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I'm working through the problems in Project Euler as a way of learning Haskell, and I find that my programs are a lot slower than a comparable C version, even when compiled. What can I do to speed up my Haskell programs? For example, my brute-force solution to Problem 14 is: import Data.Int import Data.Ord import Data.List searchTo = 1000000 nextNumber :: Int64 -> Int64 nextNumber n | even n = n `div` 2 | otherwise = 3 * n + 1 sequenceLength :: Int64 -> Int sequenceLength 1 = 1 sequenceLength n = 1 + (sequenceLength next) where next = nextNumber n longestSequence = maximumBy (comparing sequenceLength) [1..searchTo] main = putStrLn $ show $ longestSequence Which takes around 220 seconds, while an "equivalent" brute-force C version only takes 1.2 seconds. #include <stdio.h> int main(int argc, char **argv) { int longest = 0; int terms = 0; int i; unsigned long j; for (i = 1; i <= 1000000; i++) { j = i; int this_terms = 1; while (j != 1) { this_terms++; if (this_terms > terms) { terms = this_terms; longest = i; } if (j % 2 == 0) j = j / 2; else j = 3 * j + 1; } } printf("%d\n", longest); return 0; } What am I doing wrong? Or am I naive to think that Haskell could even approach C's speed? (I'm compiling the C version with gcc -O2, and the Haskell version with ghc --make -O).

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