Pattern matching error in haskell -


hello have been attempting answer question deals checking if number prime number. came code below: 

isitprime :: int->bool isitprime n     | n<=1 = false    | otherwise = isitprime2 n (n-1)  isitprime2 :: int->int->bool isitprime2 x y    | y > 1 && x `mod` y == 0 = false    | y == 1 && x `mod` y == 0 = true

when run in winhugs, returns error saying "pattern matching failure: isitprime2 a-1 " value greater 2.

however returns false values directly multiplied 2, e.g. isitprime2 2 1 returns false, isitprime2 4 2, isitprime2 6 3, isitprime2 10 5 etc. return false.

what going wrong , why?

thanks :d

the problem function isitprime2 doesn't handle cases. happens when:

  • y > 1 && x mod y != 0
  • y == 1 && x mod y != 0

handle other cases , code work fine. can use otherwise clause handling edge case:

isitprime2 :: int->int->bool isitprime2 x y    | y > 1 && x `mod` y == 0 = false    | y == 1 && x `mod` y == 0 = true   | otherwise = ??? -- handle edge case

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