On Fri, 17 Jun 2011, Simon Peyton-Jones wrote:
BUT (A) means that this module becomes un-compilable: module Main where import Random import Data.List Why? Because 'Random' comes from 'haskell98' and 'Data.List' comes from 'base'. But if you say ghc -c Main.hs -package base -package haskell98 then the (implicit) import of 'Prelude' will say "Ambiguous module name: Prelude", because it's exported by both 'base' and 'haskell98'. To fix this you have to change 'import Random' to 'import System.Random'. But the latter's API is different, so you may have to change the source code that uses it.
It would mean to change the import to import System.Random import Data.List which is fairly easy and would cleanly separate between haskell98-based code and base-based code. If someone wants to mix haskell98 and base, then he might want to write: {-# LANGUAGE NoImplicitPrelude #-} import Random import Data.List import haskell98:Prelude