Re: [Haskell-cafe] Are there arithmetic composition of functions?

The 17 at the end should be 12, or the 2 passed into (f+g+2) should be 3. On Mon, Mar 19, 2012 at 10:38 AM, Ozgur Akgun 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, 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

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