On Thu, Aug 25, 2011 at 04:47:30PM +0100, Ozgur Akgun wrote:
> Hi,
>
> cabal installing haskell-src-exts fails, because of an unlisted dependency
> to the happy executable.

It does list a dependency on happy:

   Build-Tools:          happy >= 1.17

If I understand correctly, the problem is that cabal does not track
packages which only install executables.  So all it can do is give an
error if a 'happy' executable is not found; there is no way to have it
automatically install happy if it is not.  This is a well-known
limitation of cabal-install rather than a problem with the
 haskell-src-exts package in particular.