Huh. What OS?

Could this be an issue wth your path?

Failing that
Try 
>cabal update ; cabal install happy ; cabal alex

Unless there's some reason you can't use cabal-install?

On Thursday, August 22, 2013, Simon Peyton-Jones wrote:

Urk. The Haskell Platform claims to include Happy and Alex.  http://www.haskell.org/platform/contents.html

 

But 2013.2.0.0 doesn’t.   Is that intentional?

 

That’s a big problem for people using HP to build GHC.  I’m installing 2012.4.0.0 in the hope that it does.  No, nor does 2012.2

 

Am I just being stupid here?

 

Simon