We intend to provide more and more ready-to-use Haskell code, so that every program doesn't have to invent everything from scratch.
At the moment, we supply a part of the HBC library, as well as the beginnings of one of our own ("GHC library").
If you provide a `-syslib <name>' option, then the interfaces for that library will come into scope (and may be `import'ed), and the code will be added in at link time.