[perarneng]

I spent a week with Clojure and coming from other functional languages my problem was not Clojure, it was dynamic typing. I got strange bugs in the standard library because I accidentally sent in nested incompatible instances of objects and it was really hard to figure out what was wrong in a quick way. With typesafe languages you are stopped at compile time.

[wellpast]

Clojure was explicitly designed to be dynamic. It’s a feature, not a bug.

https://clojure.org/about/dynamic

Until you get better at not making mistakes that the training wheels of a static type system “protect” you from, lean into the REPL as a means to build up small correct expressions into larger ones.

[IceDane]

"Until you get better" is such an arrogant take.

It's not just about skill. It's about maintainability, ease of refactor, and modeling invariants in your code in a way that they can be checked by the machine (the compiler) without every single developer having to maintain them in their head.

Clojure even knows this is an issue and many people use `spec` to sort of retrofit static typing.

Dynamic typing was, is and always will be a mistake. There is nothing you can do with dynamic typing that you cannot do with a sufficiently powerful static type system - and it doesn't have to be something absurd like Haskell's. You basically just need structural typing and type inference and some type-level programming constructs.

The worst part about Clojure is the community. Rich Hickey has cult-like status and the only thing clojurians can do is parrot his inane commentary.

[weavejester]

I too agree that "until you get better" isn't a good take. To err is human, and even the most experienced developers make mistakes.

That said, you don't get static typing for free. As with many things it's a trade-off: you catch some errors at compile time in exchange for working within the confines of the type system. The ultimate hope is that the time you spend fiddling with types is going to be less than the time you spend debugging type errors.

> There is nothing you can do with dynamic typing that you cannot do with a sufficiently powerful static type system - and it doesn't have to be something absurd like Haskell's. You basically just need structural typing and type inference and some type-level programming constructs.

Haskell doesn't have a complex type system for no reason; it's necessary to encompass everything it wishes to do, and even then it's not as flexible as a dynamically typed language.

For instance, how would you statically type Clojure's `assoc` function? It's not at all trivial if you want to retain the type information of the keys and values.

[IceDane]

The problem with your counter-argument is that it hinges on a false premise: That you need or even want a function like `assoc` which is polymorphic over everything. It's an extremely overloaded function which does a lot of things at once, and in many circles and arguably in general within the realm of software design, this is considered a smell.

In practice, what you want is something that allows you to do this safely for the concrete type you're working with. If you want an abstraction that covers all of it, there are ways to achieve this in a type-safe manner, such as traits/type classes. Even in clojure, you're not working with everything at once all the time. You are working with a record, or a vector, or whatever. The fact that you can use one function for all of them is mostly just needless cleverness. In Clojure, you have to keep the type of the data you are working with in your head at all times, because even though `assoc` "just works" for many cases, that's not true in all cases. It will happily insert an integer key into a record without issue, which may or may not be waht you want. But you can also try to insert an atom key into a vector, which then crashes loudly. This is clearly an asymmetry in the abstraction.

Moreover, pointing out that Haskell cannot do what you'd want to do in this case doesn't make a lot of sense. I mentioned Haskell precisely because its type system is extremely powerful and complicated to understand for a lot of people, but still doesn't achieve the kind of flexibility we are looking for - it lacks row polymorphism.

To answer your actual question: Typing a function like that for the individual cases is bordering on trivial in a language such as typescript. For the record case, you don't even need it, because in practice, you get the correct type inference for free by just spreading one object into another.

[weavejester]

I don't see an asymmetry in the abstraction. Both vectors and maps are associative structures - you can assign a key to a value - the only difference is that vectors have a more constrained keyspace (i.e. ordered, consecutive integers starting from zero).

But that wasn't really my point. Even if we limit `assoc` solely to maps it would still be difficult to type effectively.

For instance, suppose we have some code like:

    (let [m* (assoc m :number 3)]
      (:number m*))

We can see that the return type of this expression is obviously an integer, but what is the type of m*? How do we type m* such that (:number m*) can be inferred to be an integer by the compiler?

Most statically typed languages sidestep this problem: instead of using an open data structure like a map, a closed structure like a record or class is used instead, and these structures must be explicitly typed by the user.

The problem with this approach is that now every record is specific and bespoke. You lose access to all the general-purpose functions that operate on generic data structures, and as records and classes are closed, you also lose the ability to extend them.

This is the ultimate problem with static type systems: you're trading capability for safety. If you're programming within a static type system, there are options that are simply not available or feasible to use.

[IceDane]

> I don't see an asymmetry in the abstraction. Both vectors and maps are associative structures - you can assign a key to a value - the only difference is that vectors have a more constrained keyspace (i.e. ordered, consecutive integers starting from zero).

The asymmetry lies in the fact that it's an overloaded function that's supposed to do the right things every time, but in some cases, it does what is arguably the wrong thing, silently, and in others, it refuses to do the wrong thing and fails loudly. It's better that it fails loudly, of course, but the point is that the ergonomics of the abstraction is lessened because you can't just assume it will work. You effectively have to keep the types of all the things involved in your head and/or trace them to ensure that you don't run into a crash.

> We can see that the return type of this expression is obviously an integer, but what is the type of m? How do we type m such that (:number m*) can be inferred to be an integer by the compiler?

This is trivial in TypeScript. You can see it in action here: https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAtjAvD...

  const m = { name: "weavejester", active: true };

  const mStar = { ...m, number: 3 };
  //    ^? const mStar: { number: number, name: string, active: boolean }

  const x = mStar.number;
  //    ^? const x: number

> This is the ultimate problem with static type systems: you're trading capability for safety. If you're programming within a static type system, there are options that are simply not available or feasible to use.

This is just not true. It's true for some certain specific static type systems, but not true in general, and that brings me back to my original thesis: You just need a sufficiently capable type system with the right properties - structural/row polymorphism, ish, plus type inference. And also my Haskell point: it doesn't have to be an incredibly complicated type system that is beyond mortal ken. TypeScript is already doing this and it's arguably one of the most used programming languages on earth.

[wellpast]

“Until you get better” at pedaling, training wheels can help.

It’s not an arrogant take; it’s arrogant to think you know static typing is a requirement for developing software well.

[IceDane]

It's not about "knowing" anything. It's about admitting that humans are fallible meat computers that can't hold invariants in their head across thousands or millions of lines of code and possibly an exponential number of interactions. It's using the technology we are capable of building to help us because it's the obvious thing to do. The notion of dynamic typing as an attractive programming model hinges entirely on the hypothesis that it lets you somehow express things that you need or want to be able to express that static typing prevents you from doing, and that is demonstrably false. The `assoc` example above is a perfect example.

[wellpast]

> that can't hold invariants in their head across thousands or millions of lines of code and possibly an exponential number of interactions.

There’s your problem. And static typing won’t save you either.

The skill is not that, it’s the ability to compose and evolve systems such that you don’t have to hold so much state in your head.

(Btw that property can hold for a million LOC codebase.)

[moi2388]

It’s both.