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General-purpose text-checker interface for Emacs text editor
Emacs Lisp

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Wcheck Mode

General-purpose text-checker interface for Emacs text editor


  1. Introduction
  2. Features
  3. How does it compare to other spell-checkers?
  4. Install
  5. Configuration and basic usage
  6. Examples
  7. The source code repository
  8. Copyright and license

1. Introduction

Wcheck mode is a general-purpose text-checker interface for Emacs text editor. Wcheck mode a minor mode which provides an on-the-fly text checker. It checks the visible text area, as you type, and possibly highlights some parts of it. What is checked and how are all configurable.

Wcheck mode can use external programs or Emacs Lisp functions for checking text. For example, Wcheck mode can be used with spell-checker programs such as Ispell, Enchant and Hunspell, but actually any tool that can receive text from standard input stream and send text to standard output can be used. Wcheck mode sends parts of buffer’s content to an external program or an Emacs Lisp function and, based on their output, decides if some parts of text should be marked in the buffer.

2. Features

In Wcheck mode’s configuration different configuration units are called languages. In terms of a spelling checker it is natural to think of them as different human languages. Wcheck mode is not limited to that, though. Language is just a configuration unit for certain kind of text checking purpose.

Each language can use its own checker engine (external program or a function), command-line arguments and other settings, such as the regular expressions and syntax table that are used to match words (or other text elements) in Emacs buffer. User can choose which face is used to mark text elements in buffer.

User can create language-specific and major mode specific settings defining which faces to read or skip in buffers. A typical use for this feature is to spell-check only those areas in buffer which are written in the target language. For example, in email messages usually the message body and Subject header are important enough to spell-check. In programming modes user could spell-check only documentation strings and comments (or the opposite if you want to use Wcheck mode to check keywords and syntax of the programming language itself).

Wcheck mode can also be configured to offer any kind of actions for marked text. Actions are presented to user through a menu which is activated either by (1) clicking the right mouse button on a marked text or (2) executing interactive command wcheck-actions while the cursor (the point) is on a marked text.

If you use Wcheck mode as a spelling checker then it’s natural to configure an action menu that offers spelling suggestions for the misspelled word. The action menu could also have an option to add the marked word to spell-checker’s dictionary, so that the word is recognized in the future. That’s only one application for Wcheck mode, though. Wcheck mode can be configured to find almost any kind of text elements from buffer, mark them, and offer any kind of actions for marked text.

3. How does it compare to other spell-checkers?

The open design makes Wcheck mode (internally) quite different from spell-checkers like Flyspell mode and Speck mode. They are specific tools for spell-checking through Ispell or compatible program and are therefore very much tied to Ispell’s features and command-line interface. This can be useful if you want to use Ispell or fully compatible program for spell-checking natural languages. However, not all human languages can be supported through Ispell and there can also be other kind of text-checking needs.

The motivation behind Wcheck mode is to offer more general-purpose and configurable interface for text checking. It can be configured to work with almost anything: user’s custom shell, Awk or Perl scripts, Lisp functions or other checkers and text filters. Even if you only need a spelling checker for human languages Wcheck mode can be a good choice. It has more configuration possibilities than other spell-checkers and the on-the-fly checker performs very well. It’s a true real-time checker.

4. Install

Put wcheck-mode.el file to some directory in your Emacs’s load-path and add the following lines to Emacs’s initialization file (~/.emacs):

(autoload 'wcheck-mode "wcheck-mode"
  "Toggle wcheck-mode." t)
(autoload 'wcheck-change-language "wcheck-mode"
  "Switch wcheck-mode languages." t)
(autoload 'wcheck-actions "wcheck-mode"
  "Open actions menu." t)
(autoload 'wcheck-jump-forward "wcheck-mode"
  "Move point forward to next marked text area." t)
(autoload 'wcheck-jump-backward "wcheck-mode"
  "Move point backward to previous marked text area." t)

5. Configuration and basic usage

The internal documentation of variable wcheck-language-data has a complete description on how to configure Wcheck mode language data. For easy configuration you can use the options in the customize group named wcheck (M-x customize-group RET wcheck RET).

It might be convenient to bind Wcheck mode commands to some easily accessible keys, for example:

(global-set-key (kbd "C-c s") 'wcheck-mode)
(global-set-key (kbd "C-c l") 'wcheck-change-language)
(global-set-key (kbd "C-c c") 'wcheck-actions)
(global-set-key (kbd "C-c n") 'wcheck-jump-forward)
(global-set-key (kbd "C-c p") 'wcheck-jump-backward)

Interactive command wcheck-mode toggles the text-checker minor mode for the current buffer. Command wcheck-change-language is used to switch languages and command wcheck-actions (or the right mouse button) opens an actions menu for marked text. Commands wcheck-jump-forward and wcheck-jump-backward jump to next or previous marked text area.

A note for Emacs Lisp programmers: Emacs Lisp function wcheck-marked-text-at returns information about marked text at a buffer position. Programmers can use it to perform any kind of actions for marked text. Function wcheck-query-language-data can be used for querying effective configuration data for any language.

6. Examples

Here are some examples on how you can fill the wcheck-language-data variable. The value is a list of language configurations:

(setq wcheck-language-data
        ("another language"

Perhaps the most common use for Wcheck mode is to spell-check human languages with Ispell (or compatible) spelling checker. Let’s start with examples on how to configure that.

The following settings configure two languages which are named “British English” and “Finnish”. The former language uses Ispell program as the spell-checker engine. The latter uses Enchant which has an Ispell-compatible command-line interface. Both languages use Wcheck mode’s actions feature to offer spelling suggestions for misspelled words. Since both spelling checkers print spelling suggestions in the Ispell format we use built-in function wcheck-parser-ispell-suggestions to parse the output and populate the actions (spelling suggestions) menu for user.

("British English"
 (program . "/usr/bin/ispell")
 (args "-l" "-d" "british")
 (action-program . "/usr/bin/ispell")
 (action-args "-a" "-d" "british")
 (action-parser . wcheck-parser-ispell-suggestions))

 (program . "/usr/bin/enchant")
 (args  "-l" "-d" "fi")
 (syntax . my-finnish-syntax-table)
 (action-program . "/usr/bin/enchant")
 (action-args "-a" "-d" "fi")
 (action-parser . wcheck-parser-ispell-suggestions))

The “Finnish” language above used a special syntax table called my-finnish-syntax-table. It could be defined like this:

(defvar my-finnish-syntax-table
  (copy-syntax-table text-mode-syntax-table))

(modify-syntax-entry ?- "w" my-finnish-syntax-table)

It copies text-mode-syntax-table (which Wcheck mode uses by default) and sets the syntactic meaning of the ASCII hyphen character (-) to a word character (“w”). Wcheck mode and its regular expression search will use that syntax table when scanning buffers’ content in that language.

Below is an example on how to add an “Add to dictionary” feature to the actions menu, among spelling suggestions. First, there’s the language configuration. The example below is similar to the “British English” configuration above except that Enchant spell-checker is used and action-parser is a custom function (which will be defined later).

("British English"
 (program . "/usr/bin/enchant")
 (args "-l" "-d" "en_GB")
 (action-program . "/usr/bin/enchant")
 (action-args "-a" "-d" "en_GB")
 (action-parser . enchant-suggestions-menu))

The action parser is custom function enchant-suggestions-menu. It will call wcheck-parser-ispell-suggestions and then add “Add to dictionary” option in the front of the spelling suggestions list. Choosing that option from the actions menu will call function enchant-add-to-dictionary (will be defined later).

(defun enchant-suggestions-menu (marked-text)
  (cons (cons "[Add to dictionary]" 'enchant-add-to-dictionary)

Now we need to define the function enchant-add-to-dictionary. Below is an example that works in GNU/Linux systems (with Enchant spell-checker). For British English language the user dictionary file is ~/.config/enchant/en_GB.dic. Actually the language code is extracted automatically from wcheck-language-data variable, so the same function works with any Enchant language.

(With small modifications it should work with other spelling checkers and operating systems.)

(defvar enchant-dictionaries-dir "~/.config/enchant")

(defun enchant-add-to-dictionary (marked-text)
  (let* ((word (aref marked-text 0))
         (language (aref marked-text 4))
         (file (let ((code (nth 1 (member "-d" (wcheck-query-language-data
                                                language 'action-args)))))
                 (when (stringp code)
                   (concat (file-name-as-directory enchant-dictionaries-dir)
                           code ".dic")))))

    (when (and file (file-writable-p file))
        (insert word) (newline)
        (append-to-file (point-min) (point-max) file)
        (message "Added word \"%s\" to the %s dictionary"
                 word language)))))

Spell-checking human languages is not the only application for Wcheck mode. The following configuration adds language called “Trailing whitespace” which finds and marks all trailing whitespace characters (spaces and tabs) on buffer’s lines. It uses regular expressions to match the whitespace. The checker program is the Emacs Lisp function identity which just returns its argument unchanged. The action-program option and feature is used to build an action menu with just one option: remove the whitespace. It replaces the original whitespace string with empty string.

("Trailing whitespace"
 (program . identity)
 (action-program . (lambda (marked-text)
                     (list (cons "Remove whitespace" ""))))
 (face . highlight)
 (regexp-start . "")
 (regexp-body . "[ \t]+")
 (regexp-end . "$")
 (regexp-discard . "")

Sometimes it’s useful to highlight only a small number of keywords in buffer. The following example adds a language called “Highlight FIXMEs” to mark “FIXME” words. FIXME is some programmers’ convention to put reminders in source code that some parts are not complete yet and will be fixed or completed later. In source code files such keywords are written in program’s comments only, not in the actual code, so we use read-or-skip-faces feature to scan only the comments. This example configures it for emacs-lisp-mode and c-mode. In all other major modes FIXMEs are marked everywhere.

("Highlight FIXMEs"
 (program . (lambda (strings)
              (when (member "FIXME" strings)
                (list "FIXME"))))
 (face . highlight)
  ((emacs-lisp-mode c-mode) read font-lock-comment-face)

The following example adds a language “email” for highlighting email addresses from buffer and creating an action menu which has option to start composing mail to that address. Here’s the language configuration:

 (program . email-address-detect)
 (face . highlight)
 (case-fold . t)
 (regexp-start . "\\<")
 (regexp-body . "\\S-+@\\S-+")
 (regexp-end . "\\>")
 (regexp-discard . "")
 (action-program . email-action-menu)

Then the needed functions:

(defun email-address-detect (strings)
  (let (addresses)
    (dolist (string strings addresses)
      (when (string-match "\\<[a-z.-]+\\>@\\<[a-z.-]+\\>" string)
        (push (match-string-no-properties 0 string) addresses)))))

(defun email-action-menu (marked-text)
  (list (cons (concat "Mail to <" (aref marked-text 0) ">")
              (lambda (marked-text)
                (compose-mail (aref marked-text 0))))))

Note that detecting all valid email addresses is difficult and a much more advanced parser is needed for that. Feel free to replace the detection function with a better one.

7. The source code repository

GitHub repository URL: <>

The branch named master is the release branch and it should always be safe to use. New features and experimental code are developed in other branches and possibly merged to master when they are ready.

8. Copyright and license

Copyright (C) 2009-2012 Teemu Likonen <>

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

The license text: <>

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