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Re: Anaphoric macros: increase visibility

From: Tino Calancha
Subject: Re: Anaphoric macros: increase visibility
Date: Sun, 15 Jan 2017 19:24:56 +0900 (JST)
User-agent: Alpine 2.20 (DEB 67 2015-01-07)

Hi Michael,

I sometimes think that `if-let*' would be a better name for `if-let'
because bindings can refer (and naturally most of the time do) refer to other 

I also often think that `and-let' (or `and-let*' ...)  would be a better name
for `when-let' (because the expressions for the bindings are `and'ed,
sot the whole thing feels more like `and' to me).
I am in the middle of the 2 names:
*) and-let* suggests me that the bindings are `and'ed
**) but when-let* suggests me that the second argument is a list of
    expressions, i.e., not just a form.

(pcase-let ((`(,a ,b) '(1 2 3)))
  (list a b))

==> (1 2)

although the pattern doesn't match.
I can be bitten with that pitfall as well.

I think I would prefer something like

#+begin_src emacs-lisp
(defmacro pwhen (pairs &rest body)
 (declare (indent 1))
 `(pcase nil ((and ,@(mapcar (lambda (pair) (cons 'let pair)) pairs)) ,@body)))
It might be useful.

I'm using `when-let' and `if-let' a lot, but I'm still not sure
in which direction we should develop this approach.
I think we should have an imagination of where the travel should
end before adding more *-let macros.

A possible starting point is puting all together in
subr-x.el after a heading

;;; Anaphoric macros.

and perform the improvements in naming discussed in this thread:

1) Move `ibuffer-aif', `ibuffer-awhen' to subr-x.el and rename as
   `if-it', `when-it'.  Add aliases to them `aif', `awhen'.

2) `if-let' --> `if-let*'.  Add alias `if-let' for
   backward compatibility.

3) `when-let' --> `when-let*' (or `and-let*').  Add alias.

Once they are all together is easier to see what macro is missing
which could be useful.


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