // Bad → +1
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must(5) catch { r = r + 100; }; // success → body skipped
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r = r + classify(0); // Empty → 2
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r = r + classify(8); // success → 0
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he := handle_some(0); // Empty re-raised
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if he == error.Empty { r = r + 4; } // +4
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hb := handle_some(-1); // Bad swallowed → success
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if hb == error.Bad { r = r + 50; } // not taken
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r = r + mclassify(-1); // Bad → 11
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print("catch result: {}\n", r); // 1+2+4+11 = 18
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return r;
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}
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