\input TeX4ht.sty
 \Preamble{html,sty}      \EndPreamble
 
 \input  ProTex.sty
 \AlProTex{java,<<<>>>,list,title,`}
 
 
 \HCode{<APPLET CODE="turtle.class" WIDTH="300" HEIGHT="300"
 > </APPLET>}
 
 
 \HPage{code}
 
 A mini-turtle program.
 
 \<turtle\><<<
 import java.applet.*;
 import java.awt.*;
 public class turtle extends Applet
 {
 
    Graphics g;
    `<vars`>
    `<turtle functions`>
    public void init()
    {
      `<initial state`>
      `<draw interface`>
    }
    public void paint(Graphics g) {
      this.g = g;
      `<execute commands`>
    }
    public boolean action(Event e,Object o)
    {
      `<get command`>
      repaint();
      return true;
    }
 
 }
 >>>
 
 
 The turtle can move forward without trace, move forward
 while tracing its path, and rotate.
 
 
 \<turtle functions\><<<
    void Move(int x, int y){ this.x += x;  this.y -= y; }
 
    void Move(int r){ x += (int) (r * Math.cos(d));
                      y -= (int) (r * Math.sin(d)); }
 
    void Line(int x, int y){
       g.drawLine( this.x, this.y,  this.x+x, this.y-y );
       Move(x,y);
    }
    void Line(int r){
     Line(   (new Double(r * Math.cos(d))).intValue(),
             (new Double( r * Math.sin(d) )).intValue() ); }
 
    void Rotate(int d){
       this.d += d * 3.14  / 180;
       while( 6.28 < this.d ){ this.d -= 6.28; }
       while( this.d < 0 ){ this.d += 6.28; }
    }
 
 >>>
 
 
 The text field may be modified by the users.
 
 \<vars\><<<
 Button moveButton,
        lineButton,
        clearButton,
        rotateButton;
 TextField in;
 >>>
 
 
 \<draw interface\><<<
 clearButton  = new Button("Clear");   add(clearButton);
 moveButton   = new Button("Move");    add(moveButton);
 lineButton   = new Button("Line");    add(lineButton);
 rotateButton = new Button("Rotate");  add(rotateButton);
 in           = new TextField(3);      add(in);
 in.setText( "50" );
 >>>
 
 
 \<execute commands\><<<
       int i;
   x = 150; y = 150; d = 0;
   for( i=0; i<N; i+=2 ){
 
      switch( command[i] ) {
 
 case   `<Line op`>:{    Line( command[i+1] ); break; }
 case   `<Move op`>:{    Move( command[i+1] ); break; }
 case `<Rotate op`>:{  Rotate( command[i+1] ); break; }
 
 }
 }
 >>>
 
 \<get command\><<<
 if("Clear".equals(o)) {  `<initial state`>  }
 else{
 
    if(  "Line".equals(o)){  command[N]=`<Line op`>;   }
    if(  "Move".equals(o)){  command[N]=`<Move op`>;   }
    if("Rotate".equals(o)){  command[N]=`<Rotate op`>; }
 
    String s =  new String( in.getText() );
    Integer i = new  Integer(     s  );
    command[N+1]=   i.intValue();
    N+=2;
 
 }
 >>>
 
 \<vars\><<<
 int command[] = new int[300];
 >>>
 
 \<Line op\><<<
 1
 >>>
 
 \<Move op\><<<
 2
 >>>
 
 \<Rotate op\><<<
 3
 >>>
 
 
 \<initial state\><<<
 N = 0;
 >>>
 
 \<vars\><<<
 int N;
 int x, y;
 double d;
 >>>
 
 
 \OutputCode\<turtle\>
 
 \EndHPage{}
 
 \bye