[jude-]

> This comment is simply incorrect. The gas limits do make smart contracts decidable. It is a mathematical fact.

This line of reasoning does not help me write better code, and does not address the parent's concerns. Using this argument, I can say that every single program I will ever run in my lifetime is also decidable, since eventually the computer I'm using to run it will stop working. This of course does not mean that I will write bug-free code, nor does it mean that I will write code that is feasible to prove correct.

What I want is a decidable programming language where it is always feasible to reason about the smart contract's halting states for arbitrary input. Bitcoin and its derivatives let me do this. Ethereum does not.

[nicksdjohnson]

Sure it does - the marvelous thing about a turing-complete virtual machine is that you can write a decidable language that compiles to EVM bytecode.

[jude-]

Sorry, I didn't qualify "always feasible" well enough. What I meant was, I want it to be feasible to reason about the halting states of every single smart-contract that will ever interact with my code. Not just the ones that I write, but also the ones that are reachable from my smart contract's call graph, and the ones that call into my smart contract.

If I can do this, then I can feasibly reason about how my code will react to other peoples' inputs (e.g. I can prove the absence of DAO-like re-entrance bugs). The fact that Ethereum allows smart contracts to be written in undecidable languages means that this is not feasible in practice.

[nicksdjohnson]

I don't think I follow - why would you need to reason about your callers' internal states in order to prove properties about your own contract?

[jude-]

Because in practice, I'm trying to reason about the consequences of submitting a given transaction. A transaction can invoke many smart contracts in addition to mine. It's not enough for my code to be correct; every piece of code the transaction causes to run has to be correct as well.

[nicksdjohnson]

If you want to know what a given transaction will do, you can simply run it locally; no need for formal analysis. Formal analysis is useful for proving properties about your program like "the total balance will always equal the sum of the accounts" and "transfers never increase the sender's balance".

[jude-]

I want to know what any possible transaction can do. See my sibling comments.