Self modifying code, lambda calculus - Re: ENIAC programming

Rich Alderson RichA at
Thu Sep 17 18:49:59 CDT 2015

From: Paul Koning
Sent: Thursday, September 17, 2015 9:02 AM

> In any case, I do not believe the original statement.  First of all, it is
> well known that no computer can solve "all problems" (see Gödel).  For those
> it *can* solve, as far as I know, a Turing machine can solve a superset of
> what a stored program computer can handle,

All right so far.

> and a Turing machine does NOT have self-modifying code.

<choke><spit><soda on keyboard>

Excuse me????

A Turing machine is the very essence of self-modifying code, by its very
definition!  You have the infinite memory tape, divided into cells, a reader,
and a writer.  The reader looks at a cell and performs the action required by
the symbol read there.  Possible actions include erasing the symbol already
present and writing a new symbol; once that is done, the reader looks at the
new symbol and performs the action required by *that* symbol.

Lather, rinse, repeat.  (Interrupt when out of shampoo.)


Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

mailto:RichA at

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