GNU bug report logs - #13345
24.2.91; Wrong assumption in a hash table example + fix

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Ari Roponen <ari.roponen <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2.91; Wrong assumption in a hash table example + fix
Date: Thu, 03 Jan 2013 14:01:17 +0200

In file doc/lispref/hash.texi, there is an example:

    @example
    (defun case-fold-string= (a b)
      (compare-strings a nil nil b nil nil t))
    (defun case-fold-string-hash (a)
      (sxhash (upcase a)))

    (define-hash-table-test 'case-fold
      'case-fold-string= 'case-fold-string-hash)

    (make-hash-table :test 'case-fold)
    @end example

The documentation of `define-hash-table-test' says:

    The function @var{test-fn} should accept two arguments, two keys, and
    return non-@code{nil} if they are considered ``the same''.

In the above example, the test function returns always non-nil, because
it assumes `compare-strings' returns nil for differing strings. The
patch below fixes this wrong assumption.


2013-01-03  Ari Roponen  <ari.roponen <at> gmail.com>  (tiny change)

	* hash.texi (Defining Hash): Fix example.


=== modified file 'doc/lispref/hash.texi'
--- doc/lispref/hash.texi	2013-01-01 09:11:05 +0000
+++ doc/lispref/hash.texi	2013-01-03 10:50:19 +0000
@@ -293,7 +293,7 @@
 
 @example
 (defun case-fold-string= (a b)
-  (compare-strings a nil nil b nil nil t))
+  (eq t (compare-strings a nil nil b nil nil t)))
 (defun case-fold-string-hash (a)
   (sxhash (upcase a)))
 


In GNU Emacs 24.2.91.9 (x86_64-unknown-linux-gnu, GTK+ Version 3.7.2)
 of 2013-01-03 on arirop
Bzr revision: 111125 rgm <at> gnu.org-20130103063325-sx99hs1usiuqlxvb
Windowing system distributor `Fedora Project', version 11.0.11300000
System Description:	Fedora release 18 (Spherical Cow)

-- 
Ari Roponen

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