[Haskell] overuse of maybe and [] in prelude and libs

[Simon Marlow]

> But, either way, I'm assuming I can't do this
> (making up syntax):
> 
>    import Data.FiniteMap using MyPrelude as Prelude
> 
> So that every place in FiniteMap that Prelude
> functions are called, MyPrelude functions are
> called instead?  Then I could simply redefine just
> and nothing as return and mzero.

Not possible with GHC, I'm afraid.  At least, not at the moment.  We
would have to retain a strong separation between Data.FiniteMap and
Prelude, such as you would do if the Prelude were dynamically linked,
and GHC doesn't do that.  

Indeed, doing so would probably have a significant impact on
performance, because the compiler wouldn't be able to take advantage of
any knowledge about the Prelude except for the types of functions when
compiling Data.FiniteMap.

Cheers,
	Simon