Suggestion regarding (.) and map

David Menendez dave at
Thu Apr 24 22:16:46 EDT 2008

On Thu, Apr 24, 2008 at 6:06 PM, Twan van Laarhoven <twanvl at> wrote:
> 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.

I'd much rather keep composition and functor map separate. I'm still
not entirely sure that generalizing (.) to other morphisms in the
Category class is a good idea. Function composition gets used a *lot*,
and I imagine we'd loose a lot of inlining if it became a class

>  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?)

As much as I like Applicative, I dislike the name "<*>". To me, it
makes more sense to use "<$>" for <*>, since it's application of
wrapped functions. I've used "$^" as a synonym for fmap (because it's
lifted application).

It would be nice to have sugar for idiom brackets. You can simulate
them with a class, but the result typically doesn't stand out enough
visually as being special syntax.

Dave Menendez <dave at>

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