(    Turtle Graphics I, screen 1          )››DECIMAL››TABLE SINES›0000 , 0175 , 0349 , 0523 , 0698 ,›0872 , 1045 , 1219 , 1392 , 1564 ,›1736 , 1908 , 2079 , 2250 , 2419 ,›2588 , 2756 , 2924 , 3090 , 3256 ,›3420 , 3584 , 3746 , 3907 , 4067 ,›4226 , 4384 , 4540 , 4695 , 4848 ,›5000 , 5150 , 5299 , 5446 , 5592 ,›5736 , 5878 , 6018 , 6157 , 6293 ,›6428 , 6561 , 6691 , 6820 , 6947 ,›7071 , 7193 , 7314 , 7431 , 7547 ,›7660 , 7771 , 7880 , 7986 , 8090 ,›8192 , 8290 , 8387 , 8480 , 8572 ,›8660 , 8746 , 8829 , 8910 , 8988 ,›9063 , 9135 , 9205 , 9272 , 9336 ,›9397 , 9455 , 9511 , 9563 , 9613 ,›9659 , 9703 , 9744 , 9781 , 9816 ,›9848 , 9877 , 9903 , 9925 , 9945 ,›9962 , 9976 , 9986 , 9994 , 9998 ,›10000 , -->›››(    Turtle Graphics I, screen 2       )››: (SIN)    ( n1 --- n2 )›      DUP 90 > IF›  180 SWAP - THEN›            SINES ;››: SIN      ( n1 --- n2 )›  ( Returns 10000 times the sine )›  ( of n1 degrees. )›                 360 MOD›              DUP 0< IF›            360 + THEN›          DUP 180 > IF›  180 - (SIN) MINUS ELSE›              (SIN) THEN ;››: COS    ( n1 --- n2 )›  ( Returns 10000 times the cosine )›  ( of n1 degrees. )›  360 MOD   90 + SIN ;››-->›››( 32 Turtle Graphics I, screen 3       )›: SIN*   ( n1 n2 --- n3 )›  ( Returns n1 times the sine of )›  ( n2 degrees. )›  SIN 10000 */ ;››: COS*   ( n1 n2 --- n3 )›  ( Returns n1 times the cosine of )›  ( n2 degrees. )›  COS 10000 */ ;››-->›››( 33 Turtle Graphics I, screen 4a      )››0 VARIABLE TO-FLAG››CODE TO   ( --- )›  1 # LDA, TO-FLAG STA,›      NEXT JMP, END-CODE››: VALUE›                         0 CONSTANT›                              ;CODE›              TO-FLAG LDA, 0= IF,›         2 # LDY, W )Y LDA, PHA,›  INY, W )Y LDA, PUSH JMP, ELSE,›          0 # LDA, TO-FLAG STA,›   BOT LDA, 2 # LDA, W )Y STA,›    BOT 1+ LDA, INY, W )Y STA,›                 POP JMP, THEN,›                      END-CODE››-->›››( 34 Turtle Graphics I, screen 4b      )››0 VARIABLE TO-FLAG››: TO›  1 TO-FLAG ! ;››: VALUE›          <BUILDS 0 ,›  DOES> TO-FLAG @ IF›        0 TO-FLAG !›             !   ELSE›             @   THEN ;›››-->›››(    Turtle Graphics I, screen 5      )››VOCABULARY CLIPPING  IMMEDIATE››CLIPPING DEFINITIONS››VALUE LEFT          VALUE TOP›VALUE RIGHT         VALUE BOTTOM››2 BASE !››: CODE    ( p --- n )›                         0›             OVER TOP < IF›     1000 + SWAP DROP ELSE›          SWAP BOTTOM > IF›               0100 + THEN›                       THEN›             OVER LEFT < IF›     0001 + SWAP DROP ELSE›          SWAP RIGHT > IF›               0010 + THEN›                       THEN ;›-->››(    Turtle Graphics I, screen 6       )››VALUE X1›VALUE Y1›VALUE C1›VALUE X2›VALUE Y2›VALUE C2›VALUE C››: CLIP_X    ( n1 --- n2 )›      Y1 _›   X2 X1 _›   Y2 Y1 _›  */  X1 +;››: CLIP_y    ( n1 --- n2 )›      X1 _›   Y2 Y1 _›   X2 X1 _›  */  Y1 +;››-->›››( 37 Turtle Graphics I, screen 7        )››2 BASE !››: WHERE?    ( --- p )›                     C 0001 AND IF›           LEFT LEFT CLIP_Y ELSE›                   C 0010 AND IF›           RIGHT  RIGHT CLIP_Y  ELSE›                   C 0100 AND IF›       BOTTOM CLIP_X  BOTTOM ELSE›                    C 1000 AND IF›            TOP CLIP_X  TOP  THEN›                              THEN›                               THEN›                                THEN ;›DECIMAL››: HERE!   ( p --- )›                                C C1 = IF›  TO Y1  TO X1  X1 Y1 CODE TO C1  ELSE›  TO Y2  TO X2  X2 Y2 CODE TO C2  THEN ;››-->›››( 38 Turtle Graphics I, screen 8       )››FORTH DEFINITIONS››: CLIP    ( p1 p2 --- p1' p2' t )›          (       or            )›          ( p1 p2 --- f         )›                           CLIPPING›   TO Y2   TO X2  X2 Y2 CODE TO C2›   TO Y1   TO X1  X1 Y1 CODE TO C1›                             BEGIN›                    C1 C2 OR WHILE›                     C1 C2 AND IF›                        0 ;S THEN›                            C1 IF›                     C1 TO C ELSE›                     C2 TO C THEN›               WHERE? HERE! REPEAT›                     X1 Y1 X2 Y2 1 ;››-->›››( 39 Turtle Graphics I, screen 9       )››: GRAPHICS    ( n --- )›   ( Clears the screen and sets it up )›   ( for graphics mode n with a text )›   ( window. )›   >R    SETUP S   CLOSE S›    SPLIT-SCREEN    R> GR. ;››: LINE    ( p1 p2 --- )›   ( Displays whatever piece of the )›   ( line from p1 to p2 is within )›   ( the clipping window. )›        CL# @ COLOR›            CLIP IF›   PLOT DRAWTO THEN ;››;S›