Cabal fails to install package with executables

[Isaac Jones]

> Installing: /opt/lib/Wash-2hs-1.4.34 & /opt/bin Wash-2hs-1.4.34...
> copy dist/build/wash2hs to /opt/bin/wash2hs
> *** Exception: dist/build/wash2hs: copyFile: does not exist (No such  
> file or directory)

This is a known bug with cabal 1.0 (which is what GHC currently comes
with).  There's a patch that was previously posted on this list, which
you might want to forward to the GHC maintainer for your platform.

Another solution is to use a newer version of cabal, though they are
all "unstable prerelase" versions:
http://haskell.org/cabal/download.html

peace,

  isaac