9 ms·

I'm on exactly that kind of team now. They've been working on a very simple problem for several years now and have an enormous, sophisticated, but still buggy

• yw3410 6y ago
  I am continually perplexed at the swallowing of exceptions in certain FP communities. Result types, Either et cetera make it extremely easy to swallow errors by flatMapping thoughtlessly losing the context of where they were - you typically /want/ the call stack when you hit into an exceptional flow.
  • Kototama 6y ago
    It makes the code impure (that is with side-effects). One can also argue that if you can encode the potential errors in the type they are not exceptional. It's not that bad though, because you get much less of these kind of errors than in a typical Java program (for example).
    • yw3410 6y ago
      Yes, it is a side-effect - and does make the code impure; but it's an /exceptional/ flow like OOM, infinite looping, stack overflows which also break equational reasoning. My argument is that as a programmer you /choose/ the base lemmas which you're comfortable with - with an exception you're saying for a large swathe of your code, it will assume a lemma. When is /does/ break you get to point the finger at it with a stack trace saying here is where the lemma was broken. As an aside there are nicer ways to do this ala contracts, but exceptions aren't a /bad/ way. The equivalent of try.toOption is try catch everything and discarding. The equivalent of flatMapping without adding surrounding context is equivalent to try catch rethrowing. Both of these are /much/ too common in FP codebases.
      • joshlemer 6y ago
        This is spot on! Way too often in Scala codebases, which tend to wrap IO calls in Future or similar is that you'll have chains of side effecting futures like readFromDb() .flatMap(x => doSomethingElse(x)) .flatMap(x => doSomethingElseAgain(x)) .flatMap(x => onceAgain(x)) And this all gets passed up the call stack to one generic thing that basically does nothing in the case of error, maybe logging it and that's it. It's tempting to write code like this because it's so easy and looks so clean and readable, but in reality it is not how you build reliable software because what one must do in response to a failure from the first call is not the same as what one must do for a failure of the second call, or third or fourth, but this flatMap().flatMap().flatMap() style seduces the programmer into thinking they've handled errors when really they've just lumped the entire workflow as one big chain that can fail at any point and in practice usually just ignore all error cases. One strategy I find does slightly mitigate this is to use future.transformWith[S](f: Try[T] => Future[S]). This at least presents to you the opportunity to think about error handling a bit more consciously, but I still find that the chaining operator approach nudges you away from thinking about error handling because it becomes quickly difficult to read. It's probably to do with how limited the control structures are when dealing in Futures. You don't have while/if-else/etc, you must lift all your control into flatMaps and iterations are only doable via recursive calls with explicit accumulator state (yuck!) and nesting. So whereas a properly thoughtful treatment of error cases in synchronous code may take 20 or 30 lines of legible code, this gets tranformed in the async style to 20 or 30 levels of nested callbacks and recursive calls which becomes unreadable.
  • jinfiesto 6y ago
    You shouldn't swallow errors like that in FP either. You can trap the error in an effect type and throw it at the top level of your app when your effect type gets run after all of the code that processes that error value has a chance to recover. See something like Zio for an example, though you can do similar things without Zio.
    • randmeerkat 6y ago
      If the team uses Zio, or maybe they’ve gotten lost in the religious war of Scalaz, vs Cats, vs Zio... One of the major issues I have with Scala is how fragmented the community is. Everyone has an opinion on how something should be done and everyone thinks that everyone else is wrong.
      • monksy 6y ago
        Well you have extremist who believe that you have to cull the community due to a few bad (but still contributing) apples. Additionally you have a big lightbending company that produces some questionable contributions to the community as if it's the "scala-endorsed way". Don't get me started with the whole forcing of "lets be python like" initiatives as of late.
    • spion 6y ago
      And will you get a call trace when you do that?
      • hderms 6y ago
        we use error types that extend Exception specifically for the purpose of getting a call trace. A lot of people hate doing this but it's been extremely helpful on our project
        • yw3410 6y ago
          We do this too - but the other problem you get is that Exception aren't treated specially (like Any and Nothing) in the inference hierarchy so errors are liable to "collapse" to Throwable or Exception. I like wrapping them with a new type if possible to stop this behaviour.
  • dkarl 6y ago
    As I am slowly acquiring the habits of thought that make it possible to read and write FP code at a reasonable speed, I'm horrified by how much idiomatic Scala FP code relies on projecting certain assumptions onto types and operations that seem, at first glance, to be neutral mathematical abstractions. For example, I find myself hating the Either type, because I feel like there is a socially established convention that one half of the Either is the type that matters, the value that you want, the value that is the point of the computation you're doing, and the other half is a garbage value that should never be directly handled. So I really feel like I should conform to the convention and reserve Either for cases where one of the possible types doesn't matter. But how often is it true that one side of the Either doesn't matter? People want me to encode success/failure in an Either type, but if I do that, are they going to treat failure with the care it deserves? I often handle Either (and Option) using pattern matching when I feel it's important to give both code paths equal importance and equal visibility in the code, but people change it because flatMap is supposedly more idiomatic, and they believe that eliminating pattern matching from their code is a sign of sophistication. I feel like this stems from a strong desire among FP folks for the happy path to be the only one visible in the code, and the non-happy path to work by invisible magic. Maybe there are some brilliant programmers who achieve this by careful programming, but there are people mimicking them who seem to rely more on faith than logical analysis. They just flatMap their way through everything and trust that this results in correct behavior for the "less important" cases. I'm sorry that this turned into a bit of a rant, but I'm entirely fed up with it, and it accounts for a lot of what I dislike about the code I work with on a daily basis.
    • Fellshard 6y ago
      I've been working through 'Haskell From First Principles', and it turned on a lightbulb: the 'right' half of Either is the 'important' one because its type variable is free to change. instance Functor (Either a) where -- a is fixed here! fmap :: (b -> c) -> Either a b -> Either a c fmap _ (Left l) = Left l fmap f (Right r) = Right (f r) As a general rule, the last type parameter of a type carries special significance: the same applies to Tuples. You _can_ trivially construct a type where the two labels are swapped; it's just labels, Left and Right aren't intrinsically important, except insofar as they reflect the positions of the type arguments in written text. data Either' a b = Left b | Right a
  • spion 6y ago
    I think the solution is to have typed exception modelled as polymorphic variants. Something similar to Swift.
  • AzzieElbab 6y ago
    How do you mean? If your either turned left you should be stuck with that exact left and no amount of flatmapping should effect your stack, it simply does not kick in unless you added something like leftmap that swallows the exception
  • lmm 6y ago
    The call stack is "magic" built into the language, so as soon as you're not using the "blessed" way of error handling, you lose it and need to rebuild the same functionality "by hand". I agree that some kind of logical call stack is a very useful thing to have, and I'd recommend implementing something along the lines of https://github.com/lancewalton/treelog https://github.com/lancewalton/treelog that provides it.
• brabel 6y ago
  I am fairly certain the jury is out on this question: It's always better to write simple, almost dumb code that anyone can understand than to use advanced abstractions from category theory or whatever. Why? Because every single study or anedocte I've ever heard is like yours: adding complex abstractions to code do NOT make it more reliable. But they do make it much harder to modify, understand, and fix. FP tought us that unconstrained mutable state is very bad, and that has helped us immensely in the mundane languages of the world (Java, C#, C++, Go). But I think it's time to learn the other lesson from FP: overly complex abstractions are also very bad and should NOT be used willy nilly as they simply have a very low or negative cost-benefit.
  • aapppwe 6y ago
    i think it depends if you need it, rust for example is quite complex, but it solves a class of issue that other language have trouble solving while maintaining speed
  • einpoklum 6y ago
    > adding complex abstractions to code do NOT make it more reliable. Sometimes false. If the (more) complex abstractions are in well-tested libraries that haven't been written solely for your code. > But [complex abstractions] do make [your code] much harder to modify, Not necessarily. You can separate concerns; you can isolate changes; and you hopefully reduce the amount of code you've written yourself, significantly even. > [complex abstractions] do make [your code] much harder to understand This is as likely false as it is true. > [complex abstractions] do make [your code] much harder to fix Again, this very much depends. If you're using a well-tested, widely-used external library with those abstractions, it may well be easier to fix your own code.
  • MikeDelta 6y ago
    When I was young I though that good writers are the ones who write such complex sentences that nobody can understand. Later I learned that good writers are clear and understandable. I used to write complex code because I found it elegant. Now I write simple code because I enjoy breaking down a complex problem into its simplest form, which for me means I fully understand the problem.
• dnanabkchsbxb 6y ago
  Reading this thread is giving me some catharsis. I worked on a large project in a big tech company where the org’s leadership was ideologically determined to build everything in Scala. We ended up with dozens of engineers and failed to deliver basic functionality. The leadership eventually left the company and now they are running a startup with a few of the Scala savants from the old team. They got lots of funding and they invited me to visit to get me to join. They showed me the awesome type system they had implemented and tried to demo it but the product was broken in five ways.
  • ta988 6y ago
    I don't think it is a Scala problem but more of a leadership/organizational problem. If you look at Jane street, they do everything in OCaml which is an interesting choice to say the least, but their stuff works, evolve and they can demonstrate...
    • dnanabkchsbxb 6y ago
      Yeah, I don’t think Scala itself caused the problem. There was this mindset: “if we just properly model the universe in the type system, the solution will just fall out!” Because that was the obsession, they ended up spending all their time iterating on this perfect type system and not enough on the product. I think people with that issue are more likely to want to use Scala.
• jmfldn 6y ago
  "I'm on exactly that kind of team now. They've been working on a very simple problem for several years now and have an enormous, sophisticated, but still buggy and unstable solution. They're really smart people, and they had to be extremely capable programmers to get this far, but the embarrassing question is, how would a team of mediocre developers have tackled this problem? They would have picked a mediocre language" I don't mean to be rude to your colleagues, but almost by implication in what you've said, they're not good programmers. Being a good programmer is nothing to do with leveraging a fancy FP language. It's about delivering working, maintainable, testable code. Whether you write buggy spaghetti code in Go or misuse Scala, its the same root problem. I've been a Scala dev for five years, worked on some massive projects and it's been a dream. As long as you agree on a style, don't go crazy with the language and use it with discernment, it's a joy to work with. It's a sharp tool though and it takes discernment to know how to wield it appropriately. I don't know if that's a downside, it's more a warning.
  • jgwil2 6y ago
    I think people can be good programmers and poor software architects at the same time. Sounds like that's what has happened in this case: brilliant abstractions that are misused and result in a buggy product and less productive team.
    • jmfldn 6y ago
      "I think people can be good programmers and poor software architects at the same time. Sounds like that's what has happened in this case: brilliant abstractions that are misused and result in a buggy product and less productive team." That's fair. I guess if by good programmer we mean, fluency with the language and algorithms / abstractions /types etc then perhaps they qualify. I really meant something more like "software engineer" ie. someone who can architect a simple, sane, working solution adhering to the usual best practices of good software construction. Maybe there's a missing piece between being a good coder vs scaling this knowledge up to the application level. The latter is indeed a much rarer skill and too often, people without it influence major decisions.
• tikhonj 6y ago
  > how would a team of mediocre developers have tackled this problem? In my experience, mediocre developers would stick to a simple language like Python and only use simple Python features... and write a completely impenetrable, 100% coupled and wholly unreadable mess that would make you wish for over-engineered Scala. Don't even get me started on what happens with "simple" distributed computing tools like Hive... I see people complain about languages like Scala leading to over-engineering and I just don't get it: have you not worked with sub-par Python or JavaScript code? Sure, poorly designed complex solutions have problems, but so do under-abstracted codebases! Bad code is bad code, and I don't think it's meaningful to say that "over-engineering" is categorically worse than "under-engineering". I actually worked with somebody who wrote pathologically over-complicated Haskell. Had some friction between us over that. His Python code? Somehow even worse. No serious language I've seen at either end of the abstraction-friendly spectrum (not Haskell/Scala nor Go/Java/Python/etc) puts a meaningful floor on code quality. An inexpressive language can have a low ceiling for how good code is, but restrict or simplify the language however you like and people will still happily write utterly unworkable code. I've found that languages—especially less common languages thanks to the "nobody gets fired for IBM" effect—get used as scapegoats for not talking about cultural issues. If people on the team are writing clearly poor, over-complicated and bug-riddled code, it means there is some sort of technical leadership shortcoming, and it would not be any better if they were using Java instead. (I mean, have you seen Enterprise™ Java™ codebases?) And, at the same time, it's clear that a Scala codebase with tasteful technical direction and leadership—conveyed through team culture, code reviews, shared expectations... etc—can be absolutely great to work in. At this point, I'm leery of blaming languages for programming problems without a clear mechanism. "The language lets people do bad things" isn't a real mechanism because all languages do bad things. "The language attracts people who like complexity" seems specious too. (Again, let's not blame languages for hiring and cultural problems!) "The languages defaults incentivize poor code" is a better argument, although it can be a bit fuzzy. And arguments like "language A doesn't have capability B that we need" or "language C allows classes of bugs other languages don't which empirically cause problems" are the most compelling of all.