Subject: Emacs-25: inaccuracy in documentation of `mapconcat' in .../lispref/functions.texi

From: Alan Mackenzie <[email-masked]>
Date: Sun, 6 Dec 2015 10:26:22 +0000

Hello, Emacs.

In the elisp manual, mapconcat is described thusly:

     `mapconcat' applies FUNCTION to each element of SEQUENCE: the
     results, which must be strings, are concatenated.  Between each
              ^^^^^^^^^^^^^^^^^^^^^
     pair of result strings, `mapconcat' inserts the string SEPARATOR.
                                                 ^^^^^^^^^^
     Usually SEPARATOR contains a space or comma or other suitable
     punctuation.

The results returned by FUNCTION need not be strings; they may be of any
sequence type acceptable to `concat'.  The same applies to SEPARATOR.

Either the code or the documentation is wrong.  I strongly believe it's
the documentation.

Here's a patch to fix it.  I will apply this patch to the emacs-25 branch
soon, if I don't hear any objections.

diff --git a/doc/lispref/functions.texi b/doc/lispref/functions.texi
index 8835667..1b949f2 100644
--- a/doc/lispref/functions.texi
+++ b/doc/lispref/functions.texi
@@ -861,13 +861,15 @@ Mapping Functions
 
 @defun mapconcat function sequence separator
 @code{mapconcat} applies @var{function} to each element of
-@var{sequence}: the results, which must be strings, are concatenated.
-Between each pair of result strings, @code{mapconcat} inserts the string
+@var{sequence}: the results, which must be sequences, are
+concatenated.  These result sequences are usually strings, but may
+also be lists of numbers or vectors of numbers.  Between each pair of
+result sequences, @code{mapconcat} inserts the sequence
 @var{separator}.  Usually @var{separator} contains a space or comma or
 other suitable punctuation.
 
 The argument @var{function} must be a function that can take one
-argument and return a string.  The argument @var{sequence} can be any
+argument and return a sequence.  The argument @var{sequence} can be any
 kind of sequence except a char-table; that is, a list, a vector, a
 bool-vector, or a string.

-- 
Alan Mackenzie (Nuremberg, Germany).