Re: [Haskell-cafe] Making monadic code more concise

On Mon, Nov 15, 2010 at 6:43 PM, Ling Yang wrote:

... One alternate way of doing this, however, is instancing the typeclasses of the ordinary values with their monadic versions:

instance (Num a) => Num (Prob a) where        (+) = liftM2 (+)        (*) = liftM2 (*)        abs = liftM abs        signum = liftM signum        fromInteger = return . fromInteger

instance (Fractional a) => Fractional (Prob a) where        fromRational = return . fromRational        (/) = liftM2 (/)

You may also like to look at Conal Elliott's applicative-numbers package: http://hackage.haskell.org/package/applicative-numbers Bas