Indeed. The base3/base4 simultaneous install. http://haskell.org/haskellwiki/Upgrading_packages#runhaskell Two solutions: cabal install quickcheck (will determine the base dependency correct). or: runhaskell Setup.hs configure --constraint='base<4' dominic.steinitz:

Having been a happy user of QuickCheck 2 for many years, I now find it won't build under ghc 6.10.1. Before I investigate further, has anyone encountered this problem and has a fix?

Thanks, Dominic.

...

C:\Users\Dom\QuickCheck>Setup build Preprocessing library QuickCheck-2.0... Building QuickCheck-2.0... [2 of 9] Compiling Test.QuickCheck.Exception ( Test\QuickCheck\Exception.hs, dis t\build\Test\QuickCheck\Exception.o )

Test\QuickCheck\Exception.hs:12:31: Class `Exception' used as a type In the type `Exception' In the type `Either Exception a' In the type `IO (Either Exception a)'

Test\QuickCheck\Exception.hs:15:36: Class `Exception' used as a type In the type `Exception' In the type `Either Exception a' In the type `IO (Either Exception a)'

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