---+ Using SWI-Prolog with GNU Emacs

There is an excellent Prolog mode for GNU Emacs _and_ XEmacs. It is
maintained by Stefan Bruda and available from
https://bruda.ca/emacs/prolog_mode_for_emacs

The mode plays nicely with SWI-Prolog and other Prolog systems. It
features syntax highlighting, automatic indentation, a predicate menu,
and full interaction with a Prolog process.

The Prolog mode that is included in GNU Emacs ships with regressions
that have been
[reported](https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21526) but
not yet resolved. Therefore, we recommend to use Stefan Bruda's
version of the mode as described in the following.

---++ Installation Hints for GNU Emacs

   1. Download the file `prolog.el` from
      https://bruda.ca/emacs/prolog_mode_for_emacs and save it in your
      `load-path` so that Emacs can find it.

   2. Optionally, you can _byte-compile_ `prolog.el` for better
      performance. Load `prolog.el` into Emacs and do
      =|M-x byte-compile-file RET|=.

   3. Add the following lines to =|~/.emacs|= (=|~/_emacs|= on Windows):

	==
        (autoload 'prolog-mode "prolog" "Major mode for editing Prolog programs." t)
        (add-to-list 'auto-mode-alist '("\\.pl\\'" . prolog-mode))
	==

      Where is *|~/_emacs|*?

      ~ is a shortcut for the home directory, on Windows it is system
      and language specific. It may be for example =|C:\|= or
      =|C:\Dokumente|=. The best way to find "~" is: select
      "Files->Open.." and enter "~". Then Emacs prints the directory
      name and contents.

   4. Customize the Prolog mode. The following page explains how to
      enable electric indentation, syntax checking and PceEmacs-style
      comments: https://www.metalevel.at/pceprolog/

---++ ediprolog: Run Prolog queries in Emacs

**ediprolog** allows you to interact with SWI-Prolog in all Emacs
buffers. You can quickly consult buffers and regions, and run queries
that are embedded in your source files. ediprolog is available from:
https://github.com/triska/ediprolog

---++ Ptags: create Prolog tags for Emacs

Djamé Seddah pointed to the existence of ptags, a program to make
tag-files for finding definitions in Prolog programs. This is the
[[original
site][http://www-2.cs.cmu.edu/afs/cs.cmu.edu/project/ai-repository/ai/lang/prolog/util/ptags/0.html]].
We have a local copy of the c-code: [[ptags.tgz][<ptags.tgz>]]