Make 'mapconcat' argument 'separator' optional

* src/fns.c (Fmapconcat): Make third 'separator' argument
optional.  (Bug#50965)
* doc/lispref/functions.texi (Mapping Functions): Update
documentation for above change.
* test/src/fns-tests.el (fns-tests-mapconcat): New test.

* doc/misc/cl.texi (Obsolete Setf Customization): Don't use third
mapconcat argument in example.
* lisp/emacs-lisp/subr-x.el (string-join): Doc fix.

diff --git a/doc/lispref/functions.texi b/doc/lispref/functions.texi
index c856557c3cba0054031cfdaba46253116599b154..3163300184aa1983fbac885a0902a903ebfefbba 100644 (file)
--- a/doc/lispref/functions.texi
+++ b/doc/lispref/functions.texi
@@ -961,14 +961,14 @@ side-effects only---the values it returns are ignored, not collected
 into a list.  @code{mapc} always returns @var{sequence}.
 @end defun
 
-@defun mapconcat function sequence separator
+@defun mapconcat function sequence &optional separator
 @code{mapconcat} applies @var{function} to each element of
 @var{sequence}; the results, which must be sequences of characters
 (strings, vectors, or lists), are concatenated into a single string
 return value.  Between each pair of result sequences, @code{mapconcat}
 inserts the characters from @var{separator}, which also must be a
-string, or a vector or list of characters.  @xref{Sequences Arrays
-Vectors}.
+string, or a vector or list of characters; a @code{nil} value is
+treated as the empty string.  @xref{Sequences Arrays Vectors}.
 
 The argument @var{function} must be a function that can take one
 argument and returns a sequence of characters: a string, a vector, or
@@ -986,8 +986,7 @@ string.
 
 @group
 (mapconcat (lambda (x) (format "%c" (1+ x)))
-           "HAL-8000"
-           "")
+           "HAL-8000")
      @result{} "IBM.9111"
 @end group
 @end example

diff --git a/doc/misc/cl.texi b/doc/misc/cl.texi
index 1e5d40b037735d6024c7d590d703eb93da92a75e..04e2c71a2b97b60c1ba0b9157d8ddb572a6767b9 100644 (file)
--- a/doc/misc/cl.texi
+++ b/doc/misc/cl.texi
@@ -5030,7 +5030,7 @@ The above @code{incf} example could be written using
 @ignore
 (defmacro concatf (place &rest args)
   (gv-letplace (getter setter) place
-    (macroexp-let2 nil v (mapconcat 'identity args "")
+    (macroexp-let2 nil v (mapconcat 'identity args)
       (funcall setter `(concat ,getter ,v)))))
 @end ignore
 @end defmac

diff --git a/etc/NEWS b/etc/NEWS
index 2dcd12f22ff64903066c29fbc9bad187ffadcc70..e9fcfba425198e803c26153da7d287a7787dfdca 100644 (file)
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -118,6 +118,10 @@ with recent versions of Firefox.
 \f
 * Lisp Changes in Emacs 29.1
 
++++
+** Third 'mapconcat' argument 'separator' is now optional.
+An explicit nil always meant the empty string, now it can be left out.
+
 ---
 ** Themes can now be made obsolete.
 Using 'make-obsolete' on a theme is now supported.  This will make

diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index ecd3ca831e8bac5cae06c2907859726258529238..8d6bb19fd49527fff8003da1e70df824f85ec1c0 100644 (file)
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -208,7 +208,9 @@ The variable list SPEC is the same as in `if-let'."
   (string= string ""))
 
 (defsubst string-join (strings &optional separator)
-  "Join all STRINGS using SEPARATOR."
+  "Join all STRINGS using SEPARATOR.
+Optional argument SEPARATOR must be a string, a vector, or a list of
+characters; nil stands for the empty string."
   (mapconcat #'identity strings separator))
 
 (define-obsolete-function-alias 'string-reverse 'reverse "25.1")

diff --git a/src/fns.c b/src/fns.c
index a72e41aee5bda860a9af8f2d97faa0888dc2bc13..61182852ba70da8fc3ab863c47e1f94a3c5ee494 100644 (file)
--- a/src/fns.c
+++ b/src/fns.c
@@ -2852,12 +2852,16 @@ mapcar1 (EMACS_INT leni, Lisp_Object *vals, Lisp_Object fn, Lisp_Object seq)
   return leni;
 }
 
-DEFUN ("mapconcat", Fmapconcat, Smapconcat, 3, 3, 0,
+DEFUN ("mapconcat", Fmapconcat, Smapconcat, 2, 3, 0,
        doc: /* Apply FUNCTION to each element of SEQUENCE, and concat the results as strings.
 In between each pair of results, stick in SEPARATOR.  Thus, " " as
   SEPARATOR results in spaces between the values returned by FUNCTION.
+
 SEQUENCE may be a list, a vector, a bool-vector, or a string.
-SEPARATOR must be a string, a vector, or a list of characters.
+
+Optional argument SEPARATOR must be a string, a vector, or a list of
+characters; nil stands for the empty string.
+
 FUNCTION must be a function of one argument, and must return a value
   that is a sequence of characters: either a string, or a vector or
   list of numbers that are valid character codepoints.  */)

diff --git a/test/src/fns-tests.el b/test/src/fns-tests.el
index 57594572094eed6f6afb07f6e0331ca236cb3e53..2d641cc311114968e6d5e3fbdc9d9569b9c8769f 100644 (file)
--- a/test/src/fns-tests.el
+++ b/test/src/fns-tests.el
@@ -430,6 +430,23 @@
                    (buffer-hash))
                  (sha1 "foo"))))
 
+(ert-deftest fns-tests-mapconcat ()
+  (should (string= (mapconcat #'identity '()) ""))
+  (should (string= (mapconcat #'identity '("a" "b")) "ab"))
+  (should (string= (mapconcat #'identity '() "_") ""))
+  (should (string= (mapconcat #'identity '("A") "_") "A"))
+  (should (string= (mapconcat #'identity '("A" "B") "_") "A_B"))
+  (should (string= (mapconcat #'identity '("A" "B" "C") "_") "A_B_C"))
+  ;; non-ASCII strings
+  (should (string= (mapconcat #'identity '("Ä" "ø" "☭" "தமிழ்") "_漢字_")
+                   "Ä_漢字_ø_漢字_☭_漢字_தமிழ்"))
+  ;; vector
+  (should (string= (mapconcat #'identity ["a" "b"] "") "ab"))
+  ;; bool-vector
+  (should (string= (mapconcat #'identity [nil nil] "") ""))
+  (should-error (mapconcat #'identity [nil nil t])
+                :type 'wrong-type-argument))
+
 (ert-deftest fns-tests-mapcan ()
   (should-error (mapcan))
   (should-error (mapcan #'identity))