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Re: Anaphoric macros: increase visibility
From: |
Michael Heerdegen |
Subject: |
Re: Anaphoric macros: increase visibility |
Date: |
Sun, 15 Jan 2017 03:26:23 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.1.91 (gnu/linux) |
Michael Heerdegen <address@hidden> writes:
> And I often think that it would be cool to couple them with pcase
> pattern matching. OTOH we already have `pcase-let', but I can't get
> along with its semantics, e.g.
>
> (pcase-let ((`(,a ,b) '(1 2 3)))
> (list a b))
>
> ==> (1 2)
>
> although the pattern doesn't match.
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)))
#+end_src
This is similar to `when-let' but instead of a non-nil test, you can use
any test you want (via pattern matching). There would not be an
implicit test for whether a matched expression evals to something
non-nil, however.
Example:
#+begin_src emacs-lisp
(defun test-pwhen (thing)
(pwhen ((`(,x ,y) thing)
((pred identity) x))
(message "passed with x: %S and y:%S" x y)))
#+end_src
(test-pwhen 37)
==> nil
(test-pwhen '(1 2 3))
==> nil
(test-pwhen '(nil 32))
==> nil
(test-pwhen '(1 2))
==> "passed with x: 1 and y:2"
Michael.
- Anaphoric macros: increase visibility, Tino Calancha, 2017/01/13
- Re: Anaphoric macros: increase visibility, Michael Heerdegen, 2017/01/13
- Re: Anaphoric macros: increase visibility, Tino Calancha, 2017/01/14
- Re: Anaphoric macros: increase visibility, Michael Heerdegen, 2017/01/14
- On the naming/behavior of {if, when}-let (was Re: Anaphoric macros: increase visibility), Mark Oteiza, 2017/01/14
- Re: Anaphoric macros: increase visibility,
Michael Heerdegen <=
- Re: Anaphoric macros: increase visibility, Tino Calancha, 2017/01/15
- Re: Anaphoric macros: increase visibility, Stefan Monnier, 2017/01/15
- Re: Anaphoric macros: increase visibility, Tino Calancha, 2017/01/15
- Re: Anaphoric macros: increase visibility, Stefan Monnier, 2017/01/15
Re: Anaphoric macros: increase visibility, Dmitri Paduchikh, 2017/01/14
- Re: Anaphoric macros: increase visibility, Tino Calancha, 2017/01/14
- Re: Anaphoric macros: increase visibility, Dmitri Paduchikh, 2017/01/14
- Re: Anaphoric macros: increase visibility, Michael Heerdegen, 2017/01/14
- Re: Anaphoric macros: increase visibility, Dmitri Paduchikh, 2017/01/14
- Re: Anaphoric macros: increase visibility, Michael Heerdegen, 2017/01/14