[Nix-dev] haskell: overriding mtl/any builtin

[Mateusz Kowalczyk]

Hi,

GHC ships with a bunch of libraries that are exposed. How can we
override those so that the compilation still succeeds and we don't end
up with two versions in scope?

A sample use-case is using things which depend on ‘mtl’ >2.1.2. Usually
I try to work with upstream to make the bound more flexible but this is
suboptimal.

In this case the problem is with the Haskell ‘cgi’ package which needs
mtl 2.2.1: they had fixed up some failures for 7.8.3 so that it could
compile but we fail at the configure stage. Normally a user would just
cabal-install mtl so how do we adapt? Assume jailbreak doesn't work.
-- 
Mateusz K.