[dgb23]

Your computer is also not a Turing Machine. The regex that you use is not really a regular language. Your functions and logic are not referentially transparent, because well, they have to run on a computer.

But it's useful to learn the foundational mathematics of these things as there is a direct relationship between them.

SQL has semantics that can be understood by relational algebra of relational bags. It's of course not a 1:1 translation, but the mathematical underpinnings are explained there. It's useful to learn the simpler, more abstract thinking tool in order to understand the concrete programming tool.

[thrown123098]

My computer is very much a Turing machine since each time it runs out of disk space I can buy more disks. The fact you think a Turing machine has infinite memory rather than finite but arbitrarily large memory tells me all I need to know about the sorry state of your theoretical education.

[rrobukef]

A Turing machine is a mathematical concept. It has, by definition, infinite memory. A computer is just a real machine that can do similar things as a Linear Bounded Automaton, a Turing machine's little brother who'll never do quite the same things.

[thrown123098]

Wrong: https://en.wikipedia.org/wiki/Arbitrarily_large

[rrobukef]

There is a physical limit to the number of disks you can add to your CPU. There is a physical limit to the memory you can address in your CPU (48-bits). It is not arbitrarily large.

Also wrong for Turing Machines, it really is infinite. That's a big difference to arbitrarily large. The halting problem is undecidable for TM's but not for arbitrarily large (you'll need precise definitions though).

[thrown123098]

It is left as an exercise to the reader to find a natural number which isn't arbitrarily large but calculable.

[rrobukef]

The tape size needed for a Turing machine is incalculable. Here's a reference to a proof: https://scottaaronson.blog/?p=2725.

The machine with 7918-states, Z, stops (well, Z cannot be proven to run infinitly long) iff. ZFC is consistent. For this it needs a finite amount of space but we cannot calculate how much. If we could calculate an upper bound we've proven ZFC is consistent.

[bigbillheck]

> each time it runs out of disk space I can buy more disks.

There's only so many that you can buy.

[dgb23]

How much does an infinite amount of disk space cost?

[oriolid]

Nothing, if it's your users who buy it instead of you.