A mapping function applies a given function to each element of a
list or other collection. Emacs Lisp has three such functions;
mapcar
and mapconcat
, which scan a list, are described
here. For the third mapping function, mapatoms
, see
section Creating and Interning Symbols.
mapcar
applies function to each element of sequence
in turn, and returns a list of the results.
The argument sequence may be a list, a 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 'char-to-string "abc")
=> ("a" "b" "c")
;; Call each function in my-hooks
.
(mapcar 'funcall my-hooks)
(defun mapcar* (f &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 f (mapcar 'car args))
(apply 'mapcar* f
;; Recurse for rest of elements.
(mapcar 'cdr args)))))
(mapcar* 'cons '(a b c) '(1 2 3 4))
=> ((a . 1) (b . 2) (c . 3))
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 argument function must be a function that can take one argument and return a string.
(mapconcat 'symbol-name '(The cat in the hat) " ") => "The cat in the hat" (mapconcat (function (lambda (x) (format "%c" (1+ x)))) "HAL-8000" "") => "IBM.9111"
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