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In trying to learn Haskell, I have implemented a pi calculation in order to understand functions and recursion properly. Using the Leibniz Formula for calculating pi, I came up with the following, which prints pi to the tolerance of the given parameter, and the number of recursive function calls in order to get that value: reverseSign :: (Fractional a, Ord a) => a -> a reverseSign num = ((if num > 0 then -1 else 1) * (abs(num) + 2)) piCalc :: (Fractional a, Integral b, Ord a) => a -> (a, b) piCalc tolerance = piCalc' 1 0.0 tolerance 0 piCalc' :: (Ord a, Fractional a, Integral b) => a -> a -> a -> b -> (a, b) piCalc' denom prevPi tolerance count = if abs(newPi - prevPi) < tolerance then (newPi, count) else piCalc' (reverseSign denom) newPi tolerance (count + 1) where newPi = prevPi + (4 / denom) So when I run this in GHCI, it seems to work as expected: *Main> piCalc 0.001 (3.1420924036835256,2000) But if I set my tolerance too fine, this happens: *Main> piCalc 0.0000001 (3.1415927035898146,*** Exception: stack overflow This seems wholly counter-intuitive to me; the actual calculation works fine, but just trying to print how many recursive calls fails?? Why is this so?

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