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;;; completion.el --- dynamic word-completion code
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;; Copyright (C) 1990, 1993, 1995 Free Software Foundation, Inc.
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;; Maintainer: FSF
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;; Keywords: abbrev
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;; Author: Jim Salem <alem@bbnplanet.com> of Thinking Machines Inc.
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;;  (ideas suggested by Brewster Kahle)
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;; This file is part of GNU Emacs.
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;; GNU Emacs 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, or (at your option)
;; any later version.

;; GNU Emacs 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 GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

;;; Commentary:
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;;; 
;;; What to put in .emacs
;;;-----------------------
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;;; (load "completion")
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;;; (initialize-completions)

;;;---------------------------------------------------------------------------
;;; Documentation [Slightly out of date]
;;;---------------------------------------------------------------------------
;;;  (also check the documentation string of the functions)
;;;
;;; Introduction
;;;---------------
;;;  
;;;     After you type a few characters, pressing the "complete" key inserts
;;; the rest of the word you are likely to type.  
;;;
;;; This watches all the words that you type and remembers them.  When 
;;; typing a new word, pressing "complete" (meta-return) "completes" the
;;; word by inserting the most recently used word that begins with the 
;;; same characters.  If you press meta-return repeatedly, it cycles
;;; through all the words it knows about.
;;;
;;;  If you like the completion then just continue typing, it is as if you
;;; entered the text by hand.  If you want the inserted extra characters 
;;; to go away, type control-w or delete.  More options are described below.
;;;
;;;  The guesses are made in the order of the most recently "used".  Typing
;;; in a word and then typing a separator character (such as a space) "uses" 
;;; the word.  So does moving a cursor over the word.  If no words are found, 
;;; it uses an extended version of the dabbrev style completion.
;;;
;;;   You automatically save the completions you use to a file between 
;;; sessions.  
;;;
;;;   Completion enables programmers to enter longer, more descriptive 
;;; variable names while typing fewer keystrokes than they normally would.
;;;
;;;
;;; Full documentation
;;;---------------------
;;;
;;;   A "word" is any string containing characters with either word or symbol 
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;;; syntax.  [E.G. Any alphanumeric string with hyphens, underscores, etc.]
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;;; Unless you change the constants, you must type at least three characters
;;; for the word to be recognized.  Only words longer than 6 characters are
;;; saved.
;;;
;;;   When you load this file, completion will be on.  I suggest you use the
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;;; compiled version (because it is noticeably faster).
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;;;
;;;  M-X completion-mode toggles whether or not new words are added to the
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;;; database by changing the value of enable-completion.
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;;;
;;;  SAVING/LOADING COMPLETIONS
;;;   Completions are automatically saved from one session to another
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;;; (unless save-completions-flag or enable-completion is nil).
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;;; Loading this file (or calling initialize-completions) causes EMACS
;;; to load a completions database for a saved completions file 
;;; (default: ~/.completions).  When you exit, EMACS saves a copy of the
;;; completions that you 
;;; often use.  When you next start, EMACS loads in the saved completion file.
;;;
;;;   The number of completions saved depends loosely on 
;;; *saved-completions-decay-factor*.  Completions that have never been 
;;; inserted via "complete" are not saved.  You are encouraged to experiment
;;; with different functions (see compute-completion-min-num-uses).
;;;
;;;   Some completions are permanent and are always saved out.  These 
;;; completions have their num-uses slot set to T.  Use 
;;; add-permanent-completion to do this
;;;
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;;;   Completions are saved only if enable-completion is T.  The number of old
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;;; versions kept of the saved completions file is controlled by 
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;;; completions-file-versions-kept.
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;;;
;;; COMPLETE KEY OPTIONS
;;;   The complete function takes a numeric arguments.  
;;;  control-u :: leave the point at the beginning of the completion rather 
;;;               than the middle.
;;;  a number  :: rotate through the possible completions by that amount
;;;  `-'       :: same as -1 (insert previous completion)
;;;
;;; HOW THE DATABASE IS MAINTAINED
;;;  <write>
;;;
;;; UPDATING THE DATABASE MANUALLY
;;;   m-x kill-completion 
;;;     kills the completion at point.
;;;   m-x add-completion
;;;   m-x add-permanent-completion
;;;   
;;; UPDATING THE DATABASE FROM A SOURCE CODE FILE
;;;   m-x add-completions-from-buffer
;;;     Parses all the definition names from a C or LISP mode buffer and
;;;     adds them to the completion database.
;;;
;;;   m-x add-completions-from-lisp-file 
;;;     Parses all the definition names from a C or Lisp mode file and
;;;     adds them to the completion database.
;;;
;;; UPDATING THE DATABASE FROM A TAGS TABLE
;;;   m-x add-completions-from-tags-table
;;;     Adds completions from the current tags-table-buffer.
;;;
;;; HOW A COMPLETION IS FOUND
;;;  <write>
;;;
;;; STRING CASING
;;;   Completion is string case independent if case-fold-search has its 
;;;  normal default of T.  Also when the completion is inserted the case of the
;;;  entry is coerced appropriately.  
;;;  [E.G.  APP --> APPROPRIATELY     app --> appropriately  
;;;         App --> Appropriately]
;;;
;;; INITIALIZATION
;;;  The form `(initialize-completions)' initializes the completion system by 
;;; trying to load in the user's completions.  After the first cal, further 
;;; calls have no effect so one should be careful not to put the form in a 
;;; site's standard site-init file.
;;;
;;;---------------------------------------------------------------------------
;;;
;;;

;;;---------------------------------------------------------------------------
;;; Functions you might like to call
;;;---------------------------------------------------------------------------
;;;
;;;  add-completion  string &optional num-uses
;;;    Adds a new string to the database
;;;
;;;  add-permanent-completion  string
;;;    Adds a new string to the database with num-uses = T
;;;

;;;  kill-completion string
;;;    Kills the completion from the database.
;;;
;;;  clear-all-completions
;;;    Clears the database
;;;
;;;  list-all-completions
;;;    Returns a list of all completions.
;;;
;;;
;;;  next-completion string &optional index
;;;    Returns a completion entry that starts with string.
;;;
;;;  find-exact-completion string
;;;    Returns a completion entry that exactly matches string.
;;;
;;;  complete
;;;    Inserts a completion at point
;;;
;;;  initialize-completions
;;;    Loads the completions file and sets up so that exiting emacs will 
;;;  save them.
;;;
;;;  save-completions-to-file &optional filename  
;;;  load-completions-from-file &optional filename
;;;
;;;-----------------------------------------------
;;; Other functions
;;;-----------------------------------------------
;;;
;;;  get-completion-list string
;;;
;;; These things are for manipulating the structure
;;;  make-completion string num-uses
;;;  completion-num-uses completion 
;;;  completion-string completion
;;;  set-completion-num-uses completion num-uses
;;;  set-completion-string completion string
;;;  
;;;

;;;-----------------------------------------------
;;; To Do :: (anybody ?)
;;;-----------------------------------------------
;;;
;;;   Implement Lookup and keyboard interface in C
;;;   Add package prefix smarts (for Common Lisp)
;;;   Add autoprompting of possible completions after every keystroke (fast
;;;      terminals only !)
;;;   Add doc. to texinfo
;;;
;;;
;;;-----------------------------------------------
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;;; Change Log:
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;;;-----------------------------------------------
;;;    Sometime in '84 Brewster implemented a somewhat buggy version for 
;;; Symbolics LISPMs.
;;;    Jan. '85 Jim became enamored of the idea and implemented a faster, 
;;; more robust version.
;;;    With input from many users at TMC, (rose, craig, and gls come to mind),
;;; the current style of interface was developed. 
;;;    9/87, Jim and Brewster took terminals home.  Yuck.  After 
;;; complaining for a while Brewester implemented a subset of the current 
;;; LISPM version for GNU Emacs.  
;;;    8/88  After complaining for a while (and with sufficient 
;;; promised rewards), Jim reimplemented a version of GNU completion
;;; superior to that of the LISPM version.
;;;
;;;-----------------------------------------------
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;;; Acknowledgements
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;;;-----------------------------------------------
;;;  Cliff Lasser (cal@think.com), Kevin Herbert (kph@cisco.com),
;;;  eero@media-lab, kgk@cs.brown.edu, jla@ai.mit.edu,
;;;
;;;-----------------------------------------------
;;; Change Log
;;;-----------------------------------------------
;;; From version 9 to 10
;;;  - Allowance for non-integral *completion-version* nos.
;;;  - Fix cmpl-apply-as-top-level for keyboard macros
;;;  - Fix broken completion merging (in save-completions-to-file)
;;;  - More misc. fixes for version 19.0 of emacs
;;;
;;; From Version 8 to 9
;;;  - Ported to version 19.0 of emacs (backcompatible with version 18)
;;;  - Added add-completions-from-tags-table (with thanks to eero@media-lab)
;;;
;;; From Version 7 to 8
;;;  - Misc. changes to comments
;;;  - new completion key bindings: c-x o, M->, M-<, c-a, c-e
;;;  - cdabbrev now checks all the visible window buffers and the "other buffer"
;;;  - `%' is now a symbol character rather than a separator (except in C mode)
;;;
;;; From Version 6 to 7
;;;  - Fixed bug with saving out .completion file the first time
;;;
;;; From Version 5 to 6
;;;  - removed statistics recording
;;;  - reworked advise to handle autoloads
;;;  - Fixed fortran mode support
;;;  - Added new cursor motion triggers
;;;
;;; From Version 4 to 5
;;;  - doesn't bother saving if nothing has changed
;;;  - auto-save if haven't used for a 1/2 hour
;;;  - save period extended to two weeks
;;;  - minor fix to capitalization code
;;;  - added *completion-auto-save-period* to variables recorded.
;;;  - added reenter protection to cmpl-record-statistics-filter
;;;  - added backup protection to save-completions-to-file (prevents 
;;;    problems with disk full errors)

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;;; Code:

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;;;---------------------------------------------------------------------------
;;; User changeable parameters
;;;---------------------------------------------------------------------------

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(defvar enable-completion t
  "*Non-nil means enable recording and saving of completions.
If nil, no new words added to the database or saved to the init file.")
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(defvar save-completions-flag t
  "*Non-nil means save most-used completions when exiting Emacs.
See also `saved-completions-retention-time'.")
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(defvar save-completions-file-name "~/.completions"
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  "*The filename to save completions to.")

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(defvar save-completions-retention-time 336
  "*Discard a completion if unused for this many hours.
\(1 day = 24, 1 week = 168).  If this is 0, non-permanent completions
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will not be saved unless these are used.  Default is two weeks.")
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(defvar completion-on-separator-character nil
  "*Non-nil means separator characters mark previous word as used.
This means the word will be saved as a completion.")
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(defvar completions-file-versions-kept kept-new-versions
  "*Number of versions to keep for the saved completions file.")
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(defvar completion-prompt-speed-threshold 4800
  "*Minimum output speed at which to display next potential completion.")
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(defvar completion-cdabbrev-prompt-flag nil
  "*If non-nil, the next completion prompt does a cdabbrev search.
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This can be time consuming.")

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(defvar completion-search-distance 15000
  "*How far to search in the buffer when looking for completions.
In number of characters.  If nil, search the whole buffer.")
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(defvar completions-merging-modes '(lisp c)
  "*List of modes {`c' or `lisp'} for automatic completions merging.
Definitions from visited files which have these modes
are automatically added to the completion database.")
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;;;(defvar *record-cmpl-statistics-p* nil
;;;  "*If non-nil, record completion statistics.")
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;;;(defvar *completion-auto-save-period* 1800
;;;  "*The period in seconds to wait for emacs to be idle before autosaving
;;;the completions.  Default is a 1/2 hour.")
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(defconst completion-min-length nil ;; defined below in eval-when
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  "*The minimum length of a stored completion.
DON'T CHANGE WITHOUT RECOMPILING !  This is used by macros.")

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(defconst completion-max-length nil ;; defined below in eval-when
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  "*The maximum length of a stored completion.
DON'T CHANGE WITHOUT RECOMPILING !  This is used by macros.")

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(defconst completion-prefix-min-length nil ;; defined below in eval-when
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  "The minimum length of a completion search string.
DON'T CHANGE WITHOUT RECOMPILING !  This is used by macros.")

(defmacro eval-when-compile-load-eval (&rest body)
  ;; eval everything before expanding
  (mapcar 'eval body)
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  (cons 'progn body))
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(eval-when-compile
  (defvar completion-gensym-counter 0)
  (defun completion-gensym (&optional arg)
    "Generate a new uninterned symbol.
The name is made by appending a number to PREFIX, default \"G\"."
    (let ((prefix (if (stringp arg) arg "G"))
	  (num (if (integerp arg) arg
		 (prog1 completion-gensym-counter
		   (setq completion-gensym-counter (1+ completion-gensym-counter))))))
      (make-symbol (format "%s%d" prefix num)))))

(defmacro completion-dolist (spec &rest body)
  "(completion-dolist (VAR LIST [RESULT]) BODY...): loop over a list.
Evaluate BODY with VAR bound to each `car' from LIST, in turn.
Then evaluate RESULT to get return value, default nil."
  (let ((temp (completion-gensym "--dolist-temp--")))
    (append (list 'let (list (list temp (nth 1 spec)) (car spec))
		  (append (list 'while temp
				(list 'setq (car spec) (list 'car temp)))
			  body (list (list 'setq temp
					   (list 'cdr temp)))))
	    (if (cdr (cdr spec))
		(cons (list 'setq (car spec) nil) (cdr (cdr spec)))
	      '(nil)))))

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(defun completion-eval-when ()
  (eval-when-compile-load-eval
   ;; These vars. are defined at both compile and load time.
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   (setq completion-min-length 6)
   (setq completion-max-length 200)
   (setq completion-prefix-min-length 3)))
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(completion-eval-when)
 
;;;---------------------------------------------------------------------------
;;; Internal Variables
;;;---------------------------------------------------------------------------

(defvar cmpl-initialized-p nil
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  "Set to t when the completion system is initialized.
Indicates that the old completion file has been read in.")
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(defvar cmpl-completions-accepted-p nil
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  "Set to t as soon as the first completion has been accepted.
Used to decide whether to save completions.")
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(defvar cmpl-preceding-syntax)
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(defvar completion-string)
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;;;---------------------------------------------------------------------------
;;; Low level tools
;;;---------------------------------------------------------------------------

;;;-----------------------------------------------
;;; Misc.
;;;-----------------------------------------------

(defun minibuffer-window-selected-p ()
  "True iff the current window is the minibuffer."
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  (window-minibuffer-p (selected-window)))
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;; This used to be `(eval form)'.  Eval FORM at run time now.
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(defmacro cmpl-read-time-eval (form)
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  form)
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;;;-----------------------------------------------
;;; String case coercion
;;;-----------------------------------------------

(defun cmpl-string-case-type (string)
  "Returns :capitalized, :up, :down, :mixed, or :neither."
  (let ((case-fold-search nil))
    (cond ((string-match "[a-z]" string)
	   (cond ((string-match "[A-Z]" string)
		  (cond ((and (> (length string) 1)
			      (null (string-match "[A-Z]" string 1)))
			 ':capitalized)
			(t
			 ':mixed)))
		 (t ':down)))
	  (t
	   (cond ((string-match "[A-Z]" string)
		  ':up)
		 (t ':neither))))
    ))

;;; Tests -
;;; (cmpl-string-case-type "123ABCDEF456") --> :up
;;; (cmpl-string-case-type "123abcdef456") --> :down
;;; (cmpl-string-case-type "123aBcDeF456") --> :mixed
;;; (cmpl-string-case-type "123456")       --> :neither
;;; (cmpl-string-case-type "Abcde123")     --> :capitalized

(defun cmpl-coerce-string-case (string case-type)
  (cond ((eq case-type ':down) (downcase string))
	((eq case-type ':up) (upcase string))
	((eq case-type ':capitalized)
	 (setq string (downcase string))
	 (aset string 0 (logand ?\337 (aref string 0)))
	 string)
	(t string)
	))

(defun cmpl-merge-string-cases (string-to-coerce given-string)
  (let ((string-case-type (cmpl-string-case-type string-to-coerce))
	)
    (cond ((memq string-case-type '(:down :up :capitalized))
	   ;; Found string is in a standard case.  Coerce to a type based on
	   ;; the given string
	   (cmpl-coerce-string-case string-to-coerce
			       (cmpl-string-case-type given-string))
	   )
	  (t
	   ;; If the found string is in some unusual case, just insert it
	   ;; as is
	   string-to-coerce)
	  )))

;;; Tests -
;;; (cmpl-merge-string-cases "AbCdEf456" "abc")     --> AbCdEf456
;;; (cmpl-merge-string-cases "abcdef456" "ABC")     --> ABCDEF456
;;; (cmpl-merge-string-cases "ABCDEF456" "Abc")     --> Abcdef456
;;; (cmpl-merge-string-cases "ABCDEF456" "abc")     --> abcdef456


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(defun cmpl-hours-since-origin ()
  (let ((time (current-time)))
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    (truncate
     (+ (* (/ (car time) 3600.0) (lsh 1 16))
	(/ (nth 2 time) 3600.0)))))
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;;;---------------------------------------------------------------------------
;;; "Symbol" parsing functions
;;;---------------------------------------------------------------------------
;;; The functions symbol-before-point, symbol-under-point, etc. quickly return
;;; an appropriate symbol string.  The strategy is to temporarily change
;;; the syntax table to enable fast symbol searching.  There are three classes
;;; of syntax in these "symbol" syntax tables ::
;;;
;;; syntax (?_) - "symbol" chars (e.g. alphanumerics)
;;; syntax (?w) - symbol chars to ignore at end of words (e.g. period).  
;;; syntax (? ) - everything else
;;;
;;; Thus by judicious use of scan-sexps and forward-word, we can get
;;; the word we want relatively fast and without consing.  
;;;
;;; Why do we need a separate category for "symbol chars to ignore at ends" ?
;;; For example, in LISP we want starting :'s trimmed 
;;; so keyword argument specifiers also define the keyword completion.  And,
;;; for example, in C we want `.' appearing in a structure ref. to
;;; be kept intact in order to store the whole structure ref.; however, if 
;;; it appears at the end of a symbol it should be discarded because it is
;;; probably used as a period.

;;; Here is the default completion syntax ::
;;; Symbol chars :: A-Z a-z 0-9 @ / \ * + ~ $ < > %
;;; Symbol chars to ignore at ends :: _ : . -
;;; Separator chars. :: <tab> <space> ! ^ & ( ) = ` | { } [ ] ; " ' #
;;;                     , ? <Everything else>

;;; Mode specific differences and notes ::
;;;  LISP diffs ->
;;;    Symbol chars :: ! & ? = ^
;;;
;;; C diffs ->
;;;   Separator chars :: + * / : %
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;;;  A note on the hyphen (`-').  Perhaps the hyphen should also be a separator
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;;; char., however, we wanted to have completion symbols include pointer 
;;; references.  For example, "foo->bar" is a symbol as far as completion is
;;; concerned.
;;;
;;; FORTRAN diffs ->
;;;   Separator chars :: + - * / :
;;;
;;; Pathname diffs ->
;;;   Symbol chars :: .
;;;  Of course there is no pathname "mode" and in fact we have not implemented
;;; this table.  However, if there was such a mode, this is what it would look
;;; like.

;;;-----------------------------------------------
;;; Table definitions
;;;-----------------------------------------------

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(defun cmpl-make-standard-completion-syntax-table ()
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  (let ((table (make-syntax-table)) ;; default syntax is whitespace
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	i)
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    ;; alpha chars
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    (setq i 0)
    (while (< i 26)
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      (modify-syntax-entry (+ ?a i) "_" table)
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      (modify-syntax-entry (+ ?A i) "_" table)
      (setq i (1+ i)))
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    ;; digit chars.
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    (setq i 0)
    (while (< i 10)
      (modify-syntax-entry (+ ?0 i) "_" table)
      (setq i (1+ i)))
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    ;; Other ones
    (let ((symbol-chars '(?@ ?/ ?\\ ?* ?+ ?~ ?$ ?< ?> ?%))
	  (symbol-chars-ignore '(?_ ?- ?: ?.))
	  )
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      (completion-dolist (char symbol-chars)
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	(modify-syntax-entry char "_" table))
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      (completion-dolist (char symbol-chars-ignore)
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	(modify-syntax-entry char "w" table)
	)
      )
    table))

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(defconst cmpl-standard-syntax-table (cmpl-make-standard-completion-syntax-table))
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(defun cmpl-make-lisp-completion-syntax-table ()
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  (let ((table (copy-syntax-table cmpl-standard-syntax-table))
	(symbol-chars '(?! ?& ?? ?= ?^))
	)
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    (completion-dolist (char symbol-chars)
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      (modify-syntax-entry char "_" table))
    table))
	   
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(defun cmpl-make-c-completion-syntax-table ()
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  (let ((table (copy-syntax-table cmpl-standard-syntax-table))
	(separator-chars '(?+ ?* ?/ ?: ?%))
	)
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    (completion-dolist (char separator-chars)
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      (modify-syntax-entry char " " table))
    table))

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(defun cmpl-make-fortran-completion-syntax-table ()
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  (let ((table (copy-syntax-table cmpl-standard-syntax-table))
	(separator-chars '(?+ ?- ?* ?/ ?:))
	)
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    (completion-dolist (char separator-chars)
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      (modify-syntax-entry char " " table))
    table))

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(defconst cmpl-lisp-syntax-table       (cmpl-make-lisp-completion-syntax-table))
(defconst cmpl-c-syntax-table          (cmpl-make-c-completion-syntax-table))
(defconst cmpl-fortran-syntax-table    (cmpl-make-fortran-completion-syntax-table))
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(defvar cmpl-syntax-table cmpl-standard-syntax-table
  "This variable holds the current completion syntax table.")
(make-variable-buffer-local 'cmpl-syntax-table)

;;;-----------------------------------------------
;;; Installing the appropriate mode tables
;;;-----------------------------------------------

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(add-hook 'lisp-mode-hook
	  '(lambda ()
	     (setq cmpl-syntax-table cmpl-lisp-syntax-table)))
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(add-hook 'c-mode-hook
	  '(lambda ()
	     (setq cmpl-syntax-table cmpl-c-syntax-table)))
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(add-hook 'fortran-mode-hook
	  '(lambda ()
	     (setq cmpl-syntax-table cmpl-fortran-syntax-table)
	     (completion-setup-fortran-mode)))
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;;;-----------------------------------------------
;;; Symbol functions
;;;-----------------------------------------------
(defvar cmpl-symbol-start nil
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  "Holds first character of symbol, after any completion symbol function.")
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(defvar cmpl-symbol-end nil
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  "Holds last character of symbol, after any completion symbol function.")
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;;; These are temp. vars. we use to avoid using let.
;;;   Why ?  Small speed improvement.
(defvar cmpl-saved-syntax nil)
(defvar cmpl-saved-point nil)

(defun symbol-under-point ()
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  "Returns the symbol that the point is currently on.
But only if it is longer than `completion-min-length'."
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  (setq cmpl-saved-syntax (syntax-table))
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  (unwind-protect
      (progn
	(set-syntax-table cmpl-syntax-table)
	(cond 
	;; Cursor is on following-char and after preceding-char
	  ((memq (char-syntax (following-char)) '(?w ?_))     
	   (setq cmpl-saved-point (point)
		 cmpl-symbol-start (scan-sexps (1+ cmpl-saved-point) -1)
		 cmpl-symbol-end (scan-sexps cmpl-saved-point 1))
	   ;; Remove chars to ignore at the start.
	   (cond ((= (char-syntax (char-after cmpl-symbol-start)) ?w)
		  (goto-char cmpl-symbol-start)
		  (forward-word 1)
		  (setq cmpl-symbol-start (point))
		  (goto-char cmpl-saved-point)
		  ))
	   ;; Remove chars to ignore at the end.
	   (cond ((= (char-syntax (char-after (1- cmpl-symbol-end))) ?w)
		  (goto-char cmpl-symbol-end)
		  (forward-word -1)
		  (setq cmpl-symbol-end (point))
		  (goto-char cmpl-saved-point)
		  ))
	   ;; Return completion if the length is reasonable.
	   (if (and (<= (cmpl-read-time-eval completion-min-length)
			(- cmpl-symbol-end cmpl-symbol-start))
		    (<= (- cmpl-symbol-end cmpl-symbol-start)
			(cmpl-read-time-eval completion-max-length)))
	       (buffer-substring cmpl-symbol-start cmpl-symbol-end)))))
    (set-syntax-table cmpl-saved-syntax)))
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;;; tests for symbol-under-point
;;;  `^' indicates cursor pos. where value is returned
;;;  simple-word-test
;;;  ^^^^^^^^^^^^^^^^  --> simple-word-test
;;;  _harder_word_test_
;;;  ^^^^^^^^^^^^^^^^^^ --> harder_word_test
;;;  .___.______.
;;;  --> nil
;;;  /foo/bar/quux.hello
;;;  ^^^^^^^^^^^^^^^^^^^ --> /foo/bar/quux.hello
;;;

(defun symbol-before-point ()
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  "Returns a string of the symbol immediately before point.
Returns nil if there isn't one longer than `completion-min-length'."       
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  ;; This is called when a word separator is typed so it must be FAST !
  (setq cmpl-saved-syntax (syntax-table))
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  (unwind-protect
      (progn
	(set-syntax-table cmpl-syntax-table)
	;; Cursor is on following-char and after preceding-char
	(cond ((= (setq cmpl-preceding-syntax (char-syntax (preceding-char))) ?_)
	       ;; Number of chars to ignore at end.
	       (setq cmpl-symbol-end (point)
		     cmpl-symbol-start (scan-sexps cmpl-symbol-end -1)
		     )
	       ;; Remove chars to ignore at the start.
	       (cond ((= (char-syntax (char-after cmpl-symbol-start)) ?w)
		      (goto-char cmpl-symbol-start)
		      (forward-word 1)
		      (setq cmpl-symbol-start (point))
		      (goto-char cmpl-symbol-end)
		      ))
	       ;; Return value if long enough.
	       (if (>= cmpl-symbol-end
		       (+ cmpl-symbol-start
			  (cmpl-read-time-eval completion-min-length)))
		   (buffer-substring cmpl-symbol-start cmpl-symbol-end))
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	       )
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	      ((= cmpl-preceding-syntax ?w)
	       ;; chars to ignore at end
	       (setq cmpl-saved-point (point)
		     cmpl-symbol-start (scan-sexps cmpl-saved-point -1))
	       ;; take off chars. from end
	       (forward-word -1)
	       (setq cmpl-symbol-end (point))
	       ;; remove chars to ignore at the start
	       (cond ((= (char-syntax (char-after cmpl-symbol-start)) ?w)
		      (goto-char cmpl-symbol-start)
		      (forward-word 1)
		      (setq cmpl-symbol-start (point))
		      ))
	       ;; Restore state.
	       (goto-char cmpl-saved-point)
	       ;; Return completion if the length is reasonable
	       (if (and (<= (cmpl-read-time-eval completion-min-length)
			    (- cmpl-symbol-end cmpl-symbol-start))
			(<= (- cmpl-symbol-end cmpl-symbol-start)
			    (cmpl-read-time-eval completion-max-length)))
		   (buffer-substring cmpl-symbol-start cmpl-symbol-end)))))
    (set-syntax-table cmpl-saved-syntax)))
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;;; tests for symbol-before-point
;;;  `^' indicates cursor pos. where value is returned
;;;  simple-word-test
;;;  ^ --> nil
;;;   ^ --> nil
;;;          ^  --> simple-w
;;;                  ^ --> simple-word-test
;;;  _harder_word_test_
;;;                   ^  --> harder_word_test
;;;                    ^  --> harder_word_test
;;;          ^ --> harder
;;;  .___....
;;;  --> nil

(defun symbol-under-or-before-point ()
  ;;; This could be made slightly faster but it is better to avoid
  ;;; copying all the code.
  ;;; However, it is only used by the completion string prompter.
  ;;; If it comes into common use, it could be rewritten.
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  (cond ((memq (progn
		 (setq cmpl-saved-syntax (syntax-table))
		 (unwind-protect
		     (progn
		       (set-syntax-table cmpl-syntax-table)
		       (char-syntax (following-char)))
		   (set-syntax-table cmpl-saved-syntax)))
	       '(?w ?_))
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	 (symbol-under-point))
	(t
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	 (symbol-before-point))))
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(defun symbol-before-point-for-complete ()
  ;; "Returns a string of the symbol immediately before point
  ;; or nil if there isn't one.  Like symbol-before-point but doesn't trim the
  ;; end chars."
  ;; Cursor is on following-char and after preceding-char
  (setq cmpl-saved-syntax (syntax-table))
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  (unwind-protect
      (progn
	(set-syntax-table cmpl-syntax-table)
	(cond ((memq (setq cmpl-preceding-syntax (char-syntax (preceding-char)))
		     '(?_ ?w))
	       (setq cmpl-symbol-end (point)
		     cmpl-symbol-start (scan-sexps cmpl-symbol-end -1)
		     )
	       ;; Remove chars to ignore at the start.
	       (cond ((= (char-syntax (char-after cmpl-symbol-start)) ?w)
		      (goto-char cmpl-symbol-start)
		      (forward-word 1)
		      (setq cmpl-symbol-start (point))
		      (goto-char cmpl-symbol-end)
		      ))
	       ;; Return completion if the length is reasonable.
	       (if (and (<= (cmpl-read-time-eval
			     completion-prefix-min-length)
			    (- cmpl-symbol-end cmpl-symbol-start))
			(<= (- cmpl-symbol-end cmpl-symbol-start)
			    (cmpl-read-time-eval completion-max-length)))
		   (buffer-substring cmpl-symbol-start cmpl-symbol-end)))))
    ;; Restore syntax table.
    (set-syntax-table cmpl-saved-syntax)))
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;;; tests for symbol-before-point-for-complete
;;;  `^' indicates cursor pos. where value is returned
;;;  simple-word-test
;;;  ^ --> nil
;;;   ^ --> nil
;;;          ^  --> simple-w
;;;                  ^ --> simple-word-test
;;;  _harder_word_test_
;;;                   ^  --> harder_word_test
;;;                    ^  --> harder_word_test_
;;;          ^ --> harder_
;;;  .___....
;;;  --> nil



;;;---------------------------------------------------------------------------
;;; Statistics Recording
;;;---------------------------------------------------------------------------

;;; Note that the guts of this has been turned off.  The guts
;;; are in completion-stats.el.

;;;-----------------------------------------------
;;; Conditionalizing code on *record-cmpl-statistics-p*
;;;-----------------------------------------------
;;; All statistics code outside this block should use this
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(defmacro cmpl-statistics-block (&rest body))
;;;  "Only executes body if we are recording statistics."
;;;  (list 'cond
;;;	(list* '*record-cmpl-statistics-p* body)
;;;	))		 
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;;;-----------------------------------------------
;;; Completion Sources
;;;-----------------------------------------------

;; ID numbers
(defconst cmpl-source-unknown 0)
(defconst cmpl-source-init-file 1)
(defconst cmpl-source-file-parsing 2)
(defconst cmpl-source-separator 3)
(defconst cmpl-source-cursor-moves 4)
(defconst cmpl-source-interactive 5)
(defconst cmpl-source-cdabbrev 6)
(defconst num-cmpl-sources 7)
(defvar current-completion-source cmpl-source-unknown)



;;;---------------------------------------------------------------------------
;;; Completion Method #2: dabbrev-expand style
;;;---------------------------------------------------------------------------
;;;
;;;   This method is used if there are no useful stored completions.  It is 
;;; based on dabbrev-expand with these differences :
;;;   1) Faster (we don't use regexps)
;;;   2) case coercion handled correctly
;;; This is called cdabbrev to differentiate it.
;;;   We simply search backwards through the file looking for words which
;;; start with the same letters we are trying to complete.
;;;

(defvar cdabbrev-completions-tried nil)
;;;  "A list of all the cdabbrev completions since the last reset.")

(defvar cdabbrev-current-point 0)
;;;  "The current point position the cdabbrev search is at.")

(defvar cdabbrev-current-window nil)
;;;  "The current window we are looking for cdabbrevs in.  T if looking in
;;; (other-buffer), NIL if no more  cdabbrevs.")

(defvar cdabbrev-wrapped-p nil)
;;;  "T if the cdabbrev search has wrapped around the file.")

(defvar cdabbrev-abbrev-string "")
(defvar cdabbrev-start-point 0)
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(defvar cdabbrev-stop-point)
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;;; Test strings for cdabbrev
;;; cdat-upcase   ;;same namestring
;;; CDAT-UPCASE   ;;ok
;;; cdat2         ;;too short
;;; cdat-1-2-3-4  ;;ok
;;; a-cdat-1      ;;doesn't start correctly
;;; cdat-simple   ;;ok


(defun reset-cdabbrev (abbrev-string &optional initial-completions-tried)
  "Resets the cdabbrev search to search for abbrev-string.
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during the search."
  (setq cdabbrev-abbrev-string abbrev-string
	cdabbrev-completions-tried
	(cons (downcase abbrev-string) initial-completions-tried)
	)
  (reset-cdabbrev-window t)
  )

(defun set-cdabbrev-buffer ()
  ;; cdabbrev-current-window must not be NIL
  (set-buffer (if (eq cdabbrev-current-window t)
		  (other-buffer)
		  (window-buffer cdabbrev-current-window)))
  )


(defun reset-cdabbrev-window (&optional initializep)
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  "Resets the cdabbrev search to search for abbrev-string."
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  ;; Set the window
  (cond (initializep
	 (setq cdabbrev-current-window (selected-window))
	 )
	((eq cdabbrev-current-window t)
	 ;; Everything has failed
	 (setq cdabbrev-current-window nil))
	(cdabbrev-current-window
	 (setq cdabbrev-current-window (next-window cdabbrev-current-window))
	 (if (eq cdabbrev-current-window (selected-window))
	     ;; No more windows, try other buffer.
	     (setq cdabbrev-current-window t)))
	)
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  (if cdabbrev-current-window
      (save-excursion
	(set-cdabbrev-buffer)
	(setq cdabbrev-current-point (point)
	      cdabbrev-start-point cdabbrev-current-point
	      cdabbrev-stop-point
	      (if completion-search-distance
		  (max (point-min)
		       (- cdabbrev-start-point completion-search-distance))
		  (point-min))
	      cdabbrev-wrapped-p nil)
	)))
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(defun next-cdabbrev ()
  "Return the next possible cdabbrev expansion or nil if there isn't one.
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`reset-cdabbrev' must've been called already.
This is sensitive to `case-fold-search'."
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  ;; note that case-fold-search affects the behavior of this function
  ;; Bug: won't pick up an expansion that starts at the top of buffer
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  (if cdabbrev-current-window
      (let (saved-point 
	    saved-syntax
	    (expansion nil)
	    downcase-expansion tried-list syntax saved-point-2)
	(save-excursion
	  (unwind-protect
	      (progn
		;; Switch to current completion buffer
		(set-cdabbrev-buffer)
		;; Save current buffer state
		(setq saved-point  (point)
		      saved-syntax (syntax-table))
		;; Restore completion state
		(set-syntax-table cmpl-syntax-table)
		(goto-char cdabbrev-current-point)
		;; Loop looking for completions
		(while
		    ;; This code returns t if it should loop again
		    (cond
		      (;; search for the string
		       (search-backward cdabbrev-abbrev-string cdabbrev-stop-point t)
		       ;; return nil if the completion is valid
		       (not
			(and
			 ;; does it start with a separator char ?
			 (or (= (setq syntax (char-syntax (preceding-char))) ? )
			     (and (= syntax ?w)
				  ;; symbol char to ignore at end.  Are we at end ?
				  (progn
				    (setq saved-point-2 (point))
				    (forward-word -1)
				    (prog1
				      (= (char-syntax (preceding-char)) ? )
				      (goto-char saved-point-2)
				      ))))
			 ;; is the symbol long enough ?
			 (setq expansion (symbol-under-point))
			 ;; have we not tried this one before
			 (progn
			   ;; See if we've already used it
			   (setq tried-list cdabbrev-completions-tried
				 downcase-expansion (downcase expansion))
			   (while (and tried-list
				       (not (string-equal downcase-expansion
							  (car tried-list))))
			     ;; Already tried, don't choose this one
			     (setq tried-list (cdr tried-list))
			     )
			   ;; at this point tried-list will be nil if this
			   ;; expansion has not yet been tried
			   (if tried-list
			       (setq expansion nil)
			       t)
			   ))))
		      ;; search failed
		      (cdabbrev-wrapped-p
		       ;; If already wrapped, then we've failed completely
		       nil)
		      (t
		       ;; need to wrap
		       (goto-char (setq cdabbrev-current-point
					(if completion-search-distance
					    (min (point-max) (+ cdabbrev-start-point completion-search-distance))
					    (point-max))))

		       (setq cdabbrev-wrapped-p t))
		      ))
		;; end of while loop
		(cond (expansion
		       ;; successful
		       (setq cdabbrev-completions-tried
			     (cons downcase-expansion cdabbrev-completions-tried)
			     cdabbrev-current-point (point))))
		)
	    (set-syntax-table saved-syntax)
	    (goto-char saved-point)
	    ))
	;; If no expansion, go to next window
	(cond (expansion)
	      (t (reset-cdabbrev-window)
		 (next-cdabbrev))))))
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;;; The following must be eval'd in the minibuffer ::
;;; (reset-cdabbrev "cdat")
;;; (next-cdabbrev)  --> "cdat-simple"
;;; (next-cdabbrev)  --> "cdat-1-2-3-4"
;;; (next-cdabbrev)  --> "CDAT-UPCASE"
;;; (next-cdabbrev)  --> "cdat-wrapping"
;;; (next-cdabbrev)  --> "cdat_start_sym"
;;; (next-cdabbrev)  --> nil
;;; (next-cdabbrev)  --> nil
;;; (next-cdabbrev)  --> nil

;;; _cdat_start_sym
;;; cdat-wrapping


;;;---------------------------------------------------------------------------
;;; Completion Database
;;;---------------------------------------------------------------------------

;;; We use two storage modes for the two search types ::
;;;  1) Prefix {cmpl-prefix-obarray} for looking up possible completions
;;;      Used by search-completion-next
;;;      the value of the symbol is nil or a cons of head and tail pointers
;;;  2) Interning {cmpl-obarray} to see if it's in the database
;;;      Used by find-exact-completion, completion-in-database-p
;;;      The value of the symbol is the completion entry

;;; bad things may happen if this length is changed due to the way
;;; GNU implements obarrays
(defconst cmpl-obarray-length 511)

(defvar cmpl-prefix-obarray (make-vector cmpl-obarray-length 0)
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  "An obarray used to store the downcased completion prefixes.
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Each symbol is bound to a list of completion entries.")

(defvar cmpl-obarray (make-vector cmpl-obarray-length 0)
  "An obarray used to store the downcased completions.
Each symbol is bound to a single completion entry.")

;;;-----------------------------------------------
;;; Completion Entry Structure Definition
;;;-----------------------------------------------

;;; A completion entry is a LIST of string, prefix-symbol num-uses, and
;;; last-use-time (the time the completion was last used)
;;; last-use-time is T if the string should be kept permanently
;;; num-uses is incremented everytime the completion is used.

;;; We chose lists because (car foo) is faster than (aref foo 0) and the 
;;; creation time is about the same.

;;; READER MACROS

(defmacro completion-string (completion-entry)
  (list 'car completion-entry))

(defmacro completion-num-uses (completion-entry)
  ;;  "The number of times it has used.  Used to decide whether to save 
  ;; it."
  (list 'car (list 'cdr completion-entry)))

(defmacro completion-last-use-time (completion-entry)
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  ;;  "The time it was last used.  In hours since origin.  Used to decide
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  ;; whether to save it.  T if one should always save it."
  (list 'nth 2 completion-entry))

(defmacro completion-source (completion-entry)
  (list 'nth 3 completion-entry))

;;; WRITER MACROS
(defmacro set-completion-string (completion-entry string)
  (list 'setcar completion-entry string))

(defmacro set-completion-num-uses (completion-entry num-uses)
  (list 'setcar (list 'cdr completion-entry) num-uses))

(defmacro set-completion-last-use-time (completion-entry last-use-time)
  (list 'setcar (list 'cdr (list 'cdr completion-entry)) last-use-time))

;;; CONSTRUCTOR
(defun make-completion (string)
  "Returns a list of a completion entry."
  (list (list string 0 nil current-completion-source)))

;; Obsolete
;;(defmacro cmpl-prefix-entry-symbol (completion-entry)
;;  (list 'car (list 'cdr completion-entry)))



;;;-----------------------------------------------
;;; Prefix symbol entry definition
;;;-----------------------------------------------
;;; A cons of (head . tail)

;;; READER Macros

(defmacro cmpl-prefix-entry-head (prefix-entry)
  (list 'car prefix-entry))

(defmacro cmpl-prefix-entry-tail (prefix-entry)
  (list 'cdr prefix-entry))

;;; WRITER Macros

(defmacro set-cmpl-prefix-entry-head (prefix-entry new-head)
  (list 'setcar prefix-entry new-head))

(defmacro set-cmpl-prefix-entry-tail (prefix-entry new-tail)
  (list 'setcdr prefix-entry new-tail))

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;;; Constructor
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(defun make-cmpl-prefix-entry (completion-entry-list)
  "Makes a new prefix entry containing only completion-entry."
  (cons completion-entry-list completion-entry-list))

;;;-----------------------------------------------
;;; Completion Database - Utilities
;;;-----------------------------------------------

(defun clear-all-completions ()
  "Initializes the completion storage.  All existing completions are lost."
  (interactive)
  (setq cmpl-prefix-obarray (make-vector cmpl-obarray-length 0))
  (setq cmpl-obarray (make-vector cmpl-obarray-length 0))
  (cmpl-statistics-block
    (record-clear-all-completions))
  )

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(defvar completions-list-return-value)

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(defun list-all-completions ()
  "Returns a list of all the known completion entries."
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  (let ((completions-list-return-value nil))
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    (mapatoms 'list-all-completions-1 cmpl-prefix-obarray)
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    completions-list-return-value))
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(defun list-all-completions-1 (prefix-symbol)
  (if (boundp prefix-symbol)
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      (setq completions-list-return-value
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	    (append (cmpl-prefix-entry-head (symbol-value prefix-symbol))
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		    completions-list-return-value))))
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(defun list-all-completions-by-hash-bucket ()
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  "Return list of lists of known completion entries, organized by hash bucket."
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  (let ((completions-list-return-value nil))
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    (mapatoms 'list-all-completions-by-hash-bucket-1 cmpl-prefix-obarray)
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    completions-list-return-value))
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(defun list-all-completions-by-hash-bucket-1 (prefix-symbol)
  (if (boundp prefix-symbol)
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      (setq completions-list-return-value
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	    (cons (cmpl-prefix-entry-head (symbol-value prefix-symbol))
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		  completions-list-return-value))))
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;;;-----------------------------------------------
;;; Updating the database
;;;-----------------------------------------------
;;;
;;;   These are the internal functions used to update the datebase
;;;
;;;
(defvar completion-to-accept nil)
  ;;"Set to a string that is pending its acceptance."
  ;; this checked by the top level reading functions

(defvar cmpl-db-downcase-string nil)
  ;; "Setup by find-exact-completion, etc.  The given string, downcased."
(defvar cmpl-db-symbol nil)
  ;; "The interned symbol corresponding to cmpl-db-downcase-string.
  ;; Set up by cmpl-db-symbol."
(defvar cmpl-db-prefix-symbol nil)
  ;; "The interned prefix symbol corresponding to cmpl-db-downcase-string."
(defvar cmpl-db-entry nil)
(defvar cmpl-db-debug-p nil
  "Set to T if you want to debug the database.")

;;; READS
(defun find-exact-completion (string)
  "Returns the completion entry for string or nil.
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Sets up `cmpl-db-downcase-string' and `cmpl-db-symbol'."
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  (and (boundp (setq cmpl-db-symbol
		     (intern (setq cmpl-db-downcase-string (downcase string))
			     cmpl-obarray)))
       (symbol-value cmpl-db-symbol)
       ))

(defun find-cmpl-prefix-entry (prefix-string)
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  "Returns the prefix entry for string.
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Sets `cmpl-db-prefix-symbol'.
Prefix-string must be exactly `completion-prefix-min-length' long
and downcased.  Sets up `cmpl-db-prefix-symbol'."
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  (and (boundp (setq cmpl-db-prefix-symbol
		     (intern prefix-string cmpl-prefix-obarray)))
       (symbol-value cmpl-db-prefix-symbol)))

(defvar inside-locate-completion-entry nil)
;; used to trap lossage in silent error correction

(defun locate-completion-entry (completion-entry prefix-entry)
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  "Locates the completion entry.
Returns a pointer to the element before the completion entry or nil if
the completion entry is at the head.
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Must be called after `find-exact-completion'."
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  (let ((prefix-list (cmpl-prefix-entry-head prefix-entry))
	 next-prefix-list
	 )
    (cond
      ((not (eq (car prefix-list) completion-entry))
       ;; not already at head
       (while (and prefix-list
		   (not (eq completion-entry
			    (car (setq next-prefix-list (cdr prefix-list)))
			    )))
	 (setq prefix-list next-prefix-list))
       (cond (;; found
	      prefix-list)
	     ;; Didn't find it.  Database is messed up.
	     (cmpl-db-debug-p
	      ;; not found, error if debug mode
	      (error "Completion entry exists but not on prefix list - %s"
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		     completion-string))
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	     (inside-locate-completion-entry
	      ;; recursive error: really scrod
	      (locate-completion-db-error))
	     (t
	       ;; Patch out
	       (set cmpl-db-symbol nil)
	       ;; Retry
	       (locate-completion-entry-retry completion-entry)
	       ))))))

(defun locate-completion-entry-retry (old-entry)
  (let ((inside-locate-completion-entry t))
    (add-completion (completion-string old-entry)
		    (completion-num-uses old-entry)
		    (completion-last-use-time old-entry))
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    (let* ((cmpl-entry (find-exact-completion (completion-string old-entry)))
	   (pref-entry
	    (if cmpl-entry
		(find-cmpl-prefix-entry
		  (substring cmpl-db-downcase-string
			     0 completion-prefix-min-length))))
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	  )
      (if (and cmpl-entry pref-entry)
	  ;; try again
	  (locate-completion-entry cmpl-entry pref-entry)
	  ;; still losing
	  (locate-completion-db-error))
      )))

(defun locate-completion-db-error ()
  ;; recursive error: really scrod
  (error "Completion database corrupted.  Try M-x clear-all-completions.  Send bug report.")
  )

;;; WRITES
(defun add-completion-to-tail-if-new (string)
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  "If STRING is not in the database add it to appropriate prefix list.
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STRING is added to the end of the appropriate prefix list with
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num-uses = 0.  The database is unchanged if it is there.  STRING must be
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longer than `completion-prefix-min-length'.
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This must be very fast.
Returns the completion entry."
  (or (find-exact-completion string)
      ;; not there
      (let (;; create an entry
	    (entry (make-completion string))
	    ;; setup the prefix
	    (prefix-entry (find-cmpl-prefix-entry
			    (substring cmpl-db-downcase-string 0
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				       (cmpl-read-time-eval
					completion-prefix-min-length))))
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	    )
	;; The next two forms should happen as a unit (atomically) but
	;; no fatal errors should result if that is not the case.
	(cond (prefix-entry
	       ;; These two should be atomic, but nothing fatal will happen
	       ;; if they're not.
	       (setcdr (cmpl-prefix-entry-tail prefix-entry) entry)
	       (set-cmpl-prefix-entry-tail prefix-entry entry))
	      (t
	       (set cmpl-db-prefix-symbol (make-cmpl-prefix-entry entry))
	       ))
	;; statistics
	(cmpl-statistics-block
	  (note-added-completion))
	;; set symbol
	(set cmpl-db-symbol (car entry))
	)))

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(defun add-completion-to-head (completion-string)
  "If COMPLETION-STRING is not in the database, add it to prefix list.
We add COMPLETION-STRING to the head of the appropriate prefix list,
or it to the head of the list.
COMPLETION-STRING must be longer than `completion-prefix-min-length'.
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Updates the saved string with the supplied string.
This must be very fast.
Returns the completion entry."
  ;; Handle pending acceptance
  (if completion-to-accept (accept-completion))
  ;; test if already in database
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  (if (setq cmpl-db-entry (find-exact-completion completion-string))
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      ;; found
      (let* ((prefix-entry (find-cmpl-prefix-entry
			     (substring cmpl-db-downcase-string 0
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					(cmpl-read-time-eval
					 completion-prefix-min-length))))
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	     (splice-ptr (locate-completion-entry cmpl-db-entry prefix-entry))
	     (cmpl-ptr (cdr splice-ptr))
	     )
	;; update entry
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	(set-completion-string cmpl-db-entry completion-string)
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	;; move to head (if necessary)
	(cond (splice-ptr
	       ;; These should all execute atomically but it is not fatal if
	       ;; they don't.
	       ;; splice it out
	       (or (setcdr splice-ptr (cdr cmpl-ptr))
		   ;; fix up tail if necessary
		   (set-cmpl-prefix-entry-tail prefix-entry splice-ptr))
	       ;; splice in at head
	       (setcdr cmpl-ptr (cmpl-prefix-entry-head prefix-entry))
	       (set-cmpl-prefix-entry-head prefix-entry cmpl-ptr)
	       ))
	cmpl-db-entry)
    ;; not there
    (let (;; create an entry
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	  (entry (make-completion completion-string))
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	  ;; setup the prefix
	  (prefix-entry (find-cmpl-prefix-entry
			  (substring cmpl-db-downcase-string 0
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				     (cmpl-read-time-eval
				      completion-prefix-min-length))))
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	  )
      (cond (prefix-entry
	     ;; Splice in at head
	     (setcdr entry (cmpl-prefix-entry-head prefix-entry))
	     (set-cmpl-prefix-entry-head prefix-entry entry))
	    (t
	     ;; Start new prefix entry
	     (set cmpl-db-prefix-symbol (make-cmpl-prefix-entry entry))
	     ))
      ;; statistics
      (cmpl-statistics-block
	(note-added-completion))
      ;; Add it to the symbol
      (set cmpl-db-symbol (car entry))
      )))
      
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(defun delete-completion (completion-string)
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  "Deletes the completion from the database.
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String must be longer than `completion-prefix-min-length'."
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  ;; Handle pending acceptance
  (if completion-to-accept (accept-completion))
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  (if (setq cmpl-db-entry (find-exact-completion completion-string))
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      ;; found
      (let* ((prefix-entry (find-cmpl-prefix-entry 
			     (substring cmpl-db-downcase-string 0
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					(cmpl-read-time-eval
					 completion-prefix-min-length))))
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	     (splice-ptr (locate-completion-entry cmpl-db-entry prefix-entry))
	     )
	 ;; delete symbol reference
	 (set cmpl-db-symbol nil)
	 ;; remove from prefix list
	 (cond (splice-ptr
		;; not at head
		(or (setcdr splice-ptr (cdr (cdr splice-ptr)))
		    ;; fix up tail if necessary
		    (set-cmpl-prefix-entry-tail prefix-entry splice-ptr))
		)
	       (t
		;; at head
		(or (set-cmpl-prefix-entry-head
		      prefix-entry (cdr (cmpl-prefix-entry-head prefix-entry)))
		    ;; List is now empty
		    (set cmpl-db-prefix-symbol nil))
		))
	 (cmpl-statistics-block
	   (note-completion-deleted))
	 )
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      (error "Unknown completion `%s'" completion-string)
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      ))

;;; Tests --
;;;  - Add and Find -
;;; (add-completion-to-head "banana")     --> ("banana" 0 nil 0)
;;; (find-exact-completion "banana")      --> ("banana" 0 nil 0)
;;; (find-exact-completion "bana")        --> nil
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banana" ...))
;;; (cdr (find-cmpl-prefix-entry "ban"))  --> (("banana" ...))
;;; (add-completion-to-head "banish")     --> ("banish" 0 nil 0)
;;; (find-exact-completion "banish")      --> ("banish" 0 nil 0)
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banish" ...) ("banana" ...))
;;; (cdr (find-cmpl-prefix-entry "ban"))  --> (("banana" ...))
;;; (add-completion-to-head "banana")     --> ("banana" 0 nil 0)
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banana" ...) ("banish" ...))
;;; (cdr (find-cmpl-prefix-entry "ban"))  --> (("banish" ...))
;;;
;;;  - Deleting -
;;; (add-completion-to-head "banner")     --> ("banner" 0 nil 0)
;;; (delete-completion "banner")        
;;; (find-exact-completion "banner")      --> nil
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banana" ...) ("banish" ...))
;;; (cdr (find-cmpl-prefix-entry "ban"))  --> (("banish" ...))
;;; (add-completion-to-head "banner")     --> ("banner" 0 nil 0) 
;;; (delete-completion "banana")        
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banner" ...) ("banish" ...))
;;; (cdr (find-cmpl-prefix-entry "ban"))  --> (("banish" ...))
;;; (delete-completion "banner")        
;;; (delete-completion "banish")                 
;;; (find-cmpl-prefix-entry "ban")        --> nil
;;; (delete-completion "banner")          --> error
;;;
;;; - Tail -
;;; (add-completion-to-tail-if-new "banana") --> ("banana" 0 nil 0)
;;; (car (find-cmpl-prefix-entry "ban"))     --> (("banana" ...))
;;; (cdr (find-cmpl-prefix-entry "ban"))     --> (("banana" ...))
;;; (add-completion-to-tail-if-new "banish") --> ("banish" 0 nil 0)
;;; (car (find-cmpl-prefix-entry "ban"))     -->(("banana" ...) ("banish" ...))
;;; (cdr (find-cmpl-prefix-entry "ban"))     -->(("banish" ...))
;;;


;;;---------------------------------------------------------------------------
;;; Database Update :: Interface level routines
;;;---------------------------------------------------------------------------
;;; 
;;; These lie on top of the database ref. functions but below the standard
;;; user interface level


(defun interactive-completion-string-reader (prompt)
  (let* ((default (symbol-under-or-before-point))
	 (new-prompt
	  (if default
	      (format "%s: (default: %s) " prompt default)
	      (format "%s: " prompt))
	   )
	 (read (completing-read new-prompt cmpl-obarray))
	 )
    (if (zerop (length read)) (setq read (or default "")))
    (list read)
    ))

(defun check-completion-length (string)
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  (if (< (length string) completion-min-length)
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      (error "The string `%s' is too short to be saved as a completion"
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	     string)
      (list string)))

(defun add-completion (string &optional num-uses last-use-time)
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  "Add STRING to completion list, or move it to head of list.
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The completion is altered appropriately if num-uses and/or last-use-time is 
specified."
  (interactive (interactive-completion-string-reader "Completion to add"))
  (check-completion-length string)
  (let* ((current-completion-source (if (interactive-p)
					cmpl-source-interactive
					current-completion-source))
	 (entry (add-completion-to-head string)))
    
    (if num-uses (set-completion-num-uses entry num-uses))
    (if last-use-time
	(set-completion-last-use-time entry last-use-time))
    ))

(defun add-permanent-completion (string)
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  "Add STRING if it isn't already listed, and mark it permanent."
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  (interactive
    (interactive-completion-string-reader "Completion to add permanently"))
  (let ((current-completion-source (if (interactive-p)
				       cmpl-source-interactive
				       current-completion-source))
	)
    (add-completion string nil t)
    ))

(defun kill-completion (string)
  (interactive (interactive-completion-string-reader "Completion to kill"))
  (check-completion-length string)
  (delete-completion string)
  )

(defun accept-completion ()
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  "Accepts the pending completion in `completion-to-accept'.
This bumps num-uses.  Called by `add-completion-to-head' and 
`completion-search-reset'."
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  (let ((string completion-to-accept)
	;; if this is added afresh here, then it must be a cdabbrev
	(current-completion-source cmpl-source-cdabbrev)
	entry
	)
    (setq completion-to-accept nil)
    (setq entry (add-completion-to-head string))
    (set-completion-num-uses entry (1+ (completion-num-uses entry)))
    (setq cmpl-completions-accepted-p t)
    ))

(defun use-completion-under-point ()
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  "Add the completion symbol underneath the point into the completion buffer."
  (let ((string (and enable-completion (symbol-under-point)))
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	(current-completion-source cmpl-source-cursor-moves))
    (if string (add-completion-to-head string))))
	
(defun use-completion-before-point ()
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  "Add the completion symbol before point into the completion buffer."
  (let ((string (and enable-completion (symbol-before-point)))
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	(current-completion-source cmpl-source-cursor-moves))
    (if string (add-completion-to-head string))))

(defun use-completion-under-or-before-point ()
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  "Add the completion symbol before point into the completion buffer."
  (let ((string (and enable-completion (symbol-under-or-before-point)))
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	(current-completion-source cmpl-source-cursor-moves))
    (if string (add-completion-to-head string))))

(defun use-completion-before-separator ()
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  "Add the completion symbol before point into the completion buffer.
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Completions added this way will automatically be saved if
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`completion-on-separator-character' is non-nil."
  (let ((string (and enable-completion (symbol-before-point)))
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	(current-completion-source cmpl-source-separator)
	entry)
    (cmpl-statistics-block
      (note-separator-character string)
      )
    (cond (string
	   (setq entry (add-completion-to-head string))
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	   (if (and completion-on-separator-character
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		      (zerop (completion-num-uses entry)))
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	       (progn
		 (set-completion-num-uses entry 1)
		 (setq cmpl-completions-accepted-p t)))))
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    ))

;;; Tests --
;;;  - Add and Find -
;;; (add-completion "banana" 5 10)  
;;; (find-exact-completion "banana")  --> ("banana" 5 10 0)
;;; (add-completion "banana" 6)     
;;; (find-exact-completion "banana")  --> ("banana" 6 10 0)
;;; (add-completion "banish")
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banish" ...) ("banana" ...))
;;;
;;;  - Accepting -
;;; (setq completion-to-accept "banana")
;;; (accept-completion)                   
;;; (find-exact-completion "banana")      --> ("banana" 7 10)
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banana" ...) ("banish" ...))
;;; (setq completion-to-accept "banish")
;;; (add-completion "banner")           
;;; (car (find-cmpl-prefix-entry "ban"))
;;;        --> (("banner" ...) ("banish" 1 ...) ("banana" 7 ...))
;;;
;;;  - Deleting -
;;; (kill-completion "banish")          
;;; (car (find-cmpl-prefix-entry "ban"))  --> (("banner" ...) ("banana" ...))


;;;---------------------------------------------------------------------------
;;; Searching the database
;;;---------------------------------------------------------------------------
;;; Functions outside this block must call completion-search-reset followed
;;; by calls to completion-search-next or completion-search-peek
;;;

;;; Status variables
;; Commented out to improve loading speed
(defvar cmpl-test-string "")
;;  "The current string used by completion-search-next."
(defvar cmpl-test-regexp "")
;;  "The current regexp used by completion-search-next. 
;;   (derived from cmpl-test-string)"
(defvar cmpl-last-index 0)
;;  "The last index that completion-search-next was called with."
(defvar cmpl-cdabbrev-reset-p nil)
;;  "Set to t when cdabbrevs have been reset."
(defvar cmpl-next-possibilities nil)
;;   "A pointer to the element BEFORE the next set of possible completions.
;;  cadr of this is the cmpl-next-possibility"
(defvar cmpl-starting-possibilities nil)
;;  "The initial list of starting possibilities."
(defvar cmpl-next-possibility nil)
;;   "The cached next possibility."
(defvar cmpl-tried-list nil)
;;   "A downcased list of all the completions we have tried."


(defun completion-search-reset (string)
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  "Set up the for completion searching for STRING.
STRING must be longer than `completion-prefix-min-length'."
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  (if completion-to-accept (accept-completion))
  (setq cmpl-starting-possibilities
	(cmpl-prefix-entry-head
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	  (find-cmpl-prefix-entry
	   (downcase (substring string 0 completion-prefix-min-length))))
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	cmpl-test-string string
	cmpl-test-regexp (concat (regexp-quote string) "."))
  (completion-search-reset-1)
  )

(defun completion-search-reset-1 ()
  (setq cmpl-next-possibilities cmpl-starting-possibilities
	cmpl-next-possibility   nil
	cmpl-cdabbrev-reset-p nil
	cmpl-last-index -1
	cmpl-tried-list nil
	))

(defun completion-search-next (index)
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  "Return the next completion entry.
If INDEX is out of sequence, reset and start from the top.
If there are no more entries, try cdabbrev and returns only a string."
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  (cond
    ((= index (setq cmpl-last-index (1+ cmpl-last-index)))
     (completion-search-peek t))
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    ((< index 0)
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     (completion-search-reset-1)
     (setq cmpl-last-index index)
     ;; reverse the possibilities list
     (setq cmpl-next-possibilities (reverse cmpl-starting-possibilities))
     ;; do a "normal" search
     (while (and (completion-search-peek nil)
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		 (< (setq index (1+ index)) 0))