emacs/lisp/tempo.el

;;; tempo.el --- Flexible template insertion -*- lexical-binding: t; -*-

;; Copyright (C) 1994-1995, 2001-2024 Free Software Foundation, Inc.

;; Author: David Kågedal <davidk@lysator.liu.se>
;; Created: 16 Feb 1994
;; Kågedal's last version number: 1.2.4
;; Keywords: abbrev, extensions, languages, tools

;; This file is part of GNU Emacs.

;; 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 3 of the License, 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.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This file provides a simple way to define powerful templates, or
;; macros, if you wish.  It is mainly intended for, but not limited to,
;; other programmers to be used for creating shortcuts for editing
;; certain kind of documents.  It was originally written to be used by
;; a HTML editing mode written by Nelson Minar <nelson@santafe.edu>,
;; and his html-helper-mode.el is probably the best example of how to
;; use this program.

;; A template is defined as a list of items to be inserted in the
;; current buffer at point.  Some of the items can be simple strings,
;; while other can control formatting or define special points of
;; interest in the inserted text.

;; If a template defines a "point of interest" that point is inserted
;; in a buffer-local list of "points of interest" that the user can
;; jump between with the commands `tempo-backward-mark' and
;; `tempo-forward-mark'.  If the template definer provides a prompt for
;; the point, and the variable `tempo-interactive' is non-nil, the
;; user will be prompted for a string to be inserted in the buffer,
;; using the minibuffer.

;; The template can also define one point to be replaced with the
;; current region if the template command is called with a prefix (or
;; a non-nil argument).

;; More flexible templates can be created by including Lisp symbols,
;; which will be evaluated as variables, or lists, which will be
;; evaluated as Lisp expressions.

;; See the documentation for tempo-define-template for the different
;; items that can be used to define a tempo template.

;; One of the more powerful features of tempo templates are automatic
;; completion.  With every template can be assigned a special tag that
;; should be recognized by `tempo-complete-tag' and expanded to the
;; complete template.  By default the tags are added to a global list
;; of template tags, and are matched against the last word before
;; point.  But if you assign your tags to a specific list, you can also
;; specify another method for matching text in the buffer against the
;; tags.  In the HTML mode, for instance, the tags are matched against
;; the text between the last `<' and point.

;; When defining a template named `foo', a symbol named
;; `tempo-template-foo' will be created whose value as a variable will
;; be the template definition, and its function value will be an
;; interactive function that inserts the template at the point.

;; The latest tempo.el distribution can be fetched from
;; ftp.lysator.liu.se in the directory /pub/emacs

;; There is also a WWW page at
;; https://www.lysator.liu.se/~davidk/elisp/ which has some information

;;; Known bugs:

;; If the 'o is the first element in a template, strange things can
;; happen when the template is inserted at the beginning of a
;; line. This is due to strange behavior in open-line. But it should
;; be easily avoided.

;; The 'o tag is also a problem when including the region. This will
;; be looked into.

;; Clicking mouse-2 in the completion buffer gives strange results.

;; There is a bug in some emacs versions that prevents completion from
;; working. If it doesn't work for you, send me a note indicating your
;; emacs version and your problems.

;;; Contributors:

;; These people have given me important feedback and new ideas for
;; tempo.el. Thanks.

;; Nelson Minar <nelson@santafe.edu>
;; Richard Stallman <rms@gnu.org>
;; Lars Lindberg <Lars.Lindberg@sypro.cap.se>
;; Glen Whitney <Glen.Whitney@math.lsa.umich.edu>

;;; Code:

;;; User options

(defgroup tempo nil
  "Flexible template insertion."
  :prefix "tempo-"
  :group 'tools)

(defcustom tempo-interactive nil
  "Prompt user for strings in templates.
If this variable is non-nil, `tempo-insert' prompts the
user for text to insert in the templates."
  :type 'boolean)

(defcustom tempo-insert-region nil
  "Automatically insert current region when there is a `r' in the template
If this variable is nil, `r' elements will be treated just like `p'
elements, unless the template function is given a prefix (or a non-nil
argument).  If this variable is non-nil, the behavior is reversed.

In Transient Mark mode, this option is unused."
  :type 'boolean)

(defcustom tempo-show-completion-buffer t
  "If non-nil, show a buffer with possible completions, when only
a partial completion can be found."
  :type 'boolean)

(defcustom tempo-leave-completion-buffer nil
  "If nil, a completion buffer generated by \\[tempo-complete-tag]
disappears at the next keypress; otherwise, it remains forever."
  :type 'boolean)

;;; Internal variables

(defvar tempo-insert-string-functions nil
  "List of functions to run when inserting a string.
Each function is called with a single arg, STRING and should return
another string.  This could be used for making all strings upcase by
setting it to (upcase), for example.")

(defvar tempo-tags nil
  "An association list with tags and corresponding templates.")

(defvar-local tempo-local-tags '((tempo-tags . nil))
  "A list of locally installed tag completion lists.
It is an association list where the car of every element is a symbol
whose variable value is a template list.  The cdr part, if non-nil,
is a function or a regexp that defines the string to match.  See the
documentation for the function `tempo-complete-tag' for more info.

`tempo-tags' is always in the last position in this list.")

(defvar-local tempo-collection nil
  "A collection of all the tags defined for the current buffer.")

(defvar-local tempo-dirty-collection t
  "Indicates if the tag collection needs to be rebuilt.")

(defvar-local tempo-marks nil
  "A list of marks to jump to with \\[tempo-forward-mark] and \\[tempo-backward-mark].")

(defvar-local tempo-match-finder "\\b\\([[:word:]]+\\)\\="
  "The regexp or function used to find the string to match against tags.

If `tempo-match-finder' is a string, it should contain a regular
expression with at least one \\( \\) pair.  When searching for tags,
`tempo-complete-tag' calls `re-search-backward' with this string, and
the string between the first \\( and \\) is used for matching against
each string in the tag list.  If one is found, the whole text between
the first \\( and the point is replaced with the inserted template.

You will probably want to include \\=\\= at the end of the regexp to
make sure that the string is matched only against text adjacent to the
point.

If `tempo-match-finder' is a symbol, it should be a function that
returns a pair of the form (STRING . POS), where STRING is the string
used for matching and POS is the buffer position after which text
should be replaced with a template.")

(define-obsolete-variable-alias 'tempo-user-elements 'tempo-user-element-functions "30.1")
(defvar tempo-user-element-functions nil
  "Element handlers for user-defined elements.
This is an abnormal hook where the functions are called with one argument
\(an element in a template) and they should return something to be sent to
`tempo-insert' if they recognize the argument, and nil otherwise.")

(defvar-local tempo-named-insertions nil
  "Temporary storage for named insertions.")

(defvar-local tempo-region-start (make-marker)
  "Region start when inserting around the region.")

;; Insertion by the template at the region start position should move
;; the marker to preserve the original region contents.
(set-marker-insertion-type tempo-region-start t)

(defvar-local tempo-region-stop (make-marker)
  "Region stop when inserting around the region.")

;;; Functions

;;
;; tempo-define-template

(defun tempo-define-template (name elements &optional tag documentation taglist)
  "Define a template.
This function creates a template variable `tempo-template-NAME' and an
interactive function `tempo-template-NAME' that inserts the template
at the point.  The created function is returned.

NAME is a string that contains the name of the template, ELEMENTS is a
list of elements in the template, TAG is the tag used for completion,
DOCUMENTATION is the documentation string for the insertion command
created, and TAGLIST (a symbol) is the tag list that TAG (if provided)
should be added to.  If TAGLIST is nil and TAG is non-nil, TAG is
added to `tempo-tags'.  If TAG already corresponds to a template in
the tag list, modify the list so that TAG now corresponds to the newly
defined template.

The elements in ELEMENTS can be of several types:

 - A string: It is sent to the hooks in `tempo-insert-string-functions',
   and the result is inserted.
 - The symbol `p': This position is saved in `tempo-marks'.
 - The symbol `r': If `tempo-insert' is called with ON-REGION non-nil
   the current region is placed here.  Otherwise it works like `p'.
 - (p PROMPT <NAME> <NOINSERT>): If `tempo-interactive' is non-nil, the
   user is prompted in the minibuffer with PROMPT for a string to be
   inserted.  If the optional parameter NAME is non-nil, the text is
   saved for later insertion with the `s' tag.  If there already is
   something saved under NAME that value is used instead and no
   prompting is made.  If NOINSERT is provided and non-nil, nothing is
   inserted, but text is still saved when a NAME is provided.  For
   clarity, the symbol `noinsert' should be used as argument.
 - (P PROMPT <NAME> <NOINSERT>): Works just like the previous tag, but
   forces `tempo-interactive' to be true.
 - (r PROMPT <NAME> <NOINSERT>): Like the previous tag, but if
   `tempo-interactive' is nil and `tempo-insert' is called with
   ON-REGION non-nil, the current region is placed here.  This usually
   happens when you call the template function with a prefix argument.
 - (s NAME): Inserts text previously read with the (p ..) construct.
   Finds the insertion saved under NAME and inserts it.  Acts like `p'
   if `tempo-interactive' is nil.
 - `&': If there is only whitespace between the line start and point,
   nothing happens.  Otherwise a newline is inserted.
 - `%': If there is only whitespace between point and end of line,
   nothing happens.  Otherwise a newline is inserted.
 - `n': Inserts a newline.
 - `>': The line is indented using `indent-according-to-mode'.  Note
   that you often should place this item after the text you want on
   the line.
 - `r>': Like `r', but it also indents the region.
 - (r> PROMPT <NAME> <NOINSERT>): Like (r ...), but is also indents
   the region.
 - `n>': Inserts a newline and indents line.
 - `o': Like `%' but leaves the point before the newline.
 - nil: It is ignored.
 - Anything else: Each function in `tempo-user-element-functions' is called
   with it as argument until one of them returns non-nil, and the
   result is inserted.  If all of them return nil, it is evaluated and
   the result is treated as an element to be inserted.  One additional
   tag is useful for these cases.  If an expression returns a list (l
   foo bar), the elements after `l' will be inserted according to the
   usual rules.  This makes it possible to return several elements
   from one expression."
  (let* ((template-name (intern (concat "tempo-template-"
				       name)))
	 (command-name template-name))
    (set template-name elements)
    (fset command-name (lambda (&optional arg)
			 (:documentation
			  (or documentation (concat "Insert a " name ".")))
			 (interactive "*P")
			 (tempo-insert-template template-name
			                        (if tempo-insert-region
			                            (not arg) arg))))
    (and tag
	 (tempo-add-tag tag template-name taglist))
    command-name))

;;;
;;; tempo-insert-template

(defun tempo-insert-template (template on-region)
  "Insert a template.
TEMPLATE is the template to be inserted.  If ON-REGION is non-nil the
`r' elements are replaced with the current region.  In Transient Mark
mode, ON-REGION is ignored and assumed true if the region is active."
  (unwind-protect
      (progn
	(if (or (and transient-mark-mode
		     mark-active))
	    (setq on-region t))
	(and on-region
	     (set-marker tempo-region-start (min (mark) (point)))
	     (set-marker tempo-region-stop (max (mark) (point))))
	(if on-region
	    (goto-char tempo-region-start))
	(save-excursion
	  (tempo-insert-mark (point-marker))
          (mapc (lambda (elt)
                  (tempo-insert elt on-region))
		(symbol-value template))
	  (tempo-insert-mark (point-marker)))
	(tempo-forward-mark))
    (tempo-forget-insertions)
    (and transient-mark-mode
	 (deactivate-mark))))

;;;
;;; tempo-insert

(defun tempo-insert (element on-region)
  "Insert a template ELEMENT.
Insert one element from a template.  If ON-REGION is non-nil the `r'
elements are replaced with the current region.

See documentation for `tempo-define-template' for the kind of elements
possible."
  (pcase element
    ((pred stringp) (tempo-process-and-insert-string element))
    (`(p . ,rest) (tempo-insert-prompt-compat rest))
    (`(P . ,rest) (let ((tempo-interactive t))
                    (tempo-insert-prompt-compat rest)))
    ;; (`(v ,name ,data) (tempo-save-named name nil data))
    (`(r . ,rest) (if on-region
	              (goto-char tempo-region-stop)
	            (tempo-insert-prompt-compat rest)))
    (`(r> . ,rest) (if on-region
                       (progn
                         (goto-char tempo-region-stop)
                         (indent-region tempo-region-start
                                        tempo-region-stop))
                       (tempo-insert-prompt-compat rest)))
    (`(s ,name) (tempo-insert-named name))
    (`(l . ,rest) (dolist (elt rest) (tempo-insert elt on-region)))
    ('p (tempo-insert-mark (point-marker)))
    ('r (if on-region
	    (goto-char tempo-region-stop)
	  (tempo-insert-mark (point-marker))))
    ('r> (if on-region
	     (progn
	       (goto-char tempo-region-stop)
	       (indent-region tempo-region-start tempo-region-stop))
	   (tempo-insert-mark (point-marker))))
    ('> (indent-according-to-mode))
    ('& (if (not (or (= (current-column) 0)
		     (save-excursion
		       (re-search-backward
			"^\\s-*\\=" nil t))))
	    (insert "\n")))
    ('% (if (not (or (eolp)
		     (save-excursion
		       (re-search-forward
			"\\=\\s-*$" nil t))))
	    (insert "\n")))
    ('n (insert "\n"))
    ('n> (insert "\n") (indent-according-to-mode))
    ;; Bug: If the 'o is the first element in a template, strange
    ;; things can happen when the template is inserted at the
    ;; beginning of a line.
    ('o (if (not (or on-region
		     (eolp)
		     (save-excursion
		       (re-search-forward
			"\\=\\s-*$" nil t))))
	    (open-line 1)))
    ('nil nil)
    (_ (tempo-insert (or (tempo-is-user-element element)
			 (eval element t))
		     on-region))))

;;;
;;; tempo-insert-prompt

(defun tempo-insert-prompt-compat (prompt)
  "Compatibility hack for `tempo-insert-prompt'.
PROMPT can be either a prompt string, or a list of arguments to
`tempo-insert-prompt', or nil."
  (if (consp prompt)			; not nil either
      (apply #'tempo-insert-prompt prompt)
    (tempo-insert-prompt prompt)))

(defun tempo-insert-prompt (prompt &optional save-name no-insert)
  "Prompt for a text string and insert it in the current buffer.
If the variable `tempo-interactive' is non-nil the user is prompted
for a string in the minibuffer, which is then inserted in the current
buffer.  If `tempo-interactive' is nil, the current point is placed on
`tempo-mark'.

PROMPT is the prompt string, SAVE-NAME is a name to save the inserted
text under.  If the optional argument NO-INSERT is non-nil, no text is
inserted.  This can be useful when there is a SAVE-NAME.

If there already is a value for SAVE-NAME, it is used and the user is
never prompted."
  (let (insertion
	(previous (and save-name
		       (tempo-lookup-named save-name))))
    (cond
     ;; Insert  previous value, unless no-insert is non-nil
     ((and previous
	   (not no-insert))
      (tempo-insert-named save-name)) ; A double lookup here, but who
				      ; cares
     ;; If no-insert is non-nil, don't insert the previous value. Just
     ;; keep it
     (previous
      nil)
     ;; No previous value. Prompt or insert mark
     (tempo-interactive
      (if (not (stringp prompt))
	  (error "tempo: The prompt (%s) is not a string" prompt))
      (setq insertion (read-string prompt))
      (or no-insert
	  (insert insertion))
      (if save-name
	  (tempo-save-named save-name insertion)))
     (t
      (tempo-insert-mark (point-marker))))))

;;;
;;; tempo-is-user-element

(defun tempo-is-user-element (element)
  "Try all the user-defined element handlers in `tempo-user-element-functions'."
  (run-hook-with-args-until-success 'tempo-user-element-functions element))

;;;
;;; tempo-forget-insertions

(defun tempo-forget-insertions ()
  "Forget all the saved named insertions."
  (setq tempo-named-insertions nil))

;;;
;;; tempo-save-named

(defun tempo-save-named (name data)	; Had an optional prompt for 'v
  "Save some data for later insertion.
The contents of DATA is saved under the name NAME.

The data can later be retrieved with `tempo-lookup-named'.

This function returns nil, so it can be used in a template without
inserting anything."
  (setq tempo-named-insertions
	(cons (cons name data)
	      tempo-named-insertions))
  nil)

;;;
;;; tempo-lookup-named

(defun tempo-lookup-named (name)
  "Lookup some saved data under the name NAME.
Returns the data if NAME was found, and nil otherwise."
  (cdr (assq name tempo-named-insertions)))

;;;
;;; tempo-insert-named

(defun tempo-insert-named (name)
  "Insert the previous insertion saved under a named specified in NAME.
If there is no such name saved, a tempo mark is inserted.

Note that if the data is a string, it will not be run through the string
processor."
  (let* ((insertion (tempo-lookup-named name)))
    (cond ((null insertion)
	   (tempo-insert-mark (point-marker)))
	  ((stringp insertion)
	   (insert insertion))
	  (t
	   (tempo-insert insertion nil)))))


;;;
;;; tempo-process-and-insert-string

(defun tempo-process-and-insert-string (string)
  "Insert a string from a template.
Run a string through the preprocessors in `tempo-insert-string-functions'
and insert the results."
  (cond ((null tempo-insert-string-functions)
	 nil)
	((symbolp tempo-insert-string-functions)
	 (setq string
	       (funcall tempo-insert-string-functions string)))
	((listp tempo-insert-string-functions)
	 (dolist (fn tempo-insert-string-functions)
	   (setq string (funcall fn string))))
	(t
	 (error "Bogus value in tempo-insert-string-functions: %s"
		tempo-insert-string-functions)))
  (insert string))

;;;
;;; tempo-insert-mark

(defun tempo-insert-mark (mark)
  "Insert a mark `tempo-marks' while keeping it sorted."
  (cond ((null tempo-marks) (setq tempo-marks (list mark)))
	((< mark (car tempo-marks)) (setq tempo-marks (cons mark tempo-marks)))
	(t (let ((lp tempo-marks))
	     (while (and (cdr lp)
			 (<= (car (cdr lp)) mark))
	       (setq lp (cdr lp)))
	     (if (not (= mark (car lp)))
		 (setcdr lp (cons mark (cdr lp))))))))

;;;
;;; tempo-forward-mark

(defun tempo-forward-mark ()
  "Jump to the next mark in `tempo-marks'."
  (interactive)
  (let ((next-mark (catch 'found
		     (mapc
                      (lambda (mark)
                        (if (< (point) mark)
                            (throw 'found mark)))
		      tempo-marks)
		     ;; return nil if not found
		     nil)))
    (if next-mark
	(goto-char next-mark))))

;;;
;;; tempo-backward-mark

(defun tempo-backward-mark ()
  "Jump to the previous mark in `tempo-marks'."
  (interactive)
  (let ((prev-mark (catch 'found
		     (let (last)
		       (mapc
                        (lambda (mark)
                          (if (<= (point) mark)
                              (throw 'found last))
                          (setq last mark))
			tempo-marks)
		       last))))
    (if prev-mark
	(goto-char prev-mark))))

;;;
;;; tempo-add-tag

(defun tempo-add-tag (tag template &optional tag-list)
  "Add a template tag.
Add the TAG, that should complete to TEMPLATE to the list in TAG-LIST,
or to `tempo-tags' if TAG-LIST is nil.  If TAG was already in the list,
replace its template with TEMPLATE."

  (interactive "sTag: \nCTemplate: ")
  (if (null tag-list)
      (setq tag-list 'tempo-tags))
  (let ((entry (assoc tag (symbol-value tag-list))))
    (if entry
        ;; Tag is already in the list, assign a new template to it.
        (setcdr entry template)
      ;; Tag is not present in the list, add it with its template.
      (set tag-list (cons (cons tag template) (symbol-value tag-list)))))
  ;; Invalidate globally if we're modifying 'tempo-tags'.
  (tempo-invalidate-collection (eq tag-list 'tempo-tags)))

;;;
;;; tempo-use-tag-list

(defun tempo-use-tag-list (tag-list &optional completion-function)
  "Install TAG-LIST to be used for template completion in the current buffer.
TAG-LIST is a symbol whose variable value is a tag list created with
`tempo-add-tag'.

COMPLETION-FUNCTION is an obsolete option for specifying an optional
function or string that is used by \\[tempo-complete-tag] to find a
string to match the tag against.  It has the same definition as the
variable `tempo-match-finder'.  In this version, supplying a
COMPLETION-FUNCTION just sets `tempo-match-finder' locally."
  (setf (alist-get tag-list tempo-local-tags) completion-function)
  (if completion-function
      (setq tempo-match-finder completion-function))
  (tempo-invalidate-collection))

;;;
;;; tempo-invalidate-collection

(defun tempo-invalidate-collection (&optional global)
  "Mark the tag collection as obsolete.
Whenever it is needed again it will be rebuilt.  If GLOBAL is non-nil,
mark the tag collection of all buffers as obsolete, not just the
current one."
  (if global
      (dolist (buffer (buffer-list))
        (with-current-buffer buffer
          (when (assq 'tempo-dirty-collection (buffer-local-variables))
            (setq tempo-dirty-collection t))))
    (setq tempo-dirty-collection t)))

;;;
;;; tempo-build-collection

(defun tempo-build-collection ()
  "Build a collection of all the tags and return it.
If `tempo-dirty-collection' is nil, the old collection is reused."
  (prog1
      (or (and (not tempo-dirty-collection)
	       tempo-collection)
	  (setq tempo-collection
		(apply #'append
                       (mapcar (lambda (tag-list)
					; If the format for
					; tempo-local-tags changes,
					; change this
                                 (eval (car tag-list) t))
			       tempo-local-tags))))
    (setq tempo-dirty-collection nil)))

;;;
;;; tempo-find-match-string

(defun tempo-find-match-string (finder)
  "Find a string to be matched against a tag list.
FINDER is a function or a string.  Returns (STRING . POS), or nil
if no reasonable string is found."
  (cond ((stringp finder)
	 (if (save-excursion (re-search-backward finder nil t))
	     (cons (match-string 1)   ; This seems to be a bug in Emacs (?)
		   (match-beginning 1))
	   nil))
	(t
	 (funcall finder))))

;;;
;;; tempo-complete-tag

(defun tempo-complete-tag (&optional silent)
  "Look for a tag and expand it.
All the tags in the tag lists in `tempo-local-tags'
\(this includes `tempo-tags') are searched for a match for the text
before the point.  The way the string to match for is determined can
be altered with the variable `tempo-match-finder'.  If
`tempo-match-finder' returns nil, then the results are the same as
no match at all.

If a single match is found, the corresponding template is expanded in
place of the matching string.

If a partial completion or no match at all is found, and SILENT is
non-nil, the function will give a signal.

If a partial completion is found and `tempo-show-completion-buffer' is
non-nil, a buffer containing possible completions is displayed."

  ;; This function may look like a hack, but this is how I want it to
  ;; work.
  (interactive "*")
  (let* ((collection (tempo-build-collection))
	 (match-info (tempo-find-match-string tempo-match-finder))
	 (match-string (car match-info))
	 (match-start (cdr match-info))
	 (exact (assoc match-string collection))
	 (compl (or (car exact)
		    (and match-info (try-completion match-string collection)))))
    (if compl (delete-region match-start (point)))
    (cond ((null match-info) (or silent (ding)))
	  ((null compl) (or silent (ding)))
	  ((eq compl t) (tempo-insert-template
			 (cdr (assoc match-string
				     collection))
			 nil))
	  (t (if (setq exact (assoc compl collection))
		 (tempo-insert-template (cdr exact) nil)
	       (insert compl)
	       (or silent (ding))
	       (if tempo-show-completion-buffer
		   (tempo-display-completions match-string
					      collection)))))))


;;;
;;; tempo-display-completions

(defun tempo-display-completions (string tag-list)
  "Show a buffer containing possible completions for STRING."
  (if tempo-leave-completion-buffer
      (with-output-to-temp-buffer "*Completions*"
	(display-completion-list
	 (completion-hilit-commonality (all-completions string tag-list)
				       (length string))))
    (save-window-excursion
      (with-output-to-temp-buffer "*Completions*"
	(display-completion-list
	 (completion-hilit-commonality (all-completions string tag-list)
				       (length string))))
      (sit-for 32767))))

;;;
;;; tempo-expand-if-complete

(defun tempo-expand-if-complete ()
  "Expand the tag before point if it is complete.
Returns non-nil if an expansion was made and nil otherwise.

This could as an example be used in a command that is bound to the
space bar, and looks something like this:

\(defun tempo-space ()
  (interactive \"*\")
  (or (tempo-expand-if-complete)
      (insert \" \")))"

  (interactive "*")
  (let* ((collection (tempo-build-collection))
	 (match-info (tempo-find-match-string tempo-match-finder))
	 (match-string (car match-info))
	 (match-start (cdr match-info))
	 (exact (assoc match-string collection)))
    (if exact
	(progn
	  (delete-region match-start (point))
	  (tempo-insert-template (cdr exact) nil)
	  t)
      nil)))

(provide 'tempo)

;;; tempo.el ends here