js.compile.ignore=true
=====
>>> main.whiley
type Rec is {int f, int g}

function setz(Rec rec, int x) -> (Rec r)
ensures r.f == x && r.g == rec.g:
    return rec{f:=x}
    
public export method test():
   Rec rs = {f:1,g:2}
   assert setz(rs,0) == {f:0,g:2}
   assert setz(rs,2) == {f:2,g:2}
   assert setz(rs,3) == {f:3,g:2}   
---