cabal "fails" with no explanation

[Stefan O'Rear]

stefan at stefans:/usr/local/src/xmonad$ runhaskell Setup.lhs clean -v5
cleaning...
stefan at stefans:/usr/local/src/xmonad$ echo $?
1
stefan at stefans:/usr/local/src/xmonad$ ghc -V
The Glorious Glasgow Haskell Compilation System, version 6.7.20070502
stefan at stefans:/usr/local/src/xmonad$

configure, build, and install all also work but return 1.

The same issue is observed with X11-extras.

Stefan