[Haskell-cafe] >>= definition for list monad in ghc

Usually in monad tutorials, the >>= operator for the list monad is defined as: m >>= k = concat (map k m) -- or concatMap k m but in the GHC sources it's defined as: m >>= k = foldr ((++) . k) [] m As far as I can tell, this definition is equivalent to the previous one (correct me if I'm wrong), so I was wondering why this definition was chosen instead of the other one. Does anybody know? Thanks in advance, Mike