From 754bbf7a25a8dda49b5d08ef0d0443bbf5af0e36 Mon Sep 17 00:00:00 2001 From: Craig Jennings Date: Sun, 7 Apr 2024 13:41:34 -0500 Subject: new repository --- devdocs/elisp/mapping-functions.html | 62 ++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 devdocs/elisp/mapping-functions.html (limited to 'devdocs/elisp/mapping-functions.html') diff --git a/devdocs/elisp/mapping-functions.html b/devdocs/elisp/mapping-functions.html new file mode 100644 index 00000000..2f920180 --- /dev/null +++ b/devdocs/elisp/mapping-functions.html @@ -0,0 +1,62 @@ +

Mapping Functions

A mapping function applies a given function (not a special form or macro) to each element of a list or other collection. Emacs Lisp has several such functions; this section describes mapcar, mapc, mapconcat, and mapcan, which map over a list. See Definition of mapatoms, for the function mapatoms which maps over the symbols in an obarray. See Definition of maphash, for the function maphash which maps over key/value associations in a hash table.

These mapping functions do not allow char-tables because a char-table is a sparse array whose nominal range of indices is very large. To map over a char-table in a way that deals properly with its sparse nature, use the function map-char-table (see Char-Tables).

Function: mapcar function sequence +
+

mapcar applies function to each element of sequence in turn, and returns a list of the results.

The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string. The result is always a list. The length of the result is the same as the length of sequence. For example: 

(mapcar #'car '((a b) (c d) (e f)))
+     ⇒ (a c e)
+(mapcar #'1+ [1 2 3])
+     ⇒ (2 3 4)
+(mapcar #'string "abc")
+     ⇒ ("a" "b" "c")
+
+ +
;; Call each function in my-hooks.
+(mapcar 'funcall my-hooks)
+
+ +
(defun mapcar* (function &rest args)
+  "Apply FUNCTION to successive cars of all ARGS.
+Return the list of results."
+  ;; If no list is exhausted,
+  (if (not (memq nil args))
+      ;; apply function to CARs.
+      (cons (apply function (mapcar #'car args))
+            (apply #'mapcar* function
+                   ;; Recurse for rest of elements.
+                   (mapcar #'cdr args)))))
+
+ +
(mapcar* #'cons '(a b c) '(1 2 3 4))
+     ⇒ ((a . 1) (b . 2) (c . 3))
+
+
+
Function: mapcan function sequence +
+

This function applies function to each element of sequence, like mapcar, but instead of collecting the results into a list, it returns a single list with all the elements of the results (which must be lists), by altering the results (using nconc; see Rearrangement). Like with mapcar, sequence can be of any type except a char-table. 

;; Contrast this:
+(mapcar #'list '(a b c d))
+     ⇒ ((a) (b) (c) (d))
+;; with this:
+(mapcan #'list '(a b c d))
+     ⇒ (a b c d)
+
+
+
Function: mapc function sequence +

mapc is like mapcar except that function is used for side-effects only—the values it returns are ignored, not collected into a list. mapc always returns sequence.

+
Function: mapconcat function sequence separator +
+

mapconcat applies function to each element of 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, mapconcat inserts the characters from separator, which also must be a string, or a vector or list of characters. See Sequences Arrays Vectors.

The argument function must be a function that can take one argument and returns a sequence of characters: a string, a vector, or a list. The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string. 

(mapconcat #'symbol-name
+           '(The cat in the hat)
+           " ")
+     ⇒ "The cat in the hat"
+
+ +
(mapconcat (lambda (x) (format "%c" (1+ x)))
+           "HAL-8000"
+           "")
+     ⇒ "IBM.9111"
+
+
+
+

+ Copyright © 1990-1996, 1998-2022 Free Software Foundation, Inc.
Licensed under the GNU GPL license.
+ https://www.gnu.org/software/emacs/manual/html_node/elisp/Mapping-Functions.html +

+
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