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SICStus Prolog Frequently Asked Questions

This is a compilation of frequently asked question related to SICStus Prolog.

Node:About This Document, Next:, Previous:Top, Up:Top

About This Document

This is a compilation of frequently asked question related to SICStus Prolog.

It is maintained by the SICStus Prolog support team. Any questions about this FAQ should be sent to Questions about SICStus Prolog should be addressed as follows:

This FAQ is not intended for questions about the Prolog language in general. There is a specific Prolog FAQ for that, available at

[PM] address verified for 3.8.6

Node:Introduction, Next:, Previous:About This Document, Up:Top


What is SICStus Prolog?

Prolog is a simple but powerful programming language developed at the University of Marseilles, as a practical tool for programming in logic. From a user's point of view the major attraction of the language is ease of programming. Clear, readable, concise programs can be written quickly with few errors.

SICStus Prolog is owned and maintained by the Swedish Institute of Computer Science. Parts of the system were developed by the project "Industrialization of SICStus Prolog" in collaboration with Ericsson Telecom AB, NobelTech Systems AB, Infologics AB and Televerket.

SICStus Prolog follows the mainstream Prolog tradition in terms of syntax and built-in predicates. As of release 3.8, SICStus Prolog provides two execution modes: the iso mode, which is fully compliant with the International Standard ISO/IEC 13211-1 (PROLOG: Part 1--General Core); and the sicstus mode, which is largely compatible with, e.g., C-Prolog and Quintus Prolog, supports code written in earlier versions of SICStus Prolog.

Where can I get more information about SICStus Prolog?

The main source of information about SICStus Prolog is the WWW-site at

and in particular the User's Manual, Release Notes, and this FAQ list, at
Does SICStus run on platform XYZ?

SICStus runs under most UNIX dialects and under Windows 95/98/NT/2000. Release 3.8 is actively being supported on the following platforms:

What do I need to run SICStus?
How can I get SICStus?

SICStus is a commercial product and licensing information can be found on the WWW-site ( Free evaluation licenses are available.

Upon completed license agreement, you will receive a mail containing download instructions including confidential passwords and encryption keys. Be sure to read the Release Notes before installation.

If you are a university student, your department may have acquired the right to sub-license SICStus to its students. If that is the case, your department should provide to you download instructions and license codes for the relevant distributions. Your professor should know.

How do I report a bug or some other problem?

If you think you've discovered a bug or if you have another problem, first read this FAQ list and the release notes. If these do not address your problem, submit a bug report by filling in the form:

Node:Installation problems, Next:, Previous:Introduction, Up:Top

Installation problems

Some of the problems in this sections are UNIX (Windows) specific. These are marked [UNIX] ([Windows]).

Node:Windows Installer Problems, Next:, Up:Installation problems

Windows Installer Problems

Question: [Windows NT]
The installer complains that MSIEXEC cannot be found.

This happens if the installing user does not have Administrator rights. Either install as the user Administrator or ensure that the installing user have these rights during installation. If this is unclear, please contact your system administrator.

This problem should not happen on Windows 95, 98 or 2000.

Node:Corrupted binary files, Next:, Previous:Windows Installer Problems, Up:Installation problems

Corrupted binary files

Question: [UNIX]
gzip says "stdin not in gzip format".

This means that the input piped to gzip has been corrupted in some way. Consider the command line:

% cat file.tar.gz.crypt | crypt password | gzip -cd > file.tar

There are two common reasons this occurs. Either the password is incorrect, whereby gzip gets a corrupt .gz file as input. Or, the original file file.tar.gz.crypt was downloaded incorrectly, typically in ASCII mode instead of binary mode.

Node:Linux C libraries, Next:, Previous:Corrupted binary files, Up:Installation problems

Linux C libraries

Question: [UNIX]
I get the message ".../sp.exe: no such file or directory" when running SICStus, even though sp.exe is there. What's wrong?

This error message appears when SICStus has been compiled using a different version of than your machine has installed. The message "no such file or directory" does not refer to sp.exe but to the particular version that SICStus expects.

SICStus is currently available as binary distributions for, a.k.a. glibc, versions 2.0 and 2.1. Make sure to download the correct version.

Node:Encryption tools, Next:, Previous:Linux C libraries, Up:Installation problems

Encryption tools

Question: [UNIX]
There is no "crypt" program on my Linux machine. How do I unpack the SICStus distributions?

The crypt program is not included in Linux-distributions since the code in it is not free. A replacement can be downloaded from

Download it, unpack it and follow the instructions in README.

Node:Configure options, Next:, Previous:Encryption tools, Up:Installation problems

Configure options

These issues are mainly of concern when building SICStus from a source distribution.

Question: [UNIX]
I've changed the arguments to configure, but nothing happens. Why?

The configure script maintains a cache-file called config.cache. This file has to be removed between configure-runs if you've changed the arguments. Alternatively, you can specify --cache-file=/dev/null, causing configure to avoid creating a cache-file entirely.

Question: [UNIX]
The configure script seems to ignore some of my options. Why?

Make sure that there is no site-wide configuration file ( If configure finds one, it will print a message similar to:

loading site script /usr/local/etc/
creating cache ./config.cache
checking SICStus version... 3.8.5

In this case, configure has found a in /usr/local/etc.

The solution is to either remove the file or to set the environment variable CONFIG_SITE to an empty file of your choice. For example, assuming csh:

% setenv CONFIG_SITE ./
% echo "# empty" > ./

Node:Password problems, Next:, Previous:Configure options, Up:Installation problems

Password problems

Question: [Windows]
When asked for the installation password, I typed it but it doesn't work. Why?

There are three pieces of information that you must not mix up.

Node:Problems getting started, Previous:Password problems, Up:Installation problems

Problems getting started

I get the message "Failed to locate bootfile". What's wrong?

The message "Failed to locate bootfile" means that SICStus cannot find either spds.sav or sprt.sav, depending on whether you are executing a Development System or a Runtime System. If you are running a Runtime System, you may want to read the chapter "Runtime Systems" in the User's Manual. If you want to execute Runtime Systems on machines which do not have SICStus installed (a.k.a. target machines), read the sections "Runtime Systems on Target Machines" and the documentation the SP_PATH variable in the Release Notes and User's Manual.

If you get this message running a Development System, your installation is probably inconsistent. Reinstall SICStus and try again.

^D doesn't seem to bring me back a level down after break. What's wrong?

The manual assumes that ^D is the EOF character. Under Windows, however, it's ^Z. In most contexts, the term end_of_file terminated by a full stop (.) can be typed instead of the EOF character.

Node:Runtime problems, Next:, Previous:Installation problems, Up:Top

Runtime problems

Node:Memory allocation problems, Up:Runtime problems

Memory allocation problems

I get the message "Memory allocation failed"

A generic limitation of SICStus Prolog is that it cannot use more than 256 Mb of virtual memory on 32-bit architectures. This is an artifact of the tagged pointer scheme that we use. We have plans for replacing the tagging scheme, but it's a long term project.

Under Linux on x86, the limit is 128 Mb due to the fact that Linux sbrk() returns memory starting at 0x08000000. So with a better Linux sbrk(), the limit would be 256 Mb there too. An experimental workaround for Linux is available from

Node:Generic Prolog Programming, Next:, Previous:Runtime problems, Up:Top

Generic Prolog Programming

How can I split a module into several source code files?

You need a main file for the module, e.g. and several subfiles, e.g.,, ... Lay out the main file as follows:

:- module(ModuleName, ExportList).

... clauses/directives ...

:- ensure_loaded(sub1).

.. clauses/directives ...

:- ensure_loaded(sub2).

The subfiles can contain any clauses and directives, including ensure_loaded/1 directives, but not module/2 directives.

How can I write access predicates for terms without paying a performance penalty?

There is support for unfolding predicates at compile time: user:goal_expansion/3. For example, assume that is_ornode(X) (is_andnode(X)) is true if the shape (principal functor) of X is or/2 (and/2). If you consult the following:

:- multifile

:- dynamic

user:goal_expansion(is_ornode(Term), _, Term=or(_,_)).
user:goal_expansion(is_andnode(Term), _, Term=and(_,_)).

plan_tree( [N|_Rest], _GuidanceNodes, _Indent ) :-
plan_tree( [N|_Rest], _GuidanceNodes, _Indent ) :-

then plan_tree/3 becomes transformed to:

plan_tree([A|_], _, _) :- A=and(_,_).
plan_tree([A|_], _, _) :- A=or(_,_).

If you are using fcompile/1, make sure that the definition of user:goal_expansion/3, and anything else that the compiler needs to know, has been loaded at fcompile time. A common idiom is:

?- ensure_loaded(SetOfFiles), fcompile(SetOfFiles).

Note that fcompile/1 is obsolescent with the introduction of partial saved states (.po files).

Note also that plan_tree/3 will not be able to determinately select a matching clause based on A, as predicates are indexed on the shape of the first argument only, which is a list in both clauses. Achieving indexing on A is the subject of the next question.

Is SICStus capable of folding unifications across :- to determinately select a matching clause?

Consider the following clauses, with the above goal expansion:

plan_tree( [N|_Rest], _GuidanceNodes, _Indent ) :-
plan_tree( [N|_Rest], _GuidanceNodes, _Indent ) :-

In SICStus, as in most WAMs, indexing is done on the shape of the first argument. If all arguments are distinct variables A, B, C, ..., and the first goal is A = Term, indexing will be done on the shape of Term.

So to enable indexing on the shape of N, you must transform the clause e.g. to:

plan_tree( [N|_Rest], _GuidanceNodes, _Indent ) :-
        plan_tree_flat( N, _Rest, _GuidanceNodes, _Indent ).

plan_tree_flat(N, _Rest, _GuidanceNodes, _Indent ) :-
plan_tree_flat(N, _Rest, _GuidanceNodes, _Indent ) :-

With the above goal expansion, this code will indeed index on N.

Why doesn't this Fibonacci program work?

Here's some code that purports to print all the Fibonacci numbers. The author of the code expected retract/1 to backtrack forever, finding ever new fibs/2 facts.

print_fibs :-
        write(F1), nl,
        F3 is F1+F2,

If you run it:

| ?- print_fibs.


It doesn't work because of the semantics for calls to dynamic predicates in the presence of asserts and retracts. SICStus Prolog complies with the ISO Prolog standard in this respect. Clause 7.5.4 of the standard reads:

Any change in the database that occurs as the result of executing a goal (for example, when the activator of a subgoal is a call of assertz/1 or retract/1) shall affect only an activation whose execution begins afterwards. The change shall not affect any activation that is currently being executed.

In the above example, the retract/1 goal is unaffected by the subsequent assert, and only succeeds once.

The query X=[97|X], name(A,X). loops. Is it a bug?
It is possible, and sometimes useful, to write programs which unify a variable to a term in which that variable occurs, thus creating a cyclic term. The usual LP theory forbids the creation of cyclic terms, dictating that an occurs-check should be done each time a variable is unified with a term. Unfortunately, an occurs-check would be so expensive as to render Prolog impractical as a programming language. Thus cyclic terms may be created and may cause loops trying to print them.

SICStus Prolog mitigates the problem by its ability to unify, compare assert, and copy cyclic terms without looping. The write_term/[2,3] built-in predicate can optionally handle cyclic terms. Unification with occurs-check is available as a built-in predicate. Predicates testing (a)cyclicity are available in a library package. Other predicates usually do not handle cyclic terms well.

Node:Interfacing with other Langauges, Next:, Previous:Generic Prolog Programming, Up:Top

Interfacing with other Langauges

Node:Interfacing with UNIX, Next:, Up:Interfacing with other Langauges

Interfacing with UNIX

Question: [UNIX]
How can I turn a Prolog source file into a UNIX script, to be invoked from the command line or from a Web application, for example?

Wrap the file into an executable Shell script which simply invokes SICStus. Informational messages can be filtered out by redirecting stderr to /dev/null. For example:

exec sicstus 2> /dev/null -f -a "$@" <<EOF

% Tell SICStus to consult the sources.
% The embedded command invokes main(Args)
% where Args is the script's arguments passed as a list of atoms.


main(Args) :-
    format('Hello world!\n\c
            Invoked with args = ~q\n', [Args]).

	prolog_flag(argv, Args), main(Args).

The above script can be invoked as follows:

scheutz>./ a 236U ka=ka
Hello world!
Invoked with args = [a,'236U','ka=ka']

Node:Interfacing with C plus plus, Next:, Previous:Interfacing with UNIX, Up:Interfacing with other Langauges

Interfacing with C++

TODO: write.

Node:Interfacing with Visual Basic, Next:, Previous:Interfacing with C plus plus, Up:Interfacing with other Langauges

Interfacing with Visual Basic

Node:Interfacing with Tcl/Tk, Next:, Previous:Interfacing with Visual Basic, Up:Interfacing with other Langauges

Interfacing with Tcl/Tk

Node:Installing the Tcl/Tk library module under UNIX, Next:, Up:Interfacing with Tcl/Tk

Installing the Tcl/Tk library module under UNIX

NOTE: This section applies to UNIX binary distributions only.

As of 3.8, the Tcl/Tk library module is automatically configured by the installation script (InstallSICStus), after asking a few simple questions.

When InstallSICStus asks for the "Tcl/Tk installation path", which path should I specify?

The installation path should be specified such that installation-path/lib contains the Tcl/Tk libraries (libtcl<version>.so). This is the same as the value of the --prefix options specified to Tcl/Tk's configure-script.

My Tcl and Tk installation are not in the same directory. What should I do?

Unfortunately, there is no solution to this yet. You need to install Tcl/Tk in the same directory in order for InstallSICStus to find them.

Node:Configuring the Tcl/Tk library module under Windows, Next:, Previous:Installing the Tcl/Tk library module under UNIX, Up:Interfacing with Tcl/Tk

Configuring the Tcl/Tk library module under Windows

I need to use a different Tcl/Tk version from the one SICStus is compiled against. How do I do?

The symptoms of this is that Windows complains about not finding tcl<ver>.dll.

SICStus 3.8.6 is compiled against Tcl/Tk version 8.2. If you want to use another Tcl/Tk version, you need to recompile library(tcltk). You can do this by following these steps:

(Please do not embark on this unless you are fairly familiar with command-prompts and compilation procedures).

  1. You need MSVC version 6.0 or later. 5.x or 4.x might work but have not been tested.
  2. Compile the Tcl/Tk object code:
    % cd library/tcltk
    % cl -Ic:/progra~1/Tcl/include -Ic:/progra~1/sicstu~1/include -c *.c
    If you do not have a shell which expands "*.c", you need to replace "*.c" with the name of all C source files in library/tcltk.
  3. Build the foreign resource (assuming Bash/Cygwin):
    % cd library
    % ../bin/splfr tcltk/*.obj \
      c:/progra~1/Tcl/lib/tcl82.lib c:/progra~1/Tcl/lib/tk82.lib
    Again, you might need to spell out "*.obj". Also, don't forget to adjust the actual paths to your needs.

    The following sample session shows how it may look:

    % cl -Ic:/progra~1/Tcl/include -Ic:/progra~1/sicstu~1/include -c *.c
    Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 11.00.7022 for 80x86
    Copyright (C) Microsoft Corp 1984-1997. All rights reserved.
    tkterm.c(231) : warning C4113: 'void (__cdecl *)(void)' differs in parameter lists from 'v
    oid (__cdecl *)(void )'
    Generating Code...
    % ../bin/splfr tcltk/*.obj \
      c:/progra~1/Tcl/lib/tcl82.lib c:/progra~1/Tcl/lib/tk82.lib
    SICStus 3.8.5 (Windows_NT-4-586): Fri Jan 08 09:44:23 1999
    Licensed to SICS
    {C:\TEMP\tcltkglu.c generated, 40 msec}
       Creating library C:\TEMP\junk.lib and object C:\TEMP\junk.exp

  4. Test your new resource:
    % sicstus
    SICStus 3.8.5 (x86-win32-nt-4): Fri Jan 08 09:44:23 1999
    Licensed to SICS
    | ?- use_module(library(tcltk)).
    {loading c:/program files/sicstus prolog/library/tcltk.po...}
    {loaded c:/program files/sicstus prolog/library/tcltk.po in module tcltk, 90 msec 27664 bytes}

Node:Compiling SICStus with Tcl/Tk support, Next:, Previous:Configuring the Tcl/Tk library module under Windows, Up:Interfacing with Tcl/Tk

Compiling SICStus with Tcl/Tk support

NOTE: This section is only relevant when compiling source distributions with support for Tcl/Tk.

Most UNIX machines today have Tcl/Tk preinstalled. This reduces the risk of installation difficulties since the linker and the runtime linker usually finds Tcl/Tk in its default paths. Most other installation and/or configuration problems related to Tcl/Tk are caused by improper installation or installation in a path where the linker and runtime linker cannot find Tcl/Tk.

Tcl/Tk is configured for installation similar to SICStus; by the use of a configure script generated by GNU Autoconf. The installation directory is specified by the --prefix option. The value of this option is referred to as the installation-dir below.

The configure-script complains that it cannot find Tcl_Init and/or Tk_Init. What should I do?

The following message from configure indicates that it could not link a test program with the Tcl/Tk libraries.

checking for Tcl_Init in -ltcl8.3... no
checking for Tk_Init in -ltk8.3... no

The common cause of this is that the compiler cannot find -ltcl8.3 and/or -ltk8.3 (or whichever version it tries to find), usually because Tcl/Tk has been installed in a non-standard directory (i.e. different from /usr/lib, /usr/local/lib, etc.).

If you've installed Tcl/Tk in installation-dir, specify the following to configure:

% ./configure --with-tcltk=installation-dir more options

The problem can occur even if the Tcl/Tk shared libraries can be found, but the link-phase failed due to other reasons. If this occurs, it is often useful to look in config.log, where output from compilation stages etc. is logged.

I've installed Tcl and Tk in different directories. What do I do?

You can use:

% ./configure --with-tcl=tclinstallpath --with-tk=tkinstallpath
There are no shared Tcl/Tk libraries. What has happened?

You need to specify --enable-shared when configuring Tcl/Tk. This is not enabled by default.

Node:Generic Tcl/Tk problems, Previous:Compiling SICStus with Tcl/Tk support, Up:Interfacing with Tcl/Tk

Generic Tcl/Tk problems

I get the message "tcl_new/1 - Can't find a usable init.tcl in the following directories..."

This means that Tcl/Tk can't find its libraries of tcl-code needed for operation. This occurs when Tcl/Tk has been built but not properly installed. You have the option of stating the location of the libraries by means of the environment variables TCL_LIBRARY and TK_LIBRARY. See also the Tcl/Tk documentation.

Another reason for this could be if you are not using SICStus 3.8.1 or later. The original SICStus 3.8 did not initialize Tcl/Tk correctly.

I get the message "tcl_eval/3 - can't read `var(Tree)': no such variable"

This message can appear in Tcl code which tries to access Prolog variables. Example:

tk_test :-
              global var
              set Tree []
              set Children []
              set GrandChildren []
              prolog {get_tree(Tree),
                     make_children(Tree, Children),
                     make_grandChildren(Tree, Children, GrandChildren)}
              puts "$var(Tree) $var(Children) $var(GrandChildren) "
              ', _),

The problem is that the argument to the prolog function is just a string that is interpreted by Prolog as a goal. There is no connection between the Prolog variables Tree, Children and GrandChildren and the Tcl-variables with the same name. After returning from prolog, the values which the Prolog variables have been bound to are assigned to the array variable prolog_variables.

So replacing $var in your example with $prolog_variables, makes it work.

Node:Interfacing with Java, Previous:Interfacing with Tcl/Tk, Up:Interfacing with other Langauges

Interfacing with Java

I'm having basic trouble in getting Java to work. What should I do?

First try to get a simple "Hello world" program to work that does not use Jasper. A large portion of the support questions we get are unrelated to the SICStus Java interface. Once you can compile and run your own Java classes it should be relatively easy to get Jasper to work.

Read the Release Notes and the User's Manual and the section in them related to Jasper.

Question: [Windows]
splfr insists on looking for JDK in C:/jdk1.2.2

Use the --with-jdk option like this:

splfr --with-jdk=D:/jdk1.3 ...
Question: [UNIX]
I want to use JDK 1.3.

As of SICStus 3.8.6 this should work. Read the release notes for important information about JDK 1.3 and JDK 1.3.1.

I want to use Jasper from an applet, but my browser won't let me. What's wrong?

Jasper is built as a layer on top of SICStus' C-Prolog interface and hence Jasper needs to be able to call methods declared as native (i.e., C functions). For security reasons, this is prohibited in applets.

This is a serious restriction, and future versions of Jasper will most likely allow connecting to the Prolog engine via sockets.

I get the message "Failed to locate bootfile" when running java ClassUsingJasper. What's wrong?

The answer to this (and related questions) can be found in the Jasper chapter of the Release Notes, section "Getting Started".

Node:Standard Prolog compliance, Next:, Previous:Interfacing with other Langauges, Up:Top

Standard Prolog compliance

SICStus 3.8 supports standard Prolog, adhering to the International Standard ISO/IEC 13211-1 (PROLOG: Part 1--General Core). At the same time it also supports programs written in earlier versions of SICStus. This is achieved by introducing two execution modes iso and sicstus. Users can change between the modes using the Prolog flag language. Main issues:

Node:Miscellany, Previous:Standard Prolog compliance, Up:Top


Question: [Windows]
How do I save a transcript of my Prolog session on Windows?
As of 3.8.3 the Windows console (spwin.exe) can save a transcript of the interaction with the Prolog top-level. The command is under the File menu. You may wish to increase the number of save lines in the Windows Settings (under the Settings menu).
Question: [Windows]
How do increase the number of history lines used by the Windows console (spwin.exe)?

See Command line editing.

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