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 M 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 IP_HOST port connect standard streams to host IP_HOST at port port
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

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

Table of Contents

Running YAP Interactively

Running Prolog Files