Topic: letstalkbitcoin on committed tx, homomorphic value, fungibility, privacy (Read 4159 times)

@d'aniel Turing completeness has a very specific academic definition that the language I am co-designing probably won't meet[1], but that distinction is not interesting or important. In a Turing-complete language you can write an infinite loop, but why would you ever need to do that in practice? There are more limited forms of recursion and required type safety which allow expression of solutions to nearly all real world problems, or the emulation of space- or time-constrained variants of Turing-complete solutions.

I don't consider this overkill or window dressing at all. There are some very serious applications (e.g. restricted buy back) which require these features if they are to be emulated in Script; I wouldn't be working on this otherwise. We should probably move this to the thread linked to by Adam, however.

[1] I haven't seen this proven yet, but it looks like we'll probably have to choose between decidability and Turing-completeness in the type system, and for this application decidability is far more important as I foresee wallets using theorem proving to determine script safety and to categorize / quarantine coins by their attached covenants. For similar reasons, it may make sense to restrict ourselves to a total functional programming language (which restricts the range of expressible programs to those which are provably terminating, and therefore not Turing-complete in the strict sense, but nevertheless sufficiently expressive just about any actual use).

Listening to Adam's interview was one of the best hour and forty-five minutes I've spent in a long time.  Adam has a lot of really great ideas for the bitcoin community, and we'd do well to take him seriously.  These are the ideas which I think are the most important:

1. Preservation of fungibility through enhanced privacy.
2. Releasing major changes to the protocol as a parallel implementation that allows migration of coins from the old to the new.
3. Focusing on the improvement of bitcoin rather than wasting time and resources on alt coins (with point 2 considered when major improvements require a hard fork).

Adam, I sent you a nice tip, but it's orders of magnitude below the value you've added to the community.  It's unfortunate that you haven't profited more from cryptocurrencies given your contributions over the years.

I moved this question about risks with turing complete scripting to this thread on turing complete / ethereum and added some comments.

https://bitcointalk.org/index.php?topic=431513.new#new

Adam

Thanks d'aniel.  My initial feeling is that Turing-completeness is not necessary for bitcoin and would very likely lead to unforeseen problems and instability (mostly related to the halting problem).  Money isn't a computer.

Here's a recent discussion on this: https://bitcointalksearch.org/topic/turing-complete-language-vs-non-turing-complete-ethereum-vs-bitcoin-431513

I'm drinking wine and haven't looked into Ethereum at all, so please excuse me if I'm being ignorant, but even NAND gates and Rule #110 Wolfram Cellular Automaton are Turing complete, no?  The complexity required for universal computation is surprisingly low. 

I worry about too much misplaced hype coming from Ethereum, leading to the problem Adam mentioned, so it'd be nice to take the wind out of their sails with a script 2.0.  Adam said in the interview that Mark Friedenbach (maaku) was working on a good implementation.  I doubt it'll be Turing-complete, like Ethereum's, as that's likely overkill/window dressing.

What an enthralling discussion! I took notes as I listened. Andreas asking questions? You know its got to be informative.
Would love to see the content of this show written up as an article (not a transcript), with references. The information was tightly packed, and that's saying something for a longer show.

Most fascinating idea I picked out was the Bitcoin-Dev idea, whereby new features could be tested on a prototype track and bitcoin could be moved into it. Has any work been done on it since October? Loved the thought that all mindshare should be focused on Bitcoin.

Next most interesting: scripts disabled in Bitcoin.  And of course, fungibility needs anonymity.

So regarding scripts and Bitcoin-Dev, what is the current thinking regarding re-implementing all of the scripts in Bitcoin?
Is anyone considering it? If so, how would it be similar or different from what they are proposing in Ethereum?

Forgot to link that topic.  You can see the comments yourself below threads (positive).  1-way peg doesnt need any bitcoin main protocol changes we could do it now.

A new even better but bitcoin-main change-requiring variant figured out since.  And someone who can comment if they wish said on #bitcoin-wizards IRC (about the hard fork of this variant) that a) maybe it can be done without a hard fork, and b) anyway its the "one change to rule them all".  Ie after you've done it, other changes can happen on a pegged merge-mined side chain with no bitcoin main security risk.

Bitcoin-dev threads see comments for yourself (thread comments are at visible at the bottom of the pages):