Haskell has algebraic data types, which are much more expressive than conventional types. You can see that from his example. Of course, the types don't define the functionality, but they narrow it down much more quickly than the ints of C and Java (similar to google ranking of search results).

Python documentation, in contrast, seems to downplay (read: hide) the return type! It's not helpful to me (maybe I'm doing it wrong, or just not used to it). For example: http://docs.python.org/library/httplib.html#httplib.HTTPConn...