Am Sonntag 29 März 2009 19:00:37 schrieb TG:
On Sat, 28 Mar 2009 17:34 -0400, "Brent Yorgey"
wrote:
Moreover, I've put the 'RealFrac' by looking at ":t floor".
What kind of class constraint whould you put for doing eg:
frac x = x - fromInteger (floor (sqrt x) )
since 'floor' takes fractional and 'sqrt' takes RealFrac? Some kind of super-class?
Every instance of RealFrac must also be an instance of Fractional, so just putting RealFrac would be fine. (And I didn't have this memorized, I just started up ghci and typed ':info Fractional' and ':info RealFrac' to see how they are declared.)
Hmm, I gave the wrong types for floor and sqrt above (oops) but your answer should still be valid as a way of looking at things So floor :: (RealFrac a, Integral b) => a -> b sqrt :: (Floating a) => a -> a and looking as you suggest, (Real a, Fractional a) => RealFrac a (Fractional a) => Floating a So in this case the answer is... frac :: (Floating a, RealFrac a) => a -> a frac x = x - fromInteger (floor (sqrt x)) No, common! Please tell me I'm wrong, that there's a simpler way!
Slightly simpler type signature: frac :: RealFloat a => a -> a Prelude> :i RealFloat class (RealFrac a, Floating a) => RealFloat a where floatRadix :: a -> Integer floatDigits :: a -> Int floatRange :: a -> (Int, Int) decodeFloat :: a -> (Integer, Int) encodeFloat :: Integer -> Int -> a exponent :: a -> Int significand :: a -> a scaleFloat :: Int -> a -> a isNaN :: a -> Bool isInfinite :: a -> Bool isDenormalized :: a -> Bool isNegativeZero :: a -> Bool isIEEE :: a -> Bool atan2 :: a -> a -> a -- Defined in GHC.Float instance RealFloat Double -- Defined in GHC.Float instance RealFloat Float -- Defined in GHC.Float
Clear, qualified answers and a bit of showing off for having
something
to aspire too. Thank you guys! -- TG cowscanfly@airpost.net