Editing L-system (section)

===Example 7: fractal plant ===
{{See also|Barnsley fern}}

:     '''variables''' :   X F
:     '''constants''' :   + &minus; [ ]
:     '''start'''     :   -X
:     '''rules'''     :   (X → F+[[X]-X]-F[-FX]+X), (F → FF)
:     '''angle'''     :   25°

First one needs to initialize an empty stack. This follows the LIFO (Last in, First Out) method to add and remove elements. 
Here, F means "draw forward", − means "turn right 25°", and + means "turn left 25°". X does not correspond to any drawing action and is used to control the evolution of the curve. The square bracket "[" corresponds to saving the current values for position and angle, so the position and angle are pushed to the top of the stack, when the "]" token is encountered, the stack is popped and the position and angle are reset. Every "[" comes before every "]" token.

[[File:Fractal-plant.svg|alt=|left]][[File:Fractal_Farn.gif|alt=]]{{center|1=Fractal plant for ''n'' = 6}}