Arie Groeneveld wrote: : | Looking at the result of my rewriting gives me the idea it isn't | Haskelly enough. | | Anyways, here's my interpretation: | | -- period m/n base = (period length, preperiod digits, period digits) | period :: Integer -> Integer -> Integer -> (Int, ([Integer], [Integer])) : Haskelliness I'd be inclined to try using a Rational (from Data.Ratio) and the properFraction function, instead of numerators and denominators and gcd. You could do away with the parts where you subscript a linked list, if you did something with elem and zip and span instead of findIndex and splitAt. Instead of translating Nothing to -1 and Just i to i, you could use the result of findIndex directly in a case expression. Correctness *Main> period 8 70 10 (6,([0],[5,7,1,4,2,8])) That should be (6,([1],[1,4,2,8,5,7])). Regards, Tom