code = code.replace(/[\s]/g, ' '); // replace all spaces characters to standard space

  code = code.replace(/\[/g, ' [ '); // add space before

  code = code.replace(/\]/g, ' ] '); // and after brackets

  tokens = code.split(" ");

  tokens = tokens.filter(e => e); // remove empty tokens

  return tokens;

}

​

function execTokens(tokens, firstIndex, lastIndex) {

  let index = firstIndex;

  while (index < lastIndex) {

        let token = tokens[index++];

    //console.log(token);

    if (commands[token]) {

        index = commands[token](tokens, index);

      }

  }

}

​

function forward(tokens, index) {

  turtle.move(tokens[index++]);

  return index;

}

​

function backward(tokens, index) {

  turtle.move(-tokens[index++]);

  return index;

}

​

function right(tokens, index) {

  turtle.turn(tokens[index++]);

  return index;

}

​

function left(tokens, index) {

  turtle.turn(-tokens[index++]);

  return index;

}

​

function penup(tokens, index) {

  turtle.pen = false;

  return index;

}

​

function pendown(tokens, index) {

  turtle.pen = true;

  return index;

}

​

function repeat(tokens, index) {

  let n = tokens[index++];

  let bracket = 0;

  let firstIndex = 0;

  let lastIndex = 0;

  while (index < tokens.length) {

        let token = tokens[index++];

    if (token == '[') {

      if (bracket++ == 0) {

        firstIndex = index;

      }

    }

    else if (token == ']') {

      if (--bracket == 0) {

        lastIndex = index;

        break;

      }

    }

  }

  if (firstIndex && lastIndex) {

    for(let i = 0; i < n; i++) {

      execTokens(tokens, firstIndex, lastIndex - 1);  

    }

    return lastIndex;

  }

  return index;

}

​

function to(tokens, index) {

  let name = tokens[index++];

  let firstIndex = index;

  console.log('to: ' + name);

  while (index < tokens.length) {

        let token = tokens[index++];

    if (token == 'end') {

      let lastIndex = index;

      commands[name] = function(tokens, index) {

        execTokens(tokens, firstIndex, lastIndex - 1);

        return index;

      }  

      break;

    }

  }

  return index; 

}

​

function setpencolor(tokens, index) {

  if (tokens[index++] == '[') {

    let r = tokens[index++];

    let g = tokens[index++];

    if (g == ']') {

        stroke(parseInt(r)); // gray 

    } else {

      let b = tokens[index++];

      if (b == ']') {

        stroke(parseInt(r), parseInt(g)); // gray + alpha

      } else {

        let a = tokens[index++];

        if (a == ']') {

          stroke(parseInt(r), parseInt(g), parseInt(b)); // rgb

        }                                                                                                                       

        else if (tokens[index++] == ']') {

          stroke(parseInt(r), parseInt(g), parseInt(b), parseInt(a)); // rgba

        }

      }

    }

  } 

  return index; 

}

​

const commands = {

  "fd": forward,

  "forward:": forward,

  "bk": backward,

  "backward": backward,

  "rt": right,

  "right": right,

  "lt": left,

  "left": left,  

  "pu": penup,

  "penup": penup,

  "pd": pendown,

  "pendown": pendown,

  "repeat": repeat,

  "to": to,

  "setpencolor": setpencolor,

  "setpc": setpencolor

}

​

class Turtle {

  constructor(x, y, angle) {

    this.x = x;

    this.y = y;

    this.dir = angle;

  }

​

  reset() {

    //console.log(this.x, this.y, this.dir);

    translate(this.x, this.y);

    rotate(this.dir);

    stroke(255);

    strokeWeight(2);

    this.pen = true;

  }

​

  move(amt) {

    amt = parseInt(amt);

    if (this.pen) {

      line(0, 0, amt, 0);

    }

    translate(amt, 0);

  }

​

  turn(angle) {

    rotate(angle);

  }

}