A simple implementation of Lindenmayer systems (also called
L-systems, substitution systems) is provided. In basic form, a
Lindenmayer system consists of a starting string of symbols from
an alphabet, and has repeated transitions applied to it, specified
by a list of transition search-and-replace rules.
In addition to the standard formulation, two alternative
implementations are included: sequential systems, in which at most
one rule is applied; and tag systems, in which the transition only
takes place at the beginning and end of the string.