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+;;; regi.el --- REGular expression Interpreting engine
+
+;; Author: 1993 Barry A. Warsaw, Century Computing, Inc. <bwarsaw@cen.com>
+;; Maintainer:    bwarsaw@cen.com
+;; Created:       24-Feb-1993
+;; Version:       1.8
+;; Last Modified: 1993/06/01 21:33:00
+;; Keywords:      regular expression regexp matching text
+
+;; Copyright (C) 1993 Barry A. Warsaw
+
+;; This file is not yet part of GNU Emacs.
+;;
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2 of the License, or
+;; (at your option) any later version.
+;; 
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;; 
+;; You should have received a copy of the GNU General Public License
+;; along with this program; if not, write to the Free Software
+;; Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+;; LCD Archive Entry
+;; regi|Barry A. Warsaw|bwarsaw@cen.com
+;; |REGular expression Interpreting engine
+;; |1993/06/01 21:33:00|1.8|
+
+;;; Code:
+
+
+(defun regi-pos (&optional position col-p)
+  "Return the character position at various buffer positions.
+Optional POSITION can be one of the following symbols:
+
+`bol'  == beginning of line
+`boi'  == beginning of indentation
+`eol'  == end of line [default]
+`bonl' == beginning of next line
+`bopl' == beginning of previous line
+
+Optional COL-P non-nil returns `current-column' instead of character position."
+  (save-excursion
+    (cond
+     ((eq position 'bol)  (beginning-of-line))
+     ((eq position 'boi)  (back-to-indentation))
+     ((eq position 'bonl) (forward-line 1))
+     ((eq position 'bopl) (forward-line -1))
+     (t (end-of-line)))
+    (if col-p (current-column) (point))))
+
+(defun regi-mapcar (predlist func &optional negate-p case-fold-search-p)
+  "Build a regi frame where each element of PREDLIST appears exactly once.
+The frame contains elements where each member of PREDLIST is
+associated with FUNC, and optionally NEGATE-P and CASE-FOLD-SEARCH-P."
+  (let (frame tail)
+    (if (or negate-p case-fold-search-p)
+        (setq tail (list negate-p)))
+    (if case-fold-search-p
+        (setq tail (append tail (list case-fold-search-p))))
+    (while predlist
+      (let ((element (list (car predlist) func)))
+        (if tail
+            (setq element (append element tail)))
+        (setq frame (append frame (list element))
+              predlist (cdr predlist))
+        ))
+    frame))
+
+
+(defun regi-interpret (frame &optional start end)
+  "Interpret the regi frame FRAME.
+If optional START and END are supplied, they indicate the region of
+interest, and the buffer is narrowed to the beginning of the line
+containing START, and beginning of the line after the line containing
+END.  Otherwise, point and mark are not set and processing continues
+until your FUNC returns the `abort' symbol (see below).  Beware!  Not
+supplying a START or END could put you in an infinite loop.
+
+A regi frame is a list of entries of the form:
+
+     (PRED FUNC [NEGATE-P [CASE-FOLD-SEARCH]])
+
+PRED is a predicate against which each line in the region is tested,
+and if a match occurs, FUNC is `eval'd.  Point is then moved to the
+beginning of the next line, the frame is reset and checking continues.
+If a match doesn't occur, the next entry is checked against the
+current line until all entries in the frame are checked.  At this
+point, if no match occurred, the frame is reset and point is moved to
+the next line.  Checking continues until every line in the region is
+checked.  Optional NEGATE-P inverts the result of PRED before FUNC is
+called and `case-fold-search' is bound to the optional value of
+CASE-FOLD-SEARCH for the PRED check.
+
+PRED can be a string, variable, function or one of the following
+symbols: t, nil, `begin', `end', and `every'.  If PRED is a string, or
+a variable or list that evaluates to a string, it is interpreted as a
+regular expression and is matched against the current line (from the
+beginning) using `looking-at'.  If PRED does not evaluate to a string,
+it is interpreted as a binary value (nil or non-nil).
+
+PRED can also be one of the following symbols:
+
+t       -- always produces a true outcome
+`begin' -- always executes before anything else
+`end'   -- always executes after everything else
+`every' -- execute after frame is matched on a line
+
+Note that NEGATE-P and CASE-FOLD-SEARCH are meaningless if PRED is one
+of these special symbols.  Only the first occurance of each symbol in
+a frame entry is used, the rest are ignored.
+
+Your FUNC can return values which control regi processing.  If a list
+is returned from your function, it can contain any combination of the
+following elements:
+
+the symbol `continue'
+     Tells regi to continue processing frame-entries after a match,
+     instead of resetting to the first entry and advancing to the next
+     line, as is the default behavior.  When returning this symbol,
+     you must take care not to enter an infinite loop.
+
+the symbol `abort'
+     Tells regi to terminate processing this frame.  any end
+     frame-entry is still processed.
+
+the list `(frame . NEWFRAME)'
+     Tells regi to use NEWFRAME as its current frame.  In other words,
+     your FUNC can modify the executing regi frame on the fly.
+
+the list `(step . STEP)'
+     Tells regi to move STEP number of lines forward during normal
+     processing.  By default, regi moves forward 1 line.  STEP can be
+     negative, but be careful of infinite loops.
+
+You should usually take care to explicitly return nil from your
+function if no action is to take place.  Your FUNC will always be
+`eval'ed.  The following variables will be temporarily bound to some
+useful information:
+
+`curline'
+     the current line in the buffer, as a string
+
+`curframe'
+     the full, current frame being executed
+
+`curentry'
+     the current frame entry being executed."
+
+  (save-excursion
+    (save-restriction
+      (let (begin-tag end-tag every-tag current-frame working-frame donep)
+
+        ;; set up the narrowed region
+        (and start
+             end
+             (let* ((tstart start)
+                    (start (min start end))
+                    (end   (max start end)))
+               (narrow-to-region
+                (progn (goto-char end) (regi-pos 'bonl))
+                (progn (goto-char start) (regi-pos 'bol)))))
+
+        ;; lets find the special tags and remove them from the working
+        ;; frame. note that only the last special tag is used.
+        (mapcar
+         (function
+          (lambda (entry)
+            (let ((pred (car entry))
+                  (func (car (cdr entry))))
+              (cond
+               ((eq pred 'begin) (setq begin-tag func))
+               ((eq pred 'end)   (setq end-tag func))
+               ((eq pred 'every) (setq every-tag func))
+               (t
+                (setq working-frame (append working-frame (list entry))))
+               ) ; end-cond
+              )))
+         frame) ; end-mapcar
+
+        ;; execute the begin entry
+        (eval begin-tag)
+
+        ;; now process the frame
+        (setq current-frame working-frame)
+        (while (not (or donep (eobp)))
+          (let* ((entry            (car current-frame))
+                 (pred             (nth 0 entry))
+                 (func             (nth 1 entry))
+                 (negate-p         (nth 2 entry))
+                 (case-fold-search (nth 3 entry))
+                 match-p)
+            (catch 'regi-throw-top
+              (cond
+               ;; we are finished processing the frame for this line
+               ((not current-frame)
+                (setq current-frame working-frame) ;reset frame
+                (forward-line 1)
+                (throw 'regi-throw-top t))
+               ;; see if predicate evaluates to a string
+               ((stringp (setq match-p (eval pred)))
+                (setq match-p (looking-at match-p)))
+               ) ; end-cond
+
+              ;; now that we've done the initial matching, check for
+              ;; negation of match
+              (and negate-p
+                   (setq match-p (not match-p)))
+
+              ;; if the line matched, package up the argument list and
+              ;; funcall the FUNC
+              (if match-p
+                   (let* ((curline (buffer-substring
+                                    (regi-pos 'bol)
+                                    (regi-pos 'eol)))
+                          (curframe current-frame)
+                          (curentry entry)
+                          (result (eval func))
+                          (step (or (cdr (assq 'step result)) 1))
+                          )
+                     ;; changing frame on the fly?
+                     (if (assq 'frame result)
+                         (setq working-frame (cdr (assq 'frame result))))
+
+                     ;; continue processing current frame?
+                     (if (memq 'continue result)
+                         (setq current-frame (cdr current-frame))
+                       (forward-line step)
+                       (setq current-frame working-frame))
+
+                     ;; abort current frame?
+                     (if (memq 'abort result)
+                         (progn
+                           (setq donep t)
+                           (throw 'regi-throw-top t)))
+                     ) ; end-let
+
+                ;; else if no match occurred, then process the next
+                ;; frame-entry on the current line
+                (setq current-frame (cdr current-frame))
+
+                ) ; end-if match-p
+              ) ; end catch
+            ) ; end let
+
+          ;; after every cycle, evaluate every-tag
+          (eval every-tag)
+          ) ; end-while
+
+        ;; now process the end entry
+        (eval end-tag)))))
+
+
+(provide 'regi)
+;;; regi.el ends here