Improve the documentation for 'nil?'.

* libguile/boolean.c (scm_nil_p): Improve docstring.
* doc/ref/api-languages.texi (Nil): Add documentation for 'nil?', along
with a description of how Elisp interprets Scheme booleans and
end-of-list.

1 files changed, 11 insertions, 2 deletions

diff --git a/libguile/boolean.c b/libguile/boolean.c
index f8c773839..635c14905 100644
--- a/libguile/boolean.c
+++ b/libguile/boolean.c
@@ -1,4 +1,5 @@
-/*	Copyright (C) 1995, 1996, 2000, 2001, 2006, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
+/* Copyright (C) 1995, 1996, 2000, 2001, 2006, 2008-2011, 2018
+ *   Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -64,7 +65,15 @@ SCM_DEFINE (scm_not, "not", 1, 0, 0,
 
 SCM_DEFINE (scm_nil_p, "nil?", 1, 0, 0,
             (SCM x),
-            "Return @code{#t} iff @var{x} is nil, else return @code{#f}.")
+            "Return @code{#t} if @var{x} would be interpreted as @code{nil}\n"
+            "by Emacs Lisp code, else return @code{#f}.\n"
+            "\n"
+            "@example\n"
+            "(nil? #nil) @result{} #t\n"
+            "(nil? #f)   @result{} #t\n"
+            "(nil? '())  @result{} #t\n"
+            "(nil? 3)    @result{} #f\n"
+            "@end example")
 #define FUNC_NAME s_scm_nil_p
 {
   return scm_from_bool (scm_is_lisp_false (x));