initial commit

README.md

@@ -0,0 +1,35 @@
+# Lindenmayer Turtle Generator
+
+draws a lindenmayer system using simple turtle graphics.
+
+currently very basic, models the following system:
+
+```
+# genesis
+X
+
+# rules
+F -> FF
+X -> X -> F-[[X]+X]+F[+FX]-X
+```
+
+is also slow and badly written, ¯\_(ツ)_/¯
+
+## dependencies
+
+```
+raco pkg install htdp-lib
+raco pkg install pict-lib
+```
+
+## running
+
+> WARNING: will overwrite 'test-plant.png' in working directory
+
+```
+racket lindenmayer.rkt
+```
+
+## author
+
+theArborist

lindenmayer.rkt

@@ -0,0 +1,62 @@
+#lang racket
+
+(require graphics/value-turtles)
+(require file/convertible)
+
+(define forward 3)
+(define theta 20)
+(define generations 6)
+
+(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)]
+    [else `(,sym)]))
+
+(define (season plant)
+  (foldr append '()
+         (map tend plant)))
+
+(define (grow seed years)
+  (if (<= years 0)
+      seed
+      (grow (season seed) (- years 1))))
+
+(define init-turtle
+  (set-pen-width (turtles 600 800 300 400 (/ pi -2))
+                 1))
+(define state '())
+
+(define (step-turtle op turtle)
+  (cond
+    [(eq? op 'F) (draw forward turtle)]
+    [(eq? op 'm) (turn theta turtle)]
+    [(eq? op 'p) (turn (* -1 theta) turtle)]
+    [(eq? op 'l) (begin (set! state
+                              (cons (turtle-state turtle)
+                                    state))
+                        turtle)]
+    [(eq? op 'r) (restore-turtle-state turtle
+                   (begin (let ([s (car state)])
+                            (set! state (cdr state))
+                            s)))]
+    [else turtle]))
+
+(define (run-turtle plant turtle)
+  (if (null? plant)
+    turtle
+    (run-turtle (cdr plant)
+                (step-turtle (car plant) turtle))))
+
+(define (write-plant turtle filename)
+  (let ([file (open-output-file filename #:exists 'replace)]
+        [pict (convert (turtles-pict turtle) 'png-bytes)])
+    (write-bytes pict file)))
+
+(define (test-plant)
+  (let ([plant (grow '(X) generations)])
+    (begin (set! state '())
+           (write-plant (run-turtle plant init-turtle)
+                        "test-plant.png"))))
+
+(test-plant)