Haskell is a purely functional language in this sense. http://en.wikipedia.org/wiki/Pure_function http://en.wikipedia.org/wiki/Pure_function http://en.wikiped

Haskell is a purely functional language in this sense. http://en.wikipedia.org/wiki/Pure_function http://en.wikipedia.org/wiki/Pure_function http://en.wikipedia.org/wiki/Purely_functional http://en.wikipedia.org/wiki/Purely_functional Haskell has taken functional purity and ran with it. It's proof that you can eliminate side effects (sans the sin bin) and still actually get things done. The benefits of this can be seen in the papers written by SPJ, Wadler, etc. Moreover some features from Haskell/FP have influenced the mainstream programming community (Java generics). As far as I know Erlang is not purely functional, nor does it try to be. On top of that, I think Erlang's emphasis is more on the actor model / message passing than it is on functional programming. That's my take at least.