instance Num Dynamic

Dynamic.hs

module Dynamic where

import Control.Applicative
import Data.Dynamic

please = maybe (error "dynamic typing is bad :(") toDyn

pleaseApp2 :: (Rational -> Rational -> Rational)
           -> (Dynamic -> Dynamic -> Dynamic)
pleaseApp2 f a b = please $ f <$> fromDynamic a <*> fromDynamic b

instance Num Dynamic where
    fromInteger = toDyn . toRational
    (+) = pleaseApp2 (+)
    (*) = pleaseApp2 (*)
    (-) = pleaseApp2 (-)
    abs    = please . fmap abs    . fromDynamic
    signum = please . fmap signum . fromDynamic

instance Fractional Dynamic where
    fromRational = toDyn
    (/) = pleaseApp2 (/)

dynamicDouble :: Dynamic -> Double
dynamicDouble = maybe (error "dynamic typing, uh ._.") fromRational . fromDynamic