enhanced-boolean provides a canonical way of converting generalized booleans to booleans.

⚓ Overview

Traditionally, if you wanted to convert a generalized boolean to a boolean, there were multiple equivalent ways to do it, none of which is clearly the canonical way or particularly compelling:

(not (null foo))

(if foo t nil)

(when foo t)

It's particularly painful if you need a function that does this:

(mapcar (lambda (value)
          (not (null value)))
        '(t true nil false 0 () #() "" #\0))


(defun %boolean (value)
  (not (null value)))

(mapcar #'%boolean '(t true nil false 0 () #() "" #\0))

The crux of the problem is that the Common Lisp standard unfortunately omits to specify this trivial function (which users are forbidden from defining directly on the standard symbol boolean):

(defun boolean (generalized-boolean)
  (if generalized-boolean
      t
      nil))

This unfortunate omission has personally caused me extensive and repeated inconvenience and agony over the years (as this greatly offends my sense of aesthetics), as well as to many others I'm sure. In many programming languages, such an unfortunate limitation to a built-in construct could not be easily or satisfactorily overcome, and might even require help from the language's designers and implementors to vanquish, if ever even accomplished, even after years of begging. (For instance, many languages have a predefined list of reserved keywords with hardcoded behavior.)

enhanced-boolean simply provides a portable, robust, performant version of this function that acts as a drop-in replacement for cl:boolean.

⚓ Dictionary