[Haskell-cafe] Being Compatible

Hi, I have appreciated some of the comments here about what exactly is standardized. My next question is how to work at the greatest number of places. I am working on a library of Haskell-related utilities. There is some code in there that works with binary I/O, and some code that works with rawSystem(), etc. Some of these are not supported on Hugs, nhc98, or ghc5 to varying degrees. My initial thought was to use the cpp-style ifdefs I've seen elsewhere to mask those unsupported features on those particular systems. But Hugs at least doesn't support that, and I've found it extremely difficult to find a list of predefined macros for the other systems anyway. What is the suggested way to work around these problems?