[taolson]

An example where this is useful is to help inline otherwise recursive functions, by writing the function to take some useful parameters first, then return a recursive function which takes the remaining parameters. This allows the function to be partially in-lined, resulting in better performance due to the specialization on the first parameters. For example, foldr:

foldr f z = go

  where

    go [] = z

    go (x : xs) = f x (go xs)

when called with (+) and 0 can be inlined to

go xs = case xs of

    [] -> 0

    (x : xs) = x + go xs

which doesn't have to create a closure to pass around the function and zero value, and can subsequently inline (+), etc.