RE: Calling an external command from a Haskell program

PS. why the differences in default access to standard modules? should GHC be more restrictive there?

No, this is a feature. See http://www.haskell.org/ghc/docs/latest/html/users_guide/x1097.html#GHCI-SCOP... in particular section 3.4.1.1. Cheers, Simon