Hi Bulat,
i think that the best way is to
module FilePath
import FilePath.Windows as Windows import FilePath.Unix as Unix
isProperPath = if weOnWindows then Windows.isProperPath else Unix.isProperPath
That results in an awful lot of boilerplate code (about 3 lines per function), plus reduces the amount of sharing between Windows and Unix - they are almost identical. If you look at the current method, FilePath has all the code, and Windows and Posix use clever CPP hacks to get it all working. Although these hacks are clever, I don't want them to go in base, its not good style.
then GHC can optimize it, throwing away unused branch at compile-time. and yhc will work just fine with its portable bytecode
As it stands currently, GHC can optimise and yhc can do it portably. Hugs can even use it without CPP - everyone should be happy ;) Thanks Neil