SWI-Prolog 7.7.23：全方位的编程语言实现与应用支持

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SWI-Prolog 7.7.23 是一款全面而可移植的 Prolog 编程语言实现，由 VU University Amsterdam 和 University of Amsterdam 的 Jan Wielemaker 开发。它旨在为开发者提供一个强大且可扩展的平台，支持广泛的软件应用开发，特别是在服务器端场景，由于其对多线程和 HTTP 服务器库的深度集成，非常适合构建高性能的网络应用。这款 Prolog 实现的核心优势在于其丰富的接口库，它能够与其他编程语言如 C、Java、Python 等无缝对接，便于在不同技术栈中集成和交互。此外，SWI-Prolog 提供了对 HTML/SGML/XML 和 RDF（Resource Description Framework）文档的高效管理能力，这对于处理结构化数据和网络爬虫等任务极其关键。在标准遵循上，SWI-Prolog 遵循 Edinburgh 传统，这意味着它不仅严格符合 ISO Prolog 标准，而且在兼容性方面也做得很好，与 Quintus、SICStus 和 YAP Prolog 等知名 Prolog 实现具有良好的互操作性。为了增强这种兼容性，SWI-Prolog 还开发了一个兼容框架，专门针对 YAP、SICStus 和 IF/Prolog 进行了优化和定制。对于开发者而言，SWI-Prolog 提供了一套完善的开发工具和环境，旨在简化开发过程并提升效率。无论是新手还是经验丰富的用户，都能在这个平台上找到所需的功能和资源，使其成为构建高效、模块化和可维护的逻辑编程项目的理想选择。 SWI-Prolog 7.7.23 是一个功能强大的 Prolog 实现，它将标准功能与灵活性、跨平台兼容性和对现代Web技术的支持完美结合，使得它成为开发复杂应用程序的理想选择，尤其适用于需要处理大量数据和网络通信的应用场景。

14 CHAPTER 1. INTRODUCTION

recompiles modiﬁed parts of the source code using the make/0 command. The system can

be instructed to open an arbitrary editor on the right ﬁle and line based on its source database.

It ships with various graphical tools and can be combined with the SWI-Prolog editor, PDT

(Eclipse plugin for Prolog), VScode or GNU-Emacs.

• Fast compiler

Even very large applications can be loaded in seconds on most machines. If this is not enough,

there is the Quick Load Format. See qcompile/1 and qsave program/2.

• Transparent compiled code

SWI-Prolog compiled code can be treated just as interpreted code: you can list it, trace it, etc.

This implies you do not have to decide beforehand whether a module should be loaded for

debugging or not, and the performance of debugged code is close to that of normal operation.

• Source level debugger

The source level debugger provides a good overview of your current location in the search tree,

variable bindings, your source code and open choice points. Choice point inspection provides

meaningful insight to both novices and experienced users. Avoiding unintended choice points

often provides a huge increase in performance and a huge saving in memory usage.

• Proﬁling

SWI-Prolog offers an execution proﬁler with either textual output or graphical output. Finding

and improving hotspots in a Prolog program may result in huge speedups.

• Flexibility

SWI-Prolog can easily be integrated with C, supporting non-determinism in Prolog calling C

as well as C calling Prolog (see section 12). It can also be embedded in external programs (see

section 12.5). System predicates can be redeﬁned locally to provide compatibility with other

Prolog systems.

• Threads

Robust support for multiple threads may improve performance and is a key enabling factor for

deploying Prolog in server applications.

• Interfaces

SWI-Prolog ships with many extension packages that provide robust interfaces to processes,

encryption, TCP/IP, TIPC, ODBC, SGML/XML/HTML, RDF, JSON, YAML, HTTP, graphics

and much more.

1.4 Support the SWI-Prolog project

You can support the SWI-Prolog project in several ways. Academics are invited to cite one of the

publications

on SWI-Prolog. Users can help by identifying and/or ﬁxing problems with the code or

its documentation.

. Users can contribute new features or, more lightweight, contribute packs

. Com-

mercial users may consider contacting the developers

to sponsor the development of new features or

seek for opportunities to cooperate with the developers or other commercial users.

http://www.swi-prolog.org/Publications.html

http://www.swi-prolog.org/howto/SubmitPatch.html

http://www.swi-prolog.org/pack/list

mailto:info@swi-prolog.org

SWI-Prolog 7.7 Reference Manual

1.5. IMPLEMENTATION HISTORY 15

1.5 Implementation history

SWI-Prolog started back in 1986 with the requirement for a Prolog that could handle recursive inter-

action with the C-language: Prolog calling C and C calling Prolog recursively. In those days Prolog

systems were not very aware of their environment and we needed such a system to support interactive

applications. Since then, SWI-Prolog’s development has been guided by requests from the user com-

munity, especially focussing on (in arbitrary order) interaction with the environment, scalability, (I/O)

performance, standard compliance, teaching and the program development environment.

SWI-Prolog is based on a simple Prolog virtual machine called ZIP [Bowen et al., 1983,

Neumerkel, 1993] which deﬁnes only 7 instructions. Prolog can easily be compiled into this lan-

guage, and the abstract machine code is easily decompiled back into Prolog. As it is also possible

to wire a standard 4-port debugger in the virtual machine, there is no need for a distinction between

compiled and interpreted code. Besides simplifying the design of the Prolog system itself, this ap-

proach has advantages for program development: the compiler is simple and fast, the user does not

have to decide in advance whether debugging is required, and the system only runs slightly slower in

debug mode compared to normal execution. The price we have to pay is some performance degra-

dation (taking out the debugger from the VM interpreter improves performance by about 20%) and

somewhat additional memory usage to help the decompiler and debugger.

SWI-Prolog extends the minimal set of instructions described in [Bowen et al., 1983] to improve

performance. While extending this set, care has been taken to maintain the advantages of decompi-

lation and tracing of compiled code. The extensions include specialised instructions for uniﬁcation,

predicate invocation, some frequently used built-in predicates, arithmetic, and control (;/2, |/2),

if-then (->/2) and negation-by-failure (\+/1).

1.6 Acknowledgements

Some small parts of the Prolog code of SWI-Prolog are modiﬁed versions of the corresponding Edin-

burgh C-Prolog code: grammar rule compilation and writef/2. Also some of the C-code originates

from C-Prolog: ﬁnding the path of the currently running executable and some of the code underlying

absolute

file name/2. Ideas on programming style and techniques originate from C-Prolog

and Richard O’Keefe’s thief editor. An important source of inspiration are the programming tech-

niques introduced by Anjo Anjewierden in PCE version 1 and 2.

Our special thanks go to those who had the fate of using the early versions of this system, sug-

gested extensions or reported bugs. Among them are Anjo Anjewierden, Huub Knops, Bob Wielinga,

Wouter Jansweijer, Luc Peerdeman, Eric Nombden, Frank van Harmelen, Bert Rengel.

Martin Jansche (jansche@novell1.gs.uni-heidelberg.de) has been so kind to reor-

ganise the sources for version 2.1.3 of this manual. Horst von Brand has been so kind to ﬁx many

typos in the 2.7.14 manual. Thanks! Randy Sharp ﬁxed many issues in the 6.0.x version of the manual.

Bart Demoen and Tom Schrijvers have helped me adding coroutining, constraints, global variables

and support for cyclic terms to the kernel. Tom Schrijvers has provided a ﬁrst clp(fd) constraint solver,

the CHR compiler and some of the coroutining predicates. Markus Triska contributed the current

clp(fd) implementation as well as the clp(b) implementation.

Tom Schrijvers and Bart Demoen initiated the implementation of delimited continuations (sec-

tion 4.10), which was used by Benoit Desouter and Tom Schrijvers to implement tabling (section 7)

as a library. Fabrizio Riguzzi added a ﬁrst implementation for mode directed tabling (section 7.3).

The SWI-Prolog 7 extensions (section 5) are the result of a long heated discussion on the mail-

SWI-Prolog 7.7 Reference Manual

18 CHAPTER 2. OVERVIEW

Starting SWI-Prolog on Windows

After SWI-Prolog has been installed on a Windows system, the following important new things are

available to the user:

• A folder (called directory in the remainder of this document) called swipl containing the

executables, libraries, etc., of the system. No ﬁles are installed outside this directory.

• A program swipl-win.exe, providing a window for interaction with Prolog. The program

swipl.exe is a version of SWI-Prolog that runs in a console window.

• The ﬁle extension .pl is associated with the program swipl-win.exe. Opening a .pl

ﬁle will cause swipl-win.exe to start, change directory to the directory in which the ﬁle to

open resides, and load this ﬁle.

The normal way to start the likes.pl ﬁle mentioned in section 2.1.1 is by simply double-

clicking this ﬁle in the Windows explorer.

2.1.2 Adding rules from the console

Although we strongly advice to put your program in a ﬁle, optionally edit it and use make/0 to reload

it (see section 2.1.4), it is possible to manage facts and rules from the terminal. The most conveniant

way to add a few clauses is by consulting the pseudo ﬁle user. The input is ended using the system

end-of-ﬁle character.

?- [user].

|: hello :- format(’Hello world˜n’).

|: ˆD

true.

?- hello.

Hello world

true.

The predicates assertz/1 and retract/1 are alternatives to add and remove rules and facts.

2.1.3 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 = hvaluei if it can prove the goal for a certain

X. The user can type the semi-colon (;) or spacebar

if (s)he wants another solution. Use the RETURN

key if you do not want to see the more answers. Prolog completes the output with a full stop (.) if

the user uses the RETURN key or Prolog knows there are no more answers. If Prolog cannot ﬁnd

(more) answers, it writes false. Finally, Prolog answers using an error message to indicate the query

or program contains an error.

On most installations, single-character commands are executed without waiting for the RETURN key.

SWI-Prolog 7.7 Reference Manual

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