yap-6.3/docs/yap.md

	
This file documents the YAP Prolog System version 6.3.4, a high-performance Prolog compiler developed at LIACC, Universidade do Porto. YAP is based on David H. D. Warren's WAM (Warren Abstract Machine), with several optimizations for better performance. YAP follows the Edinburgh tradition, and is largely compatible with DEC-10 Prolog, Quintus Prolog, and especially with C-Prolog.

+ @ref DownloadInstall

+ @ref Run

+ @ref YAPLoading

+ @ref YAPBuiltins

+ @ref YAPExtensions

+ @ref YAPProgramming
	
+ @ref ChYInterface

+ @ref YAPLibrary

+ @ref  SWILibrary
  
+ @ref Packages
		
		
\author Vitor Santos Costa,
\author Luís Damas,
\author Rogério Reis
\author Rúben Azevedo


© 1989-2014 L. Damas, V. Santos Costa and Universidade
do Porto.
Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions.

\htmlonly

This file contains extracts of the SWI-Prolog manual, as written by Jan
Wielemaker. Our thanks to the author for his kind permission in allowing
us to include his text in this document.

\endhtmlonly

@section Intro Introduction

This document provides User information on version 6.3.4 of
YAP (<em>Yet Another Prolog</em>). The YAP Prolog System is a
high-performance Prolog compiler developed at LIACC, Universidade do
Porto. YAP provides several important features:

  + Speed: YAP is widely considered one of the fastest available
Prolog systems.

  + Functionality: it supports stream Input/Output, sockets, modules,
exceptions, Prolog debugger, C-interface, dynamic code, internal
database, DCGs, saved states, co-routining, arrays, threads.

  + We explicitly allow both commercial and non-commercial use of YAP.


YAP is based on the David H. D. Warren's WAM (Warren Abstract Machine),
with several optimizations for better performance. YAP follows the
Edinburgh tradition, and was originally designed to be largely
compatible with DEC-10 Prolog, Quintus Prolog, and especially with
C-Prolog.

YAP implements most of the ISO-Prolog standard. We are striving at
full compatibility, and the manual describes what is still
missing. The manual also includes a (largely incomplete) comparison
with SICStus Prolog.

The document is intended neither as an introduction to Prolog nor to the
implementation aspects of the compiler. A good introduction to
programming in Prolog is the book @cite TheArtOfProlog , by
L. Sterling and E. Shapiro, published by "The MIT Press, Cambridge
MA". Other references should include the classical @cite ProgrammingInProlog , by W.F. Clocksin and C.S. Mellish, published by
Springer-Verlag.

YAP 4.3 is known to build with many versions of gcc (\<= gcc-2.7.2, \>=
gcc-2.8.1, \>= egcs-1.0.1, gcc-2.95.\*) and on a variety of Unixen:
SunOS 4.1, Solaris 2.\*, Irix 5.2, HP-UX 10, Dec Alpha Unix, Linux 1.2
and Linux 2.\* (RedHat 4.0 thru 5.2, Debian 2.\*) in both the x86 and
alpha platforms. It has been built on Windows NT 4.0 using Cygwin from
Cygnus Solutions (see README.nt) and using Visual C++ 6.0.

The overall copyright and permission notice for YAP4.3 can be found in
the Artistic file in this directory. YAP follows the Perl Artistic
license, and it is thus non-copylefted freeware.

If you have a question about this software, desire to add code, found a
bug, want to request a feature, or wonder how to get further assistance,
please send e-mail to <yap-users AT lists.sourceforge.net>.  To
subscribe to the mailing list, visit the page
<https://lists.sourceforge.net/lists/listinfo/yap-users>.

On-line documentation is available for YAP at:

<http://www.ncc.up.pt/~vsc/YAP/>

Recent versions of YAP, including both source and selected binaries,
can be found from this same URL.

This manual was written by Vítor Santos Costa,
Luís Damas, Rogério Reis, and Rúben Azevedo. The
manual is largely based on the DECsystem-10 Prolog User's Manual by
D.L. Bowen, L. Byrd, F. C. N. Pereira, L. M. Pereira, and
D. H. D. Warren. We have  used comments from the Edinburgh Prolog
library written by R. O'Keefe. Documentation from many built-ins is
originally from the SWI-Prolog manual, with the gracious uathorization
from
Jan Wielemaker. We would also like to gratefully
acknowledge the contributions from Ashwin Srinivasian.

We are happy to include in YAP several excellent packages developed
under separate licenses. Our thanks to the authors for their kind
authorization to include these packages.

The packages are, in alphabetical order:

+ The CHR package developed by Tom Schrijvers,
Christian Holzbaur, and Jan Wielemaker.

+ The CLP(BN) package and Horus toolkit developed by Tiago Gomes, and Vítor Santos Costa.

+ The CLP(R) package developed by Leslie De Koninck, Bart Demoen, Tom
Schrijvers, and Jan Wielemaker, based on the CLP(Q,R) implementation
by Christian Holzbaur.

+ The CPLint package developed by Fabrizio Riguzzi's research
laboratory at the University of Ferrara. Please see

<http://www.ing.unife.it/Docenti/FabrizioRiguzzi/>

+ The CUDA interface package developed by Carlos Martínez, Jorge
Buenabad, Inês Dutra and Vítor Santos Costa.

+ The GECODE interface package developed by  Denys Duchier and Vítor Santos Costa.

+ The JPL (Java-Prolog Library) package developed by .

+ The Logtalk Object-Oriented system is developed at the University 
	of Beira Interior, Portugal, by Paulo Moura:

    <http://logtalk.org/>

    Logtalk is no longer distributed with YAP. Please use the Logtalk standalone 
	installer for a smooth integration with YAP.

+ The minisat SAT solver interface developed by Michael Codish,
 Vitaly Lagoon, and Peter J. Stuckey.

+ The MYDDAS relational data-base interface developed at the
 Universidade do Porto by Tiago Soares, Michel Ferreira, and Ricardo Rocha.

+ The PRISM logic-based
programming system for statistical modeling developed at the Sato
Research Laboratory, TITECH, Japan.

+ The ProbLog 1 system developed by the ProbLog team in the
DTAI group of KULeuven. For general information on ProbLog 1 and 2, please see
    
    <http://dtai.cs.kuleuven.be/problog>

+ The real R interface package developed by 	Nicos Angelopoulos,
Vítor Santos Costa, João Azevedo, Jan Wielemaker, and Rui Camacho.
</li>

+ YAP includes the yap2swi library that ports to YAP code from
 of SWI's PL interface. This includes the Input/Output Layer, the SWI
 Foreign Language Interface, and the RDF, archive, clib, http, odbc, plunit,
 semweb, sgml, and zlib packages written by Jan Wielemaker. Please do refer to the SWI-Prolog home page:

<http://www.swi-prolog.org>

for more information on SWI-Prolog and the SWI packages. 

@page DownloadInstall Downloading, Compiling, and Installing YAP

The latest development version of Yap-6 is yap-6.3.4 and can be
obtained from the repositories

<http://sourceforge.net/p/yap/yap-6.3>

and

<https://github.com/vscosta/yap-6.3>

Several packages are shared with SWI-Prolog and need to be obtained
from separate repositories. Proceed as follows:

~~~~~~
cd yap-6.3
git submodule init
git submodule update
~~~~~~

Most of these repositories are basically copies of the original
repositories at the SWI-Prolog site. YAP-6 will work either with or
without these packages.

@section CompilingYAP Compiling YAP

To compile YAP it should be sufficient to:

1 `autoconf`. Recent versions of YAP try to follow GNU
      conventions on where to place software.

  + The main executable is placed at  _$BINDIR_. This executa§ble is
    actually a script that calls the Prolog engine, stored at  _$LIBDIR_.

  + _$LIBDIR_ is the directory where libraries are stored. YAPLIBDIR is a
    subdirectory that contains the Prolog engine and a Prolog library.

  + _$INCLUDEDIR_ is used if you want to use YAP as a library.

  + _$INFODIR_ is where to store `info` files. Usually /usr/local/info, /usr/info, or /usr/share/info.

2 `make`.

3 If the compilation succeeds, try `./yap`.

4  If you feel satisfied with the result, do `make install`.

5 In most systems you will need to be superuser in order to do
    `make install` and `make info` on the standard directories.

@section Configuration_Options Tuning the Functionality of YAP 

Compiling YAP with the standard options give you a plain vanilla
Prolog. You can tune YAP to include extra functionality by calling
`configure` with the appropriate options:

  + `--enable-rational-trees=yes` gives you support for infinite
     rational trees.

  + `--enable-coroutining=yes` gives you support for coroutining,
    including freezing of goals, attributed variables, and
constraints. This will also enable support for infinite rational
trees.

  + `--enable-depth-limit=yes` allows depth limited evaluation, say for
implementing iterative deepening.

  + `--enable-low-level-tracer=yes` allows support for tracing all calls,
retries, and backtracks in the system. This can help in debugging your
application, but results in performance loss.

  + `--enable-wam-profile=yes` allows profiling of abstract machine
instructions. This is useful when developing YAP, should not be so
useful for normal users.

  + `--enable-condor=yes` allows using the Condor system that
support High Throughput Computing (HTC) on large collections of
distributively owned computing resources.

  + `--enable-tabling=yes` allows tabling support. This option
is still experimental.

  + `--enable-parallelism={env-copy,sba,a-cow}` allows
or-parallelism supported by one of these three forms. This option is
still highly experimental.

  + `--with-max-workers` allows definition of the maximum 
number of parallel processes (its value can be consulted at runtime 
using the flag `max_workers`).

  + `--with-gmp[=DIR]` give a path to where one can find the
`GMP` library if not installed in the default path.

  + `--enable-threads` allows using of the multi-threading 
predicates provided by YAP. Depending on the operating system, the 
option `--enable-pthread-locking` may also need to be used.

  + `--with-max-threads` allows definition of the maximum 
number of threads (the default value is 1024; its value can be consulted 
at runtime using the flag [max_threads](@ref max_threads)).



Next section discusses machine dependent details.

@section Machine_Options Tuning YAP for a Particular Machine and Compiler

The default options should give you best performance under
`GCC`. Although the system is tuned for this compiler
we have been able to compile versions of YAP under lcc in Linux,
Sun's cc compiler, IBM's xlc, SGI's cc, and Microsoft's Visual C++
6.0.

@section Tuning_for_GCC Tuning YAP for `GCC`.

YAP has been developed to take advantage of `GCC` (but not to
depend on it). The major advantage of `GCC` is threaded code and
explicit register reservation.

YAP is set by default to compile with the best compilation flags we
know. Even so, a few specific options reduce portability.  The option 

  + `--enable-max-performance=yes` will try to support the best
available flags for a specific architectural model. Currently, the option
assumes a recent version of `GCC`.
  + `--enable-debug-yap` compiles YAP so that it can be debugged
by tools such as `dbx` or `gdb`.


Here follow a few hints:

On x86 machines the flags:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
YAP_EXTRAS= ... -DBP_FREE=1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

tells us to use the `%bp` register (frame-pointer) as the emulator's
program counter. This seems to be stable and is now default.

On  Sparc/Solaris2 use:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
YAP_EXTRAS= ...   -mno-app-regs -DOPTIMISE_ALL_REGS_FOR_SPARC=1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

and YAP will get two extra registers! This trick does not work on
SunOS 4 machines.

Note that versions of GCC can be tweaked to recognize different
processors within the same instruction set, e.g. 486, Pentium, and
PentiumPro for the x86; or Ultrasparc, and Supersparc for
Sparc. Unfortunately, some of these tweaks do may make YAP run slower or
not at all in other machines with the same instruction set, so they
cannot be made default.

Last, the best options also depends on the version of GCC you are using, and
it is a good idea to consult the GCC manual under the menus "Invoking
GCC"/"Submodel Options". Specifically, you should check
`-march=XXX` for recent versions of GCC/EGCS. In the case of
`GCC2.7` and other recent versions of `GCC` you can check:

  + 486:
In order to take advantage of 486 specific optimizations in GCC 2.7.\*:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
YAP_EXTRAS= ... -m486 -DBP_FREE=1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  + Pentium:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
YAP_EXTRAS= ... -m486 -malign-loops=2 -malign-jumps=2 \
                      -malign-functions=2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  + PentiumPro and other recent Intel and AMD machines:
PentiumPros are known not to require alignment. Check your version of
`GCC` for the best `-march` option.

  + Super and UltraSparcs:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
YAP_EXTRAS= ... -msupersparc
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  + MIPS: if have a recent machine and you need a 64 bit wide address
space you can use the abi 64 bits or eabi option, as in:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CC="gcc -mabi=64" ./configure --...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Be careful. At least for some versions of `GCC`, compiling with
`-g` seems to result in broken code.

  + WIN32: GCC is distributed in the MINGW32 and CYGWIN packages.

The Mingw32 environment is available from the URL:

<http://www.mingw.org>

You will need to install the `msys` and `mingw`
packages. You should be able to do configure, make and make install.

If you use mingw32 you may want to search the contributed packages for
the `gmp` multi-precision arithmetic library. If you do setup YAP
with `gmp` note that libgmp.dll must be in the path,
otherwise YAP will not be able to execute.

The CygWin environment is available from the URL:

<http://www.cygwin.com>

and mirrors. We suggest using recent versions of the cygwin shell. The
compilation steps under the cygwin shell are as follows:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mkdir cyg
$YAPSRC/configure --enable-coroutining \\
                  --enable-depth-limit \\
                  --enable-max-performance
make
make install
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default, YAP will use the `-mno-cygwin` option to
disable the use of the cygwin dll and to enable the mingw32 subsystem
instead. YAP thus will not need the cygwin dll. It instead accesses
the system's CRTDLL.DLL `C` run time library supplied with
Win32 platforms through the mingw32 interface. Note that some older
WIN95 systems may not have CRTDLL.DLL, in this case it should
be sufficient to import the file from a newer WIN95 or WIN98 machine.

You should check the default installation path which is set to
/YAP in the standard Makefile. This string will usually
be expanded into c:\\YAP by Windows.

The cygwin environment does not provide <tt>gmp</tt> on the MINGW
subsystem. You can fetch a dll for the <tt>gmp</tt> library from
<http://www.sf.net/projects/mingwrep>.

It is also possible to configure YAP to be a part of the cygwin
environment. In this case you should use:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mkdir cyg
$YAPSRC/configure --enable-max-performance \\
                  --enable-cygwin=yes
make
make install
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
YAP will then compile using the cygwin library and will be installed
in cygwin's /usr/local. You can use YAP from a cygwin console,
or as a standalone application as long as it can find
cygwin1.dll in its path. Note that you may use to use
`--enable-depth-limit` for Aleph compatibility, and that you may
want to be sure that GMP is installed.



@subsection Compiling_Under_Visual_C Compiling Under Visual C++

YAP used to compile cleanly under Microsoft's Visual C++ release 6.0. We next
give a step-by-step review on how the core YAP compiled manually using this
environment.

First, it is a good idea to build YAP as a DLL:

  + create a project named yapdll using File.New. The project will be a
DLL project, initially empty.

Notice that either the project is named yapdll or you must replace the
preprocessors variable  _$YAPDLL_EXPORTS_ to match your project names
in the files YAPInterface.h and `c_interface.c`.

  + add all .c files in the $YAPSRC/C directory and in the
$YAPSRC\\OPTYAP directory to the Project's `Source Files` (use
FileView).

  + add all .h files in the  _$YAPSRC/H_ directory,
 _$YAPSRC\\include_ directory and in the  _$YAPSRC\\OPTYAP_
subdirectory to the Project's `Header Files`.

  + Ideally, you should now use `m4` to generate extra  .h from .m4 files and use
`configure` to create a `config.h`. Or, you can be lazy, and
fetch these files from  _$YAPSRC\\VC\\include_.

  + You may want to go to `Build.Set Active Configuration` and
set `Project Type` to `Release`

  + To use YAP's own include directories you have to set the Project
option  `Project.Project Settings.C/C++.Preprocessor.Additional Include Directories` to include the directories  _$YAPSRC\\H_,
 _$YAPSRC\\VC\\include_,  _$YAPSRC\\OPTYAP_ and
 _$YAPSRC\\include_.  The syntax is:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$YAPSRC\H, $YAPSRC\VC\include, $YAPSRC\OPTYAP, $YAPSRC\include
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  + Build: the system should generate an yapdll.dll and an yapdll.lib.

  + Copy the file yapdll.dll to your path. The file
    yapdll.lib should also be copied to a location where the linker can find it.


Now you are ready to create a console interface for YAP:

<ol>
 <li>create a second project  say `wyap` with `File.New`. The project will be a
WIN32 console project, initially empty.

  + add  _$YAPSRC\\console\\yap.c_ to the `Source Files`.

  + add  _$YAPSRC\\VC\\include\\config.h_ and the files in  _$YAPSRC\\include_ to
the `Header Files`.

  + You may want to go to `Build.Set Active Configuration` and set
`Project Type` to `Release`.

  + you will eventually need to bootstrap the system by booting from
`boot.yap`, so write:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        -b $YAPSRC\pl\boot.yap
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

in `Project.Project Settings.Debug.Program Arguments`.

  + You need the sockets and yap libraries. Add

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ws2_32.lib yapdll.lib
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

to `Project.Project Settings.Link.Object/Library Modules`

You may also need to set the `Link Path` so that VC++ will find `yapdll.lib`.

  + set `Project.Project Settings.C/C++.Preprocessor.Additional Include Directories` to include the 
 _$YAPSRC/VC/include_ and
 _$YAPSRC/include_.

The syntax is:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
$YAPSRC\VC\include, $YAPSRC\include
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  + Build the system.

  + Use `Build.Start Debug` to boot the system, and then create the saved state with

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
['$YAPSRC\\pl\\init'].
qsave_program('startup.yss').
^Z
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

That's it, you've got YAP and the saved state!
</li>
</ol>

The $YAPSRC\\VC directory has the make files to build YAP4.3.17 under VC++ 6.0.

@subsection Tuning_for_SGI_cc Compiling Under SGI's cc

YAP should compile under the Silicon Graphic's `cc` compiler,
although we advise using the GNUCC compiler, if available.

  + 64 bit
Support for 64 bits should work by using (under Bourne shell syntax):

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CC="cc -64" $YAP_SRC_PATH/configure --...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


@page Run Running YAP

We next describe how to invoke YAP in Unix systems.

@section Running_YAP_Interactively Running YAP Interactively

Most often you will want to use YAP in interactive mode. Assuming that
YAP is in the user's search path, the top-level can be invoked under
Unix with the following command:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
yap [-s n] [-h n] [-a n] [-c IP_HOST port ] [filename]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

All the arguments and flags are optional and have the following meaning:

+ -?
print a short error message.
+ -s _Size_
allocate  _Size_ KBytes for local and global stacks. The user may
specify <tt>M</tt> bytes.
+ -h _Size_
allocate  _Size_ KBytes for heap and auxiliary stacks
+ -t _Size_
allocate  _Size_ KBytes for the trail stack
+ -L _Size_ 
SWI-compatible option to allocate  _Size_ K bytes for local and global stacks, the local stack
cannot be expanded. To avoid confusion with the load option,  _Size_
must immediately follow the letter `L`.
+ -G _Size_
SWI-compatible option to allocate  _Size_ K bytes for local and global stacks; the global
stack cannot be expanded
+ -T _Size_
SWI-compatible option to allocate  _Size_ K bytes for the trail stack; the trail cannot be expanded.
+ -l  _YAP_FILE_
compile the Prolog file  _YAP_FILE_ before entering the top-level.
+ -L  _YAP_FILE_
compile the Prolog file  _YAP_FILE_ and then halt. This option is
useful for implementing scripts.
+ -g  _Goal_
run the goal  _Goal_ before top-level. The goal is converted from
an atom to a Prolog term.
+ -z  _Goal_
run the goal  _Goal_ as top-level. The goal is converted from
an atom to a Prolog term.
+ -b  _BOOT_FILE_
boot code is in Prolog file  _BOOT_FILE_. The filename must define
the predicate `'$live'/0`.
+ -c <tt>IP_HOST</tt> <tt>port</tt>
connect standard streams to host <tt>IP_HOST</tt> at port <tt>port</tt>
+ filename
restore state saved in the given file
+ -f
do not consult initial files
+ -q
do not print informational messages
+ --
separator for arguments to Prolog code. These arguments are visible
through the unix/1 built-in predicate.


Note that YAP will output an error message on the following conditions:

+ 
a file name was given but the file does not exist or is not a saved
YAP state;

+ 
the necessary amount of memory could not be allocated;

+ 
the allocated memory is not enough to restore the state.

	
    When restoring a saved state, YAP will allocate the
same amount of memory as that in use when the state was saved, unless a
different amount is specified by flags in the command line. By default,
YAP restores the file startup.yss from the current directory or from
the YAP library.

+ 
YAP usually boots from a saved state. The saved state will use the default
installation directory to search for the YAP binary unless you define
the environment variable YAPBINDIR.

+ 
YAP always tries to find saved states from the current directory
	first. If it cannot it will use the environment variable YAPLIBDIR, if
	defined, or search the default library directory.

+ 
YAP will try to find library files from the YAPSHAREDIR/library
directory.


@section Running_Prolog_Files Running Prolog Files

YAP can also be used to run Prolog files as scripts, at least in
Unix-like environments. A simple example is shown next (do not forget
that the shell comments are very important):

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#!/usr/local/bin/yap -L --
#
# Hello World script file using YAP
#
# put a dot because of syntax errors .

:- write('Hello World'), nl.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The `#!`  characters specify that the script should call the binary
file YAP. Notice that many systems will require the complete path to the
YAP binary. The `-L` flag indicates that YAP should consult the
current file when booting and then halt. The remaining arguments are
then passed to YAP. Note that YAP will skip the first lines if they
start with `#` (the comment sign for Unix's shell). YAP will
consult the file and execute any commands.

A slightly more sophisticated example is:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#!/usr/bin/yap -L --
#
# Hello World script file using YAP
# .

:- initialization(main).

main :- write('Hello World'), nl.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The `initialization` directive tells YAP to execute the goal main
after consulting the file. Source code is thus compiled and `main`
executed at the end. The `.` is useful while debugging the script
as a Prolog program: it guarantees that the syntax error will not
propagate to the Prolog code.

Notice that the `--` is required so that the shell passes the extra
arguments to YAP.  As an example, consider the following script
`dump_args`:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#!/usr/bin/yap -L --
#.

main( [] ).
main( [H|T] ) :-
        write( H ), nl,
        main( T ).

:- unix( argv(AllArgs) ), main( AllArgs ).

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you this run this script with the arguments:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./dump_args -s 10000
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
the script will start an YAP process with stack size `10MB`, and
the list of arguments to the process will be empty.

Often one wants to run the script as any other program, and for this it
is convenient to ignore arguments to YAP. This is possible by using
`L --` as in the next version of `dump_args`:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#!/usr/bin/yap -L --

main( [] ).
main( [H|T] ) :-
        write( H ), nl,
        main( T ).

:- unix( argv(AllArgs) ), main( AllArgs ).

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The `--` indicates the next arguments are not for YAP. Instead,
they must be sent directly to the argv built-in. Hence, running

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./dump_args test
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

will write `test` on the standard output.

@defgroup YAPLoading Loading and Organising YAP Programs

@page  LoadingInYap Using YAP Programs

Next, we present the main predicates and directives available to load
files and to control the Prolog environment.

 + \subpage YAPConsulting

 + \subpage YAPModules

 + \subpage YAPSaving


This chapter describes the predicates for controlling the execution of
Prolog programs.

In the description of the arguments of functors the following notation
will be used:

+ a preceding plus sign will denote an argument as an "input
 argument" - it cannot be a free variable at the time of the call; 
+ a preceding minus sign will denote an "output argument";
+ an argument with no preceding symbol can be used in both ways.

@defgroup YAPBuiltins  YAP  Built-Ins

@page  Core  Prolog Built-Ins

+ @ref YAPControl 

+ @ref arithmetic

+ @ref YAPChars

+ @ref YAP_Terms

+ @ref InputOutput

+ @ref YAPOS

+ @ref Database

+ @ref Sets

+ @ref Grammars

+ @ref Term_Modification
	   
+ @ref LoadForeign
	   
+ @ref Predicates_on_Atoms

+ @ref Flags

+ @ref Deb_Preds

@defgroup ChYInterface Foreign Language interface to YAP

YAP provides the user with three facilities for writing
predicates in a language other than Prolog. Under Unix systems,
most language implementations were linkable to `C`, and the first interface exported  the YAP machinery to the C language. YAP also implements most of the SWI-Prolog foreign language interface.
This gives portability with a number of SWI-Prolog packages and avoids garnage collection by using @ref slotInterface. Last, a new C++ based interface is 
being designed to work with the swig (@url(www.swig.org}) interface compiler.

+ The @ref c-interface exports the YAP engine.
+ The @ref swi-c-interface emulates Jan Wielemaker's SWI foreign language interface.
+ The @ref  yap-cplus-interface is desiged to interface with Object-Oriented systems.

@defgroup YAPExtensions Extensions to core Prolog.

+@ref Rational_Trees
  
+ @ref CohYroutining

+ @ref Attributed_Variables

+ @ref  DepthLimited

+ @ref  Tabling

+ @ref Threads

+ @ref Profiling

+ @ref YAPArrays

+ @ref Parallelism

@defgroup YAPLibrary The YAP Library

@page  LIbrary The YAP Library

+  @ref maplist

+  @ref Apply Apply Macros
		
+  @ref Association_Lists 
		
+  @ref AVL_Trees 
		
+  @ref  Exo_Intervals
		
+  @ref Heaps 
		
+  @ref Lists
		
+  @ref LineUtilities
		
+  @ref matrix 
		
+  @ref NonhYBacktrackable_Data_Structures 
		
+  @ref Ordered_Sets 
		
+  @ref Pseudo_Random 
		
+  @ref Queues Queues
		
+  @ref PseudoRandom
		
+  @ref RedhYBlack_Trees
		
+  @ref RegExp

+  @ref Splay_Trees 
		
+  @ref System 
		
+  @ref Terms 
		
+  @ref Tries 
		
+  @ref Cleanup 
		
+  @ref Timeout
		
+  @ref Trees
		
+  @ref UGraphs
		
+  @ref DGraphs 
		
+  @ref UnDGraphs
		
+  @ref DBUsage
		
+  @ref lambda

+  @ref clpfd
		
+  @ref Block_Diagram 
		
@defgroup YAPProgramming Programming in YAP

@page  Programming Programming in YAP

  + @ref Syntax

  + @ref Indexing

  + @ref Deb_Interaction

@defgroup SWILibrary  SWI-Prolog Libraries and Packages

@page  SWICode The SWI-Prolog Libraries and Packages

+ @ref aggregate

+ @ref date
		
+ @ref debug
		
+ @ref persistence

+ @ref pio

+ @ref predicate_options

+ @ref prolog_clause

+ @ref prolog_colour

+ @ref prolog_main

+ @ref prolog_source

+ @ref quasi_quotations

+ @ref swi_option
		
+ @ref read_util
		
+ @ref record
		
+ @ref settings
		
+ @ref shlib

+ @ref SWIclib
		
+ @ref archive

+ @ref CHR
		
+ @ref clpr
		
+ @ref http
		
+ @ref zlib


@defgroup YAPPackages The YAP packages

@page  Packages The YAP Packages

+ @ref real
		
+ @ref BDDs
		
+ @ref  Gecode

+ @ref  MYDDAS

+ @ref PFL

+ @ref ProbLog1

+ @ref YAPRaptor

+ @ref YAP-LBFGS

@defgroup SWIclib The SWI Extended Operating System Support Package
@ingroup SWILibrary

The HTTP package is a series of libraries developed by Jan Wielmaker
and the SWI-Prolog community for extended Operating System support.
Please consult clib.doc for the complete documentation.

@defgroup http The SWI http packages
@ingroup SWILibrary

The HTTP package is a series of libraries developed by Jan Wielmaker
and the SWI-Prolog community for accessing and serving data on the
web. It supports lower-level transport protocols, but also
data-representation primitives, and more. 

The port to YAP focussed on the client-side support. The server
package has not been as widely tested.

@page Compatibility Compatibility with Other Prolog systems

YAP has been designed to be as compatible as possible with
other Prolog systems, and initially with C-Prolog. More recent work on
YAP has included features initially proposed for the Quintus
and SICStus Prolog systems.

Developments since `YAP4.1.6` we have striven at making
YAP compatible with the ISO-Prolog standard. 

@section ChYProlog Compatibility with the C-Prolog interpreter

@subsection Major_Differences_with_ChYProlog Major Differences between YAP and C-Prolog.

YAP includes several extensions over the original C-Prolog system. Even
so, most C-Prolog programs should run under YAP without changes.

The most important difference between YAP and C-Prolog is that, being
YAP a compiler, some changes should be made if predicates such as
`assert`, `clause` and `retract` are used. First
predicates which will change during execution should be declared as
`dynamic` by using commands like:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:- dynamic f/n.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 where `f` is the predicate name and n is the arity of the
predicate. Note that  several such predicates can be declared in a
single command:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 :- dynamic f/2, ..., g/1.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Primitive predicates such as `retract` apply only to dynamic
predicates.  Finally note that not all the C-Prolog primitive predicates
are implemented in YAP. They can easily be detected using the
`unknown` system predicate provided by YAP.

Last, by default YAP enables character escapes in strings. You can
disable the special interpretation for the escape character by using:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:- yap_flag(character_escapes,off).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
or by using:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:- yap_flag(language,cprolog).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

@subsection Fully_ChYProlog_Compatible YAP predicates fully compatible with C-Prolog

These are the Prolog built-ins that are fully compatible in both
C-Prolog and YAP:

@subsection Not_Strictly_ChYProlog_Compatible YAP predicates not strictly compatible with C-Prolog

These are YAP built-ins that are also available in C-Prolog, but
that are not fully compatible:

@subsection Not_in_ChYProlog YAP predicates not available in C-Prolog

These are YAP built-ins not available in C-Prolog.

@subsection Not_in_YAP YAP predicates not available in C-Prolog

These are C-Prolog built-ins not available in YAP:

  + 'LC'
The following Prolog text uses lower case letters.

  + 'NOLC'
The following Prolog text uses upper case letters only.


@section SICStus_Prolog Compatibility with the Quintus and SICStus Prolog systems

The Quintus Prolog system was the first Prolog compiler to use Warren's
Abstract Machine. This system was very influential in the Prolog
community. Quintus Prolog implemented compilation into an abstract
machine code, which was then emulated. Quintus Prolog also included
several new built-ins, an extensive library, and in later releases a
garbage collector. The SICStus Prolog system, developed at SICS (Swedish
Institute of Computer Science), is an emulator based Prolog system
largely compatible with Quintus Prolog. SICStus Prolog has evolved
through several versions. The current version includes several
extensions, such as an object implementation, co-routining, and
constraints.

Recent work in YAP has been influenced by work in Quintus and
SICStus Prolog. Wherever possible, we have tried to make YAP
compatible with recent versions of these systems, and specifically of
SICStus Prolog. You should use 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:- yap_flag(language, sicstus).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
for maximum compatibility with SICStus Prolog.

@subsection Major_Differences_with_SICStus Major Differences between YAP and SICStus Prolog.

Both YAP and SICStus Prolog obey the Edinburgh Syntax and are based on
the WAM. Even so, there are quite a few important differences:

  + Differently from SICStus Prolog, YAP does not have a
notion of interpreted code. All code in YAP is compiled.

  + YAP does not support an intermediate byte-code
representation, so the `fcompile/1` and `load/1` built-ins are
not available in YAP.

  + YAP implements escape sequences as in the ISO standard. SICStus
Prolog implements Unix-like escape sequences.

  + YAP implements initialization/1 as per the ISO
standard. Use prolog_initialization/1 for the SICStus Prolog
compatible built-in.

  + Prolog flags are different in SICStus Prolog and in YAP.

  + The SICStus Prolog `on_exception/3` and
`raise_exception` built-ins correspond to the ISO built-ins
catch/3 and throw/1.

  + The following SICStus Prolog v3 built-ins are not (currently)
implemented in YAP (note that this is only a partial list):
file_search_path/2,
`stream_interrupt/3`, `reinitialize/0`, `help/0`,
`help/1`, `trimcore/0`, `load_files/1`,
load_files/2, and `require/1`.

The previous list is incomplete. We also cannot guarantee full
compatibility for other built-ins (although we will try to address any
such incompatibilities). Last, SICStus Prolog is an evolving system, so
one can be expect new incompatibilities to be introduced in future
releases of SICStus Prolog.

  + YAP allows asserting and abolishing static code during
execution through the assert_static/1 and abolish/1
built-ins. This is not allowed in Quintus Prolog or SICStus Prolog.

  + The socket predicates, although designed to be compatible with
SICStus Prolog, are built-ins, not library predicates, in YAP.

  + This list is incomplete.



The following differences only exist if the language flag is set
to `yap` (the default):

  + The consult/1 predicate in YAP follows C-Prolog
semantics. That is, it adds clauses to the data base, even for
preexisting procedures. This is different from consult/1 in
SICStus Prolog or SWI-Prolog.

  + 
By default, the data-base in YAP follows "logical update semantics", as
Quintus Prolog or SICStus Prolog do.  Previous versions followed
"immediate update semantics". The difference is depicted in the next
example:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:- dynamic a/1.

?- assert(a(1)).

?- retract(a(X)), X1 is X +1, assertz(a(X)).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
With immediate semantics, new clauses or entries to the data base are
visible in backtracking. In this example, the first call to
retract/1 will succeed. The call to  *assertz/1* will then
succeed. On backtracking, the system will retry
retract/1. Because the newly asserted goal is visible to
retract/1, it can be retracted from the data base, and
`retract(a(X))` will succeed again. The process will continue
generating integers for ever. Immediate semantics were used in C-Prolog.

With logical update semantics, any additions or deletions of clauses
for a goal 
<em>will not affect previous activations of the goal</em>. In the example,
the call to assertz/1 will not see the 
update performed by the assertz/1, and the query will have a
single solution.

Calling `yap_flag(update_semantics,logical)` will switch
YAP to use logical update semantics.

  + dynamic/1 is a built-in, not a directive, in YAP.

  + By default, YAP fails on undefined predicates. To follow default
SICStus Prolog use:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:- yap_flag(unknown,error).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  + By default, directives in YAP can be called from the top level.

@subsection Fully_SICStus_Compatible YAP predicates fully compatible with SICStus Prolog

These are the Prolog built-ins that are fully compatible in both SICStus
Prolog and YAP:

@subsection Not_Strictly_SICStus_Compatible YAP predicates not strictly compatible with SICStus Prolog

These are YAP built-ins that are also available in SICStus Prolog, but
that are not fully compatible:

@subsection Not_in_SICStus_Prolog YAP predicates not available in SICStus Prolog

These are YAP built-ins not available in SICStus Prolog.

@section ISO_Prolog Compatibility with the ISO Prolog standard

The Prolog standard was developed by ISO/IEC JTC1/SC22/WG17, the
international standardization working group for the programming language
Prolog. The book "Prolog: The Standard" by Deransart, Ed-Dbali and
Cervoni gives a complete description of this standard. Development in
YAP from YAP4.1.6 onwards have striven at making YAP
compatible with ISO Prolog. As such:

  + YAP now supports all of the built-ins required by the
ISO-standard, and,
  + Error-handling is as required by the standard.


YAP by default is not fully ISO standard compliant. You can set the 
language flag to `iso` to obtain very good
compatibility. Setting this flag changes the following:

  + By default, YAP uses "immediate update semantics" for its
database, and not "logical update semantics", as per the standard,
( (see SICStus Prolog)). This affects assert/1,
retract/1, and friends.

Calling `set_prolog_flag(update_semantics,logical)` will switch
YAP to use logical update semantics.

  + By default, YAP implements the 
atom_chars/2( (see Testing Terms)), and 
number_chars/2, ( (see Testing Terms)), 
built-ins as per the original Quintus Prolog definition, and
not as per the ISO definition.

Calling `set_prolog_flag(to_chars_mode,iso)` will switch
YAP to use the ISO definition for
atom_chars/2 and number_chars/2.

  + By default, YAP allows executable goals in directives. In ISO mode
most directives can only be called from top level (the exceptions are
set_prolog_flag/2 and op/3).

  + Error checking for meta-calls under ISO Prolog mode is stricter
than by default.

  + The strict_iso flag automatically enables the ISO Prolog
standard. This feature should disable all features not present in the
standard.



The following incompatibilities between YAP and the ISO standard are
known to still exist:

<ul>

 <li>Currently, YAP does not handle overflow errors in integer
operations, and handles floating-point errors only in some
architectures. Otherwise, YAP follows IEEE arithmetic.



Please inform the authors on other incompatibilities that may still
exist.

## Predicate Index ##


## Concept Index ##