L-SYSTEMS-EX

L-systems (Lindenmayer systems) are a parallel rewriting system invented by biologist Aristid Lindenmayer in 1968 to model plant growth. They consist of an axiom (starting string) and a set of production rules that replace characters in parallel at each iteration.

The resulting string is interpreted by a turtle — a cursor that moves around the canvas, drawing lines as it goes. Branching structures are created with [ (push state) and ] (pop state), allowing recursive tree-like forms.

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Turtle commands
Characters in theForward field move forward drawing a line (all identical; different symbols allow rules to target specific ones).
Current forward chars: F A G S D
+ — Turn right by angle
- — Turn left by angle
[ — Save position & angle (push stack)
] — Restore saved position & angle (pop stack)

Colors
0–7   Set color (configurable in the Colors row above)

Variables (inert / no-op)
All other characters likeX, Y, etc. are passed through rules unchanged and ignored by the turtle. They act as expandable placeholders.