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        warn $@;
        next;
    }
    $RESULTS = 1;
    show_results($prolog);
    while ($MORE && user_wants_more()) {
        show_results($prolog);
    }
}

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