My Humble Haskell Wish: concatSep

[Frank A. Christoph]

I have a humble wish for the Wish List.

I wish this function was in the Prelude or standard library:

  concatSep :: [a] -> [[a]] -> [a]

with semantics

  concatSep _ [] = []
  concatSep _ [xs] = [xs]
  concatSep sep (xs:xss) = xs ++ sep ++ concatSep sep xss

I use it all the time. Unfortunately, it doesn't even appear in GHC's
non-standard libraries (although there is an analogue in Pretty).

--FC