// `onfail` — cleanup that runs only when an error LEAVES the enclosing block
// (ERR step E1.7). Unlike `defer` (which runs on every exit), `onfail` fires
// on an error exit — a `raise` or a propagating `try` — and is skipped on
// success. On an error exit `defer` and `onfail` run interleaved in reverse
// declaration order. `onfail e { … }` binds the in-flight error tag.
// (Per-attempt-`try` gating and `or`-chain absorption refine this in E2.4b.)

#import "modules/std.sx";

E :: error { Bad }

inner :: (n: s32) -> !E {
    if n < 0 { raise error.Bad; }
    return;
}

// defer + onfail interleave on the error path; only defers on success.
run :: (n: s32) -> !E {
    defer  print("defer A\n");
    onfail print("onfail B\n");
    defer  print("defer C\n");
    try inner(n);                       // n<0 → propagates → onfail fires
    return;
}

// `onfail e` binds the tag.
classify :: (n: s32) -> !E {
    onfail e { if e == error.Bad { print("cleanup: bad\n"); } }
    if n < 0 { raise error.Bad; }
    return;
}

main :: () -> s32 {
    print("[fail]\n");
    a := run(-1);                       // error → defer C, onfail B, defer A
    print("[ok]\n");
    b := run(7);                        // success → defer C, defer A (no onfail)
    print("[bound]\n");
    c := classify(-1);                  // onfail binding sees Bad
    print("[done]\n");
    return 0;
}