From 82ba818ff456bcd6d56a06226e3f27e98fbb55c3 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Thu, 14 Aug 2025 22:58:58 -0500 Subject: removing all downloaded devdocs files --- devdocs/elisp/examples-of-catch.html | 34 ---------------------------------- 1 file changed, 34 deletions(-) delete mode 100644 devdocs/elisp/examples-of-catch.html (limited to 'devdocs/elisp/examples-of-catch.html') diff --git a/devdocs/elisp/examples-of-catch.html b/devdocs/elisp/examples-of-catch.html deleted file mode 100644 index d10b0589..00000000 --- a/devdocs/elisp/examples-of-catch.html +++ /dev/null @@ -1,34 +0,0 @@ -

Examples of catch and throw

One way to use catch and throw is to exit from a doubly nested loop. (In most languages, this would be done with a goto.) Here we compute (foo i j) for i and j varying from 0 to 9: 

(defun search-foo ()
-  (catch 'loop
-    (let ((i 0))
-      (while (< i 10)
-        (let ((j 0))
-          (while (< j 10)
-            (if (foo i j)
-                (throw 'loop (list i j)))
-            (setq j (1+ j))))
-        (setq i (1+ i))))))
-
-

If foo ever returns non-nil, we stop immediately and return a list of i and j. If foo always returns nil, the catch returns normally, and the value is nil, since that is the result of the while.

Here are two tricky examples, slightly different, showing two return points at once. First, two return points with the same tag, hack: 

(defun catch2 (tag)
-  (catch tag
-    (throw 'hack 'yes)))
-⇒ catch2
-
- -
(catch 'hack
-  (print (catch2 'hack))
-  'no)
--| yes
-⇒ no
-
-

Since both return points have tags that match the throw, it goes to the inner one, the one established in catch2. Therefore, catch2 returns normally with value yes, and this value is printed. Finally the second body form in the outer catch, which is 'no, is evaluated and returned from the outer catch.

Now let’s change the argument given to catch2: 

(catch 'hack
-  (print (catch2 'quux))
-  'no)
-⇒ yes
-
-

We still have two return points, but this time only the outer one has the tag hack; the inner one has the tag quux instead. Therefore, throw makes the outer catch return the value yes. The function print is never called, and the body-form 'no is never evaluated.

-

- Copyright © 1990-1996, 1998-2022 Free Software Foundation, Inc.
Licensed under the GNU GPL license.
- https://www.gnu.org/software/emacs/manual/html_node/elisp/Examples-of-Catch.html -

-
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