ANN: lsystem 1.0 -- Lindenmayer system explorer

[Erik Max Francis]

Summary

    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.

    Despite being implemented entirely in Python, for reasonable rules
    on a modern machine the system is capable of running thousands of
    generations per second.  Lindenmayer systems are found in
    artificial intelligence and artificial life and can be used to
    generate fractal patterns (usually via mapping symbols from the
    alphabet to turtle commands), organic looking patterns that can
    simulate plants or other living things, or even music.


Getting the software

    The software is available in a tarball here:
    http://www.alcyone.com/pyos/lsystem/lsystem-latest.tar.gz.

    The official URL for this Web site is
    http://www.alcyone.com/pyos/lsystem/.


Introduction

    Lindenmayer systems consist of strings of symbols from an
    "alphabet"; in this case, the alphabet is all 8-bit characters.
    The starting string is called the axiom (and is simply a string).
    Each generation, zero or more transitions are applied to the
    string, based on a list of rules.  Each rule consists of an
    "input" and an "output"; the input is the search substring and the
    output is the substring it is to be replaced with.  The ordering
    of the rules is significant.  Null strings are legal as both input
    and output; if at the input, they will match at every location,
    and if at the output, the search-and-replace will amount to a
    delete.

    In the basic implementation (the 'LSystem' class), these
    transitions are done in order.  The system scans through the
    string, checking the substring starting with the current position
    against each rule's input in order.  If that rule's input matches,
    that substring is substituted with the output string for that
    rule; thus, the ordering of rules is significant.  If no rule
    matches, that character is left alone and scanning continues.

    ...

-- 
 Erik Max Francis / max at alcyone.com / http://www.alcyone.com/max/
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