Re: [Haskell-beginners] cabal install snap-server-0.9.5.1: At least the following dependencies are missing: attoparsec >=0.10 && <0.13 && ==0.13.0.1

attoparsec >= 0.10 && < 0.14,

you could try to change the source cabal file or you could use cabal sandbox. Sandboxes are easy. They allow to install exact versions required by the package. Take a look: http://coldwa.st/e/blog/2013-08-20-Cabal-sandbox.html