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

[A.J. Bonnema]

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,
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