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/combining-conditions.html | 46 --------------------------------- 1 file changed, 46 deletions(-) delete mode 100644 devdocs/elisp/combining-conditions.html (limited to 'devdocs/elisp/combining-conditions.html') diff --git a/devdocs/elisp/combining-conditions.html b/devdocs/elisp/combining-conditions.html deleted file mode 100644 index cbc30be0..00000000 --- a/devdocs/elisp/combining-conditions.html +++ /dev/null @@ -1,46 +0,0 @@ -

Constructs for Combining Conditions

This section describes constructs that are often used together with if and cond to express complicated conditions. The constructs and and or can also be used individually as kinds of multiple conditional constructs.

Function: not condition -

This function tests for the falsehood of condition. It returns t if condition is nil, and nil otherwise. The function not is identical to null, and we recommend using the name null if you are testing for an empty list.

-
Special Form: and conditions… -
-

The and special form tests whether all the conditions are true. It works by evaluating the conditions one by one in the order written.

If any of the conditions evaluates to nil, then the result of the and must be nil regardless of the remaining conditions; so and returns nil right away, ignoring the remaining conditions.

If all the conditions turn out non-nil, then the value of the last of them becomes the value of the and form. Just (and), with no conditions, returns t, appropriate because all the conditions turned out non-nil. (Think about it; which one did not?)

Here is an example. The first condition returns the integer 1, which is not nil. Similarly, the second condition returns the integer 2, which is not nil. The third condition is nil, so the remaining condition is never evaluated. 

(and (print 1) (print 2) nil (print 3))
-     -| 1
-     -| 2
-⇒ nil
-
-

Here is a more realistic example of using and: 

(if (and (consp foo) (eq (car foo) 'x))
-    (message "foo is a list starting with x"))
-
-

Note that (car foo) is not executed if (consp foo) returns nil, thus avoiding an error.

and expressions can also be written using either if or cond. Here’s how: 

(and arg1 arg2 arg3)
-≡
-(if arg1 (if arg2 arg3))
-≡
-(cond (arg1 (cond (arg2 arg3))))
-
-
-
Special Form: or conditions… -
-

The or special form tests whether at least one of the conditions is true. It works by evaluating all the conditions one by one in the order written.

If any of the conditions evaluates to a non-nil value, then the result of the or must be non-nil; so or returns right away, ignoring the remaining conditions. The value it returns is the non-nil value of the condition just evaluated.

If all the conditions turn out nil, then the or expression returns nil. Just (or), with no conditions, returns nil, appropriate because all the conditions turned out nil. (Think about it; which one did not?)

For example, this expression tests whether x is either nil or the integer zero: 

(or (eq x nil) (eq x 0))
-
-

Like the and construct, or can be written in terms of cond. For example: 

(or arg1 arg2 arg3)
-≡
-(cond (arg1)
-      (arg2)
-      (arg3))
-
-

You could almost write or in terms of if, but not quite: 

(if arg1 arg1
-  (if arg2 arg2
-    arg3))
-
-

This is not completely equivalent because it can evaluate arg1 or arg2 twice. By contrast, (or arg1 arg2 -arg3) never evaluates any argument more than once.

-
-
Function: xor condition1 condition2 -
-

This function returns the boolean exclusive-or of condition1 and condition2. That is, xor returns nil if either both arguments are nil, or both are non-nil. Otherwise, it returns the value of that argument which is non-nil.

Note that in contrast to or, both arguments are always evaluated.

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-
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- 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/Combining-Conditions.html -

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