def tf(expr a) = if a: "true" else: "false" fi enddef;
def test(expr a, b) =
  for o = "and", "or":
    message tf(a) & " " & o & " " & tf(b);
    show a scantokens(o) b;
  endfor
  message "not " & tf(a);
  show not a enddef;