Suggestion regarding (.) and map

Twan van Laarhoven twanvl at
Thu Apr 24 18:06:58 EDT 2008

Cale Gibbard wrote:

> Hello,
> In keeping with my small but seemingly extremely controversial
> suggestions for changes to the Prelude, here's a suggestion which I
> think is elegant and worth considering for the Haskell' Prelude:
> Rename fmap to map (like it was in Haskell 1.4), and define (.) as a
> synonym for it.

One thing I fear (though that fear may be irrational) is that you get code that 
looks like "(.) . ((.) . (.) .)". To me, and I expect to many people, map and 
composition are different things, and used in different ways. If both are 
written as a dot it will take extra mental effort to decipher the meaning of a 
program. The potential for writing code that resembles the worst outputs of the 
@pl lambdabot plugin also becomes larger.

Cale: do you have some real world examples of code you wrote using (.) = fmap?

Secondly, I am really fond of the Applicative notation <$>, which goes great 
together with <*>. A lighter notation would be nice, but I see no good way to do 
that. (Perhaps we need to add syntactic sugar for idiom brackets?)


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