This is where it gets weird on my system sh-4.3$ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.8.3 sh-4.3$ ghc -Wall -We

This is where it gets weird on my system sh-4.3$ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.8.3 sh-4.3$ ghc -Wall -Werror test.hs sh-4.3$ Arch Linux 64bit. It works as expected with runhaskell though Edit: see answer below, thanks dilthomas!