Modern GHC can't mix haskell98-style flat module names like Char or IO with the current Haskell standard's hierarchical libraries.  The first step to fixing this is to remove the haskell98 dependency from the cabal file; the next is to track down and replace any imported modules that are found to be missing:  for example, Char is now Data.Char and IO is split over a number of modules in the System.IO hierarchy.  You can use Hoogle or Hayoo (Haskell-specific search engines) to find the module that provides a given function.