From: Felipe Almeida Lessa <felipe.lessa@gmail.com>
To: sdiyazg@sjtu.edu.cn
Cc: haskell-cafe@haskell.org
Date: Mon, 19 Mar 2012 14:24:13 -0300
Subject: Re: [Haskell-cafe] Are there arithmetic composition of functions?
import Control.Applicative

f, g :: Float -> Float
f x = x + 1
g x = 2 * x

h = (+) <$> f <*> g

Cheers, =)

--
Felipe.

Monadic version:

import Control.Monad

import Control.Monad.Instances

(+.) :: Num a => (a -> a) -> (a -> a) -> a -> a

(+.) = liftM2 (+)

(+..) :: Num a => (a -> a -> a) -> (a -> a -> a) -> a -> a -> a

(+..) = liftM2 $ liftM2 (+)

infixl 6 +., +..

> (sin +. cos) (pi/4)

1.414213562373095

> ((*) +.. (/)) 4 2

10.0

Deniok