Re: map.el: pcase plist keyword-only binding improvement

[Adam Porter <adam@alphapapa.net>]

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Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>     (seq-map (lambda (elt)
>>                (cond ((consp elt)
>>                       `(app (pcase--flip map-elt ,(car elt)) ,(cadr elt)))
>>                      ((keywordp elt)
>>                       ;; New clause for keyword-only elements.
>>                       (let ((var (intern (substring (symbol-name elt) 1))))
>>                         `(app (pcase--flip map-elt ,elt) ,var)))
>>                      (t
>>                       `(app (pcase--flip map-elt ',elt) ,elt))))
>>              args))
>
> Since binding the result of the match to a keyword can't work anyway,
> this seems like a very good idea.
>
>> Assuming that this change is acceptable, I would like to prepare a
>> patch, which would probably need to include NEWS and documentation
>> changes.
>
> AFAICT we don't yet have actual documentation for the map.el package, so
> only NEWS needs to be changed.
>
>> However, since the change is to map.el rather than pcase.el,
>> and since map.el is also available on ELPA,
>
> It's also distributed via GNU ELPA indeed, but taken straight from the
> emacs.git repository, so you don't need to worry about that (just
> increment the `Version:` entry at the top).

Hi Stefan,

Ok, I've attached a patch.  I tried to follow the appropriate
guidelines, but please let me know if any changes are required.

Thanks,
Adam

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From d5cb310d6fb30e2991a94e433b754c07893133ef Mon Sep 17 00:00:00 2001
From: Adam Porter <adam@alphapapa.net>
Date: Sun, 2 Feb 2020 10:17:20 -0600
Subject: [PATCH] * lisp/emacs-lisp/map.el: Add keyword-only pattern
 abbreviation

* lisp/emacs-lisp/map.el: Update version to 2.1.
((pcase-defmacro map)): Update docstring.
(map--make-pcase-bindings): Match keyword pattern.

* test/lisp/emacs-lisp/map-tests.el (test-map-plist-pcase): Add test.
---
 etc/NEWS                          |  6 ++++++
 lisp/emacs-lisp/map.el            | 17 +++++++++++------
 test/lisp/emacs-lisp/map-tests.el |  6 ++++++
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 2b9337b..7444166 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -107,6 +107,12 @@ supplied error message.
 *** New connection method "media", which allows accessing media devices
 like cell phones, tablets or cameras.
 
+** map.el
+
+*** Pcase 'map' pattern added keyword symbols abbreviation.
+A pattern like '(map :sym)' binds the map's value for ':sym' to 'sym',
+equivalent to '(map (:sym sym))'.
+
 \f
 * New Modes and Packages in Emacs 28.1
 
diff --git a/lisp/emacs-lisp/map.el b/lisp/emacs-lisp/map.el
index 67f5b3c..9c23344 100644
--- a/lisp/emacs-lisp/map.el
+++ b/lisp/emacs-lisp/map.el
@@ -4,7 +4,7 @@
 
 ;; Author: Nicolas Petton <nicolas@petton.fr>
 ;; Keywords: convenience, map, hash-table, alist, array
-;; Version: 2.0
+;; Version: 2.1
 ;; Package-Requires: ((emacs "25"))
 ;; Package: map
 
@@ -56,8 +56,10 @@ evaluated and searched for in the map.  The match fails if for any KEY
 found in the map, the corresponding PAT doesn't match the value
 associated to the KEY.
 
-Each element can also be a SYMBOL, which is an abbreviation of a (KEY
-PAT) tuple of the form (\\='SYMBOL SYMBOL).
+Each element can also be a SYMBOL, which is an abbreviation of
+a (KEY PAT) tuple of the form (\\='SYMBOL SYMBOL).  When SYMBOL
+is a keyword, it is an abbreviation of the form (:SYMBOL SYMBOL),
+useful for binding plist values.
 
 Keys in ARGS not found in the map are ignored, and the match doesn't
 fail."
@@ -486,9 +488,12 @@ Example:
 (defun map--make-pcase-bindings (args)
   "Return a list of pcase bindings from ARGS to the elements of a map."
   (seq-map (lambda (elt)
-             (if (consp elt)
-                 `(app (pcase--flip map-elt ,(car elt)) ,(cadr elt))
-               `(app (pcase--flip map-elt ',elt) ,elt)))
+             (cond ((consp elt)
+                    `(app (pcase--flip map-elt ,(car elt)) ,(cadr elt)))
+                   ((keywordp elt)
+                    (let ((var (intern (substring (symbol-name elt) 1))))
+                      `(app (pcase--flip map-elt ,elt) ,var)))
+                   (t `(app (pcase--flip map-elt ',elt) ,elt))))
            args))
 
 (defun map--make-pcase-patterns (args)
diff --git a/test/lisp/emacs-lisp/map-tests.el b/test/lisp/emacs-lisp/map-tests.el
index 06fd55f..3ffef17 100644
--- a/test/lisp/emacs-lisp/map-tests.el
+++ b/test/lisp/emacs-lisp/map-tests.el
@@ -376,5 +376,11 @@ Evaluate BODY for each created map.
                                  '((1 . 1) (2 . 5) (3 . 0)))
                  '((3 . 0) (2 . 9) (1 . 6)))))
 
+(ert-deftest test-map-plist-pcase ()
+  (let ((plist '(:one 1 :two 2)))
+    (should (equal (pcase-let (((map :one (:two two)) plist))
+                     (list one two))
+                   '(1 2)))))
+
 (provide 'map-tests)
 ;;; map-tests.el ends here
-- 
2.7.4