Re: Ambiguous types

| Of course not, show doesn't know how to show things of | arbitrary type [a]. But null is supposed to work on | _any_ list. And just from the type of emptyList, | Haskell knows that it is a list of something. But from the type you give the function `emptyList': emptyList :: Ord a => [a] we cannot derive that the type of the function `emptyList' does not matter for its result. So, the type checker will complain. If you change the implementation of a function without changing its type, the type checker should still accept the program. /Koen.