[Haskell-cafe] Please tell me this function exists

[Brian Hurt]

I know it's not hard to write, but still:

concat :: String -> [String] -> String
concat _ [] = ""
concat _ [x] = x
concat sep x:xs = x ++ sep ++ (concat sep xs)

I've got to be stupid and missing it in the standard libraries.  Please 
tell me where.  Thanks.

Brian