Re: Flipped function application

We've found with lens in practice it is actually quite useful to have (&) bind just a touch tighter than ($), but yes, we do tend to discourage users from mashing them together: makeMyLenses = makeLensesWith $ defaultRules & ... & ... & ... -Edward On Thu, Oct 10, 2013 at 2:18 PM, David Menendez wrote:

On Thu, Oct 10, 2013 at 1:08 PM, Wvv wrote:

...

We want to combine all of them, like

xs # map $ (+ 3) . snd

And xs $$ map $ (+ 3) . snd - don't look nice.

That's actually a pretty good example of why this is a bad idea. You can't know which argument is being applied first unless you know the precedence levels.

In fact, according to the fixity you initially proposed, that translates to

(xs # map) $ (+3) . snd

The corrected version, xs # (map $ (+3) . snd), isn't much better. Even with the parentheses, it's needlessly confusing. ($) and (#) should never appear in the same expression, or at least they shouldn't apply arguments to the same function. It would be like using (.) and (>>>) together.

-- Dave Menendez http://www.eyrie.org/~zednenem/

_______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries