| Presumably changing it to resultant = foldl' (+) wouldn't help much either? I think not. | Seems to me there's always a tradeoff to be made between CPU time, RAM | usage, and code size - if not other factors too. :-S But Haskell seems | to be fairly unique in that (it looks like) it's possible to transform | the code quite aggressively without too much difficulty. You wouldn't | ever want to write source code for six different versions of sum, but if | a compiler can do it automatically that's another matter. ;-) | | I guess I was assuming that a function like sum is "simple enough" to | get inlined at the call site - and hence possibly optimised at that | site. Apparently not. There is no reason in principle why not. It's just that GHC doesn't do it at the moment. | By the way, is there some way of discovering what | GHC has "really" done with your code, rather than what you "think" it's | done? Yes: -ddump-simpl. Simon