adhoc polymorphism trouble

ghci> e: test.hs

is_prime :: (Integral a, RealFrac a, Floating a) => a -> Bool
is_prime x | x < 3 = True
           | otherwise =  not (any (mod0_p x) (candidates x))

mod0_p :: (Integral a) => a -> a -> Bool
mod0_p x y = (mod x y ) == 0

candidates :: (Integral t, Floating a, RealFrac a) => a -> [t]
candidates x = [y| y <- [2 .. (floor (sqrt x))]]

:load test.hs

Main> is_prime 6

interactive>:1:0:
   Ambiguous type variable `t' in the constraints:
     `Floating t'
       arising from a use of `is_prime' at <interactive>:1:0-9
     `Integral t'
       arising from a use of `is_prime' at <interactive>:1:0-9
     `RealFrac t'
       arising from a use of `is_prime' at <interactive>:1:0-9
   Probable fix: add a type signature that fixes these type variable(s)

なんでなのかしら。
intの世界から少しはみ出すとえらい目に会うな。

単純にfromIntegralという関数を使って型変換するしかないみたい。

is_prime :: (Integral a) => a -> Bool
is_prime x | x < 3 = True
| otherwise = not (any (mod0_p x) (candidates x))

mod0_p :: (Integral a) => a -> a -> Bool
mod0_p x y = (mod x y ) == 0

candidates :: (Integral t, Integral a) => a -> [t]
candidates x = [y| y <- [2 .. (floor (sqrt (fromIntegral x)))]]