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From: wij <wyniijj5@gmail.com>
Newsgroups: comp.theory
Subject: Re: How to write a self-referencial TM?
Date: Thu, 15 May 2025 09:58:13 +0800
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On Thu, 2025-05-15 at 09:38 +0800, wij wrote:
> On Wed, 2025-05-14 at 17:19 -0700, Keith Thompson wrote:
> > Andy Walker <anw@cuboid.co.uk> writes:
> > > On 14/05/2025 21:16, Richard Heathfield wrote:
> > > > On 14/05/2025 21:00, Keith Thompson wrote:
> > > > > I presume that one-way and two-way infinite tapes are computation=
ally
> > > > > equivalent, so the distinction doesn't matter all that much.
> > >=20
> > > 	Indeed, there are lots of computationally equivalent versions:
> > >=20
> > > =C2=A0-- two or more tapes [indeed, two-dimensional tapes]
> > > =C2=A0-- one-way or two-way
> > > =C2=A0-- "paper" tapes where you can punch holes to change the conten=
t but not
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 stick the chad back in to "unpunch" th=
e holes
> > > =C2=A0-- two symbol, three symbol, ...
> > > =C2=A0-- move two or more spaces at a time
> > > =C2=A0-- others I've forgotten
> >=20
> > Not to mention the very common variant where landing on Free Parking
> > means you get all the money from the center of the board.=C2=A0 Or was =
that
> > something else?
> >=20
> > [...]
>=20
> // Manpage of class Spu
> NAME
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Spu - Class of general purpose Soft-=
CPU
>=20
> SYNOPSIS
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Except POD types, C structures, all =
types are declared in namespace Wy.
>=20
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 #include <CSCall/Sct.h>
>=20
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Spu=C2=A0 (Soft=C2=A0 CPU)=C2=A0 is=
=C2=A0 a revised model of Turing Machine and a class that
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 acts like a general purpose CPU-base=
d computing machine to=C2=A0 provide=C2=A0 se=E2=80=90
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 mantics for computing language and f=
or remote program communication.
>=20
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 The=C2=A0 main differences of Spu an=
d general purpose CPU (or TM) is that Spu
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 has no =C2=B4register=C2=B4 nor =C2=
=B4flag=C2=B4, Spu has only a tape. The tape is initially
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 empty. Every object (referred to as =
tape variable) in the tape is=C2=A0 allo=E2=80=90
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cated via instruction Alloc and iden=
tified by a continuous index number.
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Tape variable can be any C++ type, i=
ncluding Spu.
>=20
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 The=C2=A0 instruction=C2=A0 of Spu i=
s application definable. Except necessary few,
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 about=C2=A0 >30=C2=A0 instructions=
=C2=A0 are=C2=A0 defined=C2=A0 for=C2=A0 convenience,=C2=A0  see=C2=A0=C2=
=A0 manpage
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Wy.Sct(3wy).
>=20
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Documentation following omits the sc=
ope name Wy::Sct for each occurrence
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 of Spu for clearity.
>=20
> [cut]
> ----------------------
>=20
> 1. In Spu, objects in the tape are allocated (constructed).
> 2. Accessing the tape outside range will throw an error.
> 3. Instructions in Spu are class members. 'instructions' can be considere=
d=20
> =C2=A0=C2=A0 variable or stateful (useful in developing theory), because =
data structure=C2=A0
> =C2=A0=C2=A0 related to instruction is considered part of the instruction=
, simiar to the
> =C2=A0=C2=A0 OO concept of C++ class.
> 4. Multi-tasking can be modeled by multi-instances of Spu (or tape variab=
le
> =C2=A0=C2=A0 can be an Spu object)
>=20

With the issue of TM's tape at least, I think Spu is more *realistic* than =
TM.