IPFail.hs:6:18:
    Could not deduce (Num Bool) arising from the literal `5'
    from the context (?x::Int)
      bound by the type signature for f0 :: (?x::Int) => () -> Bool
      at IPFail.hs:6:1-24
    Possible fix:
      add (Num Bool) to the context of
        the type signature for f0 :: (?x::Int) => () -> Bool
      or add an instance declaration for (Num Bool)
    In the expression: 5
    In the expression: let ?x = 5 in ?x
    In an equation for `f0': f0 () = let ?x = 5 in ?x