I'm running into problems with generating an arbitrary function of type Double -> Double. Specifically, the following code: {-# LANGUAGE PatternSignatures #-} import Test.QuickCheck import Text.Show.Functions prop_ok (f :: Double -> Double) = f (-5.5) `seq` True prop_bug (f :: Double -> Double) = f (-5.6) `seq` True main = do putStr "prop_ok:\t" >> quickCheck prop_ok putStr "prop_bug:\t" >> quickCheck prop_bug On an Intel Core 2 Duo running Mac OS 10.5.4 with GHC 6.8.2 the output I get is prop_ok: OK, passed 100 tests. prop_bug: Test: Prelude.(!!): negative index On Intel Xeon running RedHat with GHC 6.8.2 both tests hang. Has anyone seen this before? Is it fixed in QuickCheck2? Thanks, Patrick