lsystem

A simple utility to produce L-System stacks. (16 sloc)

See: https://en.wikipedia.org/wiki/L-system

Usage:

var lsystem = require('lsystem')
/**
 * @param (v: String): String rule (see below)
 * @param {Number} iterations
 * @param {Mixed} initial value
 * @param (v: String): void callback with the next value
 */
lsystem(rule, 10, 'F', onnext)

/**
 * Koch curve formula:
 * variables : F
 * constants : +-
 * start  : F
 * rules  : (F → F+F−F−F+F)
 *
 * @param {String} v the letter to convert
 *
 * @return {String} the transformed string or the given one (constants)
 */
function rule (v) {
  switch (v) {
    case 'F':
      return 'F+F-F-F+F'
  }

  return v
}

const tree = []
function onnext(v) {
  tree.push(v)
}

console.log(tree)

API:

lsystem([number of occurences], [rule], [initial data])

Output of node example.js:

Algae
A
AB
ABA
ABAAB
FractalTree
0
1[0]0
11[1[0]0]1[0]0
1111[11[1[0]0]1[0]0]11[1[0]0]1[0]0
Cantor
A
ABA
ABABBBABA
ABABBBABABBBBBBBBBABABBBABA
Koch
F
F+F-F-F+F
F+F-F-F+F+F+F-F-F+F-F+F-F-F+F-F+F-F-F+F+F+F-F-F+F
F+F-F-F+F+F+F-F-F+F-F+F-F-F+F-F+F-F-F+F+F+F-F-F+F+F+F-F-F+F+F+F-F-F+F-F+F-F-F+F-F+F-F-F+F+F+F-F-F+F-F+F-F-F+F+F+F-F-F+F-F+F-F-F+F-F+F-F-F+F+F+F-F-F+F-F+F-F-F+F+F+F-F-F+F-F+F-F-F+F-F+F-F-F+F+F+F-F-F+F+F+F-F-F+F+F+F-F-F+F-F+F-F-F+F-F+F-F-F+F+F+F-F-F+F
Fractal
X
F[-X][X]F[-X]+FX
FF[-F[-X][X]F[-X]+FX][F[-X][X]F[-X]+FX]FF[-F[-X][X]F[-X]+FX]+FFF[-X][X]F[-X]+FX
FFFF[-FF[-F[-X][X]F[-X]+FX][F[-X][X]F[-X]+FX]FF[-F[-X][X]F[-X]+FX]+FFF[-X][X]F[-X]+FX][FF[-F[-X][X]F[-X]+FX][F[-X][X]F[-X]+FX]FF[-F[-X][X]F[-X]+FX]+FFF[-X][X]F[-X]+FX]FFFF[-FF[-F[-X][X]F[-X]+FX][F[-X][X]F[-X]+FX]FF[-F[-X][X]F[-X]+FX]+FFF[-X][X]F[-X]+FX]+FFFFFF[-F[-X][X]F[-X]+FX][F[-X][X]F[-X]+FX]FF[-F[-X][X]F[-X]+FX]+FFF[-X][X]F[-X]+FX