This instance can be made more general without changing the code; change the first line to
instance Num a => Num (e -> a) where I think this version doesn't even require FlexibleInstances. This lets you do f x = if x then 2 else 3 g x = if x then 5 else 10 -- f + g = \x -> if x then 7 else 13 -- ryan On Mon, Mar 19, 2012 at 10:38 AM, Ozgur Akgun <[email protected]> wrote: > Hi, > > If you are feeling adventurous enough, you can define a num instance for > functions: > > {-# LANGUAGE FlexibleInstances #-} > > instance Num a => Num (a -> a) where > f + g = \ x -> f x + g x > f - g = \ x -> f x - g x > f * g = \ x -> f x * g x > abs f = abs . f > signum f = signum . f > fromInteger = const . fromInteger > > ghci> let f x = x * 2 > ghci> let g x = x * 3 > ghci> (f + g) 3 > 15 > ghci> (f+g+2) 2 > 17 > > HTH, > Ozgur > > > On 19 March 2012 16:57, <[email protected]> wrote: > >> By arithmetic I mean the everyday arithmetic operations used in >> engineering. >> In signal processing for example, we write a lot of expressions like >> f(t)=g(t)+h(t)+g'(t) or f(t)=g(t)*h(t). >> I feel it would be very natural to have in haskell something like >> g::Float->Float >> --define g here >> h::Float->Float >> --define h here >> f::Float->Float >> f = g+h --instead of f t = g t+h t >> --Of course, f = g+h is defined as f t = g t+h t >> > > > _______________________________________________ > Haskell-Cafe mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/haskell-cafe > >
_______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
