Re: Add flipped fmap

On Wed, Apr 07, 2010 at 03:33:51PM +0200, Johan Tibell wrote:

Hi Felipe,

Hello! :)

On Wed, Apr 7, 2010 at 3:09 PM, Felipe Lessa wrote:

...

I've needed <$$> many times and had to use 'flip fmap' instead.

In my opinion this is not a good criteria for including a function. [snip]

I think I understand your point very well. I'm also not fond of adding shortcuts, and that's why I said I used 'flip fmap' while I could have defined <$$> myself instead. My reasons for adding this particular function are: 1) <$> is very useful because it is infix, while `fmap` is ugly and doesn't have a nice fixity. -- Prelude> :t \f g x -> f . g `fmap` x <interactive>:1:10: Precedence parsing error cannot mix `.' [infixr 9] and `fmap' [infixl 9] in the same infix expression -- Prelude Control.Applicative> :t \f g x -> f . g <$> x \f g x -> f . g <$> x :: (Functor f) => (b -> c) -> (a -> b) -> f a -> f c -- <$$> will be as concise and useful as <$>, maybe even more, because `flip fmap` isn't valid. 2) Simmetry, as the ticket says.

Yet, if we add all the function compositions that some group of people use in their code our APIs get much more complicated.

I completely agree, but I think you're overreacting to this proposal (no offense intended, please :]). I don't see a tendency of adding every combinator to the libraries, and I don't think this proposal will change anything. Cheers, -- Felipe.