[Haskell] newbie question: variable not in scope: "isSpace"

If I use isSpace from the hugs interpretor, it works. If I use isSpace from a test.hs file I get the error message: Undefined variable "isSpace" From ghc I get the error message: Variable not in scope: "isSpace" What is wrong? Guus. -- A.J. Bonnema, Leiden The Netherlands, user #328198 (Linux Counter http://counter.li.org)