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    }
}

sub show_results {
    return unless $RESULTS;
    my ($prolog) = @_;
    my $results = $prolog->results;
    $results ||= ''; # otherwise it's an arrayref
    print $OUT $results, " ";
    unless ($results) {
        print $OUT "No\n";
        $RESULTS = 0;
    }
}

sub user_wants_more {
    return unless $RESULTS;
    ReadMode 'cbreak';
    my $key = ReadKey(0);
    ReadMode 'normal';
    if (';' eq $key) {
        print $OUT ";\n\n";
        return 1;
    }
    print $OUT "\n\nYes\n" if $RESULTS;
    return;
}

my $offset;
sub help {
    $offset ||= tell DATA;
    seek DATA, $offset, 0;
    pod2usage({
        -verbose => 2, 
        -input   => \*DATA,
        -exitval => 'NOEXIT',
    });
}

__DATA__

=head1 NAME 

aiprolog --  A simple Prolog shell using AI::Prolog.

=head1 SYNOPSIS

 usage: aiprolog <optional prolog program name>

=head1 DESCRIPTION

C<aiprolog> is a simple prolog shell using L<AI::Prolog> as the backend.

See the documentation for more detail on the Prolog features that L<AI::Prolog>
currently accepts.

=head2 Commands

Commands specific to aiprolog shell:

 "% more"     -- enables prompting for more results (default)
 "% no more"  -- disables prompting for more results
 "% nomore"   -- same as "no more"
 "% halt"     -- stops the shell
 "% help"     -- display this message

Note that the percent sign must preceed the command.  The percent sign
indicates a Prolog comment.  Without that, aiprolog will think you're trying to
execute a prolog command.

aiprolog-specific commands are case-insensitive.

=head2 Typical session

Save the following to a file named "append.pro":

 append([],X,X).
 append([W|X], Y, [W|Z]) :- append(X,Y,Z).

Then load it into the C<aiprolog> shell by typing this at a shell:

 aiprolog path/to/append.pro

Alternatively, once in the shell, you can load the program with:

 consult('path/to/append.prog').

In the shell, you should be greeted by a query prompt "?-".  At this prompt,
you can issue queries against the program.  Try entering the following query:

 append(X,Y,[1,2,3,4]).

The shell should respond with this:

 append([],[1,2,3,4],[1,2,3,4]) ;

It should then appear to hang.  It's waiting for you to type a character.  If
you type a semi-colon, it will attempt to resatisfy the query.  If you keep
doing that until there are no more valid results left, you'll see this:

 ?- append(X,Y,[1,2,3,4]).

 append([],[1,2,3,4],[1,2,3,4]) ;

 append([1],[2,3,4],[1,2,3,4]) ;

 append([1,2],[3,4],[1,2,3,4]) ;

 append([1,2,3],[4],[1,2,3,4]) ;

 append([1,2,3,4],[],[1,2,3,4]) ; 

 No
 
 ?-

The "No" is just Prolog's way of telling you there are no more results which
satisfy your query.  If you stop trying to satisfy results before all solutions
have been found, you might see something like this:

 ?- append(X,Y,[1,2,3,4]).