Hi Folks, Richard Bird write on page 91 of his book, "Introduction to Functional Programming using Haskell": The datatype of lists is the workhorse of functional programming. Notice that he does not say that lists are the workhorse of "Haskell." No. He makes a much broader statement. Lists are the workhorse of Haskell and Lisp and Miranda and all the functional languages. Lists are a key part of functional languages. On page 95 he defines the list concatenation operator: (++) :: [a] -> [a] -> [a] [] ++ ys = ys (x:xs) ++ ys = x : (xs ++ ys) Then on page 96 he states: Once one has come to grips with the definition of ++, one has understood a good deal about how lists work in functional languages. Again notice that he does not say that by coming to grips with the definition of ++ one will have a good understanding of how lists work in "Haskell." No. He makes a much broader statement. One will have a good understanding of how lists work in all functional languages. Although the syntax may change, this definition of concatenation is for all functional languages. Wow! That is so cool. /Roger