On Fri, 11 Jan 2008, Luke Palmer wrote:
So, when you write the number 3 in Haskell, GHC converts this to essentially (Prelude.fromInteger (3::Integer)) in its internal format. So it doesn't matter if you import Prelude (), Prelude's version of fromInteger still gets called. If you give -fno-implicit-prelude, then this is converted to simply (fromInteger (3::Integer)), without the hard-coded prelude reference. That means you could write your own version of fromInteger that does something different. A common usage for -fno-implicit-prelude (insofar as it is used at all, which is seldom) is to replace the standard Num hierarchy with a saner one, with numeric literals resolving to that one instead.
There are a few other hard-coded references to Prelude in the internal format, but I don't remember what they are offhand. -fno-implicit-prelude gets rid of those, too.
For details, see: http://www.haskell.org/ghc/docs/latest/html/users_guide/ghc-language-feature... I have summarized the answers so far: http://www.haskell.org/haskellwiki/No_import_of_Prelude