Introduction to Logo Turtle

LogoTurtle is currently the FIRST and only one Chrome Extension for Turtle Graphics. I have also written a PHP version of Logo Interpreter in 2006 but that runs only on the server.

Previous Contributions

v0.0.6: Turtle Programming v0.0.6: Adding Circle, MoveTo, Turn and Screen!
v0.0.5: Turtle Programming v0.0.5: Adding IF/ELSE and STOP!
v0.0.4: LogoTurtle: Make Variables and Comments
v0.0.3: Turtle Graphics Programming Update: Adding text, jump, dot, fontsize, download as png
v0.0.2: LogoTurtle v0.0.2: ShowTurtle, HideTurtle, Color, Width and Help.
Teach Your Kids Programming - The First Logo Interpreter (Turtle Graphics) in Chrome Extension!
v0.0.1

v0.0.7 New Features

Along with bug fixes and code tweaks, This Commit has added the support of function declaration and function invoke with parameters

This is the most useful, important and most difficult feature of the LOGO parser!

Screenshots

The following LOGO source code has a two recursive functional call. I have spent quite some time and came across the same problem that I had years ago when writing the PHP Logo Parser. The fix is to copy the variables before recursive calls and restore them once the function calls return so the variables value update do not affect globally.

ht cs to tree :size
  if (:size<10) [stop]
  fd :size
  lt 30 tree :size*0.7  ; left branch, recursive
  rt 60 tree :size*0.7  ; right branch, recursive
  lt 30 
  bk :size
end

pu fd -120 pd tree 100

Version 0.0.7 supports single-line comments that are denoted using ; or # or //

How to Parse To/End LOGO function in Javascript?

The following Javascript parses the TO/END LOGO function pairs and stores it in class attribute this.funs dictionary. The content of the dictionary value is an array of [function parameters, function body].

case "to": // define a function
    let next_word;
    let funs_name = y.word.trim();
    if (!isValidVarName(funs_name)) {
        this.pushErr(word, LOGO_ERR_INVALID_FUN_NAME, funs_name);
        return false;
    }
    i = y.next;
    let start_fun_idx = i;
    let end_fun_idx = -1;
    for (;;) {
        let prev = i;
        next_word = getNextWord(s, i, U);
        i = next_word.next;
        if (next_word.word.toLowerCase() == 'end') {
            end_fun_idx = prev;
            break;
        }
        if ((next_word.word == '' || next_word.next >= U)) {
            this.pushErr(word, LOGO_ERR_MISSING_END, next_word);
            return false;
        }
    }
    if (end_fun_idx == -1) {
        this.pushErr(word, LOGO_ERR_MISSING_END, '');
        return false;                       
    }
    let funs_s = s.substring(start_fun_idx, end_fun_idx).trim();
    if (funs_s && y) {
        let ii = 0;
        let UU = s.length;
        let funs_params = []; // funs parameter
        let j = ii;
        while (ii < U) {
            j = ii;
            let to_word = getNextWord(funs_s, ii, UU);
            ii = to_word.next;
            if (to_word.word.startsWith(':')) {
                let to_word_param = to_word.word.substring(1);
                if (!isValidVarName(to_word_param)) {
                    this.pushErr(word, LOGO_ERR_INVALID_VAR_NAME, to_word_param);
                    return false;
                }
                funs_params.push(to_word_param);
            } else {
                break;
            }                           
        }
        let funs_body = funs_s.substring(j, UU).trim();
        // declare the function
        this.funs[funs_name] = [funs_params, funs_body];
    }
    break;