When I turned on "-Wall" knob at compile time, I got a message: Warning: Module `System.Cmd' is imported, but nothing from it is used, except perhaps instances visible in `System.Cmd' To suppress this warning, use: import System.Cmd() Then I did four experiments as follows at compile time: 1) import System.Environment 2) import System.Environment() 3) import System.Environment(only the functions I used) 4) -- import System.Environment It turned out that case 1-3) have the size after compilation, and that case 4) has smaller size than the others. Can we make GHC a little bit more intelligent to automatically exclude unused modules at compile time as in case 4)? (Am I just too lazy to add several dashes?) Thanks, Hong