L-systems - OpenProcessing

mySketch
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let x, y; // the current position of the turtle
let currentangle = 60; // which way the turtle is pointing
let step = 1.2; // how much the turtle moves with each 'F'
let angle = -1; // how much the turtle turns with a '-' or '+'
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let thestring = 'F+F-F-F'; // "axiom" or start of the string
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let numloops = 7; // how many iterations to pre-compute
let therules = []; // array for rules
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therules[0] = ['F', 'F+X-F']; // first rule
therules[1] = ['X', 'F-X-F']; // first rule
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let whereinstring = 0; // where in the L-system are we?
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function setup() {
  angle = 180*(PI/2.2)/PI
  
  let hh = 1000;
  createCanvas(hh, hh);
  background(250);
  
  stroke(0, 7);
  strokeWeight(2)
  
  // start the x and y position at lower-left corner
  x = width/2;
  y = height/2;
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  // COMPUTE THE L-SYSTEM
  for (let i = 0; i < numloops; i++) {
    thestring = lindenmayer(thestring);
  }
  
  //console.log(thestring);
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}
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function draw() {
  
  for (let j = 0; j < 7000; j++) {
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  // draw the current character in the string:
  drawIt(thestring[whereinstring]);
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  whereinstring++;
    
  if (whereinstring > thestring.length-1) whereinstring = 0;
    
  }
}
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// interpret an L-system
function lindenmayer(s) {
  let outputstring = ''; // start a blank output string
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  // iterate through 'therules' looking for symbol matches:
  for (let i = 0; i < s.length; i++) {
    let ismatch = 0; // by default, no match
    for (let j = 0; j < therules.length; j++) {
      if (s[i] == therules[j][0])  {
        outputstring += therules[j][1]; // write substitution
        ismatch = 1; // we have a match, so don't copy over symbol
        break; // get outta this for() loop
      }
    }
    // if nothing matches, just copy the symbol over.
    if (ismatch == 0) outputstring+= s[i];
  }
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  return outputstring; // send out the modified string
}
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// this is a custom function that draws turtle commands
function drawIt(k) {
  if (k=='F') { // draw forward
    // polar to cartesian based on step and currentangle:
    let x1 = x + step*cos(radians(currentangle));
    let y1 = y + step*sin(radians(currentangle));
    line(x, y, x1, y1); // connect the old and the new
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    // update the turtle's position:
    x = x1;
    y = y1;
  } else if (k == '+') {
    currentangle += angle; // turn left
  } else if (k == '-') {
    currentangle -= angle; // turn right
  }
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}