SWI-Prolog 8.0.3英文手册：全面编程语言支持与服务器应用优化

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SWI-Prolog 用户手册 8.0.3 版本是一份详尽且便携式的 Prolog 编程语言实现文档。作为一款功能全面且高度可移植的工具，它旨在为各种应用提供强大而可扩展的支持。该版本包含众多接口库，这些库涵盖了与其他编程语言（如C、Java等）、数据库（如SQL、NoSQL）、图形处理以及网络通信的交互能力。对于处理HTML/SGML/XML和RDF（Resource Description Framework）文档，SWI-Prolog提供了深厚的支持，这使其在构建服务器应用时尤为得心应手，特别是因为它具有强大的多线程支持和内置的HTTP服务器库。 SWI-Prolog的设计遵循爱丁堡传统，即在遵循ISO Prolog标准的基础上，它与Quintus、SICStus和YAP Prolog等其他流行的Prolog方言保持兼容。为了促进这种兼容性，SWI-Prolog开发了一套兼容框架，这个框架最初是与YAP合作创建的，并已经针对YAP、SICStus和IF/Prolog进行了定制化。在开发环境方面，SWI-Prolog致力于提供良好的用户体验，包括直观的交互式模式、高效的代码编辑器集成、以及丰富的调试和性能分析工具。此外，它还支持模块化编程，允许开发者组织代码结构，便于维护和复用。用户可以利用内置的文档生成工具来自动化文档编写，这对于大型项目来说尤其有益。该手册详细介绍了如何安装和配置SWI-Prolog，包括不同操作系统上的安装步骤，以及如何配置和管理其丰富的库和工具。此外，还包括了核心语言特性介绍，如控制结构、数据类型、并发编程、以及高级特性如异常处理和并发控制。在应用示例部分，手册展示了如何使用SWI-Prolog解决实际问题，如自然语言处理、人工智能、图形处理、Web服务开发等。用户可以通过阅读这些实例理解如何将理论知识转化为实际代码，并学习如何利用SWI-Prolog的强大功能来提升工作效率。 SWI-Prolog 8.0.3 用户手册为开发者提供了一个全方位的指南，无论你是初学者还是经验丰富的Prolog程序员，都能从中找到所需的信息和资源，以充分发挥SWI-Prolog在现代软件开发中的潜力。

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 8.0 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 8.0 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 8.0 Reference Manual

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