added line variables

lindenmayer.rkt

@@ -3,14 +3,16 @@
 (require graphics/value-turtles)
 (require file/convertible)
 
-(define forward 3)
+(define start '(X))
+(define forward 4)
 (define theta 20)
-(define generations 6)
+(define generations 7)
+(define thick 8)
 
 (define (tend sym)
   (cond
     [(eq? sym 'F) '(F F)]
-    [(eq? sym 'X) '(F m l l X r p X r p F l p F X r m X)]
+    [(eq? sym 'X) '(d F m l l X r p X r p F l p F X r m X)]
     [else `(,sym)]))
 
 (define (season plant)
@@ -24,7 +26,7 @@
 
 (define init-turtle
   (set-pen-width (turtles 600 800 300 400 (/ pi -2))
-                 1))
+                 thick))
 (define state '())
 
 (define (step-turtle op turtle)
@@ -32,14 +34,25 @@
     [(eq? op 'F) (draw forward turtle)]
     [(eq? op 'm) (turn theta turtle)]
     [(eq? op 'p) (turn (* -1 theta) turtle)]
+    [(eq? op 'u) (set-pen-width turtle
+                   (+ 1 (turtles-pen-width turtle)))]
+    [(eq? op 'd) (set-pen-width turtle
+                   (- (turtles-pen-width turtle) 1))]
     [(eq? op 'l) (begin (set! state
                               (cons (turtle-state turtle)
                                     state))
+                        (set! thick
+                              (cons (turtles-pen-width turtle)
+                                    thick))
                         turtle)]
-    [(eq? op 'r) (restore-turtle-state turtle
-                   (begin (let ([s (car state)])
+    [(eq? op 'r) (let ([s (car state)]
+                       [t (car thick)])
+                   (begin 
                      (set! state (cdr state))
-                            s)))]
+                     (set! thick (cdr thick))
+                     (set-pen-width
+                       (restore-turtle-state turtle s)
+                       t)))]
     [else turtle]))
 
 (define (run-turtle plant turtle)
@@ -54,7 +67,7 @@
     (write-bytes pict file)))
 
 (define (test-plant)
-  (let ([plant (grow '(X) generations)])
+  (let ([plant (grow start generations)])
     (begin (set! state '())
            (write-plant (run-turtle plant init-turtle)
                         "test-plant.png"))))