4 Conditional L-systems

An L-system with parameters can dispatch on those parameters, picking between rewrites for a single symbol. For example:

#lang lindenmayer racket

## axiom ##

A(0)

## rules ##

A(d) : d > 0 -> A(d-1)

A(d) : d = 0 -> F(1/2)[+A(D)]F(1/2)B(0)

B(d) : d > 0 -> B(d-1)

B(d) : d = 0 -> F(1/2)[-B(D)]F(1/2)A(0)

F(a)         -> F(a*R)

## variables ##

D=1

R=1.36

n=20

θ=45

============================================================

(require lindenmayer/turtle)

(provide (all-from-out lindenmayer/turtle) (all-defined-out))

(define (A turtles variables . _) turtles)

(define (B turtles variables . _) turtles)

Has the A and B rules dispatch on the parameter d, to produce:

Conditionals are placed before ->, and after a :. Conditions can be joined by an &. Currently supported comparisons are: ≠ =< > ≤ ≥.