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+;;; sym-comp.el --- mode-dependent symbol completion
+
+;; Copyright (C) 2004  Dave Love
+
+;; Author: Dave Love <fx@gnu.org>
+;; Keywords: extensions
+;; $Revision: 1.2 $
+;; URL: http://www.loveshack.ukfsn.org/emacs
+
+;; This file 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.
+
+;; This file 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, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; This defines `symbol-complete', which is a generalization of the
+;; old `lisp-complete-symbol'.  It provides the following hooks to
+;; allow major modes to set up completion appropriate for the mode:
+;; `symbol-completion-symbol-function',
+;; `symbol-completion-completions-function',
+;; `symbol-completion-predicate-function',
+;; `symbol-completion-transform-function'.  Typically it is only
+;; necessary for a mode to set
+;; `symbol-completion-completions-function' locally and to bind
+;; `symbol-complete' appropriately.
+
+;; It's unfortunate that there doesn't seem to be a good way of
+;; combining this with `complete-symbol'.
+
+;; There is also `symbol-completion-try-complete', for use with
+;; Hippie-exp.
+
+;;; Code:
+
+;;;; Mode-dependent symbol completion.
+
+(defun symbol-completion-symbol ()
+  "Default `symbol-completion-symbol-function'.
+Uses `current-word' with the buffer narrowed to the part before
+point."
+  (save-restriction
+    ;; Narrow in case point is in the middle of a symbol -- we want
+    ;; just the preceeding part.
+    (narrow-to-region (point-min) (point))
+    (current-word)))
+
+(defvar symbol-completion-symbol-function 'symbol-completion-symbol
+  "Function to return a partial symbol before point for completion.
+The value it returns should be a string (or nil).
+Major modes may set this locally if the default isn't appropriate.")
+
+(defvar symbol-completion-completions-function nil
+  "Function to return possible symbol completions.
+It takes an argument which is the string to be completed and
+returns a value suitable for the second argument of
+`try-completion'.  This value need not use the argument, i.e. it
+may be all possible completions, such as `obarray' in the case of
+Emacs Lisp.
+
+Major modes may set this locally to allow them to support
+`symbol-complete'.  See also `symbol-completion-symbol-function',
+`symbol-completion-predicate-function' and
+`symbol-completion-transform-function'.")
+
+(defvar symbol-completion-predicate-function nil
+  "If non-nil, function to return a predicate for selecting symbol completions.
+The function gets two args, the positions of the beginning and
+end of the symbol to be completed.
+
+Major modes may set this locally if the default isn't
+appropriate.  This is a function returning a predicate so that
+the predicate can be context-dependent, e.g. to select only
+function names if point is at a function call position.  The
+function's args may be useful for determining the context.")
+
+(defvar symbol-completion-transform-function nil
+  "If non-nil, function to transform symbols in the symbol-completion buffer.
+E.g., for Lisp, it may annotate the symbol as being a function,
+not a variable.
+
+The function takes the symbol name as argument.  If it needs to
+annotate this, it should return a value suitable as an element of
+the list passed to `display-completion-list'.
+
+The predicate being used for selecting completions (from
+`symbol-completion-predicate-function') is available
+dynamically-bound as `symbol-completion-predicate' in case the
+transform needs it.")
+
+(defvar displayed-completions)
+
+;;;###autoload
+(defun symbol-complete (&optional predicate)
+  "Perform completion of the symbol preceding point.
+This is done in a way appropriate to the current major mode,
+perhaps by interrogating an inferior interpreter.  Compare
+`complete-symbol'.
+If no characters can be completed, display a list of possible completions.
+Repeating the command at that point scrolls the list.
+
+When called from a program, optional arg PREDICATE is a predicate
+determining which symbols are considered.
+
+This function requires `symbol-completion-completions-function'
+to be set buffer-locally.  Variables `symbol-completion-symbol-function',
+`symbol-completion-predicate-function' and
+`symbol-completion-transform-function' are also consulted."
+  (interactive)
+  ;; Fixme: Punt to `complete-symbol' in this case?
+  (unless (functionp symbol-completion-completions-function)
+    (error "symbol-completion-completions-function not defined"))
+  (let ((window (get-buffer-window "*Completions*")))
+    (let* ((pattern (or (funcall symbol-completion-symbol-function)
+                        (error "No preceding symbol to complete")))
+           (predicate (or predicate
+                          (if symbol-completion-predicate-function
+                              (funcall symbol-completion-predicate-function
+                                       (- (point) (length pattern))
+                                       (point)))))
+           (completions (funcall symbol-completion-completions-function
+                                 pattern))
+           (completion (try-completion pattern completions predicate)))
+      ;; If this command was repeated, and there's a fresh completion
+      ;; window with a live buffer and a displayed completion list
+      ;; matching the current completions, then scroll the window.
+      (unless (and (eq last-command this-command)
+                   window (window-live-p window) (window-buffer window)
+                   (buffer-name (window-buffer window))
+                   (with-current-buffer (window-buffer window)
+                     (if (equal displayed-completions
+                                (all-completions pattern completions predicate))
+                         (progn
+                           (if (pos-visible-in-window-p (point-max) window)
+                               (set-window-start window (point-min))
+                             (save-selected-window
+                               (select-window window)
+                               (scroll-up)))
+                           t))))
+        ;; Otherwise, do completion.
+        (cond ((eq completion t))
+              ((null completion)
+               (message "Can't find completion for \"%s\"" pattern)
+               (ding))
+              ((not (string= pattern completion))
+               (delete-region (- (point) (length pattern)) (point))
+               (insert completion))
+              (t
+               (message "Making completion list...")
+               (let* ((list (all-completions pattern completions predicate))
+                      ;; In case the transform needs to access it.
+                      (symbol-completion-predicate predicate)
+                      ;; Copy since list is side-effected by sorting.
+                      (copy (copy-sequence list)))
+                 (setq list (sort list 'string<))
+                 (if (functionp symbol-completion-transform-function)
+                     (setq list
+                           (mapcar (funcall
+                                    symbol-completion-transform-function)
+                                   list)))
+                 (with-output-to-temp-buffer "*Completions*"
+                   (condition-case ()
+                       (display-completion-list list pattern) ; Emacs 22
+                     (error (display-completion-list list))))
+                 ;; Record the list for determining whether to scroll
+                 ;; (above).
+                 (with-current-buffer "*Completions*"
+                   (set (make-local-variable 'displayed-completions) copy)))
+               (message "Making completion list...%s" "done")))))))
+
+(eval-when-compile (require 'hippie-exp))
+
+;;;###autoload
+(defun symbol-completion-try-complete (old)
+  "Completion function for use with `hippie-expand'.
+Uses `symbol-completion-symbol-function' and
+`symbol-completion-completions-function'.  It is intended to be
+used something like this in a major mode which provides symbol
+completion:
+
+  (if (featurep 'hippie-exp)
+      (set (make-local-variable 'hippie-expand-try-functions-list)
+           (cons 'symbol-completion-try-complete
+                 hippie-expand-try-functions-list)))"
+  (when (and symbol-completion-symbol-function
+             symbol-completion-completions-function)
+    (unless old
+      (let ((symbol (funcall symbol-completion-symbol-function)))
+        (he-init-string (- (point) (length symbol)) (point))
+        (if (not (he-string-member he-search-string he-tried-table))
+            (push he-search-string he-tried-table))
+        (setq he-expand-list
+              (and symbol
+                   (funcall symbol-completion-completions-function symbol)))))
+    (while (and he-expand-list
+                (he-string-member (car he-expand-list) he-tried-table))
+      (pop he-expand-list))
+    (if he-expand-list
+        (progn
+          (he-substitute-string (pop he-expand-list))
+          t)
+      (if old (he-reset-string))
+      nil)))
+
+;;; Emacs Lisp symbol completion.
+
+(defun lisp-completion-symbol ()
+  "`symbol-completion-symbol-function' for Lisp."
+  (let ((end (point))
+        (beg (with-syntax-table emacs-lisp-mode-syntax-table
+               (save-excursion
+                 (backward-sexp 1)
+                 (while (= (char-syntax (following-char)) ?\')
+                   (forward-char 1))
+                 (point)))))
+    (buffer-substring-no-properties beg end)))
+
+(defun lisp-completion-predicate (beg end)
+  "`symbol-completion-predicate-function' for Lisp."
+  (save-excursion
+    (goto-char beg)
+    (if (not (eq (char-before) ?\())
+        (lambda (sym)                   ;why not just nil ?   -sm
+                                        ;To avoid interned symbols with
+                                        ;no slots.  -- fx
+          (or (boundp sym) (fboundp sym)
+              (symbol-plist sym)))
+      ;; Looks like a funcall position.  Let's double check.
+      (if (condition-case nil
+              (progn (up-list -2) (forward-char 1)
+                     (eq (char-after) ?\())
+            (error nil))
+          ;; If the first element of the parent list is an open
+          ;; parenthesis we are probably not in a funcall position.
+          ;; Maybe a `let' varlist or something.
+          nil
+        ;; Else, we assume that a function name is expected.
+        'fboundp))))
+
+(defvar symbol-completion-predicate)
+
+(defun lisp-symbol-completion-transform ()
+  "`symbol-completion-transform-function' for Lisp."
+  (lambda (elt)
+    (if (and (not (eq 'fboundp symbol-completion-predicate))
+             (fboundp (intern elt)))
+        (list elt " <f>")
+      elt)))
+
+(provide 'sym-comp)
+;;; sym-comp.el ends here