original.name="TypeEquals_Valid_53"
======
>>> main.whiley
function f(int|null x) -> (int r)
ensures r == 0 || r == x:
    //
    if x is int && x >= 0:
        return x
    else:
        return 0

public export method test():
    assume f(-1) == 0
    assume f(0) == 0
    assume f(1) == 1
    assume f(2) == 2
    assume f(null) == 0    
---