I had a problem building gtk in a system with C locale. It was a not very
verbose problem, so it took me some time to figure out what was going wrong.
The problem was:
ghc --make Setup
The last command gave me only:
Setup: ./Graphics/UI/Gtk/General/IconTheme.chs: invalid argument
I could locate the problem including some putStrLn in the code, and I got to
this patch. It's going to be included in the Debian distribution.