[Nix-dev] unable to expose libraries internal to GHC?

[Peter Simons]

Hi Corey

GHC 7.8.x installs a copy of xhtml, but it doesn't make that library
visible to users.

This choice causes us serious trouble that we cannot easily resolve: we
can't install your own copy of xhtml, because it collides with GHC's
copy (as you have found out). Yet, we cannot access GHC's copy either,
so we *need* to install our own version. Duh!

I've opened a ticket [1] for this issue a while ago, but GHC HQ hasn't
addressed it yet (probably because I didn't do a good job explaining why
this is issue is significant).

Anyway, you can use 'ghcWithPackagesOld' instead of 'ghcWithPackages' to
create your environment. ghcWithPackagesOld simply ignores all
collisions and chose a "random" version of the colliding paths to
include in the derivation. This sucks from an aesthetics point of view,
but it's probably going to work fine.

I hope this helps,
Peter


[1] https://ghc.haskell.org/trac/ghc/ticket/8919