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azproduction/LICENSE.txt

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Created November 28, 2011 14:03
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A turing machine in 79! bytes of javascript
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README.md
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annotated.js
// added some curly braces for readability
function(
a, // {Object} program @see test.html for details
b, // {Number[]} tape
c, // {String} end state
d, // {String} start state
e // [{Number} = 0] caret position
) {
while(
d < c // while ! eof program
) {
/* 'e |= 0' - if e is undefined - reset to 0 else leave as is */
with (/* q = */a[d][b[e |= 0] || "B"]) { // push current program statement aka "q" to the top of current scope
b[e] = w, // chenge symbol under caret, w is the item of "q"
e += m, // move caret by ..., m is the item of "q"
d = n; // jump to next state, n is the item of "q"
}
}
return b
}
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index.js
function(a,b,c,d,e){while(d<c)with(a[d][b[e|=0]||"B"])b[e]=w,e+=m,d=n;return b}
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LICENSE.txt
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
Version 2, December 2004
Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE>
Everyone is permitted to copy and distribute verbatim or modified
copies of this license document, and changing it is allowed as long
as the name is changed.
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. You just DO WHAT THE FUCK YOU WANT TO.
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package.json
{
"name": "turing_machine",
"description": "A turing machine implementation",
"keywords": [
"turing_machine"
]
}
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test.html
<!DOCTYPE html>
<title>Foo</title>
<div>Expected value: <b>1,1,1,0,1,1,1</b></div>
<div>Actual value: <b id="ret"></b></div>
<script>
var tm = function(a,b,c,d,e){while(d<c)with(a[d][b[e|=0]||"B"])b[e]=w,e+=m,d=n;return b};
var program = {"q0": {"1": {"w": "B", "m": 1, "n": "q1"}},
"q1": {"1": {"w": "1", "m": 1, "n": "q1"},
"0": {"w": "0", "m": 1, "n": "q2"},
"B": {"w": "0", "m": 1, "n": "q2"}},
"q2": {"1": {"w": "1", "m": 1, "n": "q2"},
"B": {"w": "1", "m": -1, "n": "q3"}},
"q3": {"1": {"w": "1", "m": -1, "n": "q3"},
"0": {"w": "0", "m": -1, "n": "q3"},
"B": {"w": "1", "m": 1, "n": "q4"}},
"q4": {"1": {"w": "B", "m": 1, "n": "q1"},
"0": {"w": "0", "m": 1, "n": "q5"}}};
var tape = [1,1,1];
document.getElementById("ret").innerHTML = tm(program, tape, "q5", "q0", 0);
</script>
@azproduction
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Author

Just updated gist. Guess it's final version :) Thx for help!

@tsaniel
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tsaniel commented Dec 1, 2011 

function(a,b,c,d,e){for(;d<c;)with(a[d][b[e|=0]||"B"])b[e]=w,e+=m,d=n;return b}

The above uses the same bytes and allows we to decide the starting position(default 0).

@bjuergens
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when you change the final state in a to something falsy (e.g. "") you can drop c and save 4 symbols:
so
function(a,b,d,e){while(d)with(a[d][b[e|=0]||"B"])b[e]=w,e+=m,d=n;return b} becomes:
function(a,b,c,d,e){while(d<c)with(a[d][b[e|=0]||"B"])b[e]=w,e+=m,d=n;return b}

note: as of 2016 this still seems to be the shortest JS.TM out there. Good Job!

@zsarge
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zsarge commented Oct 4, 2020

Not to revive a thread from 2016, but the introduction of arrow functions would help here.

(Without Falsy A)

(a,b,c,d,e)=>{while(d<c)with(a[d][b[e|=0]||"B"])b[e]=w,e+=m,d=n;return b}

73 Chars

jsfiddle modified from the original author

@brixdan
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brixdan commented Mar 1, 2021

Might well happen (b[e|=0]) = 0, then ||"B" will cause absolutely wrong course of actions. It's a pure bug. Sorry.

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