ghci-haskeline (was: Re: ANNOUNCE: GHC version 6.10.1 - EditLine / terminal incompatibility?)

Judah Jacobson judah.jacobson at
Fri Nov 21 04:29:00 EST 2008

On Thu, Nov 20, 2008 at 7:16 AM, Ian Lynagh <igloo at> wrote:
> Although another option would be to make GHCi a separate (GPL) frontend
> to the (BSD) GHC API. The only downside is that (with static linking) we
> have another large binary. Another upside is that other GHC API users
> don't get an editline dependency.

I've actually been experimenting with something similar:

darcs get

If you have ghc-6.10.1, 'cabal install'ing inside that repo will give
you a version of ghci which uses Haskeline as its backend.

Basically, I copied 4 modules from the GHC source tree (GhciMonad,
InteractiveUI, GhciTags and Main) and modifed them to use Haskeline;
the rest of GHC is obtained through the API.

Current benefits over the readline/editline versions:
- Works on Windows
- Tab completion of quoted filenames within Haskell expressions
- Tab completion of Unicode identifiers (trac #2058)
- Internally, eliminates the need for some GLOBAL_VARs

The only real regression I'm aware of is that Haskeline doesn't yet
provide a way to "bind" custom key commands as in an inputrc or editrc
file.  The recent discussion has indicated how important that feature
is for some users, so it's next on my TODO list.


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