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>Now, there are perfectly valid other reasons to like static typing. I just always hear this one, especially in regards to Python, and it’s really the wrong way to look at it.

>The extra code and constraints of static typing are liabilities that should have to offer offsetting value to choose them.

Agree, agree SO much.

After years of only using statically-typed languages, and then switching to Python and Lisp, i never understood why "catching typos and type errors" was touted as the benefit. I also agree they are like a sort-of liability that has to be taken into account in order to turn it around into a benefit.

For me, it was mostly performance benefits.

Note that not talking about strong typing (vs weak typing). Strong typing is always a good thing.

> I really think this way of thinking about static typing is a very bad thing. This is not at all an actual benefit, because in any sane situation, you will use unit and integration tests that execute extremely quickly on small test data to exercise your end to end model training code.

Unit and integration tests don't write themselves, and they will always be incomplete. You can't test for everything, and what you get from them will depend on how much effort you put in.

Static typing prevents you from running code that tells the computer to do nonsensical things, and usually you'll get an error that tells you exactly what you did wrong. I see those as benefits. In languages like Ocaml or Haskell that have type inference, type annotations can even be omitted most of the time. In the effort-versus-confidence trade-off, I see static typing as low effort with a good payoff. Others might think static typing is too much work and would rather rely on tests. Both approaches are complementary; neither renders the other unnecessary or redundant.

> Turning it around to act like static typing is de facto always a benefit is a very one-sided way to look at it.

Sure, it's a trade-off. Opinions will always vary as to what an ideal productive development environment looks like and what trade-offs are worthwhile, but I think your dismissal of static typing as a tool for gaining some degree of confidence that some program will probably work correctly is also one-sided.

“You can’t test for everything” seems like a really bad counter argument in this case because you’ll still need to write the integration tests anyway, and if the tests are incomplete (which they always are, it’s life, whether you’re writing statically typed code or not, shrug), you have to improve the tests. You can still have runtime errors and incorrect logic in statically typed code... so?

Now if the process of that testing gets you 99% of the same overall job safety that you’d also get by increasing the code by 10% to add static typing annotations and data structure models (in addition to raising maintenance costs according to that 10% too, and possibly adding bugs or painting yourself into rigid, hard to refactor corners even if they confer some short term bug prevention benefit via the type checking), from tests you already need to write anyway, it’s a no-brainer.

I realize there are good uses of static typing and it can come down to style preference. But truly in this case of “what if my big scientific computing system hits a type-checking-could-prevent-it sort of bug after hours of computing time,” it’s just not a good argument.

This is why people routinely write huge scientific computing systems in Python and nobody ever worries that they hit type checking relevant errors after several hours.

Some things where type checking can really help: ensuring you’ve exhaustively handled every case in an ADT, using the type system to prove state transitions, like with phantom types, using the type system to encode side-effectfulness like Haskell monads.

These things often just aren’t important for something like a large-scale machine learning training program. The types of problems you run into just don’t happen to benefit much from that stuff, while the benefits you can get from writing quick ad hoc functions that can take arguments of unconstrained types and just make unchecked assumptions about their attributes is actually quite big.

>“You can’t test for everything” seems like a really bad counter argument in this case because you’ll still need to write the integration tests anyway

Types are nothing more than a proof that some property holds for your code (Curry-Howard correspondence). Tests are nothing but a proof that the property holds for the exact conditions. Types are always better then tests, the only question is how powerful your type system is and how much properties you could express as types. In F* or Idris you don't need tests, in OCaml and Haskell you need tests sometimes, when type system is not powerful enough, in python you have to write tests all the time.

> “Types are always better then tests, the only question is how powerful your type system is and how much properties you could express as types.”

Again, as I’ve been saying, that is a super one-sided way to look at it. Type annotations and the use of appropriate patterns required for most modern “good” static typing are costly things. Organizing things with type class patterns and algebraic data types costs you by making you write more code and more boilerplate, and have trickier things to reason about. Some languages are worse (Scala) about how bad this boilerplate affects you than others (Haskell), but the restrictions it places to facilitate the type-based proofs of safety are real. It’s not free.

Using static typing for these things is only better when (a) the overhead of adding static typing and associated pattern code (and associated maintenance of that extra code and restrictions of how you can write ad hoc code) is not too large and (b) the type-based safety proofs couldn’t have been gotten in some cheaper way.

In a case like a big model training program (a) and (b) just don’t hold. The extra boilerplate and maintenance is very meaningful. Just look at the difference between this blog post’s OCaml code and the equivalent stuff in Keras. The restrictions on ad hoc code also matter. If I can get back a dynamically typed container of settings, like a Python dict for passing into a GPUOptions setup in TensorFlow, and not bother needing to conform to certain types before being allowed to write code that just makes direct assumptions about what attributes I can access, or what dict values will be strings that can serve as args to functions expecting strings, ..., that just saves me lots of time and lets me write way shorter code, relatively speaking, because in this use case it is extremely easy to verify that the only types of data passed in will conform to the assumptions, something that can be checked with an integration test very quickly without requiring any compromise on the handling of arbitrary attributes from config dict values.

Not every case is like this. Some times going to the trouble of setting things up with static typing to prove complicated assumptions are valid within the code is better and ends up reducing code through disciplined use. Static typing can be cost-effective.

This particular use case in the blog post, though, is not one of those cases at all.

>Organizing things with type class patterns and algebraic data types costs you by making you write more code and more boilerplate

And tests are writing themselves for you?

I don’t understand why you believe that question is rhetorically interesting or connected to anything that has been discussed.

You’d have to write virtually all the same tests in this type of use case whether you are using the static typing approach or not. The tests won’t explicitly check types in the dynamic typing case, but will verify type safety for fixture settings and data indirectly, as a byproduct of all the other testing.

It seems like you are really missing the point. In use cases like a big training program, you have to write integration tests, period. The compiler is not ever a useful substitute for that in this case. Now, since we know you have to use integration tests and so the cost of writing and maintaining those tests is baked in, we can ask: will those tests also cover what a compiler could have helped with, if we’re in the dynamic programming case? Yes.

And so then the extra code we’d have to maintain and extra constraints we’d have to live with if choosing static typing turn out not to buy us anything we can’t already get with the baked-in costs of the integration tests.

Tests don’t write themselves. Why would you ever ask that type of question like you’re being cheeky and rhetorically dramatic? It reveals that you’re still stuck imagining that you’d need to write extra type-specific tests in the dynamic typing case, which misses the point of the discussion.

>You’d have to write virtually all the same tests in this type of use case whether you are using the static typing approach or not.

No, I don't need to write tests, it I could prove something with types. Here is an example of quicksort, where all invariants and properties are ensured with types, so this code does not need any tests at all.

https://github.com/FStarLang/FStar/blob/master/examples/algo...

>integration tests

You could reason about your program's correctness on any level with types.

Agreed that type-safety preventing training script failure is not the strongest argument for OCaml. In my experience, the far more compelling reason to use expressive type systems is that they allow you to be more specific about your domain models. This helps to not just prevent type errors (common but not that big of a deal) but also logic errors (I think more common, harder to suss out, and harder to catch with the equivalent amount of test coverage). This idea is often rephrased in FP communities as "Make illegal states unrepresentable."

Exactly. When we praise statically-typed languages like OCaml, Scala, and Haskell, I think people miss that we're not just talking about random type annotations. It's exactly what you describe -- we're talking about being able to model domains using the type system, which goes far, far beyond simple type errors.

Algebraic data types are the bedrock for this kind of modeling, and I can't for the life of me understand why more languages don't add them (particularly languages like Java and C#).

I applied for a more entry level software position at Jane Street, and while I would have failed the interview regardless, I had the same experience where the HR person had no idea what the interview was like.

They assured me I'd be required to write OCaml, so I spent the weekend brushing up, and that I should bring my own laptop prepared with whatever development I wanted to use. In fact it was a couple "whatever language you want" questions using their floating interview laptop, which threw me off a lot. But like I said I would have failed anyway, it's the hardest interview I've ever had.

i wouldn't sweat it. people design those interviews to make them feel better about themselves rather than as an effective way to gauge someone's aptitude to work there.

you'll notice that none of these places that ask these types of questions allow the candidate to ask them technical questions. it's always a one way street. there's times where i have "failed" interviews of this type when i could guarantee i have "simple" questions that they couldn't answer about software and programming.

I don't think I've ever had an interview where it would have been okay to quiz the interviewer on technical topics...could you explain a little better?

there's a couple things. why is it not okay? as a potential employee, you want to be sure that they have an inkling as to what they are doing and aren't just asking questions out of the "interviewing at google" book. i am not actually arguing that interviewees ask these questions (see below), but it is something to think about. i usually try to ask some questions that give me a sense of how big of a mess their software is. at one of the places i failed the final interview, i wasn't ever shown any code or product that they were working on but had a sense it was a bit of a mess with a bunch of smart people writing code with no hands at the wheel.

i have the perspective that these types of puzzle questions by the interviewer are pointless. and i was getting at the point that the interviewee asking similar pointed questions would be similarly useless. because it's easy to take that high and mighty stance instead of having a conversation. it creates an artificial environment that doesn't really exist in actual working environments.

and i generally feel that companies are far too arrogant in their hiring process. they very much create a one way dialog as if you should be thanking them for even interviewing you. they act like "we don't need you, you need us". it creates a very bad taste in my mouth, and even if i was to be offered employement by such companies, it is possible i would turn them down unless i am convinced that their work environment is distinctly different from their interviewing process.

> i wouldn't sweat it. people design those interviews to make them feel better about themselves rather than as an effective way to gauge someone's aptitude to work there.

Same reason I dislike that sort of interview. Of course the thing to do is to throw in a spanner.

"Hmm, so I guess you didn't read about the Modified Banach-Wiles-Kolmogorov algorithm? I thought that was where we were going. Ok let's do it your way."

Throw this bomb on the way out, of course.

Presumably they wouldn't be employed there if they couldn't pass the interview though?

I don’t know how long ago, but in my experience of interviewing with Jane Street (at least as an intern), they were pretty upfront about the lack of expected OCaml experience, and I was able to complete all of the on site interviews in a language of my choice. The HR/recruiting team seem eager to improve their process based on people’s feedback, so maybe this is something that took time to get right.

I don't blame the engineers at all. I thought the questions were fair and not gimmicky, just unusually difficult. I failed because I was straight out of college and it was my second real interview ever. The only issue was that the HR person was very misinformed and put me a little off balance.

Yeah likewise I hadn’t done a many real interviews before this so I guess I have nothing really to compare it to. I ended up with entirely programming questions rather than generic brain teasers, so maybe there’s a bit of a mixture of questions asked.

The type safety argument is total BS. First of all the training script will fail for the very first time if there is a type error. You'd be a moron to pass an argument of a different type 'a couple of hours' into the training. No sane programmer writes such code. What kind of nonsensical argument is this.

What I have found static typing to be really useful for is in remembering what I have coded. It's quite hard to remember a dynamic type while you are writing code, given the number of variables you are dealing with. Seeing that type definition next to your variable name is a handy reference. I find it helpful to speed up coding a bit and being able to remember a lot more clearly what I have done.

Static typing is also a nice way to communicate design intentions. But for this to work, the annotations have to be very expressive.

I don’t know the first thing about OCaml, but I have worked professionally with Haskell and static typing is a joy when it adds clarity and makes the contracts of functions instantly readable.

Contrast this with Scala, which I have also worked with professionally and the difference is stark. Scala type annotations are much harder to read, and the mechanism of implicits can make for extremely mysterious code that looks like it shouldn’t compile and only once you track down some distant implicit that’s somehow in scope, can you make sense of the way types are flowing through some function contract.

Yep agreed. Though you can communicate design intentions in comments, no ? There is another argument that programmers might not follow the comments, so strict enforcement by types helps - I don't believe in such a philosophy though. Most programmers will do the right thing and mistakes are not intentional.

It's not that they don't follow the comments, it's the fact that comments aren't executable, so they rot. People forget to update them. That can't happen with type definitions, because your code stops compiling.

Sure, comments serve their purpose, but that purpose only slightly overlaps with that of static types.

> You'd be a moron to pass an argument of a different type 'a couple of hours' into the training

Huh?! At least in non-ML code this happens all the time, data fetched by whatever thinggie that uses zillion chained libraries of code nobody has time to audit, comes in hours or days late in a long running service blowing it up... eg. "oops, point.x is now no longer and integer but more like a map[ErrorObject->vector[int]]" bc something blew up in a very unexpected way in some other nodejs code light years away from the business logic you hold in your head... (yeah, the service gets restarted, but at some point some data that should have been saved in the DB hasn't been am may need to be recovered manually from some obscure log if even recoverable)

Yeah I should have been more explicit that this comment is in reference to ML code. Training is nothing but a loop so its unlikely you pass type A in iteration 1 and type B in iteration 200. If that happens most likely your training data is messed up and type safety cannot help you as you would have compiled and tested for type A.

You could also have a complex training job that trains a shallow model for a while, then uses it to train a deeper model, or extract an embedding from some layer and train a classical prediction model that uses the embedding as the feature vector.

But the point is that the right way to ensure safety is with realistic fixture-based integration testing. That’s not what static typing is for in that type of use case and is not a de facto benefit of static typing.

in some other nodejs code

ML/DL is nothing at all like webdev :-) but these days you can compile OCaml to JavaScript if you want, I encourage you to check it out

> What I have found static typing to be really useful for is in remembering what I have coded. It's quite hard to remember a dynamic type while you are writing code, given the number of variables you are dealing with. Seeing that type definition next to your variable name is a handy reference.

If you consider this a benefit, then (for example with Python), don't you get the same benefit just by using docstrings? Stated another way, if all you want is a visual cue about what you're passing to a function and getting returned, why bother with all the scaffolding of type safety? You can get that just by using documentation facilities outlined in various languages' style guides. Those language facilities (such as docstrings) tend to be very useful and a good engineering practice in general.

The point of type safety is actually to obviate what you're talking about. Smart developers can and do make the mistakes you're saying only a moron would make, regardless of available visual cues. Offloading that decision making process to a language that complains when you make that mistake instead of being forgiving about it is entirely the point.

So I guess what I'm saying is that I'm struggling to understand why you think type safety is BS. If I read you correctly, it sounds like you'd also say that developers committing memory corruption vulnerabilities are morons, and that the scaffolding of memory management and garbage collection is BS. Why not just have explicit references a developer can read while coding to make sure they're not overflowing a container, right?

> Then the interview was nothing but deck of card puzzles and random riddles

That's really disappointing. Was the position you applied for Software Developer, or a specific deep learning position?

Specifically posted as a deep learning position.

I've always thought that static typing is the least interesting thing about functional languages.

Not all function-oriented languages use static binding. Due to how the BEAM VM works, Elixir/Erlang is very, very function-oriented but also late-bound. Nevertheless, its type system is relatively rich compared to most other late-bound languages.

It's never static binding that makes a language good or interesting, apart from performance benefits. You can get the productivity boon of early-warning type-checking with or without it. What makes a language good, in my opinion, is its ability to provide a type system that closely matches the needs of the domain in which that language is to be used. For example, game development requires a data-oriented approach, which Rust's type system practically forces the developer to adopt.

More complex software engineering problems require more expressive type systems. But unless you're the one writing TensorFlow, machine learning is insignificant from a systems engineering perspective; it's simple enough for non-programmers. Thus, expressive type systems don't seem to offer much benefit here.