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Re: dash.el [was: Re: Imports / inclusion of s.el into Emacs]

From: Richard Stallman
Subject: Re: dash.el [was: Re: Imports / inclusion of s.el into Emacs]
Date: Sat, 09 May 2020 22:33:43 -0400

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Thanks for showing me examples of dash.el.  A lot of these facilities
seem useful.  I would very much like to see the _documentation_ for how
to use it.

First, these all seem to be macros, right?

Why do some names start with a single dash and some with a double dash?

About --map-when:

  > (let ((lst '(1 2 3 4)))
  >   (pp (--map-when (= it 2) 17 lst))
  >   (pp (mapcar (lambda (it) (if (= it 2) 17 it)) lst)))

The map-when version was not self-evident to me.
I had to read the mapcar version to understand its meaning.
Once I did that, it made sense, and I can see that it is useful.
I think we should add this to Emacs, but with a couple of changes.

* Call it 'map-when' -- why use dashes?

* Change the calling convention syntax to (map-when ((= it 2) 17) lst)
  simply so it easier to see what groups with what.
  That gives it the structure of the inside of a cond.

About --remove:

That is good as is, I would just call it 'remove-if'.

  > I was going to make an example with `-flatten` but I think this page
  > is better showing my point:

I will fetch that page and look at it.

    (->> '(1 2 3) (-map 'square) (-remove 'even?)) ;; => '(1 9)

Is '-map' just another name for 'mapcar'?

After some effort I figured out what that example is doing, I think.
Indeed, it can be used.  At the same time, what advantage is that
supposed to provide over writing it the Lisp way?

   (remove-if 'evenp (mapcar 'square '(1 2 3)))

About -->:

    (--> "def" (concat "abc" it "ghi") (upcase it)) ;; => "ABCDEFGHI"

This sort of shorthand for binding a variable can make code simpler.
The name could be a good one, if there are only a few such constructs
and each one of them acts at the very general level of this one.

Do poeple see any practical problem that would result from the name -->?

Dr Richard Stallman
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)

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