I'm pretty new to Haskell, so forgive me if my question is due to my non-functional way of thinking... I have the following code: module Main where main = print solution solution = solve 1000000 solve d = countUniqueFractions d 2 1 0 canBeSimplified (a,b) = gcd a b > 1 countUniqueFractions stopD currentD currentN count | currentD > stopD = count | currentN == currentD = countUniqueFractions stopD (currentD + 1) 1 count | canBeSimplified (currentN, currentD) = countUniqueFractions stopD currentD (currentN+1) count | otherwise = countUniqueFractions stopD currentD (currentN+1) (count + 1) When I run this code, I get a stack overflow. I don't understand why. Could anyone explain please? -- View this message in context: http://www.nabble.com/Efficiency-question-tf3823154.html#a10823572 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.