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1 ;;; featurep.el --- Support functions for reader conditionals
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2
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3 ;; Copyright 1997 Naggum Software
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4
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5 ;; Author: Erik Naggum <erik@naggum.no>
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6 ;; Keywords: internal
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7
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8 ;; This file is not (yet) part of GNU Emacs, but distributed under the
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9 ;; same conditions as GNU Emacs, and is useless without GNU Emacs.
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10
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11 ;; GNU Emacs is free software; you can redistribute it and/or modify
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12 ;; it under the terms of the GNU General Public License as published by
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13 ;; the Free Software Foundation; either version 2, or (at your option)
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14 ;; any later version.
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15
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16 ;; GNU Emacs is distributed in the hope that it will be useful,
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17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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19 ;; GNU General Public License for more details.
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20
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21 ;; You should have received a copy of the GNU General Public License
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22 ;; along with GNU Emacs; see the file COPYING. If not, write to
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23 ;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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24 ;; Boston, MA 02111-1307, USA.
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25
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26 ;;; Commentary:
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27
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28 ;; The #+ and #- reader macros require support code to work properly until
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29 ;; `featurep' is enhanced in the C code. This support code is written in
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30 ;; Lisp to make it easier to experiment with the code.
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31
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32 ;;; Code:
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33
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34 (eval-when-compile (require 'cl))
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35
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36 (provide (if (string-match "XEmacs" emacs-version) 'xemacs 'emacs))
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37
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38 (defvar featurep-emacs-version nil
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39 "The version number of this Emacs, as a floating-point number.")
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40
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41 (defun featurep (fexp)
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42 "Return non-nil if feature expression FEXP is true."
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43 (typecase fexp
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142
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44 (symbol (and (memq fexp features) ;original definition
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45 t))
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140
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46 (number (>= (or featurep-emacs-version
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47 (setq featurep-emacs-version
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48 (+ emacs-major-version
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49 (/ emacs-minor-version 100.0))))
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50 fexp))
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51 (list (case (pop fexp)
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52 (not (let ((negate (pop fexp)))
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53 (if fexp
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54 (signal 'invalid-read-syntax (list fexp))
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55 (not (featurep negate)))))
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56 (and (while (and fexp (featurep (car fexp)))
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57 (pop fexp))
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58 (null fexp))
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59 (or (while (and fexp (not (featurep (car fexp))))
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60 (pop fexp))
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61 fexp)
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62 (t (signal 'invalid-read-syntax (list fexp)))))
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63 (t (signal 'invalid-read-syntax (list fexp)))))
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64
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65 ;;; featurep.el ends here
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66
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