It is somehow award that passing function as an argument slow down the program so much. Is not Haskell a functional language and this such (functional) code reuse is one of its main points?
I can think of a few reasons why function passing is slow: * There is an overhead to closure creation (I don't know how big this is in practice, but it can be significant) * GHC has little information about what function-typed variables mean, because the function they are bound to is not known until runtime. This precludes the use of inlining, rewrite rules etc, which are absolutely key factors in making Haskell fast Regarding your first example: currently GHC does not do loop unrolling. It probably should though because loop unrolling reduces braches and increases the amount of information about the execution path that is available statically (as in e.g. the case liberation transformation), which probably explains the increased performance you saw by doing it manually in your first email. Earlier this year I implemented something somewhat similar though: fusable list literals. In this example from your first email: world :: SpacePoint -> VoxelColor world point = findColor [redSphere (0,50,0) 50, greenSphere (25,-50,0) 50, blueSphere (-150,0,150) 50] where findColor [] = noColor findColor (f:fs) = case f point of Just v -> v Nothing -> findColor fs If findColor had been a function defined in terms of foldr rather than using explicit recursion, then theres a good chance GHC 6.9 would have fused it with the list to yield your optimized, loop unrolled, version: world :: SpacePoint -> VoxelColor world point = case redSphere (0,50,0) 50 point of Just v -> v Nothing -> case greenSphere (25,-50,0) 50 point of Just v -> v Nothing -> case blueSphere (-150,0,150) 50 point of Just v -> v Nothing -> noColor Incidentally, if in your most recent email castRayScene2 was your only used of castRay, GHC would have inlined the whole definition into that use site and you would have got castRayScene1 back again. So, GHC does try its best to make higher order functions fast :-). But it's quite tricky! All the best, Max