(nil and t): Add `booleanp' predicate.

diff --git a/lispref/intro.texi b/lispref/intro.texi
index b2294be4c2dd5551f8ec022173423fe7e6b466ac..61dfca64b976f215f4df7dce00863867f456905f 100644 (file)
--- a/lispref/intro.texi
+++ b/lispref/intro.texi
@@ -212,6 +212,11 @@ to use them as constants in a program.  An attempt to change their
 values results in a @code{setting-constant} error.  @xref{Constant
 Variables}.
 
+@defun booleanp object
+Return non-nil iff @var{object} is one of the two canonical boolean
+values: @code{t} or @code{nil}.
+@end defun
+
 @node Evaluation Notation
 @subsection Evaluation Notation
 @cindex evaluation notation