code/help-gnu-emacs.el

   1 ;;; help-gnu-emacs.el --- examples from help-gnu-emacs@gnu.org
   2
   3 ;; Copyright (C) 2009  contributors to help-gnu-emacs@gnu.org
   4
   5 ;; Author: authors of the contributions
   6 ;; Keywords: lisp
   7
   8 ;; This program is free software; you can redistribute it and/or modify
   9 ;; it under the terms of the GNU General Public License as published by
  10 ;; the Free Software Foundation, either version 3 of the License, or
  11 ;; (at your option) any later version.
  12
  13 ;; This program is distributed in the hope that it will be useful,
  14 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 ;; GNU General Public License for more details.
  17
  18 ;; You should have received a copy of the GNU General Public License
  19 ;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20
  21 ;;; Commentary:
  22
  23 ;; This file contains stuff found at
  24 ;; help-gnu-emacs@gnu.org, which was seems of interest
  25 ;; to preserve that way
  26
  27 ;; Please note: code here does not reflect fully
  28 ;; discussions but delivers an extract from it. As
  29 ;; functions may be defined differently, its not
  30 ;; suitable to compile it.
  31
  32
  33 ;;; Code:
  34
  35
  36 ;; Partition for Emacs Lisp
  37 ;; Marc Tfardy, bum@cyk.cyk, 28.06.2009 15:26
  38 ;;
  39 ;; Hi!
  40 ;;
  41 ;; I looking for a ELISP function that do the job like Partition in
  42 ;; Mathematica. The simplest case:
  43 ;;
  44 ;; (partition '(a b c d e f) 2)
  45 ;;
  46 ;; should return:
  47 ;; ((a b) (c d) (e f))
  48 ;;
  49 ;; Is there something ready out from the box?
  50 ;;
  51 ;; Re: Partition for Emacs Lisp
  52 ;; Pascal J. Bourguignon, pjb@informatimago.com, 28.06.2009 19:52
  53
  54 (defun partition-list (list length)
  55   (loop
  56      while list
  57      collect (subseq list 0 length)
  58      do (setf list (nthcdr length list))))
  59
  60 (defun partition-vector (vector length)
  61   (loop
  62      for i = 0 then (+ i length)
  63      while (< i (length vector))
  64      collect (subseq vector i (+ i length))))
  65
  66 (defun partition (sequence length)
  67    (etypecase sequence
  68       (list   (partition-list sequence length))
  69       (string (partition-vector sequence length)) ; emacs lisp strings are not vectors!
  70       (vector (partition-vector sequence length))))
  71
  72 ;; (partition '[a b c d e f] 2)  -> ([a b] [c d] [e f])
  73 ;; (partition '(a b c d e f) 2)  -> ((a b) (c d) (e f))
  74 ;; (partition '"abcdef" 2)       -> ("ab" "cd" "ef")
  75
  76 ;; Re: Partition for Emacs Lisp
  77 ;; Vassil Nikolov, vnikolov@pobox.com, 02:46
  78
  79 (when (and (fboundp 'featurep) (featurep 'emacs))  ;seen in comp.lang.lisp
  80   (require 'cl))
  81
  82 (defun partition (l n)  ;"demo" grade, cursorily tested
  83   "Return a list of L's consecutive sublists of length N."
  84   (assert (zerop (mod (length l) n)))
  85   (loop for l on l by #'(lambda (l) (nthcdr n l)) collect (subseq l 0 n)))
  86
  87 ;; (partition '(a b c d e f) 2)
  88 ;; => ((a b) (c d) (e f))
  89
  90 (provide 'help-gnu-emacs)
  91 ;;; help-gnu-emacs.el ends here
  92
  93