// Flow narrowing extends to binary-op OPERANDS: a `?T` proven present by a
// `!= null` guard reads as its concrete payload in arithmetic / comparison.
//
// Regression (issue 0185): an un-narrowed `?T` operand used to unwrap
// unconditionally, so `null + 10` silently yielded `10` (the zero payload).
// Narrowing is now the only implicit operand unwrap; everything else is a
// compile error (see 0922).
#import "modules/std.sx";

sum :: (a: ?i64, b: ?i64) -> i64 {
    if a == null or b == null { return -1; }
    return a + b;          // both operands narrowed
}

main :: () {
    x : ?i64 = 30;
    y : ?i64 = 12;
    if x != null and y != null {
        print("add {}\n", x + y);     // 42
        print("lt {}\n", x < y);      // false
    }
    print("sum 11: {}\n", sum(5, 6));     // 11
    print("sum null: {}\n", sum(5, null)); // -1

    // guard form narrows for the rest of the scope
    n : ?i64 = 9;
    if n == null { return; }
    print("times {}\n", n * 2);       // 18
}