Haskell Language
Haskell Introduction
Haskell on Wikipedia
OReilly's book is freely available online
[greg:~] ghci Prelude> let doubler x = x + x Prelude> factorial 5 120 Prelude> let doubler x y = x*2 + y*2 Prelude> doubler 5 7 24 Prelude> let factorial n = if n > 0 then n * factorial (n-1) else 1 Prelude> factorial 5 120 Prelude> factorial 6 720