SWI-Prolog for MS-Windows
Jan Wielemaker
VU University Amsterdam
University of Amsterdam
The Netherlands
E-mail: jan@swi-prolog.org
This document gets you started using SWI-Prolog on MS-Windows. It also describes the components and issues that are specific to MS-Windows. It is by no means a manual or Prolog tutorial. The reference manual is available online or can be downloaded in HTML and PDF format from the SWI-Prolog website, which also provides links to books, online tutorials and other Prolog-related material.

Table of Contents

1 Using SWI-Prolog
1.1 Starting Prolog and loading a program
1.2 Executing a query
1.3 Menu commands
1.4 Editing Prolog programs
1.5 Some useful commands
2 Using SWI-Prolog with C/C++
2.1 Using MSVC
2.2 Using swipl-ld.exe
3 The installation
3.1 Supported Windows versions
3.2 Choosing the file extension
3.3 Installed programs
3.4 Installed Registry keys and menus
3.5 Execution level
3.6 Creating a desktop menu item
4 The SWI-Prolog community and foundation
4.1 Website and mailing lists
4.2 About license conditions
4.3 Supporting SWI-Prolog

1 Using SWI-Prolog

1.1 Starting Prolog and loading a program

The SWI-Prolog executable swipl-win.exe can be started from the StartMenu or by opening a .pl file holding Prolog program text from the Windows explorer.1The .PL file extension can be changed during installation. See section 3.2. The installation folder (by default C:\Program Files\swipl) contains a subfolder demo with the file likes.pl. This file can be opened in Prolog from the StartMenu, by opening likes.pl in the Windows explorer or by using the following command in the Prolog application. Be sure to get the quotes right and terminate the command with a full stop (.).

?- [swi('demo/likes')].

If Prolog is started from the start menu it is passed the option --win-app, which causes it to start in the local equivalent of MyDocuments\Prolog. This folder is created if it does not exist.

1.2 Executing a query

After loading a program, one can ask Prolog queries about the program. The query below asks Prolog what food‘sam' likes. The system responds with X = <value> if it can prove the goal for a certain X. The user can type the semi-colon (;) or spacebar. If you want another solution. Use the return key if you do not want to see the more answers. Prolog completes the output a full stop (.) if the user uses the return key or Prolog knowns there are no more answers. If Prolog cannot find (more) answers, it writes false. Finally, Prolog can answer using an error message to indicate the query or program contains an error.

?- likes(sam, X).
X = dahl ;
X = tandoori ;
X = chips.


Note that the answer written by Prolog is a valid Prolog program that, when executed, produces the same set of answers as the original program.

1.3 Menu commands

The SWI-Prolog console provided by swipl-win.exe has a menu for accessing the most commonly used commands. We assume not all menu entries need to be explained in detail. We make some exceptions:

File/Reload modified files
This menu reloads all loaded source files that have been modified using the make/0 command described in section 1.5.
File/Navigator ...
Opens an explorer-like view on Prolog files and the predicates they contain.
Settings/Font ...
Allows for changing the font of the console. On some installations the default font gives redraw and cursor dislocation problems. In this case you may wish to select an alternative. Some built-in commands assume non-proportional fonts.
Settings/User init file ...
Edits the user personalisation file. If no such file exists, it first installs a default file as init.pl that contains commonly used settings in comments.
Settings/Stack sizes ...
Allows for defining the maximum size to which the various Prolog stacks are allowed to grow. The system defaults are chosen to make erroneous programs fail quickly on modest hardware. Programs with large data structures or many choice points often need larger stacks. Note that an active Prolog process growing over the size of the physical memory of your computer can make the system extremely slow.
Try to interrupt the running Prolog process. This is the same as using Control-C. Sometimes interrupts are not honoured or take very long to process. Closing the window twice provides a way to force Prolog to stop.
Run/New thread
Creates a new interactor window running in a separate thread of execution. This may be used to inspect the database or program while the main task continues.
Debug/Edit spy points ...
Edit break points on predicates. From the PceEmacs editor (see section 1.4) break points can also be set on specific calls from specific clauses.
Debug/Graphical debugger ...
Use the source-level debugger on the next spy or break point or other call that enables the debugger.
The help menu provides various starting points to related documents. Items flagged with (on www) open your default internet browser on a page of the SWI-Prolog website.

1.4 Editing Prolog programs

There are three options for editing. One is to run an editor of choice in a separate window and use the make/0 command described below to reload modified files. In addition to this option Prolog can be used to locate predicates, modules and loaded files by specifying the editor of choice for use with the edit/1 command, described below. This is achieved by editing the personalisation file (see section 1.3) and following the instructions in the comments.

The default editor is the built-in editor called PceEmacs. This editor provides colourisation support based on real-time parsing and cross-reference analysis of the program.

Other options for editing include GNU-Emacs, SWI-Prolog-Editor and the Eclipse-based PDT environment. See http://www.swi-prolog.org/IDE.html for an up-to-date overview.

1.5 Some useful commands

This section provides a very brief overview of important or commonly used SWI-Prolog predicates to control the environment.

Load a source file. On Windows, folders may be specified with the DOS/Windows \, which must be escaped, or by using the POSIX standard /. Especially when used in source code, / is to be preferred as it is portable. A Prolog list ([ ... ]) can be used to abbreviate the consult command. The file extension (.pl as well as the selected alternative) can be omitted. Here are some examples:

?- consult(likes).Load likes.pl from the current folder (see pwd/0).
?- ['C:/Program Files/pl/demo/likes']Load likes.pl using absolute path.
?- ['C:\\Program Files\\pl\\demo\\likes']Same using Windows-style path name
Print working directory (folder).
List files in current directory.
If Prolog is started by opening a .pl file in the explorer, edit this file. Also available from the menu.
Edit file, predicate, module, etc., with the given name. If multiple items are named Spec it prompts for the desired alternative.
Reload all files that have been changed since they were last loaded. Normally used after editing one or more files.
Start the graphical debugger. There are three ways to use this. Entered as a single goal at the top level, the next query will be traced. Alternatively it can be used in conjunction with the goal to be debugged: ?- gtrace, run. and finally you can include it in your program to start tracing at a particular point or under a particular condition:
        (var(X) -> gtrace ; true),
Same as gtrace, but text-based on the console.
Search for all predicates that contain Keyword in their name or short description. If a GUI environment is available the results are hyperlinks. Otherwise use help/1 to get details on selected hits.
Give help on Spec, which is normally the name of a predicate or C interface function.

2 Using SWI-Prolog with C/C++

Using MinGW or a compiler with a compatible calling format you can write C or C++ code that can be loaded into SWI-Prolog and called as a predicate. You can also embed SWI-Prolog in C/C++ applications.

Details on how to interact with Prolog are in the SWI-Prolog reference manual. The mailing list archives and TWiki web provide problems and solutions to the many problems that may occur. Documentation of the SWI-cpp.h C++ include file is available from the package documentation. This section only discusses some Windows-specific issues.

2.1 Using MSVC

Because the current versions of SWI-Prolog are compiled and linked with MinGW, we are unsure about the status with regard to compiling extensions using MSVC and embedding SWI-Prolog into MSVC projects.

Please send your comments to the SWI-Prolog mailinglist, and/or mailto:bugs@swi-prolog.org.

First of all, add the include folder of the installation to the search path for headers and the lib folder to the search path for libraries. Both DLLs (extensions) or embedded executables should link to libswipl.dll.a and, if appropriate, to the multithreaded DLL version of the MSVC runtime library.

To create extensions, create a Win32 DLL. To embed Prolog, care should be taken that Prolog can find the Prolog installation. For development, the simplest way to ensure this is by adding the installation bin folder to the %PATH% environment and calling PL_initialise() as illustrated below. PL_initialise() uses the path of the loaded libswipl.dll module to find the Prolog installation folder.2When using the C++ interface from SWI-cpp.h, these comments apply to the arguments for PlEngine().

  { static char *av[] = { "libswipl.dll", NULL };

    if ( !PL_initialise(1, av) )
    { <error>

To create an executable that does not rely on Prolog one must create a saved state of the required Prolog code and attach this to the executable. Creating saved states is described with qsave_program/2 in the reference manual. This can be attached to a state using the DOS command below to create final.exe from the executable produced by MSVC and the generated saved state.

> copy /b file.exe+file.state final.exe

2.2 Using swipl-ld.exe

The swipl-ld.exe automates most of the above complications and provides compatibility for common tasks on many platforms supported by SWI-Prolog. To use it with MinGW, set the PATH environment variables to include the SWI-Prolog binary folder as well as the MinGW binary folders (typically C:\MinGW\bin) to find gcc. An extension myext.dll can be created from the source myext.c using the command below. Add -v to see what commands are executed by swipl-ld.exe.

> swipl-ld.exe -shared -o myext myext.c

An embedded executable is created from C, C++ and Prolog files using

> swipl-ld.exe -o myexe file.c ... file.pl ...

3 The installation

3.1 Supported Windows versions

SWI-Prolog requiring Windows XP or later (XP, Vista, Windows-7). The download site of SWI-Prolog contains older binaries that run on older versions of Windows. We provide both 32-bit and 64-bit installers.

3.2 Choosing the file extension

By default, Prolog uses the .pl extension to indicate Prolog source files. Unfortunately this extension conflicts with the Perl language. If you want to use both on the same Windows machine SWI-Prolog allows you to choose a different extension during the installation. The extension .pro is a commonly used alternative. If portability is an issue, it is advised to use the alternative extension only for the load file, the source file that loads the entire program, and use the normal .pl extension for libraries and files loaded from other files.

3.3 Installed programs

The table below lists the installed components. Some components are marked (32-bits) or (64-bits). Most of this is because the 64-bit version is built using more recent tools and from more recent versions of required libraries using different naming conventions. This will probably be synchronised in the future.

bin\swipl-win.exe Default Windows application for interactive use.
bin\swipl.exe Console-based version for scripting purposes.
bin\swipl-ld.exe Linker front-end to make single-file mixed Prolog/C/C++ executables.
Important directories
bin Executables and DLL files
library Prolog library
boot Sources for system predicates
include C/C++ header files for embedding or to create extensions
xpce XPCE graphics system
xpce\prolog\lib XPCE/Prolog library
DLLs and other supporting files
boot32.prc Initial Prolog state (32-bits)
boot64.prc Initial Prolog state (64-bits)
\bin\libswipl.dll The Prolog kernel
\bin\plterm.dll The window for swipl-win.exe
\bin\pthreadVC2.dllPOSIX thread runtime library (64-bits)
Extension DLLs (plugins)
\bin\cgi.dll Gather CGI GET and POST arguments
\bin\double_metaphone.dll Soundex (sounds similar)
\bin\memfile.dll In-memory temporary‘files'
\bin\odbc4pl.dll ODBC interface
\bin\plregtry.dll Windows registry interface
\bin\porter_stem.dll Porter stemming implementation
\bin\random.dll Portable random number generator
\bin\rdf_db.dll RDF database
\bin\readutil.dll Fast reading utility
\bin\sgml2pl.dll SGML/XML parser
\bin\socket.dll Prolog socket interface
\bin\table.dll Access structured files as tables
\bin\time.dll Timing and alarm library
\bin\xpce2pl.dll The XPCE graphics system
\bin\zlib1.dll Compression library (32-bits)
\bin\zlibwapi.dll Compression library (64-bits)
\bin\zlib4pl.dll Compression library interface

3.4 Installed Registry keys and menus

The filetype .pl or chosen alternative (see section 3.2) is associated to swipl-win.exe. A chosen folder (default SWI-Prolog) is added to the start menu holding shortcuts to Prolog and some related utilities. The following registry keys are in use. The 64-bit version uses Prolog64 instead of Prolog as a key to accommodate installation of both versions on the same machine. Note that opening a .pl file can be associated with one of the installed Prolog versions only.

fileExtension Extension used for Prolog files
group Start menu group
home Installation directory
Note: thread-windows store the same info in sub-keys
Height Height of window in character units
Width Width of window in character units
X Left edge of window in pixel units
Y Top edge of window in pixel units
SaveLines Number of lines available for scrollback

3.5 Execution level

The installer asks for the admin execution level (Vista and later) to be able to write shortcuts and registry keys.

3.6 Creating a desktop menu item

If you want a desktop entry for SWI-Prolog, right-drag swipl-win.exe to the desktop and select‘Create shortcut'. Then edit the properties and add --win-app to the command line to make the application start in MyDocuments\Prolog.

4 The SWI-Prolog community and foundation

4.1 Website and mailing lists

The SWI-Prolog website is located at http://www.swi-prolog.org/.

4.2 About license conditions

The SWI-Prolog license allows it to be used in a wide variety of environments, including closed-source commercial applications. In practice, redistribution and embedding is allowed, as long as modifications to the SWI-Prolog source are published following the Free Software rules.

The SWI-Prolog kernel and foreign libraries are licensed under the Lesser General Public License (LGPL). The Prolog files are licensed under the normal General Public License GPL with an additional statement that allows for embedding in proprietary software:

As a special exception, if you link this library with other files compiled with a Free Software compiler to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not, however, invalidate any other reasons why the executable file might be covered by the GNU General Public License.

This exception is a proven construct used for libgcc, the GNU C-compiler runtime library.

4.3 Supporting SWI-Prolog

There are several ways to support SWI-Prolog:


1.3 1.4