so-called Turing-Equivalence

Francois-Rene Rideau
31 Jul 1999 12:56:29 +0200

>: Tim Bradshaw <> on comp.lang.lisp
> Another formalism of equivalent power to a UTM is the lambda calculus
I'm _sick_ of hearing such a meaningless statement
of "being of equivalent power to a UTM" repeated over and over again
as a bad excuse for bad programming language design.

I question the meaningfulness of your term "Turing-equivalence".
What definition of it do you use, if any?
Equivalent _up to what transformation_?
Do these transformation correspond to anything _remotely_ meaningful
*in presence of interactions with the external world (including users)*?

Oh yeah, if you only need to write a One Program,
that will answer the One Question,
but you must choose your machine before to learn the One Question,
then I can see interest in considering some form of Turing-equivalence
(to be specified, still), as a meaningful concept: it tells you
what class of machines you may "optimally" choose, in some sense.
But then, I can do much better, and readily tell you
the One Answer to the One Question, which is 42.

If you need more than one program, if you already have a lot of questions,
and if more questions will come constantly, depending on what you do,
then Turing-equivalence should certainly not be a sufficient criterion
for your choice of programming system
(considering language and operating system separately is a vast crookery),
although it will most likely be a necessary criterion.

I agree I still need to write a formal paper on the matter. Meanwhile,
for a few hints on how to do better than so-called "Turing-equivalence",
read this informal paper of mine:
        Metaprogramming and Free Availability of Sources

I don't think Alan Turing would have appreciated his name being associated
to the loads of non-sense hidden behind the words "Turing-equivalence".
But when you commit suicide, you cannot defend yourself anymore.
Damn British bigots who killed Turing!

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