Integrating editline with ghc

[Manuel M T Chakravarty]

Malcolm Wallace:
> Christian Maeder <Christian.Maeder at dfki.de> wrote:
>
>> 1. a _new_ readline package that only contains the interface that can
>> be implemented using libeditline _or_ libreadline. If this package is
>> call "readline" (with a new version number) most libraries i.e. like
>> Shellac would not need modifications.
>
> I totally agree.  Backwards compatibility for all the programs out  
> there
> that already use the readline package (but really don't care whether  
> it
> is actually readline or editline) is vital.  I would hate to see all
> client code forced to use CPP macros and cabal magic to select the  
> right
> package and module imports.  We can avoid such a retrograde step by
> explicitly making 'readline' the backend-agnostic package, which
> re-exports functionality from either the real readline or editline,
> depending on which is available.

I don't think we should touch the existing readline package.  It's a  
binding to readline and whether everybody likes its license or not  
doesn't matter.  Some people just want to use readline, and they  
should be able to continue to do this by importing the library called  
System.Console.Readline.

In addition System.Console.Editline should be a binding to editline.   
(Again if somebody want editline and nothing else, that's what they  
import.)

Finally, we'd like a module (let's call it EditReadline) whose  
interface coincides with the readline emulation layer of editline (ie,  
<editline/readline.h>).  This module should use editline where it is  
available and otherwise readline (if that is available).  We can argue  
about where in the hierarchy EditReadline should be located (and  
whether we want to call it EditReadline or something else).  Following  
Judah's proposal, it could be System.Console.Editline.Readline  
(essentially following the C header structure), but it could  
alternatively be System.Console.EditReadline (or something else).

I think it is important to make a clear distinction between these  
*three* interface for two reasons:

   * Both editline and readline have functionality that is not exposed  
by EditReadline (aka <editline/readline.h>).
   * Static linking against EditReadline is allowed for non-GPL  
compatible code only on systems that have editline.

Manuel