[PATCH] pcase.el: Add type pattern

[Adam Porter <adam@alphapapa.net>]

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Hi,

It seemed like an obvious and useful improvement to add a "type" pattern
to pcase, so I prepared this patch.  I wondered if checking for
predicates like this was a good way to do so, and I saw that the
cl-typep inliner does basically this, so it seems reasonable.

If this seems like an acceptable idea, please let me know if any further
changes are required.

Thanks,
Adam

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From 15248b62ada8e7d5c5484a0dd4749e057b0b8061 Mon Sep 17 00:00:00 2001
From: Adam Porter <adam@alphapapa.net>
Date: Mon, 9 Mar 2020 13:01:32 -0500
Subject: [PATCH] * lisp/emacs-lisp/pcase.el: Add type pattern

* lisp/emacs-lisp/pcase.el:
((pcase-defmacro type)): Add 'type' pattern.

* test/lisp/emacs-lisp/pcase-tests.el (pcase-tests-type): Add test.
---
 etc/NEWS                            | 7 +++++++
 lisp/emacs-lisp/pcase.el            | 8 ++++++++
 test/lisp/emacs-lisp/pcase-tests.el | 7 +++++++
 3 files changed, 22 insertions(+)

diff --git a/etc/NEWS b/etc/NEWS
index 47b87af..9190bf1 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -174,6 +174,13 @@ key             binding
 / v             package-menu-filter-by-version
 / /             package-menu-filter-clear
 
+** pcase.el
+
+*** Added Pcase 'type' pattern.
+
+A pattern like '(type integer)' is equivalent to one like
+'(pred integerp)'.
+
 \f
 * New Modes and Packages in Emacs 28.1
 
diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
index 36b93fa..4a2903b 100644
--- a/lisp/emacs-lisp/pcase.el
+++ b/lisp/emacs-lisp/pcase.el
@@ -977,5 +977,13 @@ \`
    ;; compounded values that are not `consp'
    (t (error "Unknown QPAT: %S" qpat))))
 
+(pcase-defmacro type (type)
+  "Pcase pattern that matches objects of TYPE."
+  (let* ((type (symbol-name type))
+	 (pred (or (intern-soft (concat type "p"))
+		   (intern-soft (concat type "-p"))
+		   (error "Unknown type: %s" type))))
+    `(pred ,pred)))
+
 (provide 'pcase)
 ;;; pcase.el ends here
diff --git a/test/lisp/emacs-lisp/pcase-tests.el b/test/lisp/emacs-lisp/pcase-tests.el
index 0b69bd9..5db8605 100644
--- a/test/lisp/emacs-lisp/pcase-tests.el
+++ b/test/lisp/emacs-lisp/pcase-tests.el
@@ -71,6 +71,13 @@ pcase-tests-member
 (ert-deftest pcase-tests-vectors ()
   (should (equal (pcase [1 2] (`[,x] 1) (`[,x ,y] (+ x y))) 3)))
 
+(ert-deftest pcase-tests-type ()
+  (should (equal (pcase 1
+                   ((type integer) 'integer))
+                 'integer))
+  (should-error (pcase 1
+                  ((type notatype) 'integer))))
+
 ;; Local Variables:
 ;; no-byte-compile: t
 ;; End:
-- 
2.7.4