I upgraded from GHC 6.6.1 to 6.8.1 and around that time I noticed that the output from an app I am working on changed. I have distilled the code down to the following example that produces different output depending on whether it is compiled with -O2 or not: main = do let (T x) = read "T 3" print $ f x print $ g x data T = T Int deriving (Read, Show) f x = truncate $ 2000 / fromIntegral ((x * 25) + 10) g :: Int -> Int g x = f x Here is the transcript from a shell (example code is saved in test.hs): $ ghc --make test.hs [1 of 1] Compiling Main ( test.hs, test.o ) Linking test ... $ ./test 23 23 $ rm test.hi test.o test $ ghc -O2 --make test.hs [1 of 1] Compiling Main ( test.hs, test.o ) Linking test ... $ ./test 23 24 It is a little disconcerting that -O2 changes the output. :-) Regards brad -- www.scoodi.com Contribute things you don't need and find things you do, all within your local community.