Making Future Posts Runnable Online with Stack Snippets

function out(text) {
  var output = document.getElementById("output");
  output.innerHTML = output.innerHTML + text;
}

function builtinRead(x) {
  if(Sk.builtinFiles === undefined || Sk.builtinFiles["files"][x] === undefined)
    throw "File not found: '" + x + "'";
  return Sk.builtinFiles["files"][x];
}

function run() {
  var program = document.getElementById("python-in").value;
  var output = document.getElementById("output");
  
  output.innerHTML = "";
  
  Sk.canvas = "canvas";
  Sk.pre = "output";
  
  Sk.configure({
    output: out,
    read: builtinRead
  });
  
  try {
    Sk.importMainWithBody("<stdin>", false, program);
  }
  catch(e) {
    throw new Error(e.toString());
  }
}

#python-in {
  border-radius: 3px;
  background: rgb(250, 250, 250);
  width: 95%;
  height: 200px;
}

#output {
  border-radius: 3px;
  background: lightgray;
  width: 95%;
  height: 200px;
  overflow: auto;
}

#canvas {
  border: 1px solid gray;
  border-radius: 3px;
  height: 400px;
  width: 400px;
}

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script src="http://www.skulpt.org/static/skulpt.min.js"></script>
<script src="http://www.skulpt.org/static/skulpt-stdlib.js"></script>

Python code:<br/>
<textarea id="python-in" name="python-in" rows="10" cols="80"></textarea><br/>
<button id="run-code" onclick="run()">Run</button><br/>
<br/>

Output:<br/>
<pre id="output" name="output" rows="10" cols="10" disabled></pre><br/>

Canvas for turtles:<br/>
<canvas height="400" width="400" id="canvas">Your browser does not support HTML5 Canvas!</canvas>

function BefungeBoard(source, constraints) {
    constraints = constraints || {
        width: 80,
        height: 25
    };

    this.constraints = constraints;
    this.grid = source.split(/\r\n|[\n\v\f\r\x85\u2028\u2029]/).map(function (line) {
        return (line + String.repeat(' ', constraints.width - line.length)).split('');
    });
    for (var i = this.grid.length; i < constraints.height; i++) {
        this.grid[i] = String.repeat(' ', constraints.width).split('');
    }

    this.pointer = {
        x: 0,
        y: 0
    };

    this.direction = Direction.RIGHT;
}

BefungeBoard.prototype.nextPosition = function () {
    var vector = this.direction.toVector(),
        nextPosition = {
            x: this.pointer.x + vector[0],
            y: this.pointer.y + vector[1]
        };

    nextPosition.x = nextPosition.x < 0 ? this.constraints.width - 1 : nextPosition.x;
    nextPosition.y = nextPosition.y < 0 ? this.constraints.height - 1 : nextPosition.y;

    nextPosition.x = nextPosition.x >= this.constraints.width ? 0 : nextPosition.x;
    nextPosition.y = nextPosition.y >= this.constraints.height ? 0 : nextPosition.y;

    return nextPosition;
};

BefungeBoard.prototype.advance = function () {
    this.pointer = this.nextPosition();
    if (this.onAdvance) {
        this.onAdvance.call(null, this.pointer);
    }
};

BefungeBoard.prototype.currentToken = function () {
    return this.grid[this.pointer.y][this.pointer.x];
};

BefungeBoard.prototype.nextToken = function () {
    var nextPosition = this.nextPosition();
    return this.grid[nextPosition.y][nextPosition.x];
};

var Direction = (function () {
    var vectors = [
        [1, 0],
        [-1, 0],
        [0, -1],
        [0, 1]
    ];

    function Direction(value) {
        this.value = value;
    }

    Direction.prototype.toVector = function () {
        return vectors[this.value];
    };

    return {
        UP: new Direction(2),
        DOWN: new Direction(3),
        RIGHT: new Direction(0),
        LEFT: new Direction(1)
    };
})();

function BefungeStack() {
    this.stack = [];
}

BefungeStack.prototype.pushAscii = function (item) {
    this.pushNumber(item.charCodeAt());
};

BefungeStack.prototype.pushNumber = function (item) {
    if (isNaN(+item)) {
        throw new Error(typeof item + " | " + item + " is not a number");
    }

    this.stack.push(+item);
};

BefungeStack.prototype.popAscii = function () {
    return String.fromCharCode(this.popNumber());
};

BefungeStack.prototype.popNumber = function () {
    return this.stack.length === 0 ? 0 : this.stack.pop();
};

function Befunge(source, constraints) {
    this.board = new BefungeBoard(source, constraints);
    this.stack = new BefungeStack();
    this.stringMode = false;
    this.terminated = false;

    this.digits = "0123456789".split('');
}

Befunge.prototype.run = function () {
    for (var i = 1; i <= (this.stepsPerTick || 10); i++) {
        this.step();
        if (this.terminated) {
            return;
        }
    }

    requestAnimationFrame(this.run.bind(this));
};

Befunge.prototype.step = function () {
    this.processCurrentToken();
    this.board.advance();
};

Befunge.prototype.processCurrentToken = function () {
    var token = this.board.currentToken();
    if (this.stringMode && token !== '"') {
        return this.stack.pushAscii(token);
    }

    if (this.digits.indexOf(token) !== -1) {
        return this.stack.pushNumber(token);
    }

    switch (token) {
        case ' ':
            while ((token = this.board.nextToken()) == ' ') {
                this.board.advance();
            }
            return;
        case '+':
            return this.stack.pushNumber(this.stack.popNumber() + this.stack.popNumber());
        case '-':
            return this.stack.pushNumber(-this.stack.popNumber() + this.stack.popNumber());
        case '*':
            return this.stack.pushNumber(this.stack.popNumber() * this.stack.popNumber());
        case '/':
            var denominator = this.stack.popNumber(),
                numerator = this.stack.popNumber(),
                result;
            if (denominator === 0) {
                result = +prompt("Illegal division by zero. Please enter the result to use:");
            } else {
                result = Math.floor(numerator / denominator);
            }

            return this.stack.pushNumber(result);
        case '%':
            var modulus = this.stack.popNumber(),
                numerator = this.stack.popNumber(),
                result;
            if (modulus === 0) {
                result = +prompt("Illegal division by zero. Please enter the result to use:");
            } else {
                result = Math.floor(numerator / modulus);
            }

            return this.stack.pushNumber(result);
        case '!':
            return this.stack.pushNumber(this.stack.popNumber() === 0 ? 1 : 0);
        case '`':
            return this.stack.pushNumber(this.stack.popNumber() < this.stack.popNumber() ? 1 : 0);
        case '>':
            this.board.direction = Direction.RIGHT;
            return;
        case '<':
            this.board.direction = Direction.LEFT;
            return;
        case '^':
            this.board.direction = Direction.UP;
            return;
        case 'v':
            this.board.direction = Direction.DOWN;
            return;
        case '?':
            this.board.direction = [Direction.RIGHT, Direction.UP, Direction.LEFT, Direction.DOWN][Math.floor(4 * Math.random())];
            return;
        case '_':
            this.board.direction = this.stack.popNumber() === 0 ? Direction.RIGHT : Direction.LEFT;
            return;
        case '|':
            this.board.direction = this.stack.popNumber() === 0 ? Direction.DOWN : Direction.UP;
            return;
        case '"':
            this.stringMode = !this.stringMode;
            return;
        case ':':
            var top = this.stack.popNumber();
            this.stack.pushNumber(top);
            return this.stack.pushNumber(top);
        case '\\':
            var first = this.stack.popNumber(),
                second = this.stack.popNumber();
            this.stack.pushNumber(first);
            return this.stack.pushNumber(second);
        case '$':
            return this.stack.popNumber();
        case '#':
            return this.board.advance();
        case 'p':
            return this.board.grid[this.stack.popNumber()][this.stack.popNumber()] = this.stack.popAscii();
        case 'g':
            return this.stack.pushAscii(this.board.grid[this.stack.popNumber()][this.stack.popNumber()]);
        case '&':
            return this.stack.pushNumber(+prompt("Please enter a number:"));
        case '~':
            return this.stack.pushAscii(prompt("Please enter a character:")[0]);
        case '.':
            return this.print(this.stack.popNumber());
        case ',':
            return this.print(this.stack.popAscii());
        case '@':
            this.terminated = true;
            return;
    }
};

Befunge.prototype.withStdout = function (printer) {
    this.print = printer;
    return this;
};

Befunge.prototype.withOnAdvance = function (onAdvance) {
    this.board.onAdvance = onAdvance;
    return this;
};

String.repeat = function (str, count) {
    var repeated = "";
    for (var i = 1; i <= count; i++) {
        repeated += str;
    }

    return repeated;
};

window['requestAnimationFrame'] = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function (callback) {
    window.setTimeout(callback, 1000 / 60);
};

(function () {
    var currentInstance = null;

    function resetInstance() {
        currentInstance = null;
    }

    function getOrCreateInstance() {
        if (currentInstance !== null && currentInstance.terminated) {
            resetInstance();
        }

        if (currentInstance === null) {
            var boardSize = Editor.getBoardSize();
            currentInstance = new Befunge(Editor.getSource(), {
                width: boardSize.width,
                height: boardSize.height
            });
            currentInstance.stepsPerTick = Editor.getStepsPerTick();

            currentInstance.withStdout(Editor.append);
            currentInstance.withOnAdvance(function (position) {
                Editor.highlight(currentInstance.board.grid, position.x, position.y);
            });
        }

        return currentInstance;
    }

    var Editor = (function (onExecute, onStep, onReset) {
        var source = document.getElementById('source'),
            sourceDisplay = document.getElementById('source-display'),
            sourceDisplayWrapper = document.getElementById('source-display-wrapper'),
            stdout = document.getElementById('stdout');
        var execute = document.getElementById('execute'),
            step = document.getElementById('step'),
            reset = document.getElementById('reset');
        var boardWidth = document.getElementById('board-width'),
            boardHeight = document.getElementById('board-height'),
            stepsPerTick = document.getElementById('steps-per-tick');

        function showEditor() {
            source.style.display = "block";
            sourceDisplayWrapper.style.display = "none";
            source.focus();
        }

        function hideEditor() {
            source.style.display = "none";
            sourceDisplayWrapper.style.display = "block";

            var computedHeight = getComputedStyle(source).height;
            sourceDisplayWrapper.style.minHeight = computedHeight;
            sourceDisplayWrapper.style.maxHeight = computedHeight;

            sourceDisplay.textContent = source.value;
        }

        function resetOutput() {
            stdout.value = null;
        }

        function escapeEntities(input) {
            return input.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
        }

        sourceDisplayWrapper.onclick = function () {
            resetOutput();
            showEditor();
            onReset && onReset.call(null);
        };
        execute.onclick = function () {
            resetOutput();
            hideEditor();
            onExecute && onExecute.call(null);
        };
        step.onclick = function () {
            hideEditor();
            onStep && onStep.call(null);
        };
        reset.onclick = function () {
            resetOutput();
            showEditor();
            onReset && onReset.call(null);
        };

        return {
            getSource: function () {
                return source.value;
            },

            append: function (content) {
                stdout.value = stdout.value + content;
            },

            highlight: function (grid, x, y) {
                var highlighted = [];
                for (var row = 0; row < grid.length; row++) {
                    highlighted[row] = [];
                    for (var column = 0; column < grid[row].length; column++) {
                        highlighted[row][column] = escapeEntities(grid[row][column]);
                    }
                }

                highlighted[y][x] = '<span class="activeToken">' + highlighted[y][x] + '</span>';
                sourceDisplay.innerHTML = highlighted.map(function (lineTokens) {
                    return lineTokens.join('');
                }).join('\n');
            },

            getBoardSize: function () {
                return {
                    width: +boardWidth.innerHTML,
                    height: +boardHeight.innerHTML
                };
            },

            getStepsPerTick: function () {
                return +stepsPerTick.innerHTML;
            }
        };
    })(function () {
        getOrCreateInstance().run();
    }, function () {
        getOrCreateInstance().step();
    }, resetInstance);
})();

.container {
    width: 100%;
}
.so-box {
    font-family:'Helvetica Neue', Arial, sans-serif;
    font-weight: bold;
    color: #fff;
    text-align: center;
    padding: .3em .7em;
    font-size: 1em;
    line-height: 1.1;
    border: 1px solid #c47b07;
    -webkit-box-shadow: 0 2px 2px rgba(0, 0, 0, 0.3), 0 2px 0 rgba(255, 255, 255, 0.15) inset;
    text-shadow: 0 0 2px rgba(0, 0, 0, 0.5);
    background: #f88912;
    box-shadow: 0 2px 2px rgba(0, 0, 0, 0.3), 0 2px 0 rgba(255, 255, 255, 0.15) inset;
}
.control {
    display: inline-block;
    border-radius: 6px;
    float: left;
    margin-right: 25px;
    cursor: pointer;
}
.option {
    padding: 10px 20px;
    margin-right: 25px;
    float: left;
}
input, textarea {
    box-sizing: border-box;
}
textarea {
    display: block;
    white-space: pre;
    overflow: auto;
    height: 75px;
    width: 100%;
    max-width: 100%;
    min-height: 25px;
}
span[contenteditable] {
    padding: 2px 6px;
    background: #cc7801;
    color: #fff;
}
#controls-container, #options-container {
    height: auto;
    padding: 6px 0;
}
#stdout {
    height: 50px;
}
#reset {
    float: right;
}
#source-display-wrapper {
    display: none;
    width: 100%;
    height: 100%;
    overflow: auto;
    border: 1px solid black;
    box-sizing: border-box;
}
#source-display {
    font-family: monospace;
    white-space: pre;
    padding: 2px;
}
.activeToken {
    background: #f88912;
}
.clearfix:after {
    content:".";
    display: block;
    height: 0;
    clear: both;
    visibility: hidden;
}
.clearfix {
    display: inline-block;
}
* html .clearfix {
    height: 1%;
}
.clearfix {
    display: block;
}

<div class="container">
    <textarea id="source" placeholder="Enter your Befunge-93 program here" wrap="off">"39-egnufeB">:#,_@</textarea>
    <div id="source-display-wrapper">
        <div id="source-display"></div>
    </div>
</div>
<div id="controls-container" class="container clearfix">
    <input type="button" id="execute" class="control so-box" value="► Execute" />
    <input type="button" id="step" class="control so-box" value="Step" />
    <input type="button" id="reset" class="control so-box" value="Reset" />
</div>
<div id="stdout-container" class="container">
    <textarea id="stdout" placeholder="Output" wrap="off" readonly></textarea>
</div>
<div id="options-container" class="container">
    <div class="option so-box">Steps per Tick: <span id="steps-per-tick" contenteditable>500</span>

    </div>
    <div class="option so-box">Board Size: <span id="board-width" contenteditable>80</span> x <span id="board-height" contenteditable>25</span>

    </div>
</div>

function inputChanged() {
    var codeText = document.getElementById('code-block');
    if (codeText.value.charAt(0) !== ':') {
        codeText.value = ':' + codeText.value;
    }
    var cursor = codeText.selectionEnd;
    if (lastText.length < codeText.value.length) { //adding characters
        if (/(\n)$/.test(codeText.value) === true || /(\n)(\n)/.test(codeText.value) === true) {
            cursor++;
        }
        codeText.value = codeText.value.replace(/(\n)$/, '\n:');
        codeText.value = codeText.value.replace(/(\n)(\n)/, '\n:\n');
    } else { //removing characters
        if (/(\n)$/.test(codeText.value) === true || /(\n)(\n)/.test(codeText.value) === true) {
            cursor--;
        }
        codeText.value = codeText.value.replace(/(\n)$/, '');
        codeText.value = codeText.value.replace(/(\n)(\n)/, '\n');
    }
    codeText.setSelectionRange(cursor, cursor);
    lastText = codeText.value;
}
function onUserInput(e){
    var output = document.getElementById('output');
    //enter has code 13
    if(awaitingInput && e.keyCode===13){
        var lines = output.value.split('\n');
        var input = lines[lines.length-1];
        if(input.indexOf('?')!==-1){
            input = input.substring(input.indexOf('?')+1,input.length);
        }
        if(newInputVarName !== null){
            var iValue = replaceVars(input);
            variables[newInputVarName]= eval(iValue);
        }else{
           output.value = output.value.substring(0,output.value.length-1);  
        }
        awaitingInput = false;
    }
}
var lastText = ':';
var L1 = [],
    L2 = [],
    L3 = [],
    L4 = [],
    L5 = [],
    L6 = []; //note - these are special. They're like variables, and are considered in replaceVars.
var tokens = [':', '-->', 'if', 'then',
    'else', 'for', 'while', ',',
    'repeat', 'end', 'disp','prompt','input',
    'pause','pxl-on','pxl-off','clrdraw'];
var variables = [];
var loopStack = []; //holds line numbers
var ifStack = [true]; //holds true or false
var typeStack = ['if'];
var repeatStack = []; //holds current iteration for repeats. NOTE: starts at 1 to accomidate repeat 0
var awaitingInput = false;
var newInputVarName=null;
var pixels = []; //96*64
var running = false;
var lineProcessing;
function run() {
    if(running===false){
        for(var pixelX=0;pixelX<96;pixelX++){
            for(var pixelY=0;pixelY<64;pixelY++){
                pixels[(pixelX,pixelY)]=0;         //doesn't work
            }
        }
        variables = [];
        loopStack = [];
        ifStack = [true];
        typeStack = ['if'];
        repeatStack = [];
        clear();
        var code = document.getElementById('code-block');
        var lines = code.value.split('\n');
        var currentLine = 0;
        variables['e'] = Math.E;
        variables['pi'] = Math.PI;
        L1.push(3);
        L1.push(4);
        lineProcessing = setInterval(function(){
            if(!awaitingInput){
                running = true;
                if(currentLine < lines.length || loopStack.length !== 0){
                    currentLine = processLine(lines,currentLine);
                    currentLine++;
                }
                else{
                    running = false;
                    lineProcessing.clearInterval();
                }
            }
        },10);
    }
}
function processLine(lines, currentLine) {
    var tokens = tokenize(lines[currentLine]);
    if (ifStack[ifStack.length - 1] === true){
        if (tokens.indexOf('-->') !== -1) {
            var index = tokens.indexOf('-->');
            for (var i = 0; i < index; i++) {
                tokens[i] = replaceVars(tokens[i]);
            }
            var value = eval(tokens[index - 1]);
            var name = tokens[index + 1];
            var listElement = false;
            if (name.length > 4) {
                if (/L[1-6]\(/.test(name) === true) {
                    var nextP = matchParenthese(name, 2);
                    var innerStuff = name.substring(3, nextP);
                    var value2 = eval(replaceVars(innerStuff));
                    var listNum = name.substring(0, 2);
                    if (value2 === Math.round(value2)) {
                        if (value2 > 0) {
                            if (listNum === 'L1') {
                                L1[value2] = value;
                            }
                            if (listNum === 'L2') {
                                L2[value2] = value;
                            }
                            if (listNum === 'L3') {
                                L3[value2] = value;
                            }
                            if (listNum === 'L4') {
                                L4[value2] = value;
                            }
                            if (listNum === 'L5') {
                                L5[value2] = value;
                            }
                            if (listNum === 'L6') {
                                L6[value2] = value;
                            }
                        } else {
                            printE('Arrays can only have positive indexes, and by some weird quirk of Texas Instruments, indexes start at 1, not 0.');
                            throw new Error();
                        }
                    } else {
                        printE('Sorry, this is not Javascript. Array indexes must be integers.');
                        throw new Error();
                    }
                }
            }
            variables[name + ""] = value;
        }
        if (tokens.indexOf('disp') !== -1) {
            var index2 = tokens.indexOf('disp');
            for (var g = index2 + 1; g < tokens.length; g++) {
                tokens[g] = replaceVars(tokens[g]);
                if (tokens[g] === ',') {} else {
                    print(eval(tokens[g]));
                }
            }
        }
        if(tokens.indexOf('prompt')!==-1){
            var pIndex = tokens.indexOf('prompt');
            var newVar = tokens[pIndex+1];
            document.getElementById('output').value += newVar+'=?';
            awaitingInput=true;
            newInputVarName = newVar;
        }
        if(tokens.indexOf('input')!==-1){
            var pIndex = tokens.indexOf('input');
            var newVar = tokens[pIndex+1];
            document.getElementById('output').value += '?';
            awaitingInput=true;
            newInputVarName = newVar;
        }
        if(tokens.indexOf('pause')!==-1){
            awaitingInput=true;
            newInputVarName = null;
        }
        if(tokens.indexOf('pxl-on')!==-1){
            var first = tokens[2].substring(1,tokens[2].length);
            var second = tokens[4].substring(0,tokens[4].length-1);
            first = replaceVars(first);
            second = replaceVars(second);
            var valueF = eval(first);
            var valueS = eval(second);
            drawPixel(valueF,valueS,1);
            pixels[(valueF,valueS)] = 1;
        }
        if(tokens.indexOf('pxl-off')!==-1){
            var first2 = tokens[2].substring(1,tokens[2].length);
            var second2 = tokens[4].substring(0,tokens[4].length-1);
            first2 = replaceVars(first2);
            second2 = replaceVars(second2);
            var valueF2 = eval(first2);
            var valueS2 = eval(second2);
            pixels[(valueF2,valueS2)] = 0;
            drawPixel(valueF2,valueS2,0);
        }
        if(tokens.indexOf('clrdraw')!==-1){
            clearPixels();
        }
        if (tokens.indexOf('if') !== -1) {
            var index3 = tokens.indexOf('if');
            tokens[index3 + 1] = replaceVars(tokens[index3 + 1]);
            var value = eval(tokens[index3 + 1]);
            ifStack.push(value);
            typeStack.push('if');
        }
        if (tokens.indexOf('while') !== -1) {
            var index4 = tokens.indexOf('while');
            var expression = tokens[index4 + 1];
            expression = replaceVars(expression);
            var value2 = eval(expression);
            if (value2 === true) {
                typeStack.push('while');
                loopStack.push(currentLine);
            } else {
                currentLine = nextEnd(currentLine, lines);
                return currentLine;
            }
        }
        if (tokens.indexOf('for') !== -1) {
            var index5 = tokens.indexOf('for');
            var varName = tokens[index5 + 1];
            varName = varName.trim();
            varName = varName.substring(1, varName.length);
            var initValue = eval(replaceVars(tokens[index5 + 3]));
            variables[varName] = initValue;
            var endingValue = eval(replaceVars(tokens[index5 + 5]));
            var increaseVal = replaceVars(tokens[index5 + 7]);
            increaseVal = eval(increaseVal.substring(0, increaseVal.length - 1));
            var diff = endingValue - initValue;
            if (sign(diff) !== sign(increaseVal) && sign(diff) !== 0) {
                currentLine = nextEnd(currentLine, lines);
                return currentLine;
            } else {
                loopStack.push(currentLine);
                typeStack.push('for');
            }
        }
        if (tokens.indexOf('repeat') !== -1) {
            var repeatVal = eval(replaceVars(tokens[1]));
            if (repeatVal === true || repeatVal === false) {
                //basically the same as a while loop...so just replace it!
                var newLine = 'while ' + '!(' + tokens[1] + ')';
                lines[currentLine] = newLine;
                currentLine--;
                return currentLine;
            } else {
                repeatStack.push(0);
                typeStack.push('repeat');
                loopStack.push(currentLine);
            }
        }
    }
    if (tokens.indexOf('else') !== -1) {
       ifStack[ifStack.length - 1] = !ifStack[ifStack.length - 1];
    }
    if (tokens.indexOf('end') !== -1) {
        if (typeStack[typeStack.length - 1] === 'if') {
            ifStack.pop();
            typeStack.pop();
        } else if (typeStack[typeStack.length - 1] === 'while') {
            var prevLineNum = loopStack[loopStack.length - 1];
            var prevLine = lines[prevLineNum];
            var prevTokens = tokenize(prevLine);
            var whileIndex = prevTokens.indexOf('while');
            var expression2 = replaceVars(prevTokens[whileIndex + 1]);
            if (eval(expression2) === true) {
                currentLine = prevLineNum - 1;
                return currentLine;
            } else {
                loopStack.pop();
                typeStack.pop();
            }
        } else if (typeStack[typeStack.length - 1] === 'repeat') {
            var line = lines[loopStack[loopStack.length - 1]];
            var tokenized = tokenize(line);
            var numTimes = eval(replaceVars(tokenized[1]));
            var currentIteration = repeatStack[repeatStack.length - 1];
            currentIteration++;
            if (currentIteration !== numTimes) {
                repeatStack[repeatStack.length - 1] = currentIteration;
                currentLine = loopStack[loopStack.length - 1]; //once currentLine++, will be on next line after repeat;
                return currentLine;
            } else {
                repeatStack.pop();
                typeStack.pop();
                loopStack.pop();
            }
        } else if (typeStack[typeStack.length - 1] === 'for') {
            var prevLineNum2 = loopStack[loopStack.length - 1];
            var prevLine2 = lines[prevLineNum2];
            var prevTokens2 = tokenize(prevLine2);
            var forIndex = prevTokens2.indexOf('for');
            var varName2 = prevTokens2[forIndex + 1];
            varName2 = varName2.substring(1, varName2.length);
            var initVal = eval(replaceVars(prevTokens2[forIndex + 3]));
            var endVal = eval(replaceVars(prevTokens2[forIndex + 5]));
            var stepVal = replaceVars(prevTokens2[forIndex + 7]);
            stepVal = eval(stepVal.substring(0, stepVal.length - 1));
            variables[varName2] = parseInt(stepVal, 10) + parseInt(variables[varName2], 10);
            var signDiff = sign(endVal - initVal);
            var condTrue = true;
            if (signDiff === 0) {
                condTrue = false;
            }
            if (signDiff === 1) {
                if (variables[varName2] > endVal) {
                    condTrue = false;
                }
            } else {
                if (variables[varName2] < endVal) {
                    condTrue = false;
                }
            }
            if (condTrue === true) {
                currentLine = prevLineNum2;
                return currentLine;
            } else {
                typeStack.pop();
                loopStack.pop();
            }
        }
    }
    return currentLine;
}

function sign(num) {
    if (num === 0) {
        return 0;
    }
    if (num > 0) {
        return 1;
    }
    return -1;
}
function drawPixel(x,y,color){//color = 0 if off, 1 if on
    var canvas = document.getElementById('canvas');
    var width = canvas.width;
    var height = canvas.height;
    var pxWidth = width/96;
    var pxHeight = height/64;
    var ctx = canvas.getContext('2d');
    if(color===1){
        ctx.fillStyle = '#000';
    }else{
        ctx.fillStyle = '#fff';
    }
    ctx.fillRect((x/96)*width, (y/64)*height,pxWidth,pxHeight);
}
function nextEnd(line, lines) {
    for (var i = line + 1; i < lines.length; i++) {
        if (lines[i].indexOf('end') !== -1) {
            return i;
        }
    }
    return line;
}

function tokenize(line) {
    line = line.trim();
    var split = [];
    var currentSplit = '';
    var cursor = 0;
    var unknown = '';
    var allTokens = tokens;
    while (cursor < line.length) {
        var lengthOfCursor = line.length - cursor;
        while (lengthOfCursor > 0) {
            var index = allTokens.indexOf(line.substring(cursor, cursor + lengthOfCursor));
            if (index !== -1) {
                if (unknown !== '') {
                    split.push(unknown.trim());
                }
                unknown = '';
                split.push(allTokens[index]);
                cursor += lengthOfCursor - 1; //for cursor++ later
                break;
            }
            lengthOfCursor--;
            if (lengthOfCursor === 0) {
                unknown = unknown.concat(line.charAt(cursor));
            }
        }
        cursor++;
    }
    if (unknown !== '') {
        split.push(unknown.trim());
    }
    return split;
}

function replaceVars(token) {
    for (var i = 0; i < tokens.length; i++) {
        if (token === tokens[i]) {
            return token;
        }
    }
    //deals with lists
    for (var cursor = 0; cursor < token.length - 1; cursor++) {
        if (/[^a-zA-Z_]L[1-6]|^L[1-6]/.test(token.substring(cursor, cursor + 3)) === true) {
            var parenthIndex;
            for (var newCurs = cursor; newCurs < token.length; newCurs++) {
                if (token.charAt(newCurs) === '(') {
                    parenthIndex = newCurs;
                    break;
                }
            }
            var nextPIndex = matchParenthese(token, parenthIndex);
            var inner = token.substring(parenthIndex + 1, nextPIndex);
            //note recursiveness, supports L1(L1(L1(5))), for example
            var innerValue = eval(replaceVars(inner));
            var num = parseInt(token.substring(parenthIndex - 1, parenthIndex));
            var realValue;
            if (num === 1) {
                realValue = L1[innerValue];
            }
            if (num === 2) {
                realValue = L2[innerValue];
            }
            if (num === 3) {
                realValue = L3[innerValue];
            }
            if (num === 4) {
                realValue = L4[innerValue];
            }
            if (num === 5) {
                realValue = L5[innerValue];
            }
            if (num === 6) {
                realValue = L6[innerValue];
            }
            if (innerValue !== Math.round(innerValue) || innerValue < 1) {
                printE('array indexes must be integers greater or equal to 1. Why? ask Texas Instruments.');
                throw new Error();
            }
            token = token.substring(0, parenthIndex - 2) + realValue + token.substring(nextPIndex + 1);
        }
    }
    //Math stuff
    var a;
    var sinFunc = function (value) {
        return Math.sin(value);
    };
    while ((a = returnValue('sin', token, sinFunc)) !== null) {
        token = a;
    }

    var cosFunc = function (value) {
        return Math.cos(value);
    };
    while ((a = returnValue('cos', token, cosFunc)) !== null) {
        token = a;
    }

    var tanFunc = function (value) {
        return Math.tan(value);
    };
    while ((a = returnValue('tan', token, tanFunc)) !== null) {
        token = a;
    }

    var asinFunc = function (value) {
        return Math.asin(value);
    };
    while ((a = returnValue('asin', token, asinFunc)) !== null) {
        token = a;
    }

    var acosFunc = function (value) {
        return Math.acos(value);
    };
    while ((a = returnValue('acos', token, acosFunc)) !== null) {
        token = a;
    }

    var atanFunc = function (value) {
        return Math.atan(value);
    };
    while ((a = returnValue('atan', token, atanFunc)) !== null) {
        token = a;
    }
    //note my calculator doesn't have atan2...

    var absFunc = function (value) {
        return Math.abs(value);
    };
    while ((a = returnValue('abs', token, absFunc)) !== null) {
        token = a;
    }

    var roundFunc = function (value) {
        return Math.round(value);
    };
    while ((a = returnValue('round', token, roundFunc)) !== null) {
        token = a;
    }

    var intFunc = function (value) {
        return Math.floor(value);
    };
    while ((a = returnValue('int', token, intFunc)) !== null) {
        token = a;
    }

    var coshFunc = function (value) {
        return (Math.pow(Math.E, value) + Math.pow(Math.E, -1 * value)) / 2;
    };
    while ((a = returnValue('cosh', token, coshFunc)) !== null) {
        token = a;
    }

    var sinhFunc = function (value) {
        return (Math.pow(Math.E, value) - Math.pow(Math.E, -1 * value)) / 2;
    };
    while ((a = returnValue('sinh', token, sinhFunc)) !== null) {
        token = a;
    }

    var tanhFunc = function (value) {
        return (Math.pow(Math.E, value) - Math.pow(Math.E, -1 * value)) / (Math.pow(Math.E, value) + Math.pow(Math.E, -1 * value));
    };
    while ((a = returnValue('tanh', token, tanhFunc)) !== null) {
        token = a;
    }

    //if token contains new variables, then initialize them with random values
    var newReg = new RegExp('([^a-zA-Z_])([a-zA-Z_]+)([^a-zA-Z_])', 'g');
    var newReg2 = new RegExp('^([a-zA-Z_]+)([^a-zA-Z_])', 'g');
    var newReg3 = new RegExp('([^a-zA-Z_])([a-zA-Z_]+)$', 'g');
    var newReg4 = new RegExp('^([a-zA-Z_]+)$', 'g');
    var match1 = token.match(newReg);
    if (match1 !== null) {
        for (var q = 0; q < match1.length; q++) {
            initializeVar(match1[q].substring(1, match1[q].length - 1));
        }
    }

    var match2 = token.match(newReg2);
    if (match2 !== null) {
        for (var w = 0; w < match2.length; w++) {
            initializeVar(match2[w].substring(0, match2[w].length - 1));
        }
    }

    var match3 = token.match(newReg3);
    if (match3 !== null) {
        for (var e = 0; e < match3.length; e++) {
            initializeVar(match3[e].substring(1, match3[e].length));
        }
    }

    var match4 = token.match(newReg4);
    if (match4 !== null) {
        for (var r = 0; r < match4.length; r++) {
            initializeVar(match4[r].substring(0, match4[r].length));
        }
    }

    var varNames = [];
    for (var key in variables) {
        if (token.indexOf(key) !== -1) {
            var regex1 = '([^a-zA-Z_])(' + key + ')([^a-zA-Z_])';
            var reg = new RegExp(regex1, 'g');
            token = token.replace(reg, '$1' + variables[key] + '$3');
            var regex2 = '(^' + key + ')([^a-zA-Z_])';
            var reg2 = new RegExp(regex2, 'g');
            token = token.replace(reg2, variables[key] + '$2');
            var regex3 = '([^a-zA-Z_])(' + key + ')$';
            var reg3 = new RegExp(regex3, 'g');
            token = token.replace(reg3, '$1' + variables[key]);
            var reg4 = new RegExp('^' + key + '$', 'g');
            token = token.replace(reg4, variables[key]);
        }
    }
    return token;
}

function matchParenthese(token, index) {
    var pStack = [];
    for (var cursor = index + 1; cursor < token.length; cursor++) {
        if (token.charAt(cursor) === '(') {
            pStack.push(1);
        }
        if (token.charAt(cursor) === ')') {
            if (pStack.length > 0) {
                pStack.pop();
            } else {
                return cursor;
            }
        }
    }
    return index;
}

function returnValue(identifyer, token, toDoFunction) { //note: do NOT include parentheses in identifyer
    for (var cursor = 0; cursor < token.length; cursor++) {
        if (token.length > cursor + identifyer.length) {
            if (token.substring(cursor, cursor + identifyer.length) === identifyer) {
                if (cursor === 0 || /^[^a-zA-Z_]/.test(token.charAt(cursor - 1)) === true) {
                    if (nextNonWhiteChar(token, cursor + identifyer.length - 1) === '(') {
                        print(identifyer);
                        var nextParen = matchParenthese(token, cursor + identifyer.length + 1);
                        var inner = token.substring(cursor + identifyer.length + 1, nextParen);
                        inner = replaceVars(inner);
                        var value = eval(inner);
                        value = toDoFunction(value);
                        return token.substring(0, cursor) + value + token.substring(nextParen + 1, token.length);
                    }
                }
            }
        }

    }
    return null;
}

function nextNonWhiteChar(token, index) { //give non-white character
    for (var i = index + 1; i < token.length; i++) {
        if (token.charAt(i) !== ' ') {
            return token.charAt(i);
        }
    }
}
function clearPixels(){
    var canvas = document.getElementById('canvas');
    canvas.getContext('2d').fillStyle = '#fff';
    canvas.getContext('2d').fillRect(0,0,canvas.width,canvas.height);
    for(var x=0;x<96;x++){
        for(var y=0;y<64;y++){
            pixels[(x,y)] = 0;
        }
    }
}
function stop(){
    running = false;
    clearInterval(lineProcessing);
}
function initializeVar(name) {
    if (!(name in variables) && name !== 'L1' && name !== 'L2' && name !== 'L3' && name !== 'L4' && name !== 'L5' && name !== 'L6') {
        variables[name] = Math.random() * 100;
    }
}

function clear() {
    document.getElementById('output').value = '';
    document.getElementById('error').value = '';
}

function printE(str) {
    document.getElementById('error').value += str + '\n'
}

function print(str) {
    document.getElementById('output').value += str + '\n';
}

<h1>Ti-Basic Interpreter</h1>


<h3>Code</h3>

<textarea id='code-block' cols='50' rows='7' oninput='inputChanged()'>:clrdraw
:for(a,2,96,2)
:for(b,(a/2)%2,64,2)
:pxl-on(a,b)
:end
:end</textarea>
<br>
<button width='20' height='10' onclick='run()'>Run</button>
    <button width='20' height='10' onclick='stop()'>Stop</button>

<h3>Output (also input)</h3>

    <textarea id='output' cols='50' rows='7' onkeypress='onUserInput(event)'></textarea>
<br>
    <canvas id='canvas' width='192' height='128'></canvas>
<br>

<textarea id='error' cols='50' rows='7'></textarea>