One of the "cool" aspects of using a client-server model for the project was that I'm no longer limited to a single "turtle" on the screen; the module supports multiple simultaneous clients.  Additionally, since there is support for quering any particular client's parameters (including screen position, angle heading, etc.), there is some interesting potential for possible games or projects which could result (Light cycles, for example).

The following code represents the Language::Logo module, which I'm planning to submit (as my first module) to CPAN.  On January 16th, I gave a presentation to Boston Perl Mongers, and was given some good feedback (including the appropriate namespace under which to register:  Language::Logo).  But I'd also like to hear comments from my fellow Perl monks, whose opinions I hold in high regard.  So please give me your feedback!

Here is the current code for Language::Logo:

#
#  Language::Logo.pm
#
#  An implementation of the Logo programming language which allows
#  multiple clients to connect simultaneously.
#
#  Written January 2007, by John C. Norton
#  Presented at Boston Perlmongers on January 16th, 2007
#


# Package header
package Logo;
our $VERSION = '1.000';              # Current version


# Strict
use strict;
use warnings;


# Libraries
use IO::Select;
use IO::Socket;
use Sys::Hostname;


#################
### Variables ###
#################
use constant PI => (4 * atan2(1, 1));

# User-defined
my $date          = '070129';             # Date last modified
my $iam           = "Language::Logo";     # Module identifier
my $d_title       = "$iam version $VERSION";

my $max_connect   = 16;         # Maximum client connections
my $retry_timeout = 10;         # Client connection timeout after N se
+conds

# Defaults
my $d_port      = "8220";       # Default socket port
my $d_update    = 10;           # Default gui update rate
my $d_bg        = "black";      # Default canvas background color
my $d_width     = 512;          # Default canvas width
my $d_height    = 512;          # Default canvas height
my $d_color     = 'white';      # Default pen/turtle color
my $d_psize     = '1';          # default pen size (thickness)
my $d_txdim     = '6';          # Default turtle x-dimension
my $d_tydim     = '9';          # Default turtle y-dimension


my @switches    = qw( name debug title bg width height update host por
+t );
my %switches    = map { $_ => 1 } @switches;

# Client-specific top-level variables (with initial values)
my $pvars = {
    'debug' => 0,
    'step'  => 0,
    'wrap'  => 0,
};

# Command aliases
my $palias = {
    'fd' => 'forward',
    'bk' => 'backward',
    'rt' => 'right',
    'lt' => 'left',
    'sh' => 'seth',
    'pu' => 'penup',
    'pd' => 'pendown',
    'ps' => 'pensize',
    'co' => 'color',
    'cs' => 'clear',
    'hm' => 'home',
    'sx' => 'setx',
    'sy' => 'sety',
    'xy' => 'setxy',
    'ht' => 'hideturtle',
    'st' => 'showturtle',
    'w'  => 'width',
    'h'  => 'height',
    'ud' => 'update',
    'bg' => 'background',
};


my $pmethods = {
    'forward'    => 'move_turtle', 
    'backward'   => 'move_turtle',
    'right'      => 'turn_turtle',
    'left'       => 'turn_turtle',
    'seth'       => 'turn_turtle',
    'penup'      => 'change_pen_state',
    'pendown'    => 'change_pen_state',
    'pensize'    => 'change_pen_size',
    'color'      => 'change_color',
    'clear'      => 'modify_canvas',
    'width'      => 'modify_canvas',
    'height'     => 'modify_canvas',
    'background' => 'modify_canvas',
    'home'       => 'reset_turtle',
    'setx'       => 'move_turtle',
    'sety'       => 'move_turtle',
    'setxy'      => 'move_turtle',
    'hideturtle' => 'show_turtle',
    'showturtle' => 'show_turtle',
    'update'     => 'change_update',
};


###################
### Subroutines ###
###################

#===================
#=== Client code ===
#===================
sub new {
    my ($class, @args) = @_;
    (ref $class) and $class = ref $class;

    # Create blessed reference
    my $self = { };
    bless $self, $class;

    # Parse optional arguments
    while (@args) {
        my $arg = shift @args;
        if ($arg =~ /^sig(.+)$/) {
            # Trap specified signals
            my $sig = uc $1;
            $SIG{$sig} = shift @args;
        } elsif (defined($switches{$arg}) and @args > 0) {
            # Assign all valid parameters
            $self->{$arg} = shift @args;
        }
    }

    # Startup a new server locally if 'host' was not defined.
    if (!defined($self->{'host'})) {
        $self->fork_server();
    }

    # Connect to the server
    $self->connect_to_server();

    # Return the object
    return $self;
}


sub disconnect {
    my ($self, $msg) = @_;
    if ($msg || 0) {
        print "$msg";
        <STDIN>;
    }
    my $sock = $self->{'socket'};
    if ($sock || 0) {
        close($sock);
    }
}


sub connect_to_server {
    my ($self) = @_;

    # Return if socket is already connected
    my $sock = $self->{'socket'} || 0;
    my $name = $self->{'name'}   || "";
    $sock and return $sock;

    # If hostname is ':', use local host
    my $host = $self->{'host'} || ':';
    ($host eq ':') and $host = hostname();

    my $port = $self->{'port'} || $d_port;
    my %params = (
        'PeerAddr'  => $host,
        'PeerPort'  => $port,
        'Proto'     => 'tcp',
        'ReuseAddr' => 1,
    );

    # Keep retrying until $retry_timeout is exceeded
    my $start = time;
    while (1) {
        ($sock = new IO::Socket::INET(%params)) and last;   # Success!
        if (time - $start > $retry_timeout) {
            die "$iam:  Failed client socket connection\n";
        }
        select(undef, undef, undef, 0.1);
    }

    # Save socket
    $self->{'socket'} = $sock;
    print $sock ":$name\n";
    chomp(my $ans = <$sock>);
    if ($ans !~ /^(\d+):(.+)$/) {
        die "$iam:  expected 'id:name', got '$ans'\n";
    }
    my ($id, $newname) = ($1, $2);
    $self->{'id'}   = $id;
    $self->{'name'} = $newname;
    $self->{'host'} = $host;
    return $sock;
}


sub host {
    my ($self) = @_;
    return $self->{'host'};
}


sub interact {
    my ($self) = @_;

    print "Type '?' for help\n";

    while (1) {
        print "$iam> ";
        my $cmd = <STDIN>;
        defined($cmd) or return;
        chomp $cmd;
        $cmd =~ s/^\s*(.*)\s*$/$1/;
        ($cmd eq 'quit' or $cmd eq 'bye' or $cmd eq 'exit') and return
+;

        if ($cmd ne "") {
            if ($cmd =~ s/^\?//) {
                my $ans = $self->ask($cmd);
                print "Response:  $ans\n";
            } else {
                my $ans = $self->command($cmd);
                $ans and print "Command ERROR:  $ans\n";
            }
        }
    }
}


sub command {
    my ($self, $cmdstr) = @_;
    my $sock = $self->connect_to_server();
    $sock or return 0;
    my @commands = split(';', $cmdstr);
    foreach my $cmd (@commands) {
        print $sock "=$cmd\n";
        my $answer = <$sock>;
        $answer or die "$iam:  server socket went away\n";
        chomp $answer;
        $answer and return $answer;
    }
    return "";
}


sub cmd {
    my $self = shift;
    return $self->command(@_);
}


sub query {
    my ($self, $cmd) = @_;
    my $sock = $self->connect_to_server();
    $sock or return 0;
    print $sock "?$cmd\n";
    chomp(my $answer = <$sock>);
    return $answer;
}


sub ask {
    my $self = shift;
    return $self->query(@_);
}


#===================
#=== Server code ===
#===================
sub fork_server {
    my ($self) = @_;

    my $b_dbg  = $self->{'debug'}  || 0;
    my $title  = $self->{'title'}  || $d_title;
    my $w      = $self->{'width'}  || $d_width;
    my $h      = $self->{'height'} || $d_height;
    my $bg     = $self->{'bg'}     || $d_bg;
    my $update = $self->{'update'} || $d_update;
    my $host   = $self->{'host'}   || hostname();
    my $port   = $self->{'port'}   || $d_port;
   
    my $fork = fork();
    defined($fork) or die "$iam:  failed to fork server\n";
    $fork and return;
    Logo->server_init($b_dbg, $title, $w, $h, $bg, $update, $host, $po
+rt);
}


sub server_init {
    my ($class, $b_dbg, $title, $w, $h, $bg, $update, $host, $port) = 
+@_;

    # Create a blessed object
    my $self = {
        'nticks'   => 0,        # Tracks number of GUI updates
        'debug'    => $b_dbg,   # Debug flag
        'count'    => 0,        # Current number of connections
        'total'    => 0,        # Total number of connections
        'clients'  => { },      # The client hash
        'names'    => { },      # The clients by name
    };
    bless $self, $class;

    # Open a socket connection at the desired port
    my %params = (
        'LocalHost' => $host,
        'LocalPort' => $port,
        'Proto'     => 'tcp',
        'Listen'    => $max_connect,
        'ReuseAddr' => 1,
    );

    # Create socket object
    my $sock = new IO::Socket::INET(%params);
    if (!$sock) {
        # Port is already in use -- client will connect to it instead
        $b_dbg and print "[Port $port already in use]\n";
        exit;
    }
    $self->{'socket'} = $sock;

    # Create select set for reading
    $self->{'select'} = new IO::Select($sock);

    # Create the GUI
    require Tk;
    $b_dbg and print "[Logo server v$VERSION on '$host']\n";
    my $mw = Tk::MainWindow->new(-title => $title);
    $self->{'mw'} = $mw;

    # Allow easy dismissal of the GUI
    $mw->bind("<Escape>" => sub { $self->server_exit });

    # Create a new canvas
    $self->clear_screen($w, $h, $bg);

    # Manage the GUI
    $self->{'repid'} = $self->set_update($update);
    Tk::MainLoop();
}


sub server_exit {
    my ($self) = @_;
    my $mw = $self->{'mw'};

    my $sel      = $self->{'select'};
    my $sock     = $self->{'socket'};
    my $pclients = $self->{'clients'};
    my $pnames   = $self->{'names'};

    close $sock;

    foreach my $name (keys %$pnames) {
        my $pclient = $pnames->{$name};
        my $fh = $pclient->{'fh'};
        $self->server_remove_client($pclients, $sel, $fh);
    }

    # Shouldn't ever get here, since when the last client exited,
    # the server should have already gone away. But just in case ...
    #
    $mw->destroy();
    exit;
}


sub set_update {
    my ($self, $update) = @_;
    ($update < 1)    and $update = 1;
    ($update > 1000) and $update = 1000;
    $self->{'update'} = $update;
    my $mw = $self->{'mw'};
    my $id = $mw->repeat($update => sub { $self->server_loop() });
    return $id;
}


sub server_loop {
    my ($self) = @_;

    # Increment tick count
    ++$self->{'nticks'};

    # Get data from the object
    my $sel      = $self->{'select'};
    my $sock     = $self->{'socket'};
    my $pclients = $self->{'clients'};

    # Handle each pending socket
    my @readable = $sel->can_read(0);
    foreach my $rh (@readable) {
        if ($rh == $sock) {
            # The main socket means a new incoming connection.
            $self->server_add_client($rh, $pclients);
        } else {
            # Service the socket
            my $text = <$rh>;

            if (defined($text)) {
                # Process packet (either command or ask)
                chomp $text;
                my $pc = $pclients->{$rh};
                $self->server_socket_input($pc, $text);
            } else {
                # Socket was closed -- remove the client
                $self->server_remove_client($pclients, $sel, $rh);
            }
        }
    }
}


sub server_add_client {
    my ($self, $rh, $pclients) = @_;

    # Accept the client connect and add the new socket
    my $sel = $self->{'select'};
    my $ns  = $rh->accept();
    $sel->add($ns);

    my $b_dbg = $self->{'debug'} || 0;
    my $peer = getpeername($ns);
    my ($port, $iaddr) = unpack_sockaddr_in($peer);
    my $remote = inet_ntoa($iaddr);

    # Get the client handshake, and send back its unique ID
    chomp(my $text = <$ns>);
    ($text =~ /^:(.*)$/) or die "Bad header, expected ':[name]', got '
+$text'";
    my $name = $1 || "";

    my $id = $self->{'total'} + 1;
    $name ||= "CLIENT$id";
    print $ns "$id:$name\n";

    my $pc = $pclients->{$ns} = {
        'id'      => $id,
        'fh'      => $ns,
        'name'    => $name,
        'remote'  => $remote,
    };

    # Create the 'turtle' object
    $self->create_turtle($pc);

    # Increment the number of connections and the total connection cou
+nt
    ++$self->{'count'};
    ++$self->{'total'};

    # Add the client's name
    $b_dbg and print "[Added socket $id => '$name']\n";
    $self->{'names'}->{$name} = $pclients->{$ns};
}


sub server_remove_client {
    my ($self, $pclients, $sel, $fh) = @_;;
    my $b_dbg = $self->{'debug'} || 0;
    my $pc = $pclients->{$fh};
    my $name = $pc->{'name'};
    my $id   = $pc->{'id'};
    $sel->remove($fh);
    close($fh);
    delete $pclients->{$fh};

    # Remove the client's name
    my $pnames = $self->{'names'};
    delete $pnames->{$name};

    # Remove the client's turtle
    my $cv    = $self->{'canvas'};
    my $ptids = $pc->{'turtle'}->{'tids'};
    ($ptids || 0) and map { $cv->delete($_) } @$ptids;

    # Decrement the global client count
    --$self->{'count'};
    $b_dbg and print "[Closed socket $id '$name']\n";

    # Exit the server if this is the last connection
    if (0 == $self->{'count'} and $self->{'total'} > 0) {
        $b_dbg and print "[Final client closed -- exiting]\n";
        $self->{'mw'}->destroy();
        exit;
    }
}


sub server_socket_input {
    my ($self, $pc, $cmd) = @_;
    my $mode = $pc->{'mode'};
    ($cmd =~ s/^=\s*//)  and return $self->server_command($pc, $cmd);
    ($cmd =~ s/^\?\s*//) and return $self->server_query($pc, $cmd);
}


sub server_command {
    my ($self, $pc, $cmdstr) = @_;
    my $id = $pc->{'id'};
    $pc->{'lastcmd'} = $cmdstr;
    $pc->{'debug'} and print "Command<$id>: '$cmdstr'\n";

    my @args = split(/\s+/, $cmdstr);
    my $cmd = shift @args;

    # Resolve any command alias
    while (defined($palias->{$cmd})) {
        my $newcmd = $palias->{$cmd};
        $cmd = $newcmd;
    }
    unshift @args, $cmd;

    # Execute one command if single-stepping is on
    if ($pc->{'step'}) {
        my $go = $self->single_step_prompt($pc, $cmd, [ @args ]);
        $go or return $self->server_reply($pc);
    }

    # Variables
    if (defined($pvars->{$cmd})) {
        return $self->set_variable($pc, @args);
    }

    # Find command in dispatch table
    my $method = $pmethods->{$cmd};
    defined($method) and return $self->$method($pc, @args);

    # Return acknowledgment
    $self->server_reply($pc, "Unknown command '$cmd'");
}


sub single_step_prompt {
    my ($self, $pc, $cmd, $pargs) = @_;
    my $cmdstr = join(" ", @$pargs);
    print "Step>  [$cmdstr]  Execute {y|n|c}? [y]";
    chomp(my $ans = <STDIN>);
    ($ans =~ /^[cC]/) and $pc->{'step'} = 0;
    return ($ans =~ /^[nN]/)? 0: 1;
}


sub server_reply {
    my ($self, $pc, $reply) = @_;
    my $fh = $pc->{'fh'};
    $reply ||= "";
    print $fh "$reply\n";
}


sub server_query {
    my ($self, $pc, $cmd) = @_;
    my $id = $pc->{'id'};
    $pc->{'debug'} and print "Request<$id>: '$cmd'\n";
    my @args = split(/\s+/, $cmd);
    $cmd = shift @args;
    my $cv = $self->{'canvas'};

    # Quit if the query contains no text
    ($cmd || 0) or return $self->server_reply($pc, "Blank query");

    # Return the specified global parameter, if defined
    if (defined($self->{$cmd})) {
        return $self->server_reply($pc, $self->{$cmd});
    }

    # Return the specified per-client parameter, if defined
    if (defined($pc->{$cmd})) {
        return $self->server_reply($pc, $pc->{$cmd});
    }

    # Return the specified per-client turtle parameter, if defined
    my $turtle = $pc->{'turtle'};
    if (defined($turtle->{$cmd})) {
        return $self->server_reply($pc, $turtle->{$cmd});
    }

    # Return an error message
    my $ans = "Unknown query '$cmd'";
    $self->server_reply($pc, $ans);
}


sub create_turtle {
    my ($self, $pc, $from) = @_;

    my $turtle = {
        'step'   => 0,          # Single step flag
        'pen'    => 0,          # Pen state:  0 = 'up', 1 = 'down'
        'color'  => $d_color,   # Pen color (also turtle color)
        'size'   => $d_psize,   # Pen size (thickness)
        'xdim'   => $d_txdim,   # Turtle x-dimension
        'ydim'   => $d_tydim,   # Turtle y-dimension
        'dist'   => 0,          # Last distance traveled (used as defa
+ult)
        'show'   => 1,          # Turtle starts out visible
    };

    # Use old turtle as a reference
    if ($from || 0) {
        map { $turtle->{$_} = $from->{$_} } (keys %$from);
    }

    $self->home_turtle($pc, $turtle);
    $self->draw_turtle($pc, $turtle);
}


sub home_turtle {
    my ($self, $pc, $turtle) = @_;
    my $cv     = $self->{'canvas'};
    my $width  = $cv->cget(-width);
    my $height = $cv->cget(-height);

    my $x = int($width  / 2);
    my $y = int($height / 2);

    $turtle->{'x'}     = $x;
    $turtle->{'y'}     = $y;
    $turtle->{'angle'} = 0;
}


sub reset_turtle {
    my ($self, $pc, $cmd) = @_;
    my $turtle = $pc->{'turtle'};
    $self->home_turtle($pc, $turtle);
    $self->draw_turtle($pc, $turtle);
    $self->server_reply($pc);
}


sub draw_turtle {
    my ($self, $pc, $turtle) = @_;

    # Erase old turtle if one exists
    my $cv    = $self->{'canvas'};
    my $ptids = $pc->{'turtle'}->{'tids'};
    if ($ptids || 0) {
        map { $cv->delete($_) } @$ptids;
        $pc->{'turtle'}->{'tids'} = 0;
    }

    # Create turtle parameters
    my $cvbg   = $cv->cget(-bg);
    my $x      = $turtle->{'x'};
    my $y      = $turtle->{'y'};
    my $xdim   = $turtle->{'xdim'};
    my $ydim   = $turtle->{'ydim'};
    my $color  = $turtle->{'color'};
    my $angle  = $turtle->{'angle'};
    my $show   = $turtle->{'show'};

    if ($turtle->{'show'}) {
        # Assign points, rotate them, and plot the turtle
        my $ppts = [ $x, $y, $x-$xdim, $y, $x, $y-2*$ydim, $x+$xdim, $
+y ];
        $ppts = $self->rotate($x, $y, $angle, $ppts);
        my @args = (-fill => $cvbg, -outline => $color);
        my $tid = $cv->createPolygon(@$ppts, @args);
        $turtle->{'tids'} = [ $tid ];
        $pc->{'turtle'} = $turtle;

        # If the pen is down, draw a circle around the current point
        $ppts = [ ];
        if ($turtle->{'pen'}) {
            $ppts = [ $x-3, $y-3, $x+3, $y+3 ];
            $tid = $cv->createOval(@$ppts, -outline => $color);
            push @{$turtle->{'tids'}}, $tid;
        }
    }

    # Save the turtle to this client's data
    $pc->{'turtle'} = $turtle;
}


sub change_update {
    my ($self, $pc, $cmd, $update) = @_;
    my $repid = $self->{'repid'};
    ($repid || 0) and $repid->cancel();
    $self->{'repid'} = $self->set_update($update);
    $self->server_reply($pc);
}


sub set_variable {
    my ($self, $pc, $param, $val) = @_;
    $pc->{$param} = $val || 0;
    $pc->{'debug'} and print "Variable '$param' set to '$val'\n";
    $self->server_reply($pc);
}


sub modify_canvas {
    my ($self, $pc, $cmd, $val) = @_;

    my $cv = $self->{'canvas'};
    ($cmd eq 'clear')      and $self->clear_screen();
    ($cmd eq 'width')      and eval {$cv->configure('-wi', $val || $d_
+width)};
    ($cmd eq 'height')     and eval {$cv->configure('-he', $val || $d_
+height)};
    ($cmd eq 'background') and eval {$cv->configure('-bg', $val || $d_
+bg)};

    my $pnames = $self->{'names'};
    foreach my $name (keys %$pnames) {
        my $pclient = $pnames->{$name};
        my $turtle = $pclient->{'turtle'};
        if ($cmd eq 'w' or $cmd eq 'h') {
            # Have to recreate the turtle
            $self->create_turtle($pclient);
        } elsif ($cmd eq 'bg') {
            # Have to redraw the turtle
            $self->draw_turtle($pclient, $turtle);
        }
    }

    $self->server_reply($pc);
}


sub clear_screen {
    my ($self, $width, $height, $bg) = @_;

    # Clear any old canvas
    my $oldcv = $self->{'canvas'};
    if ($oldcv || 0) {
        $width  ||= $oldcv->cget(-width);
        $height ||= $oldcv->cget(-height);
        $bg     ||= $oldcv->cget(-bg);
        $oldcv->packForget();
    }
    
    # Create a new canvas
    $width  ||= $d_width;
    $height ||= $d_height;
    $bg     ||= $d_bg;
    my $mw = $self->{'mw'};
    my @opts = (-bg => $bg, -width => $width, -height => $height);
    my $cv = $mw->Canvas(@opts);
    $cv->pack(-expand => 1, -fill => 'both');
    $self->{'canvas'} = $cv;

    # For each client, draw its turtle
    my $pclients = $self->{'clients'} || { };
    foreach my $pc (values %$pclients) {
        my $turtle = $pc->{'turtle'};
        $self->create_turtle($pc, $turtle);
    }
}


sub rotate {
    my ($self, $x, $y, $angle, $ppoints) = @_;
    for (my $i = 0; $i < @$ppoints; $i += 2) {
        $ppoints->[$i]   -= $x;
        $ppoints->[$i+1] -= $y;
    }
    my $ppolar = $self->rect_to_polar($ppoints);
    for (my $i = 1; $i <= @$ppolar; $i += 2) {
        $ppolar->[$i] = ($ppolar->[$i] + $angle) % 360;
    }
    $ppoints = $self->polar_to_rect($ppolar);
    for (my $i = 0; $i < @$ppoints; $i += 2) {
        $ppoints->[$i]   += $x;
        $ppoints->[$i+1] += $y;
    }
    return $ppoints;
}


sub calculate_endpoint {
    my ($self, $x, $y, $angle, $dist) = @_;
    my $prect = $self->polar_to_rect([ $dist, $angle ]);
    my ($x1, $y1) = @$prect;
    $x1 += $x;
    $y1 += $y;
    return ($x1, $y1);
}


sub rect_to_polar {
    my ($self, $ppoints) = @_;
    my $ppolar = ( );
    while (@$ppoints > 1) {
        my $x = shift @$ppoints;
        my $y = shift @$ppoints;
        my $r = sqrt($x ** 2 + $y ** 2);
        my $t = $self->rad_to_deg(atan2($y, $x));
        push @$ppolar, $r, $t;
    }
    return $ppolar;
}


sub polar_to_rect {
    my ($self, $ppoints) = @_;
    my $prect = [ ];
    while (@$ppoints > 1) {
        my $r = shift @$ppoints;
        my $t = $self->deg_to_rad(shift @$ppoints);
        my $x = $r * cos($t);
        my $y = $r * sin($t);
        push @$prect, $x, $y;
    }
    return $prect;
}


sub deg_to_rad {
    my ($self, $degrees) = @_;
    my $radians = $degrees * PI / 180;
    ($radians < 0) and $radians += 6.283185307;
    return $radians;
}


sub rad_to_deg {
    my ($self, $radians) = @_;
    my $degrees = $radians * 180 / PI;
    ($degrees < 0) and $degrees += 360;
    return $degrees;
}


sub show_turtle {
    my ($self, $pc, $cmd) = @_;
    my $b_show = ($cmd eq 'st')? 1: 0;
    my $turtle = $pc->{'turtle'};
    $turtle->{'show'} = $b_show;
    $self->draw_turtle($pc, $turtle);
    $self->server_reply($pc);
}


sub change_color {
    my ($self, $pc, $cmd, $color) = @_;
    defined($color) or return $self->syntax_error($pc);

    # Allow a random color
    if (($color || "") eq 'random') {
        $color = sprintf "#%02x%02x%02x", rand 256, rand 256, rand 256
+;
    }

    my $turtle = $pc->{'turtle'};
    $turtle->{'color'} = $color;
    $self->draw_turtle($pc, $turtle);
    $self->server_reply($pc);
}


sub change_pen_state {
    my ($self, $pc, $cmd) = @_;
    my $state = ($cmd eq 'pendown')? 1: 0;
    my $turtle = $pc->{'turtle'};
    $turtle->{'pen'} = $state;
    $self->draw_turtle($pc, $turtle);
    $self->server_reply($pc);
}


sub change_pen_size {
    my ($self, $pc, $cmd, $size, @args) = @_;
    my $turtle = $pc->{'turtle'};

    # Allow a random pen size
    if (($size || "") eq "random") {
        my $min = $args[0];
        my $max = $args[1];
        defined($min) or return $self->syntax_error($pc);
        defined($max) or return $self->syntax_error($pc);
        $size = $min + rand($max - $min);
    }

    $size ||= $d_psize;
    $turtle->{'size'} = $size;
    $self->server_reply($pc);
}


sub syntax_error {
    my ($self, $pc) = @_;
    my $cmd = $pc->{'lastcmd'};
    $self->server_reply($pc, "syntax error in '$cmd'");
}


sub turn_turtle {
    my ($self, $pc, $cmd, $newang, $arg0, $arg1) = @_;

    my $turtle = $pc->{'turtle'};
    my $angle  = $turtle->{'angle'};

    # Allow a random angle of turn
    if (($newang || "") eq 'random') {
        defined($arg0) or return $self->syntax_error($pc);
        defined($arg1) or return $self->syntax_error($pc);
        $newang = $arg0 + rand($arg1 - $arg0);
    }

    # Make angles default to right angles
    defined($newang) or $newang = 90;

    # Assign the angle
    ($cmd eq 'left')  and $angle = $angle - $newang;
    ($cmd eq 'right') and $angle = $angle + $newang;
    ($cmd eq 'seth')  and $angle = $newang;

    # Normalize the angle
    while ($angle < 0)   { $angle += 360 }
    while ($angle > 360) { $angle -= 360 }

    $turtle->{'angle'} = $angle;
    $self->draw_turtle($pc, $turtle);
    $self->server_reply($pc);
}


sub move_turtle {
    my ($self, $pc, $cmd, $dist, $arg0, $arg1) = @_;
    my $wrap   = $pc->{'wrap'} || 0;
    my $turtle = $pc->{'turtle'};
    my $angle  = $turtle->{'angle'};

    # Allow a random distance
    if (($dist || "") eq 'random') {
        defined($arg0) or return $self->syntax_error($pc);
        defined($arg1) or return $self->syntax_error($pc);
        $dist = $arg0 + rand($arg1 - $arg0);
    }

    $dist ||= $turtle->{'dist'};
    (0 == $dist) and $self->syntax_error($pc);
    $turtle->{'dist'} = $dist;
    ($cmd eq 'forward')  and $angle = ($angle + 270) % 360;
    ($cmd eq 'backward') and $angle = ($angle + 90)  % 360;
    my ($x0, $y0) = ($turtle->{'x'}, $turtle->{'y'});
    my ($x1, $y1);
    if ($cmd eq 'setx' or $cmd eq 'sety' or $cmd eq 'setxy') {
        if ($cmd eq 'setxy') {
            defined($dist) or return $self->syntax_error($pc);
            defined($arg0) or return $self->syntax_error($pc);
            ($x1, $y1) = ($dist, $arg0);
        } else {
            defined($dist) or return $self->syntax_error($pc);
            ($x1, $y1) = ($x0, $y0);
            ($x1, $y1) = ($cmd eq 'setx')? ($dist, $y0): ($x0, $dist);
        }
    } else {
        ($x1, $y1) = $self->calculate_endpoint($x0, $y0, $angle, $dist
+);
    }

    my @args = ($pc, $x0, $y0, $x1, $y1);
    return $self->move_turtle_reflect(@args) if (2 == $wrap);
    return $self->move_turtle_torus(@args)   if (1 == $wrap);
    return $self->move_turtle_normal(@args); # Assume wrap == 0
}


sub move_turtle_normal {
    my ($self, $pc, $x0, $y0, $x1, $y1) = @_;
    my $turtle = $pc->{'turtle'};
    my $pen    = $turtle->{'pen'};
    my $size   = $turtle->{'size'};
    my $color  = $turtle->{'color'};

    $self->line($pen, $x0, $y0, $x1, $y1, $color, $size);
    $self->move($pc, $x1, $y1);
    return $self->server_reply($pc);
}


sub move_turtle_torus {
    my ($self, $pc, $x0, $y0, $x1, $y1) = @_;
    my $turtle = $pc->{'turtle'};
    my $pen    = $turtle->{'pen'};
    my $size   = $turtle->{'size'};
    my $color  = $turtle->{'color'};

    # Calculate (dx, dy), which don't change for torus behavior
    my ($dx, $dy) = ($x1 - $x0, $y1 - $y0);

    while (!$self->contained($x1, $y1)) {
        my $height = $self->{'height'};
        my $width  = $self->{'width'};
        if (abs($dx) < 0.0000001) {
            # Vertical line
            my $yb = ($y1 < $y0)? 0: $height;
            $self->line($pen, $x0, $y0, $x0, $yb, $color, $size);
            ($y0, $y1) = $yb? (0, $y1-$height): ($height, $y1+$height)
+;
            $self->move($pc, $x0, $y0);
        } elsif (abs($dy) < 0.0000001) {
            # Horizontal line
            my $xb = ($x1 < $x0)? 0: $width;
            $self->line($pen, $x0, $y0, $xb, $y0, $color, $size);
            ($x0, $x1) = $xb? (0, $x1-$width): ($width, $x1+$width);
            $self->move($pc, $x0, $y0);
        } else {
            # Diagonal line
            my $m = $dy / $dx;
            my $b = $y1 - ($m * $x1);
            my $xb = ($y1 > $y0)? (($height - $b) / $m): (-$b / $m);
            my $yb = ($x1 > $x0)? (($m * $width) + $b):  $b;
            my ($xn, $yn) = ($xb, $yb);
            my $crossx = ($xb > 0 and $xb < $width)?  1: 0;
            my $crossy = ($yb > 0 and $yb < $height)? 1: 0;
            if ($crossx and !$crossy) {
                # Line intercepts x-axis
                $yb = ($y1 > $y0)? $height: 0;
                $yn = $height - $yb;
                $y1 = ($y1 > $y0)? $y1 - $height: $y1 + $height;
            } elsif ($crossy and !$crossx) {
                # Line intercepts y-axis
                $xb = ($x1 > $x0)? $width: 0;
                $xn = $width - $xb;
                $x1 = ($x1 > $x0)? $x1 - $width: $x1 + $width;
            } else {
                # Line intercepts both axes
                $xb = ($x1 > $x0)? $width:  0;
                $yb = ($y1 > $y0)? $height: 0;
                ($xn, $yn) = ($width - $xb, $height - $yb);
                $x1 = ($x1 > $x0)? $x1 - $width:  $x1 + $width;
                $y1 = ($y1 > $y0)? $y1 - $height: $y1 + $height;
            }

            $self->line($pen, $x0, $y0, $xb, $yb, $color, $size);
            ($x0, $y0) = ($xn, $yn);
            $self->move($pc, $x0, $y0);
        }
    }

    # Back within canvas
    return $self->move_turtle_normal($pc, $x0, $y0, $x1, $y1);
}


sub move_turtle_reflect {
    my ($self, $pc, $x0, $y0, $x1, $y1) = @_;
    my $turtle = $pc->{'turtle'};
    my $angle  = $turtle->{'angle'};
    my $pen    = $turtle->{'pen'};
    my $size   = $turtle->{'size'};
    my $color  = $turtle->{'color'};

    while (!$self->contained($x1, $y1)) {
        # Calculate (dx, dy), which change for reflection behavior
        my ($dx, $dy) = ($x1 - $x0, $y1 - $y0);

        my $height = $self->{'height'};
        my $width  = $self->{'width'};
        if (abs($dx) < 0.0000001) {
            # Vertical line
            my $yb = ($y1 < $y0)? 0: $height;
            $self->line($pen, $x0, $y0, $x0, $yb, $color, $size);
            $y0 = $yb;
            $y1 = ($y1 < $y0)? (- $y1): (2 * $height) - $y1;
            $self->move($pc, $x0, $y0);
            $angle = $self->adjust_angle($pc, 180 - $angle);
        } elsif (abs($dy) < 0.0000001) {
            # Horizontal line
            my $xb = ($x1 < $x0)? 0: $width;
            $self->line($pen, $x0, $y0, $xb, $y0, $color, $size);
            $x0 = $xb;
            $x1 = ($x1 < $x0)? (- $x1): (2 * $width) - $x1;
            $self->move($pc, $x0, $y0);
            $angle = $self->adjust_angle($pc, 360 - $angle);
        } else {
            # Diagonal line
            my $m = $dy / $dx;
            my $b = $y1 - ($m * $x1);
            my $xb = ($y1 > $y0)? (($height - $b) / $m): (-$b / $m);
            my $yb = ($x1 > $x0)? (($m * $width) + $b):  $b;
            my $crossx = ($xb > 0 and $xb < $width)?  1: 0;
            my $crossy = ($yb > 0 and $yb < $height)? 1: 0;
            if ($crossx and !$crossy) {
                # Line intercepts x-axis
                $yb = ($y1 > $y0)? $height: 0;
                $y1 = ($y1 > $y0)? (2 * $height - $y1): (- $y1);
            } elsif ($crossy and !$crossx) {
                # Line intercepts y-axis
                $xb = ($x1 > $x0)? $width: 0;
                $x1 = ($x1 > $x0)? (2 * $width - $x1): (- $x1);
            } else {
                # Line intercepts both axes
                $xb = ($x1 > $x0)? $width:  0;
                $yb = ($y1 > $y0)? $height: 0;
                $x1 = ($x1 > $x0)? (2 * $width  - $x1): (- $x1);
                $y1 = ($y1 > $y0)? (2 * $height - $y1): (- $y1);
            }

            $self->line($pen, $x0, $y0, $xb, $yb, $color, $size);
            ($x0, $y0) = ($xb, $yb);
            $self->move($pc, $x0, $y0);
            $angle = $self->adjust_angle($pc, 180 - $angle);
        }
    }

    # Back within canvas
    return $self->move_turtle_normal($pc, $x0, $y0, $x1, $y1);
}


sub adjust_angle {
    my ($self, $pc, $newang) = @_;
    my $turtle = $pc->{'turtle'};
    while ($newang >= 360) {
        $newang -= 360;
    }
    while ($newang < 0) {
        $newang += 360;
    }
    $turtle->{'angle'} = $newang;
    $self->draw_turtle($pc, $turtle);
    return $newang;
}


sub line {
    my ($self, $pen, $x0, $y0, $x1, $y1, $color, $size) = @_;

    # Pen is up; no need to draw
    return unless $pen;

    # Get canvas and draw line
    my $cv = $self->{'canvas'};
    my @points = ($x0, $y0, $x1, $y1, -fill => $color, -width => $size
+);
    $cv->createLine(@points);
}


sub move {
    my ($self, $pc, $x, $y) = @_;

    # Set new turtle coordinates and redraw turtle
    my $turtle = $pc->{'turtle'};
    $turtle->{'x'} = $x;
    $turtle->{'y'} = $y;
    $self->draw_turtle($pc, $turtle);
}


sub contained {
    my ($self, $x1, $y1) = @_;

    my $cv     = $self->{'canvas'};
    my $width  = $cv->cget(-width);
    my $height = $cv->cget(-height);

    $self->{'width'}  = $width;
    $self->{'height'} = $height;

    return ($x1 < 0 or $x1 > $width or $y1 < 0 or $y1 > $height)? 0: 1
+;
}


1;

__END__

=head1 NAME

Language::Logo - An implementation of the Logo programming language

=head1 SYNOPSIS

    use Language::Logo;

    my $lo = new Logo(update => 20);

    $lo->command("setxy 250 256");
    $lo->command("color yellow");
    $lo->command("pendown");

    # Draw a circle
    for (my $i = 0; $i < 360; $i += 10) {
        $lo->command("forward 10; right 10");
    }

    $lo->disconnect("Finished...")


=head1 DESCRIPTION

This module provides an implementation of the Logo programming languag
+e, with
all of the necessary drawing primitives in a Tk Canvas.  The Canvas ob
+ject is
also referred to as the "screen".

The first construction of a Language::Logo object causes a server to b
+e
created in a separate process; this server then creates a Tk GUI with 
+a
Tk::Canvas for use by the client's "turtle", and responds to all reque
+sts
from the client's commands.  In this way, multiple clients may be cons
+tructed
simultaneously -- each one with its own "turtle".

In this first release, not all of the Logo language is implemented.
Rather, the primary commands available are those which directly affect
the turtle, and are related to drawing on the screen.  The intent is t
+o
use the Logo in conjunction with Perl as a sort of "hybrid" language;
Perl us used as the higher-level language layer through which all loop
constructs, conditionals, and data-manipulation is done.  This allows
for a substantial level of programming power.



=head2 Methods

=over 4

=item I<PACKAGE>->new([I<param> => I<value>, [I<param> => I<value>, ..
+.]])

Returns a newly created C<Language::Logo> object.  No arguments are re
+quired,
but the following are allowed (each of which must be accompanied by a 
+value):

=item name I<client name>

the name of the current client.  (The default is a uniquely generated 
+name;
this parameter is not currently used, but may be used in the future to
+ force
synchronization between clients in a multiple-client scenario).

=item debug I<0 or 1>

a zero value turns debugging off (the default); a nonzero value turns
debugging on.

=item title I<main window title>

the title of the Tk window (the default is the name and current versio
+n
number of the module).

=item bg I<background color>

the starting background color of the screen (the default is black).

=item width I<screen width>

the starting width of the screen (the default is 512 pixels).

=item height I<screen height>

the starting height of the screen (the default is 512 pixels).

=item update I<update interval>

the starting update value for controlling the number of milliseconds t
+o
delay before reentering Tk's idle loop.  The fastest is therefore a va
+lue
of 1 (which updates up to 1000 times per second).

=item host I<server address>

the host computer where the server is running (the default is to use t
+he
server on the local machine).  If the host is on a remote machine, it 
+is
assumed that the remote machine has already constructed at least one
Language::Logo object which is currently running its own local server.

=item port I<server port>

the port at which to connect to the server (the default is port 8220).

=back

=item I<$OBJ>->disconnect([I<message>])

=over 4

Disconnects from the server.  If a message is supplied, the user is
prompted with the message, and the program waits until a newline is
typed before disconnecting.  This is especially useful if the client
is the only one (or last one) connected; in which case the server will
also exit upon disconnect.

=item I<$OBJ>->interact()

Enters interactive mode, whereby the user can issue Logo commands
one-at-a-time.  Queries may also be used to retrieve various informati
+on
about the state of the current client's object.

=item I<$OBJ>->query(I<parameter>)

=item I<$OBJ>->ask(I<parameter>)

Queries the object's state to get the current value for a given parame
+ter.

=item I<$OBJ>->command(I<command string>)

=item I<$OBJ>->cmd(I<command string>)

Sends a Logo command to the server.  Multiple commands may be sent at 
+the
same time by inserting a semi-colon ';' between them.  The following c
+ommands
are available:

=over 4

=item "background" or "bg" (1 argument)

Sets the background color of the screen.  Colors must be valid Tk colo
+rs,
specified either by name ("blue") or hex triplet ("#0000ff").  For exa
+mple,
"background orange".

=item "backward" or "bk" (1 argument)

Moves the turtle backwards the specified number of pixels.  If the pen
+ is
down, a line is drawn with the current color and pensize.  For example
+,
"backward 100".
[Contrast "forward"]

=item "clear" or "cs" (no arguments)

Clears the screen entirely.

=item "color" or "co" (1 argument)

Changes the current turtle color to the specified color.  Both the tur
+tle
and any items drawn by the turtle (when the pen is down) will appear i
+n this
color.  For example, "color white".

=item "forward" or "fd" (1 argument)

Moves the turtle forwards the specified number of pixels.  If the pen 
+is down,
a line is drawn with the current color and pensize.  For example, "for
+eward
100".
[Contrast "backward"]

=item "height" or "h " (1 argument)

Changes the current screen height to the specified number of pixels.
Note that, as this change applies to the Tk Canvas, it affects all
clients which are connected to the server.  For example, "height 768".
[Contrast "width"]

=item "hideturtle" or "ht" (no arguments)

Makes the turtle invisible.  Note that this is unrelated to the curren
+t
state of the pen; lines will still be drawn or not, depending on wheth
+er
the pen is up or down.  [Contrast "showturtle"]

=item "home" or "hm" (no arguments)

Puts the turtle in its original location, at the center of the screen,
+ with
a heading of due North (0 degrees).

=item "left" or "lt" (1 argument)

Rotates the turtle to the left by the specified angle, given in degree
+s.
Thus, an angle of 90 degrees will make an exact left turn; an angle of
180 degrees will make the turtle face the opposite direction.  For exa
+mple,
"left 45".  [Contrast "right"]

=item "penup" or "pu" (no arguments)

Changes the state of the turtle's "pen" so that subsequent movements o
+f the
turtle will no longer result in lines being drawn on the screen.  As a
+ visual
cue, the turtle will appear -without- the circle drawn around the curr
+ent
point.  [Contrast "pendown"]

=item "right" or "rt" (1 argument)

Rotates the turtle to the left by the specified angle, given in degree
+s.
Thus, an angle of 90 degrees will make an exact right turn; an angle o
+f
180 degrees will make the turtle face the opposite direction.  For exa
+mple,
"right 135".  [Contrast "left"]

=item "seth" or "sh" (1 argument)

Changes the turtle's heading to the specified angle.  The angle given 
+is
an absolute angle, in degrees, representing the clockwise spin relativ
+e to
due North.  Thus, a value of 0 is due North, 90 is due East, 180 is du
+e
South, and 270 is due West.  For example, "seth 225".

=item "setx" or "sx" (1 argument)

Changes the turtle's x-coordinate to the specified pixel location on t
+he
screen, without changing the value of the current y-coordinate.  The v
+alue
given is an absolute location, not one related to the previous positio
+n.
If the pen is down, a line will be drawn from the old location to the 
+new
one.  For example, "setx 128".  [Contrast "sety", "setxy" ]

=item "setxy" or "xy" (2 arguments)

Changes the turtle's x and y coordinates to the specified pixel locati
+ons
on the screen, without changing the value of the current x-coordinate.
The first argument is the new x-coordinate, the second the new y-coord
+inate.
The position of the new point represents an absolute location, not one
+ related
to the previous position.  If the pen is down, a line will be drawn fr
+om the
old location to the new one.  For example, "setxy 10 40".  [Contrast "
+setx",
"sety" ]

=item "sety" or "sy" (1 argument)

Changes the turtle's y-coordinate to the specified pixel location on t
+he
screen, without changing the value of the current x-coordinate.  The v
+alue
given is an absolute location, not one related to the previous positio
+n.
If the pen is down, a line will be drawn from the old location to the 
+new
one.  For example, "sety 256".  [Contrast "setx", "setxy" ]

=item "showturtle" or "st" (no arguments)

Makes the turtle visible.  Note that this is unrelated to the current 
+state
of the pen; lines will still be drawn or not, depending on whether the
+ pen
is up or down.  [Contrast "hideturtle"]

=item "pendown" or "pd" (no arguments)

Changes the state of the turtle's "pen" so that subsequent movements o
+f the
turtle will draw the corresponding lines on the screen.  As a visual c
+ue,
the turtle will appear with a circle drawn around the current point.
[Contrast "penup"]

=item "pensize" or "ps" (1 argument)

Changes the width of the turtle's "pen" to the given number of pixels,
+ so
that subsequent drawing will be done with the new line width.

=item "width" or "w " (1 argument)

Changes the current screen width to the specified number of pixels.
Note that, as this change applies to the Tk Canvas, it affects all
clients which are connected to the server.  For example, "width 1024".
[Contrast "height"]

=item "wrap" (1 argument)

Changes the screen "wrap" type on a per-client basis, to the specified
argument, which must be a value of 0, 1 or 2.  See L<WRAP TYPES> below
for more detailed information.

=item "update" or "ud" (1 argument)

Changes the current update value which controls the number of millisec
+onds to
delay before reentering Tk's idle loop.  A value of 1000 is the slowes
+t; it
will cause a delay of 1 second between updates.  A value of 1 is the f
+astest,
it will make the Tk window update up to 1000 times each second.

=back

=back

=head1 RANDOM VALUES

  Some of the commands can take as an argument the word "random", poss
+ibly
  followed by more arguments which modify the random behavior.  For ex
+ample,
  the command "color random" chooses a new random color for the pen, w
+hereas
  "seth random 80 100" sets the turtle heading to a random angle betwe
+en 80
  and 100 degrees.

  The number of arguments following "random" depend on the context:
 
      angles ........ 2 arguments (mininum angle, maximum angle)
      distances ..... 2 arguments (minimum distance, maximum distance)
      other ......... no arguments


=head1 WRAP TYPES

  The parameter 'wrap' defines the behavior that occurs when the
  turtle's destination point is outside of the display window.

  The allowable values for wrap are:

    0:  Normal "no-wrap" behavior
    1:  Toroidal "round-world" wrap
    2:  Reflective wrap

    Consider the following diagram:

                 +---------------o---------------+
                 |              /| (xb0,yb0)     |
                 |         <C> /                 |
                 |            /  |               |
                 |   (x2,y2) o                   |
                 | [wrap = 1]    |               |
                 |                               |
                 | [wrap = 2]    |               |
                 |   (x3,y3) o       @ (x0,y0)   |
                 |            \  |  /            |
                 |         <D> \   / <A>         |
                 |              \|/              |
                 +---------------o---------------+
                                / (xb1,yb1)
                           <B> /     
                              /  
                     (x1,y1) @ [wrap = 0]

    Point (x0,y0) represents the current location of the turtle, and
    (x1,y1) the destination point.  Since the destination is outside
    of the display window, the behavior of both the turtle and the
    drawn line will be governed by the value of the 'wrap' parameter.

    Since line segment <A> is in the visible window, it will be drawn
    in all cases.  Since line segment <B> is outside of the visible
    window, it will not be visible in all cases.

    When (wrap == 0), only line segment <A> will be visible, and the
    turtle, which ends up at point (x1,y1), will NOT.

    When (wrap == 1), the window behaves like a torus, so that line
    segment <B> "wraps" back into the window at the point (xb0,yb0).
    Thus line segments <A> and <C> are visible, and the turtle ends
    up at point (x2,y2).

    When (wrap == 2), the borders of the window are reflective, and
    line segment <B> "reflects" at the point (xb1,yb1).  Thus line
    segments <A> and <D> are visible, and the turtle ends up at the
    point (x3,y3).


=head1 EXAMPLES

The following programs show some of the various ways to use the
Language::Logo object.

    #################################
    ###  Randomly-colored designs ###
    #################################
    use Language::Logo;

    my $lo = new Logo(title => "Logo Demonstration");
    $lo->command("update 2; color random; pendown; hideturtle");

    for (my $i = 1; $i < 999; $i++) {
        my $distance = $i / 4;
        $lo->command("forward $distance; right 36.5");
        $lo->command("color random") if not ($i % 50);
    }

    $lo->disconnect("Type [RETURN] to finish...");


    ################################################
    ### Randomly placed "rings" of random widths ###
    ################################################
    use Language::Logo;

    my $lo = new Logo(title => "Random rings", update => 5);
    $lo->cmd("wrap 1");    # Toroidal wrap

    while (1) {
        $lo->cmd("pu; sx random 1 512; sy random 1 512; pd; co random"
+);
        $lo->cmd("pensize random 1 32");
        my $dist = 5 + (rand(50));
        for (my $i = 0; $i <= 360; $i += $dist) {
            $lo->cmd("fd $dist; rt $dist");
        }
    }


    ###################################
    ### Fullscreen "Frenetic Lines" ###
    ###################################
    use Language::Logo;

    my $lo = new Logo(width => 1024, height => 768, update => 3);

    # Change "1" to "2" for reflection instead of torus
    $lo->cmd("wrap 1");

    $lo->cmd("setx random 0 800");  # Choose random x-coordinate
    $lo->cmd("sety random 0 800");  # Choose random y-coordinate
    $lo->cmd("rt random 0 360");    # Make a random turn
    $lo->cmd("pd");                 # Pen down
    $lo->cmd("ht");                 # Hide turtle

    my $size = 1;  # Starting pen size

    while (1) {
        if (++$size > 48) {
            $size = 1;                  # Reset the size
            $lo->cmd("cs");             # Clear the screen
        }
        $lo->cmd("ps $size");           # Set the pensize
        $lo->cmd("color random");       # Random color
        $lo->cmd("fd 9999");            # Move the turtle
        $lo->cmd("rt random 29 31");    # Turn a random angle
    }


=head1 BUGS

The following items are not yet implemented, but are intended to be
addressed in a future version of the library:

=over 4

=item *

There is no provision for compiling "pure" Logo language code.  Such
capabilities as loops, conditionals, and subroutines must be handled
in the calling Perl program.

=item *

There is no way to change the processing speed on a per-client basis.

=item *

There is no way to synchronize multiple clients to wait for one anothe
+r.

=item *

There are still some commands which do not support a "random" paramete
+r
("setxy" and "background", for example).

=item *

There is currently no analog command to "setxy" ("offxy" ?) which chan
+ges
the position of the turtle's location I<relative> to the current point
+, as
opposed to setting it absolutely.

=item *

There is no way to synchronize multiple clients to wait for one anothe
+r.

=item *

It would be nice to be able to draw things other than lines; for examp
+le
ovals, polygons, etc.  It would also be nice to be able fill these wit
+h
a given "fill" color.

=item *

There needs to be a way to save the current screen to a file (eg. as
PostScript).


=head1 AUTHOR

John C. Norton        jcnorton@charter.net

Copyright (c) 2007 John C. Norton. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

=head1 VERSION

Version 1.000  (January 2007)

=head1 REQUIREMENTS

The Tk module is required.

=head1 SEE ALSO

perl(1)

=cut
[download]

Its documentation is in POD format; all of the basic commands are there, as well as some examples of usage.

And here are some scripts I've written to demonstrate the module:

#!/usr/bin/perl -w
#
# "logo.pl" -- a simple Logo interpreter
use strict;
use warnings;
use Language::Logo;
my $lo = new Logo()->interact();
[download]

#!/usr/bin/perl -w
#
#  "spiral.pl" (a number of other programs call this)
#
#  Draws one or more spirals using the Logo library
#
#  070108 by liverpole
#

# Strict
use strict;
use warnings;

# Libraries
use lib ".";
use Language::Logo;
use Data::Dumper;
use File::Basename;
use Getopt::Long;

# Globals
my $iam  = basename $0;
my $b_toroid = 0;
my $b_reflect = 0;
my $b_debug = 0;
my $bg = "";
my $host = "";
my $b_hide = 0;
my $color = "";
my $update = "";
my $width = "";
my $maxsize = 512;
my $minsize = 8;
my $minang = -1;
my $incr = 2;
my $startsize = 0;
my $nticks = 0;
my $tickcnt = 0;
my $pos = 0;
my $syntax = "

    syntax:  $iam  [switches]  <angle>

    Uses Logo to create a spiral with the specified update and angle.

    The update specifies the update interval of the gui (iterations
    per second between 1 (very fast) and 1000 (very slow)).

    Switches:
        -d ............ starts the Logo server in debug mode
        -t ............ 'toroidal' -- sets wrap to 1
        -r ............ 'reflect'  -- sets wrap to 2
        -h <host> ..... connects to server on given host (':' = localh
+ost)
        -x ............ hides the turtle
        -a <min> ...... use a random angle from <min> to the given <an
+gle>
        -b <color> .... specifies the Canvas background color
        -c <color> .... specifies the pen color
        -u <update> ... specifies the update speed
        -w <width> .... specifies the pen width
        -s <size> ..... specify the starting size
        -i <incr> ..... increment the size each time by <incr>
        -n <nticks> ... change the color after <nticks> 'ticks'
        -p <x,y> ...... make the starting position (X, Y)

";

# Command-line
my $result = GetOptions(
    "d"   => \$b_debug,
    "x"   => \$b_hide,
    "t"   => \$b_toroid,
    "r"   => \$b_reflect,
    "b=s" => \$bg,
    "c=s" => \$color,
    "h=s" => \$host,
    "u=s" => \$update,
    "w=s" => \$width,
    "a=s" => \$minang,
    "s=s" => \$startsize,
    "i=s" => \$incr,
    "n=s" => \$nticks,
    "p=s" => \$pos,
);
$result or die $syntax;
(my $angle = shift) or die $syntax;

# Main program

# Create Logo object
my @opts = (debug => $b_debug);
$bg   and push @opts, bg   => $bg;   # Initial canvas color
$host and push @opts, host => $host; # Connect to an existing server
my $lo = new Logo(@opts);

# Issue logo commands
$update and $lo->cmd("update $update");
if ($startsize) {
    my $half     = $startsize / 2;
    my $quarter  = $half / 2;
    $lo->cmd("rt 90; bk $quarter; lt 90; bk $half");
}
$width     and $lo->cmd("pensize $width");
$color     and $lo->cmd("color   $color");
$b_hide    and $lo->cmd("ht");
$b_toroid  and $lo->cmd("wrap 1");
$b_reflect and $lo->cmd("wrap 2");
if ($pos) {
    ($pos =~ /(\d+),(\d+)/) or die "$iam:  invalid position '$pos'\n";
    my ($x, $y) = ($1, $2);
    $lo->cmd("xy $x $y");
}
$lo->cmd("pendown");

# Create spiral
spiral($startsize, $angle);

# Disconnect from main client
$host or $lo->disconnect("Type [RETURN] to disconnect ... ");


# Subroutines
sub spiral {
    my ($size, $angle) = @_;

    while (($incr <= 0 and $size >= $minsize) ||
        ($incr >= 0 and $size <= $maxsize)) {
        $lo->cmd("forward $size");                 # Move & draw turtl
+e
        if ($minang >= 0) {
            $lo->cmd("rt random $minang $angle");  # Make a random tur
+n
        } else {
            $lo->cmd("rt $angle");                 # Turn <angle> degr
+ees
        }

        # Change pen color randomly
        if ($nticks and ++$tickcnt >= $nticks) {
            $lo->cmd("color random");
            $tickcnt = 0;
        }

        $size += $incr;
    }
}
[download]

#!/usr/bin/perl -w
#
# "boxes.pl" -- randomly colored boxes
use strict;
use warnings;

system("spiral.pl -t -x -u 1 -n 10 -s 100 -w 8 -p 200,300 -i -.01 -a 8
+5 95")
[download]

#!/usr/bin/perl -w
#
# "double.pl" -- an example of 2 simultaneous clients
use strict;
use warnings;

# Main program
if (fork) {
    system("flowers.pl  35.6");
} else {
    system("flowers.pl -h : 324.4");
}
[download]

#!/usr/bin/perl -w
#
# "flowers.pl" -- uses the "spiral.pl" program to
# create colorful growing patterns.
#
# Uses Language::Logo (in conjunction with the spiral program) to crea
+te
# different-colored growing 'flowers'.
#
#  070113 by liverpole
#

# Strict
use strict;
use warnings;

# Libraries
use File::Basename;
use Getopt::Long;

# Globals
my $iam  = basename $0;
my $host = "";
my $b_toroid = 0;
my $b_reflect = 0;
my $syntax = "
    syntax:  $iam  [switches]  <angle>

    Uses Logo (in conjunction with the spiral program) to create
    different-colored growing 'flowers'.

    Try, for example, one of:

        $iam  33
        $iam  35.9
        $iam  36
        $iam  38
        $iam  90.1
        $iam  91
        $iam  100
        $iam  134
        $iam  300

    Switches:
        -t ............ 'toroidal' -- sets wrap to 1
        -r ............ 'reflection' -- sets wrap to 2
        -h <host> ..... connects to server on given host
";


# Command-line
my $result = GetOptions(
    "h=s" => \$host,
    "t"   => \$b_toroid,
    "r"   => \$b_reflect,
);
$result or die $syntax;
(my $angle = shift) or die $syntax;
my $args = "-x -c gold -u 1 -n 90 -s 50 -i .25";
$b_toroid and $args  .= " -t";
$b_reflect and $args .= " -r";
$host and $args .= " -h $host";

# Main program
system("spiral.pl $args $angle");
[download]

#!/usr/bin/perl -w
#
#  "lines.pl" -- draws random colored lines using Logo, either with
#  a wrap of 1 (torus) or a wrap of 2 (reflection).
#
#  070116 by liverpole
#

# Strict
use strict;
use warnings;

# Libraries
use lib ".";
use Language::Logo;
use File::Basename;
use Data::Dumper;
use Getopt::Long;

# User-defined
my $nticks  = 100;      # Change color after nticks
my $tickcnt = 0;        # Number of ticks so far
my $color   = 'yellow'; # Starting pen color
my $size    = 2;        # Pen size
my $maxsize = 16;       # Maximum pen size
my $mindis  = 5;        # Minimum distance to advance
my $maxdis  = 50;       # Maximum distance to advance
my $width   = 500;      # Screen width
my $height  = 500;      # Screen height
my $dist    = 9999;     # Distance to move forward

# Globals
my $iam  = basename $0;
my $b_reflect = 0;
my $syntax = "
    syntax:  $iam  [switches]  <min angle>  <max angle>

    Tests round-world scenarios with lines which continuously change a
+ngles.
    Each time the color changes, a new random angle between <min angle
+> and
    <max angle> is chosen, and the line is rotated by that amount.

    Switches:
        -r ............ reflect mode (wrap 2) instead of torus mode (w
+rap 1)

    Try, for example, one of:

        $iam   29  31
        $iam   85  95
        $iam  170 190

";


# Command-line
my $result = GetOptions(
    "r" => \$b_reflect,
);
$result or die $syntax;
(my $minang = shift) or die $syntax;
(my $maxang = shift) or die $syntax;

# Main program

# Create Logo object
my $lo = new Logo(width => $width, height => $height);
my $wrap = $b_reflect? 2: 1;
$lo->command("wrap $wrap");
$lo->command("update 5");
$lo->command("pu");                      # Pen-up
$lo->command("setx random 0 800");       # Choose random x-coordinate
$lo->command("sety random 0 800");       # Choose random y-coordinate
$lo->command("rt random 0 360");         # Make a random turn
$lo->command("pendown; color $color");   # Start drawing
$lo->command("ht");                      # Hide turtle

while (1) {
    if (++$size > $maxsize) {
        $size = 1;
        $lo->command("cs");
    }
    $lo->command("ps $size");
    $lo->command("color random");
    $lo->command("fd $dist");
    $lo->command("rt random $minang $maxang");
}
[download]