Turtle Programming v0.0.5: Adding IF/ELSE and STOP!

Introduction to Logo Turtle

LogoTurtle is the first Chrome Extension for Turtle Graphics.

Previous Contributions

• 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.
• v0.0.1: Teach Your Kids Programming – The First Logo Interpreter (Turtle Graphics) in Chrome Extension!

Turtle Programming v0.0.5 New Features

This Commit supports IF/ELSE and STOP.

In previous versions, the LOOP program flow is supported by keyword REPEAT and the most important IF/ELSE is now implemented in this version.

Screenshots

This is how things get a little bit interesting and I believe now you can have your imaginations fly.

turtle-programming-if-else

LOGO: Source code.

ht cs make "a 1 repeat 8 [pu fd 100 pd 
repeat 12 [
  if :a%3==1 [rt 90] else [lt 90] 
  fd 30 make "a :a+1
] pu bk 100 rt 45]

How to Implement IF/ELSE in Logo/Javascript?

The IF part is similar to REPEAT and all we need to do is to parse the ELSE part.

case "if":
expr = this.evalVars(word_next, true);
try {
    word_next = eval(expr);
} catch (e) {
    this.pushErr(LOGO_ERR_EVAL, expr);
    return false;
}               
if ((word_next === '')) {                       
    this.pushErr(LOGO_ERR_MISSING_EXP, word_next);
    return false;
}
find_left = getNextWord(s, y.next, U);
if (find_left.word != '[') {
    this.pushErr(LOGO_ERR_MISSING_LEFT, find_left.word);
    return false;
}
repeat_left = find_left.next;
find_right = repeat_left + 1;
nested = 1;
// need to match [ and ]
while (find_right < U) {
    if (s[find_right] == '[') {
        nested ++;
    }                                               
        if (s[find_right] == ']') {
            nested --;
            if (nested == 0) {
                break;
            }
        }
        find_right ++;
}
if (find_right >= U) {
    this.pushWarning(LOGO_ERR_MISSING_RIGHT);                       
}
let ifelse = word_next;                 
if (ifelse) {
    // if body
    if (!this.run(s, repeat_left, find_right, depth + 1)) {
        return false;
    }
}   
find_else = getNextWord(s, find_right + 1, U);
if (find_else.word.toLowerCase() == 'else') {
    let else_block = getNextBody(s, find_else.next, U);
    if (else_block.ch != '[') {
        this.pushErr(LOGO_ERR_MISSING_LEFT, else_block.ch);
        return false;
    }
    if (!ifelse) {
        // else body
        if (!this.run(s, else_block.left, else_block.right, depth + 1)) {
            return false;
        }
    }
    i = else_block.right + 1;
} else {
    // no else block
    i = find_right + 1; 
}
break;  

Roadmap of Chrome Extension: Logo Turtle

• Add Functions
• Add IF/THEN/ELSE
• Add Variables
• Add Colors
• Add MoveTo
• Add PrintText
• Add Circle
• Add Arc
• Add Eraser
• Add Fill
• Save As Picture
• Save As Program
• Comments
• Add Recursion Support
• Add Global/Local Scopes
• etc. etc.

Technology Stack

If an App can be written in Javascript, eventually it will be written in Javascript.

Chrome Webstore

Install the Turtle Programming for Kids Now!

Contribution Welcome

Github: https://github.com/DoctorLai/LogoTurtle

• Fork it!
• Create your feature branch: git checkout -b my-new-feature
• Commit your changes: git commit -am ‘Add some feature’
• Push to the branch: git push origin my-new-feature
• Submit a pull request.

–EOF (The Ultimate Computing & Technology Blog) —