Installation from Source
~~~~~~~~~~~~~~~~~~~~~~~~
I got the source installation.
I then did the cabal thing

  runghc Setup.lhs configure
  runghc Setup.lhs build
  runghc Setup.lhs install

I needed to install the path to where happy
was installed to the windows path. 
C:\Program Files\Hakell\bin\

(Path, is set via 
Startmenu->settings->system -> advanced -> environment-variables.
The path works only if the path has \ (and not /).