Integrating editline with ghc

[Manuel M T Chakravarty]

Judah Jacobson:
> Hackage link: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/editline-0.1
> Haddock: http://code.haskell.org/editline/dist/doc/html/editline/
>
> As I've mentioned before, there are two independent modules:
> - System.Console.Editline is a very basic (and experimental) interface
> to the native editline APIs.
> - System.Console.Editline.Readline contains the readline APIs provided
> by the editline library (mostly a cut/paste of
> System.Console.Readline).
>
> Currently I'm using just the latter as a drop-in replacement for
> System.Console.Readline in ghci.  I have added a --with-editline flag
> to ghc's configure script, which has no effect if it's not specified,
> and otherwise does the following:
>
> - Throw an error (at configure time) if editline isn't present (as
> $hardtop/libraries/editline)
> - Use the editline package instead of readline when building ghc  
> stage 2
> - Use CPP to make InteractiveUI.hs (the main ghci loop) import
> System.Console.Editline.Readline instead of System.Console.Readline.
>
> Does that sound like the right way to handle this?  If so, I'll send a
> darcs patch.

Sounds good to me.

> Also, should editline be made a boot-package or an extra-package (or  
> neither)?

Given that we like this to be the default on some platforms, I believe  
it belongs into boot-packages (just like readline).

Manuel