SWI-Prolog：全面的Prolog编程语言实现

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"SWI-Prolog 开发文档" SWI-Prolog 是一个全面且可移植的Prolog编程语言实现。这个系统由Jan Wielemaker开发，其目标是成为一个强大且可扩展的实现，支持广泛的应用场景。它特别关注与各种其他语言、数据库、图形和网络的接口库，以及对HTML/SGML/XML和RDF文档的处理。 SWI-Prolog遵循“爱丁堡传统”，即在遵循ISO Prolog标准的同时，也与Quintus、SICStus和YAP Prolog等其他流行的Prolog实现保持高度兼容。它提供了一个合作框架，该框架与YAP共同开发，并针对YAP、SICStus和IF/Prolog进行了实例化，以确保不同Prolog系统的代码可互操作性。在功能特性上，SWI-Prolog的突出特点包括： 1. **多线程支持**：SWI-Prolog支持多线程，这使得它非常适合于构建服务器应用程序，因为可以并行处理多个请求，提高系统性能和响应速度。 2. **HTTP服务器库**：内置的HTTP服务器库允许开发者创建Web服务，直接在Prolog环境中处理HTTP请求，简化Web应用的开发。 3. **接口库**：提供了丰富的接口库，可以与外部系统如数据库（如SQL）、图形系统和网络通信库进行交互，极大地扩展了Prolog的实用性。 4. **XML/HTML/RDF处理**：对于XML、HTML和RDF文档，SWI-Prolog提供了强大的处理工具和支持，使得在Prolog中解析、生成和操作这些文档变得简单。 5. **开发环境**：SWI-Prolog致力于提供良好的开发环境，包括调试器、交互式shell、代码编辑和分析工具，方便程序员编写、测试和优化代码。 6. **兼容性框架**：通过兼容性框架，SWI-Prolog可以让基于其他Prolog系统的代码在SWI-Prolog下运行，降低了迁移成本。 7. **社区和文档**：SWI-Prolog有一个活跃的用户社区和详细的文档，有助于开发者解决问题和学习新技能。 SWI-Prolog是一个功能强大的Prolog实现，它的特性使其在数据处理、自然语言处理、知识表示和推理等领域有广泛的应用。通过其丰富的库和工具集，开发者可以利用Prolog的逻辑编程优势来构建复杂的软件系统。

14 CHAPTER 1. INTRODUCTION

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) 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 11). It can also be embedded in external programs (see

section 11.5). 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, 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 7.3 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.

Paul Singleton has integrated Fred Dushin’s Java-calls-Prolog side with his Prolog-calls-Java side

into the current bidirectional JPL interface package.

Richard O’Keefe is gratefully acknowledged for his efforts to educate beginners as well as valu-

able comments on proposed new developments.

SWI-Prolog 7.3 Reference Manual

18 CHAPTER 2. OVERVIEW

• 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 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.

?- 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.

2.2 The user’s initialisation ﬁle

After the system initialisation, the system consults (see consult/1) the user’s startup ﬁle. The base-

name of this ﬁle follows conventions of the operating system. On MS-Windows, it is the ﬁle swipl.

ini and on Unix systems .swiplrc. The ﬁle is searched using the file search path/2

clauses for user profile.

The table below shows the default value for this search path. The

phrase happdatai refers to the Windows CSIDL name for the folder. The actual name depends on the

Windows language. English versions typically use ApplicationData. See also win folder/2

Unix Windows

home

happdatai/SWI-Prolog

After the ﬁrst startup ﬁle is found it is loaded and Prolog stops looking for further startup ﬁles. The

name of the startup ﬁle can be changed with the ‘-f file’ option. If File denotes an absolute path,

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

The SWI-Prolog top level differs in several ways from traditional Prolog top level. The current top level was designed

in cooperation with Ulrich Neumerkel.

Older versions ﬁrst searched in the current working directory. This feature has been removed for security reasons.

Users can implement loading a setup ﬁle from the working directory in their global preference ﬁle.

SWI-Prolog 7.3 Reference Manual

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