Re: [PATCH] pcase.el: Add type pattern

[Adam Porter <adam@alphapapa.net>]

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Michael Heerdegen <michael_heerdegen@web.de> writes:

>> +(pcase-defmacro type (type)
>> +  "Pcase pattern that matches objects of TYPE."
>> +  `(pred (pcase--flip cl-typep ',type)))
>
> If we keep these semantics and the patch is accepted, you should
> document here what TYPE means.  IIUC any type expression allowed by
> `cl-typep' will be possible, right?  Then just say something like "TYPE
> is a type name like in `cl-typep'" or so.

Thanks, that's a good point.  This new patch improves the docstring and
the changes to the manual, and it adds a test for a cl-typep list form.
Please let me know if more improvements should be made.

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From e588e09a708e23e3d6e5b140c8fde4b0aabd60c3 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/cl-macs.el: Add type pattern

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

* test/lisp/emacs-lisp/pcase-tests.el (pcase-tests-type): Add test.

* doc/lispref/control.texi (pcase Macro): Update manual.

Co-authored-by: Stefan Monnier <monnier@iro.umontreal.ca>
---
 doc/lispref/control.texi            |  7 +++++++
 etc/NEWS                            |  8 ++++++++
 lisp/emacs-lisp/cl-macs.el          |  7 +++++++
 test/lisp/emacs-lisp/pcase-tests.el | 10 ++++++++++
 4 files changed, 32 insertions(+)

diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi
index c601e3a..dc91fc1 100644
--- a/doc/lispref/control.texi
+++ b/doc/lispref/control.texi
@@ -555,6 +555,13 @@ pcase Macro
 Likewise, it makes no sense to bind keyword symbols
 (@pxref{Constant Variables}).
 
+@item (type @var{type})
+Matches if @var{expval} is of type @var{type}, which is a symbol or
+list as accepted by @ref{cl-typep,,,cl,Common Lisp Extensions}.
+
+Example: @code{(type integer)}
+Example: @code{(type (integer 0 10))}
+
 @item (pred @var{function})
 Matches if the predicate @var{function} returns non-@code{nil}
 when called on @var{expval}.
diff --git a/etc/NEWS b/etc/NEWS
index 47b87af..c8227c0 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -174,6 +174,14 @@ key             binding
 / v             package-menu-filter-by-version
 / /             package-menu-filter-clear
 
+** pcase.el
+
+*** Added Pcase 'type' pattern.
+
+The new 'type' pattern compares types using 'cl-typep', which allows
+comparing simple types like '(type integer)', as well as forms like
+'(type (integer 0 10))'.
+
 \f
 * New Modes and Packages in Emacs 28.1
 
diff --git a/lisp/emacs-lisp/cl-macs.el b/lisp/emacs-lisp/cl-macs.el
index 4c2f589..dc272e3 100644
--- a/lisp/emacs-lisp/cl-macs.el
+++ b/lisp/emacs-lisp/cl-macs.el
@@ -3403,6 +3403,13 @@ cl-struct-slot-value
 
 (run-hooks 'cl-macs-load-hook)
 
+;;; Pcase type pattern.
+
+(pcase-defmacro type (type)
+  "Pcase pattern that matches objects of TYPE.
+TYPE is a symbol or list as accepted by `cl-typep', which see."
+  `(pred (pcase--flip cl-typep ',type)))
+
 ;; Local variables:
 ;; generated-autoload-file: "cl-loaddefs.el"
 ;; End:
diff --git a/test/lisp/emacs-lisp/pcase-tests.el b/test/lisp/emacs-lisp/pcase-tests.el
index 0b69bd9..97f3e55 100644
--- a/test/lisp/emacs-lisp/pcase-tests.el
+++ b/test/lisp/emacs-lisp/pcase-tests.el
@@ -71,6 +71,16 @@ 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 (equal (pcase 1
+                   ((type (integer 0 2)) 'integer-0<=n<=2))
+                 'integer-0<=n<=2))
+  (should-error (pcase 1
+                  ((type notatype) 'integer))))
+
 ;; Local Variables:
 ;; no-byte-compile: t
 ;; End:
-- 
2.7.4