// Consuming value-carrying failables with `try` and `catch` (ERR step E2.1b —
// the consumer side of the error-channel tuple ABI). `try f()` on a
// `-> (T, !E)` callee binds the value slot on success and propagates the error
// on failure (a pure-failable caller returns the tag; a value-carrying caller
// returns `{undef, tag}`). `f() catch (e) BODY` yields the value slot on success
// or the handler body's value on failure, merged through a block parameter.
// The producer side is `examples/228-value-failable.sx`.

#import "modules/std.sx";

E :: error { Bad, Empty }

parse :: (n: i32) -> (i32, !E) {
    if n < 0  { raise error.Bad; }
    if n == 0 { raise error.Empty; }
    return n * 2;
}

// value-carrying `try` in a value-carrying caller — propagates {undef, tag}.
inc :: (n: i32) -> (i32, !E) {
    v := try parse(n);
    return v + 1;
}

// value-carrying `try` in a pure-failable caller — propagates the tag.
relay :: (n: i32) -> !E {
    v := try parse(n);
    if v < 0 { raise error.Bad; }
    return;
}

// value-carrying `catch`, bare-expression fallback.
safe :: (n: i32) -> i32 {
    return parse(n) catch (e) 0;
}

// value-carrying `catch`, match-body value.
classify :: (n: i32) -> i32 {
    return parse(n) catch (e) == {
        case .Bad:   1;
        case .Empty: 2;
        else:        3
    };
}

main :: () -> i32 {
    r : i32 = 0;
    a, ea := inc(5);                      // parse(5)=10 → v=10 → 11
    if !ea { r = r + a; }                  // success → +11 (value live only when proven ok)
    b, eb := inc(-1);                      // parse(-1)=Bad → propagate {undef, Bad}
    if eb == error.Bad { r = r + 4; }      // true → +4
    er := relay(3);                        // parse(3)=6 ok → relay ok
    if er == error.Bad { r = r + 50; }     // false
    r = r + safe(7);                       // parse(7)=14 → +14
    r = r + safe(-1);                      // Bad → catch → 0
    r = r + classify(-1);                  // Bad → 1
    r = r + classify(0);                   // Empty → 2
    print("consume result: {}\n", r);      // 11+4+14+0+1+2 = 32
    return r;
}