[Haskell-cafe] already installed packages alerted as not being installed

[Daniel Kahlenberg]

Hello cafe-readers,

does anyone of you observe similar problems e. g. on a Windows with
ghc-7.0.2 setup: When I'm trying cabal install threadscope (as an
example package depending on gtk2hs, latter which I've installed using
the stepwise approach of cabal unpack first, then cabal configure
--user etc.) it complains about cairo etc. not being installed and
tries to re-install it on-the-fly, failing due to whats described her:
http://hackage.haskell.org/trac/gtk2hs/ticket/1203!

When I install cabal-dev and cab first and then re-install everything
with cab instead of cabal the issue with re-installing already
installed packages described above disappears and only an "unknown
symbol" message related to the correctly found installed cairo package
remains. So is there an error in package database handling somewhere
or changed semantics in cabal | ghc-pkg | (even) pkg-config flags I
missed?

Cheers
Daniel