primeFactorization.hs

primeFactorization :: (Integral a) => a -> [a]
primeFactorization 0 = []
primeFactorization 1 = []
primeFactorization 2 = [2]
primeFactorization x = 
    let fstf = firstFactor x
        xx = (div x fstf)
    in [fstf] ++ primeFactorization xx

firstFactor :: Integral a => a -> a
firstFactor 0 = 0
firstFactor 1 = 1
firstFactor x = firstFactor' x 2
    where firstFactor' :: Integral a => a -> a -> a
          firstFactor' xx n
              | xx `mod` n == 0 = n
              | otherwise = firstFactor' xx (n + 1)

ghciでprimeFactorization 1呼ぶと怒られる

    No instance for (Show a0) arising from a use of ‘print’
    The type variable ‘a0’ is ambiguous
    Note: there are several potential instances:
      instance Show Double -- Defined in ‘GHC.Float’
      instance Show Float -- Defined in ‘GHC.Float’
      instance (Integral a, Show a) => Show (GHC.Real.Ratio a)
        -- Defined in ‘GHC.Real’
      ...plus 24 others
    In a stmt of an interactive GHCi command: print it

Integralの割り算はdiv使うっぽい