[Nix-dev] Agda build

[Andres Loeh]

> Thanks for reviewing Peter.  It occurs to me that maybe Agda should have
> a local mtl (as haskeline) ... Andres, would that avoid the earlier problem
> related to mtl in r34358?

I'm in general in favour of trying to patch packages to build with the
later mtl rather than forcing them to use the older one. I had patched
xmobar (iirc) a few days ago, and asked a similar change to be revoked
because it was forcing xmobar to an older version of mtl after I had
already patched it to work with the latest.

Here I'd also try if Agda doesn't in fact work with mtl-2.1.1 and
transformers-3. If it really doesn't, these changes are ok.

Cheers,
  Andres