;T...!59*\1=33*++o.9=\1=2*+(1"
The T should be replaced with a literal tab character.
About Ouroboros
Each line of an Ouroboros program represents a snake eating its own tail, with the beginning of the line being the head and the end being the tail. The only control flow operations are commands to eat or regurgitate characters of the tail. When the instruction pointer reaches the last part of the line that hasn't been eaten, it loops back to the beginning. If the instruction pointer is swallowed, execution halts.
While Ouroboros has some similarities to 2D languages such as ><>, its limited control flow options presented a challenge for quine construction. The only way to skip an instruction is to put it near the end and swallow it--which means instructions near the beginning basically can't be skipped. It took some experimenting before I found a quine structure that worked.
Explanation
The core idea is similar to a ><> or Befunge quine: with a wrapping IP, a single " mark can be used to stringify the code on one pass and execute it on another. Ouroboros automatically pushes strings to the stack in reverse order, which simplifies things. However, we have to put the quotation mark at the end so we can swallow it to avoid pushing the string multiple times. That means that the code must be executed first, then the string pushed, and then the code executed again until the output is complete.
On every pass, the code does two main things: output a character and swallow 0 or more characters of code.
...!59*\1=33*++o
On the first pass, the stack is empty and treated as zero. Logically negating and multiplying by 59 gives the character code for ;, the first character of the quine. On the final pass, the 1 that was pushed right before the string (at the very end of the code) is encountered, to which we add 33 to turn it into 34, the closing ". On other passes, the character code is output unchanged. In pseudocode: output (!top)*59 + (top==1)*33 + top
.9=\1=2*+(
There are two passes on which code needs to be swallowed. On the first pass after we push the string (when we print the tab) the quotation mark has to go; and on the last pass (after we've processed the whole string and the 1 is left on the stack) two more characters are eaten to swallow the instruction pointer and end the program. On every other pass, don't eat anything. In pseudocode: swallow (top==9)+(top==1)*2
One problem remains: since we output the first character of code on the initial pass, we have to drop it (;) immediately after pushing the string so it won't be output a second time. But we don't want to drop anything on subsequent passes. Fortunately, at the end of each iteration we push another 1 to the stack, which is immediately dropped at the beginning of the next pass.
Try it out
// Define Stack class
function Stack() {
this.stack = [];
this.length = 0;
}
Stack.prototype.push = function(item) {
this.stack.push(item);
this.length++;
}
Stack.prototype.pop = function() {
var result = 0;
if (this.length > 0) {
result = this.stack.pop();
this.length--;
}
return result;
}
Stack.prototype.top = function() {
var result = 0;
if (this.length > 0) {
result = this.stack[this.length - 1];
}
return result;
}
Stack.prototype.toString = function() {
return "" + this.stack;
}
// Define Snake class
function Snake(code) {
this.code = code;
this.length = this.code.length;
this.ip = 0;
this.ownStack = new Stack();
this.currStack = this.ownStack;
this.alive = true;
this.wait = 0;
this.partialString = this.partialNumber = null;
}
Snake.prototype.step = function() {
if (!this.alive) {
return null;
}
if (this.wait > 0) {
this.wait--;
return null;
}
var instruction = this.code.charAt(this.ip);
var output = null;
console.log("Executing instruction " + instruction);
if (this.partialString !== null) {
// We're in the middle of a double-quoted string
if (instruction == '"') {
// Close the string and push its character codes in reverse order
for (var i = this.partialString.length - 1; i >= 0; i--) {
this.currStack.push(this.partialString.charCodeAt(i));
}
this.partialString = null;
} else {
this.partialString += instruction;
}
} else if (instruction == '"') {
this.partialString = "";
} else if ("0" <= instruction && instruction <= "9") {
if (this.partialNumber !== null) {
this.partialNumber = this.partialNumber + instruction; // NB: concatenation!
} else {
this.partialNumber = instruction;
}
next = this.code.charAt((this.ip + 1) % this.length);
if (next < "0" || "9" < next) {
// Next instruction is non-numeric, so end number and push it
this.currStack.push(+this.partialNumber);
this.partialNumber = null;
}
} else if ("a" <= instruction && instruction <= "f") {
// a-f push numbers 10 through 15
var value = instruction.charCodeAt(0) - 87;
this.currStack.push(value);
} else if (instruction == "$") {
// Toggle the current stack
if (this.currStack === this.ownStack) {
this.currStack = this.program.sharedStack;
} else {
this.currStack = this.ownStack;
}
} else if (instruction == "s") {
this.currStack = this.ownStack;
} else if (instruction == "S") {
this.currStack = this.program.sharedStack;
} else if (instruction == "l") {
this.currStack.push(this.ownStack.length);
} else if (instruction == "L") {
this.currStack.push(this.program.sharedStack.length);
} else if (instruction == ".") {
var item = this.currStack.pop();
this.currStack.push(item);
this.currStack.push(item);
} else if (instruction == "m") {
var item = this.ownStack.pop();
this.program.sharedStack.push(item);
} else if (instruction == "M") {
var item = this.program.sharedStack.pop();
this.ownStack.push(item);
} else if (instruction == "y") {
var item = this.ownStack.top();
this.program.sharedStack.push(item);
} else if (instruction == "Y") {
var item = this.program.sharedStack.top();
this.ownStack.push(item);
} else if (instruction == "\\") {
var top = this.currStack.pop();
var next = this.currStack.pop()
this.currStack.push(top);
this.currStack.push(next);
} else if (instruction == "@") {
var c = this.currStack.pop();
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(c);
this.currStack.push(a);
this.currStack.push(b);
} else if (instruction == ";") {
this.currStack.pop();
} else if (instruction == "+") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(a + b);
} else if (instruction == "-") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(a - b);
} else if (instruction == "*") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(a * b);
} else if (instruction == "/") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(a / b);
} else if (instruction == "%") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(a % b);
} else if (instruction == "_") {
this.currStack.push(-this.currStack.pop());
} else if (instruction == "I") {
var value = this.currStack.pop();
if (value < 0) {
this.currStack.push(Math.ceil(value));
} else {
this.currStack.push(Math.floor(value));
}
} else if (instruction == ">") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(+(a > b));
} else if (instruction == "<") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(+(a < b));
} else if (instruction == "=") {
var b = this.currStack.pop();
var a = this.currStack.pop();
this.currStack.push(+(a == b));
} else if (instruction == "!") {
this.currStack.push(+ !this.currStack.pop());
} else if (instruction == "?") {
this.currStack.push(Math.random());
} else if (instruction == "n") {
output = "" + this.currStack.pop();
} else if (instruction == "o") {
output = String.fromCharCode(this.currStack.pop());
} else if (instruction == "r") {
var input = this.program.io.getNumber();
this.currStack.push(input);
} else if (instruction == "i") {
var input = this.program.io.getChar();
this.currStack.push(input);
} else if (instruction == "(") {
this.length -= Math.floor(this.currStack.pop());
this.length = Math.max(this.length, 0);
} else if (instruction == ")") {
this.length += Math.floor(this.currStack.pop());
this.length = Math.min(this.length, this.code.length);
} else if (instruction == "w") {
this.wait = this.currStack.pop();
}
// Any unrecognized character is a no-op
if (this.ip >= this.length) {
// We've swallowed the IP, so this snake dies
this.alive = false;
this.program.snakesLiving--;
} else {
// Increment IP and loop if appropriate
this.ip = (this.ip + 1) % this.length;
}
return output;
}
Snake.prototype.getHighlightedCode = function() {
var result = "";
for (var i = 0; i < this.code.length; i++) {
if (i == this.length) {
result += '<span class="swallowedCode">';
}
if (i == this.ip) {
if (this.wait > 0) {
result += '<span class="nextActiveToken">';
} else {
result += '<span class="activeToken">';
}
result += escapeEntities(this.code.charAt(i)) + '</span>';
} else {
result += escapeEntities(this.code.charAt(i));
}
}
if (this.length < this.code.length) {
result += '</span>';
}
return result;
}
// Define Program class
function Program(source, speed, io) {
this.sharedStack = new Stack();
this.snakes = source.split(/\r?\n/).map(function(snakeCode) {
var snake = new Snake(snakeCode);
snake.program = this;
snake.sharedStack = this.sharedStack;
return snake;
}.bind(this));
this.snakesLiving = this.snakes.length;
this.io = io;
this.speed = speed || 10;
this.halting = false;
}
Program.prototype.run = function() {
this.step();
if (this.snakesLiving) {
this.timeout = window.setTimeout(this.run.bind(this), 1000 / this.speed);
}
}
Program.prototype.step = function() {
for (var s = 0; s < this.snakes.length; s++) {
var output = this.snakes[s].step();
if (output) {
this.io.print(output);
}
}
this.io.displaySource(this.snakes.map(function (snake) {
return snake.getHighlightedCode();
}).join("<br>"));
}
Program.prototype.halt = function() {
window.clearTimeout(this.timeout);
}
var ioFunctions = {
print: function (item) {
var stdout = document.getElementById('stdout');
stdout.value += "" + item;
},
getChar: function () {
if (inputData) {
var inputChar = inputData[0];
inputData = inputData.slice(1);
result = inputChar.charCodeAt(0);
} else {
result = -1;
}
var stdinDisplay = document.getElementById('stdin-display');
stdinDisplay.innerHTML = escapeEntities(inputData);
return result;
},
getNumber: function () {
while (inputData && (inputData[0] < "0" || "9" < inputData[0])) {
inputData = inputData.slice(1);
}
if (inputData) {
var inputNumber = inputData.match(/\d+/)[0];
inputData = inputData.slice(inputNumber.length);
result = +inputNumber;
} else {
result = -1;
}
var stdinDisplay = document.getElementById('stdin-display');
stdinDisplay.innerHTML = escapeEntities(inputData);
return result;
},
displaySource: function (formattedCode) {
var sourceDisplay = document.getElementById('source-display');
sourceDisplay.innerHTML = formattedCode;
}
};
var program = null;
var inputData = null;
function showEditor() {
var source = document.getElementById('source'),
sourceDisplayWrapper = document.getElementById('source-display-wrapper'),
stdin = document.getElementById('stdin'),
stdinDisplayWrapper = document.getElementById('stdin-display-wrapper');
source.style.display = "block";
stdin.style.display = "block";
sourceDisplayWrapper.style.display = "none";
stdinDisplayWrapper.style.display = "none";
source.focus();
}
function hideEditor() {
var source = document.getElementById('source'),
sourceDisplay = document.getElementById('source-display'),
sourceDisplayWrapper = document.getElementById('source-display-wrapper'),
stdin = document.getElementById('stdin'),
stdinDisplay = document.getElementById('stdin-display'),
stdinDisplayWrapper = document.getElementById('stdin-display-wrapper');
source.style.display = "none";
stdin.style.display = "none";
sourceDisplayWrapper.style.display = "block";
stdinDisplayWrapper.style.display = "block";
var sourceHeight = getComputedStyle(source).height,
stdinHeight = getComputedStyle(stdin).height;
sourceDisplayWrapper.style.minHeight = sourceHeight;
sourceDisplayWrapper.style.maxHeight = sourceHeight;
stdinDisplayWrapper.style.minHeight = stdinHeight;
stdinDisplayWrapper.style.maxHeight = stdinHeight;
sourceDisplay.textContent = source.value;
stdinDisplay.textContent = stdin.value;
}
function escapeEntities(input) {
return input.replace(/&/g, '&').replace(/</g, '<').replace(/>/g, '>');
}
function resetProgram() {
var stdout = document.getElementById('stdout');
stdout.value = null;
if (program !== null) {
program.halt();
}
program = null;
inputData = null;
showEditor();
}
function initProgram() {
var source = document.getElementById('source'),
stepsPerSecond = document.getElementById('steps-per-second'),
stdin = document.getElementById('stdin');
program = new Program(source.value, +stepsPerSecond.innerHTML, ioFunctions);
hideEditor();
inputData = stdin.value;
}
function runBtnClick() {
if (program === null || program.snakesLiving == 0) {
resetProgram();
initProgram();
} else {
program.halt();
var stepsPerSecond = document.getElementById('steps-per-second');
program.speed = +stepsPerSecond.innerHTML;
}
program.run();
}
function stepBtnClick() {
if (program === null) {
initProgram();
} else {
program.halt();
}
program.step();
}
function sourceDisplayClick() {
resetProgram();
}
.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;
}
h1 {
text-align: center;
font-family: Georgia, 'Times New Roman', serif;
}
a {
text-decoration: none;
}
input, textarea {
box-sizing: border-box;
}
textarea {
display: block;
white-space: pre;
overflow: auto;
height: 50px;
width: 100%;
max-width: 100%;
min-height: 25px;
}
span[contenteditable] {
padding: 2px 6px;
background: #cc7801;
color: #fff;
}
#stdout-container, #stdin-container {
height: auto;
padding: 6px 0;
}
#reset {
float: right;
}
#source-display-wrapper , #stdin-display-wrapper{
display: none;
width: 100%;
height: 100%;
overflow: auto;
border: 1px solid black;
box-sizing: border-box;
}
#source-display , #stdin-display{
font-family: monospace;
white-space: pre;
padding: 2px;
}
.activeToken {
background: #f93;
}
.nextActiveToken {
background: #bbb;
}
.swallowedCode{
color: #999;
}
.clearfix:after {
content:".";
display: block;
height: 0;
clear: both;
visibility: hidden;
}
.clearfix {
display: inline-block;
}
* html .clearfix {
height: 1%;
}
.clearfix {
display: block;
}
<!--
Designed and written 2015 by D. Loscutoff
Much of the HTML and CSS was taken from this Befunge interpreter by Ingo Bürk: http://codegolf.stackexchange.com/a/40331/16766
-->
<div class="container">
<textarea id="source" placeholder="Enter your program here" wrap="off">; ...!59*\1=33*++o.9=\1=2*+(1"</textarea>
<div id="source-display-wrapper" onclick="sourceDisplayClick()"><div id="source-display"></div></div></div><div id="stdin-container" class="container">
<textarea id="stdin" placeholder="Input" wrap="off"></textarea>
<div id="stdin-display-wrapper" onclick="stdinDisplayClick()"><div id="stdin-display"></div></div></div><div id="controls-container" class="container clearfix"><input type="button" id="run" class="control so-box" value="Run" onclick="runBtnClick()" /><input type="button" id="pause" class="control so-box" value="Pause" onclick="program.halt()" /><input type="button" id="step" class="control so-box" value="Step" onclick="stepBtnClick()" /><input type="button" id="reset" class="control so-box" value="Reset" onclick="resetProgram()" /></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 Second:
<span id="steps-per-second" contenteditable>20</span></div></div>
