I have the same problem as this guy: http://www.mail-archive.com/yhc%40haskell.org/msg00423.html I would really like to fix this. 1) it always builds the first time 2) it always fails after running scons clean This is major problem for me, because I need to clean and rebuild to make sure that my added libraries build correctly. I have installed working libs of Data.Map and dependencies including IORef on my machine, but I can't submit the patch yet because it doesn't build from scratch. As it is I have to darcs record and then darcs pull to a fresh repository. Passing stuff that I don't fully understand to xargs rm -rf does not appeal to me, [joke or anecdote about yet another accident with rm -rf]! Second question: is there a preferred way to rebuild Prelude.hi? I've been using yhc -c -rebuild -prelude Prelude.hs and copying the result into bootstrap/. Third question: is there a standard test suite for the base libraries? I couldn't find one in google. My only test so far is that 5 + 3 = 8 using modifyIORef to do the addition. My work so far is here: http://www.downstairspeople.org/darcs/yhc_clanehin