An apples and oranges comparison. Any difference would surely be made up by all the tests one would have to write to be sure the clojure code was free of basic errors.
That's a completely baseless assumption. I have not found the need to write any more tests in Clojure than I have in statically typed languages. The only tests my team ends up writing tend to be end-to-end specification tests, and you would want to have those in any serious project regardless of type discipline.
Tests prove the presence of bugs not their absence. You should be writing more tests if you have no static type system, in order to find the bugs that you would otherwise prove don't exist.
A static type system like Elm doesn't fix logical bugs like wrong indexing, wrong predicate etc, it just finds issues with types. Types do not contain the real logic of your program. Types are somewhat useful for verifying data is passed around in the correct shape in a program, but to say it prevents most obvious errors is naive. Not to mention in Elm you will waste tons of time doing useless tasks like writing encoders/decoders and code that could be moved to macros in a more powerful language.
> A static type system like Elm doesn't fix logical bugs
Static type systems can absolutely catch logical bugs! Proof that a list is non-empty or that a reference is never null are simple examples.
> Types do not contain the real logic of your program.
Types can completely determine the logic of many parts of your program.
In Haskell, I often don't have to write custom traversal code, it's selected for me based on the types.
> Types are somewhat useful for verifying data is passed around in the correct shape in a program
This is only the start of what types can do, try learning Haskell.
> but to say it prevents most obvious errors is naive.
No, naive is dismissing static type systems to the point that not even extra testing is done to compensate.
> Elm you will waste tons of time doing useless tasks like writing encoders/decoders and code that could be moved to macros in a more powerful language.
Elm's aim is to be a basic easy-to-learn language (no operator overloading etc). Personally, generic (polytopic) programming feels like a more elegant approach than macros. Haskell offers both.
Haskell was my first FP language, I used it for about a year, and worked with Scala briefly after. My experience is that you're really trading one set of problems for another in practice. Static typing can guarantee that you avoid a certain class of errors, but it often results in code that's longer and more difficult to understand opening opportunities for different kinds of errors. There is absolutely no empirical evidence to suggest that the trade off is strictly superior in practice.
Static typing can catch inconsistencies at the cost of structuring your code in a way that the type checker can understand. This is often at odds with making it readable for the human. A proof only has value as long as the human reader can understand it. Here's a concrete example of what I'm talking about: https://github.com/davidfstr/idris-insertion-sort/blob/maste...
An insertion sort written in Idris has over 250 lines of code that you have to understand to know that it's implemented correctly. A python version would have about 10 lines or less. I'd have much easier time guaranteeing that the 10 lines do exactly what was intended than the 250 lines of type specifications. Of course, you could relax the type guarantees in Idris as well, but at that point you accept that working around the static checker has benefit and it's just a matter of degrees of comfort.
In general, the more constraints you specify via types the more of your program logic moves into type specifications. What this really means is that you're writing a metaprogram that emits your logic. However, there's no automated checker for that metaprogram that you wrote using the types. You still have to understand it to be correct in order to know that it's doing what you want it to. At this point you're basically living in a programmer version of the Plato's Cave.
The real question is not whether you can do something using a static type system or not. The discussion has to center around how that compares to alternative approaches such as testing, gradual typing, and runtime contracts.
Sorting (TimSort) was broken for many years in Python. It was good old-fashioned logic and theorem proving, not tests or runtime assertions, that got it fixed. There is merit in proving properties of any critical implementation, no matter how difficult. However the gist you referenced looks to be someone's learning effort, so hardly a model example.
Your view on the role of types is unfortunate if you think term logic is simply mirrored at the type level (Plato's Cave). The Curry-Howard correspondence tells us to think of types as logical propositions with terms as their proofs.
Sure, you can use formal methods to prove properties that are hard to test. The point you seem to have missed is that it takes a lot of effort to do that.
The reality is that in most cases there's a cost benefit analysis regarding how much time you can spend on a particular feature and the strength of the guarantees.
>The Curry-Howard correspondence tells us to think of types as logical propositions with terms as their proofs.
Hence my point that you end up writing a metaprogram that emits the logic. Ensuring that the metaprogram is correct is a manual process. The more complex the proof, the harder it becomes to understand.
Consider Fermat's conjecture. It's trivial to state it, it's trivial to test it to be correct for a given set of inputs. However, proving it for the general case is quite difficult, and only a handful of people in the world can follow that proof.
> onsider Fermat's conjecture. It's trivial to state it, it's trivial to test it to be correct for a given set of inputs. However, proving it for the general case is quite difficult, and only a handful of people in the world can follow that proof.
This is a strawman, conventional static type system can't prove all general cases either and no body is saying that they do that. Yet, they being a superset of dynamic typing, they allow to have the same expesiveness as such by providing a bypass like 'Object' or 'any'.
