<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<div class="moz-cite-prefix">On 2016-02-26 18:29, Anders Sandberg
wrote:<br>
</div>
<blockquote cite="mid:56D0DFD1.4030008@aleph.se" type="cite">
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
<div class="moz-cite-prefix">On 2016-02-26 16:40, John Clark
wrote:<br>
</div>
<blockquote
cite="mid:CAJPayv2tGYcAcjqLv+=NP6J7RW1P_W-LqMu6-DRNQdtyOHV+8g@mail.gmail.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=UTF-8">
<div dir="ltr"><br>
<div class="gmail_extra">
<div class="gmail_quote">
<div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif"><font
size="4">No I don't mean that, I mean running
around in a circle and making no progress but having
no way to know for sure that you're running around
in a circle and making no progress. Turing proved
there is in general no way to know if you're in a
infinite loop or not.</font></div>
</div>
</div>
</div>
</div>
</blockquote>
<br>
No, he did not. You are confusing the halting theorem (there is no
algorithm that</blockquote>
<blockquote cite="mid:56D0DFD1.4030008@aleph.se" type="cite">can
determine if a program given to it will halt) with detecting an
infinite loop.</blockquote>
<br>
<span class="im"></span>
<div>For finite programs, it's the same problem. Either a program
halts or it loops forever.</div>
<span class="im">
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> Note that a program X can
be extended to a program X' (or run by an interpreter) that </div>
</blockquote>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">maintains a list of past
states and check if X returns to a previous state. It will
accurately </div>
</blockquote>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">detect its infinite
looping when it occurs.<br>
</div>
</blockquote>
<div><br>
</div>
</span>
<div>You can loop forever without ever returning to a previous
state, though:</div>
<div><br>
</div>
<div>10 LET UNBOUNDED INTEGER i = 0;</div>
<div>20 i = i + 1;</div>
<div>30 GOTO 20;</div>
<div><br>
</div>
<div>Your proposed loop detector would never detect this simple
infinite loop.</div>
<pre class="moz-signature" cols="72">--
__________
|im Tyler <a class="moz-txt-link-freetext" href="http://timtyler.org/">http://timtyler.org/</a>
</pre>
</body>
</html>