when installing the the platform on windows it would help to add an additional step to the install procedure described here:
Haskell Platform Windows installation
The missing step is to change the following in the %APPDATA%\Roaming\cabal\config file:
one has to change the colon in
extra-prog-path: C:\Program Files\Haskell Platform\8.4.3\msys\usr\bin,
C:\Users[user]\AppData\Roaming\cabal\bindir
to a semicolon
extra-prog-path: C:\Program Files\Haskell Platform\8.4.3\msys\usr\bin;
C:\Users\[user]\AppData\Roaming\cabal\bindir
otherwise some libraries can't be installed with cabbal (eg. old-time, hsdev, etc.)