Overview

Test the content of a value in Emacs Lisp.

• Quickstart
• Explanation
• Compatibility and Requirements

Quickstart

(require 'truthy)
 
(truthy "")                   ; nil
(truthy '[])                  ; nil
(truthy 0)                    ; nil
(truthy (lambda ()))          ; nil
(truthy (make-sparse-keymap)) ; nil
(truthy 1)                    ; 1
(truthy '(a b c))             ; '(a b c)
(truthy '(nil nil nil))       ; nil
(truthy '([] "" 0))           ; nil
 
(truthy-s '([] "" 0))         ; '([] "" 0)         ; shallow test
 
(truthy-l '(nil nil nil))     ; '(nil nil nil)     ; lengthwise test

Explanation

This library has no user-level interface; it is only useful for programming in Emacs Lisp. Three functions are provided:

truthy
truthy-s
truthy-l

Truthy provides an alternative measure of the "truthiness" of a value. Whereas Lisp considers any non-nil value to be "true" when evaluating a Boolean condition, truthy considers a value to be "truthy" if it has content. If the value is a string or buffer, it must have non-zero length. If a number, it must be non-zero. If a hash, it must have keys. If a window, it must be live. See the docstring to truthy for more details.

truthy always returns its argument on success.

truthy-s is the shallow version of truthy. It does not recurse into sequences, but returns success if any element of a sequence is non-nil.

truthy-l is the "lengthwise" version of truthy. It does not recurse into sequences, but returns success if the argument has length, considering only the variable portion of a data type.

To use truthy, place the truthy.el library somewhere Emacs can find it, and add the following to your ~/.emacs file:

(require 'truthy)

Compatibility and Requirements

GNU Emacs version 24.4-devel     : yes, at the time of writing
GNU Emacs version 24.3           : yes
GNU Emacs version 23.3           : yes
GNU Emacs version 22.3 and lower : no

Uses if present: list-utils.el