I'm trying to see if this is reproducible, or it's just my machine. I'm on a MacBook Pro (15-inch, Mid 2012), OS X 10.8.2, Haskell Platform 2012.4.0.0 (32 bit): $ ghci GHCi, version 7.4.2: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> properFraction (-1.1 :: Float) (-1,-0.100000024) Prelude> properFraction (1.1 :: Double) (1,0.10000000000000009) Prelude> properFraction (-1.1 :: Double) (-1,Segmentation fault: 11 'ceiling' and other code that uses properFraction segfaults on negative doubles, too. Compiled code doesn't have this defect. I'm going to try the 64 bit version to see if it resolves this problem. -Ron Alford