Hi, This is probably a simple question, but I sure don't know the answer. I'm dabbling with haskell at the moment and have hit a problem. I remember something from undergraduate school about how to write recursive functions so that they don't eat up stack space, and instead behave more like while loops (I think you had to convert them to tail-recursive forms?). I've tried different variations, and it appears that they're all using the stack and cause overflows when I expect that they wouldn't. All of these are okay on standard Hugs for n = 13000, but all except testR5 cause Control stack overflows for n = 14000. I thought that at least one of the forms of testR2, testR3 and testR4 would be recognised as tail-recursive, and executed as loops without using the stack. The stack overflow for n = 14000 appears to show me to be wrong. (For example, testR2 13000 works, but testR2 14000 gives a Control stack overflow). Can anyone help with this? I'd like to be able to process lists with over 14000 elements, so need some help. Thanks, Eoin module Test where import Numeric testR1 :: Integer -> Integer testR1 0 = 0 testR1 n = n + (testR1 (n-1)) testR2 :: Integer -> Integer testR2 n = testR2' 0 n testR2' :: Integer -> Integer -> Integer testR2' a 0 = a testR2' a n = testR2' (a+n) (n-1) testR3 :: Integer -> Integer testR3 n = testR3' n 0 testR3' :: Integer -> Integer -> Integer testR3' 0 a = a testR3' n a = testR2' (a+n) (n-1) testR4 :: Integer -> Integer testR4 n = testR4' (0,n) testR4' :: (Integer, Integer) -> Integer testR4' (a,0) = a testR4' (a,n) = testR4' (a+n,n-1) testR5 :: Integer -> Integer testR5 0 = 0 testR5 n = testR5 (n-1) -- end of module Test __________________________________________________________________ INTRODUCTORY OFFER! Tiscali Business Broadband for £15.99! http://www.tiscali-business.co.uk/broadband/?code=ZZ-MS-12KC