how is haskell the obvious choice? The parent poster talks about clojure & python -- 2 dynamically typed languages. It's going to be a world of difference moving to a statically typed one.
The change in typing is not really much of a jump when you realise that Haskell's type inference means you don't have to declare too many type signatures up front. A lot of type signatures in Haskell code are not technically necessary and are usual there for documentation.
For example, this is perfectly valid Haskell code and doesn't mention a single type:
factorial n = if n > 0 then n * factorial (n-1) else 1
The bigger conceptual shift will be from Python's mainly procedural style to Haskell's (or Clojure's) very strong emphasis on a functional style.
