You could hide Prelude and define it yourself in a different module but that would be a pretty bad idea.  Everyone who wanted to use it would have to import your module qualified and refer to it as MyModule.+, which defeats the point of making it (+) and not `myAdditionFunction` in the first place.

Haskell deliberately doesn't allow overloading.  Having (+) return something other than Num would be extremely confusing.

Hi,

Is there a way rewriting the definition of (+) so that testPlusArg returns a (Moving Double). My current intuition is that the signature [(+)  ::  a -> a  -> a] says that the type should be the same as the arguments. And indeed (:t testPlus) confirms this. But the type of  testPlusArg is a Double.

 Can I make it (Moving Double) ?

Thanks,

Pat

 

{-# LANGUAGE FlexibleInstances #-}

{-# LANGUAGE TypeSynonymInstances #-}

module Moving where

data  Time  = Time Double

type Moving v  = Time -> v

class  Number a where

 (+)  ::  a -> a  -> a

instance Number  (Moving Double) where

 (+) a b = \t -> ((a t) Prelude.+ (b t))

a,b ::  Moving Double

a (Time x) = 2.0

b (Time x) = 2.0

testPlus ::(Moving Double)

testPlus = (a Moving.+ b)

testPlusArg = (a Moving.+ b) (Time 2.0)

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