I was wondering about GHC's ability to optimize the following code module Test (test) where newtype Step a b = Step { unStep :: (a -> Step a b -> b) -> b -> b } iter :: [a] -> (a -> Step a b -> b) -> b -> b iter [] next done = done iter (x:xs) next done = next x (Step $ iter xs) count :: Int -> Char -> Step Char Int -> Int count i x step = unStep step (count $ i+1) (i+1) test :: String -> Int test xs = iter xs (count 0) 0 (test implements the string length function). The transformations steps that reduce this to the optimized version are 1- avoid forming the (iter xs) and (count i+1) closures by passing the function and the arguments instead of the function bound to the argument iter [] next i done = done iter (x:xs) next i done = next i x iter xs count i x step xs = step xs count (i+1) (i+1) test xs = iter xs count 0 0 2- specialize count for step = iter iter [] next i done = done iter (x:xs) next i done = next i x iter xs count i x xs = iter xs count (i+1) (i+1) test xs = iter xs count 0 0 3- specializing iter for next = count iter [] i done = done iter (x:xs) i done = count i x iter xs count i x xs = iter xs (i+1) (i+1) test xs = iter xs 0 0 4- inline count iter [] i done = done iter (x:xs) i done = iter xs (i+1) (i+1) test xs = iter xs 0 0 5- eliminate the done argument as it is always the same as the i argument iter [] i = i iter (x:xs) i = iter xs (i+1) test xs = iter xs 0 Currently 6.10.1 with -O2 seems stuck with regard to step 1 (eliminating the closures). Is there any hope of getting it to these transformations? Thanks! -Tyson