Turtle Graphics

Turtle graphics is a style of computer drawing based on preserved state (position and orientation) and a small number of operations against that state (forward, turn, pen up & down). SeymourPapert promoted (invented?) turtle graphics and the associated turtle geometry as a simplification that made computers and algorithmic thought accessible to kids. The state was called the turtle and programs taught the turtle how to draw.

See LogoLanguage.

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  to draw-a-box 
forward 10
turn 90
forward 10
turn 90
forward 10
turn 90
forward 10
turn 90

  to draw-a-window
draw-a-box
turn 90
draw-a-box
turn 90
draw-a-box
turn 90
draw-a-box
turn 90

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A Lindenmayer System is a 3-dimensional turtle graphics system tuned to draw fractals. FractalLifeEngine is an example of one:

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http://flea.sourceforge.net