[MarcusBrutus]

I've used Clojure in a few cases and I totally adore the simplicity of its Lisp syntax as opposed to the baroquesque abomination that is Scala. However, lack of strong typing is sorely felt. I 've done a little playground-style OCaml coding and the feeling you get with OCaml is that once your program compiles, it most likely also runs correctly. Is a Lisp language with strong typing for the Java ecosystem too much to ask? Apparently it is or else we would have had it by now.

[kazinator]

> I 've done a little playground-style OCaml coding and the feeling you get with OCaml is that once your program compiles, it most likely also runs correctly.

This is only a feeling. Without carefully testing the code to exercise its cases, all you know is that they are properly typed.

For instance, suppose we write a complicated function (or group of functions) which goes through a block of intermediate code (output of a compiler) and assigns registers to all the temporaries, introducing memory spills in situations where more variables are live than the available registers.

We might have a feeling that because this code compiles, it must be free of problems such as accidentally assigning the same register to two variables which have overlapping lifetimes.

That feeling is poorly supported by reality; it is the "safyness" of static typing.

Untested code is garbage. And thorough testing is difficult to impossible, so there is a bit of garbage in almost all software, unfortunately.

Statically type checked code has all of its code paths effectively tested by the compiler, but those tests have only the limited point of view of trying to show that the program contains a trivial type mismatch, a close cousin of the syntax error. These "tests" are not actually feeding values into the code and trying to make it fail or behave incorrectly with respect to its specification.

[cle]

I mostly agree. In an increasingly distributed, decoupled, non-monolithic, service-driven world, where service interfaces are dynamically-typed and applications are data-driven, static typing doesn't add much value. And the sophisticated type systems, that can provide better guarantees than relatively primitive type systems like Java, are quite difficult to understand and use correctly. I expect that we'll see more and more type modeling bugs as static type systems become more feature-rich and complicated.

Static typing is extraordinarily useful in large company settings, where you may own a library that is used across the company, and you can quite easily understand how your library is used in other codebases and can confidently make cross-cutting emergent patches.

I'm pretty optimistic in the direction that Clojure is heading with clojure.spec. The ideal that I hope it reaches is "inductive" type safety, where you can prove your program is typesafe with a certain probability. And the tradeoffs you get by relaxing the deductive properties and timeliness of static typing are vastly simpler expressiveness, composability, testing, etc.

[rkrzr]

> Statically type checked code has all of its code paths effectively tested by the compiler

The type checker just ensures that a program is well-typed (i.e. free of type errors).

The better the type system the more program properties can be encoded in it and the more errors it can catch (up to the point of proving correctness of your program).

But you are right that type checking alone is no substitute for testing. They are orthogonal concepts and both should be employed to ensure that your programs behave correctly.

One nice thing of statically typed languages is that they can automatically generate some tests for you, like e.g. the QuickCheck library for Erlang and Haskell.

[marcosdumay]

They are not orthogonal at all. Both verify your code against invariants. While the typing system tries to prove an invariant holds, a test tried to prove that it does not hold.

That means that false positives are the problem for typing systems, while false negatives are the problem for tests. But that's the biggest difference you will find.

One does even replace the other.

[jeremiep]

Clojure has quickcheck as well: https://github.com/clojure/test.check

[rkrzr]

Good point. Of course you have to specify the type of the values that you want to test in the test itself then, so you have to specify some types one way or the other.

[jeremiep]

You can feed those types from clojure.spec now :)

[jxm262]

I've actually felt this same way for a while now. This past year or so I've worked hard (imo) to "get" the benefits of strong typing, but can't shake the feeling that the tradeoffs just aren't worth it. I was hoping the verbosity, complexity, etc (strong types), would give me more confidence and security in my code. It always seems like a false sense of security though and I'm currnently on the fence as to whether or not it's worth it.

Is there any studies done showing that strong typing is actually a disadvantage? I've seen some stating the opposite, but nothing really stood out to me. Sorry for the long rant, but at this point I can't find anything empirically stating one is better than the other.

[kazinator]

Static typing (and other static checks) will reduce the round trips between editing and running. Some of your typos that are not syntax errors get caught and reported to you. Of course, you were going to test that code anyway. But you avoided a bit of wasted time. However, this advantage can be eroded by the trade offs.

Interesting experience recently: I added static checks to a Lisp dialect which report warnings for all occurrences of unbound variables and functions. (Not type checking, but a very basic static check). According to static proponents, bugs of this type should exist left and right if we don't have the check.

Only one instance of an unbound variable was found in the dialect's standard library: and that was a function that was added as an afterthought and never tested. The problem reproduced 100% when calling the function in any correct manner whatsoever; the function was completely broken. If it had been called just once after having been written, the problem would have been caught.

I fixed the problem so that the warning went away and caught myself almost starting to think about commit the fix, when I realized: what am I doing? I still haven't called the function. Gee, it now passes the one feeble static check that was added, so it must be correct? Haha.

[justinhj]

For me the only downside of strong typing is that code takes longer to write. It's reminiscent of my years writing C++ where often fiddling around with header files, type declarations and templates would seemingly take up more time than the actual logic of the program. For the last few years I've been working in Scala and compared to Clojure it can take longer to knock out working code. That said with the help of type inferencing and IntelliJ it is nowhere near as slow as C++ was, and now I find that the benefits of strongly typed code greatly outweigh the costs in terms of syntax and development speed.

[yawaramin]

> ... type declarations and templates would seemingly take up more time than the actual logic of the program....

Just a small point: type declarations are part of the actual logic of the program. In type theory, types are logical propositions and values are proofs of those propositions.

[Nekorosu]

This is really interesting idea. It feels obvious when you get it but I've never thought about it and I've never seen it before.

[mpweiher]

> That feeling is poorly supported by reality; it is the "safyness" of static typing.

Has that become a thing now? :))

[jeremiep]

Theres the new clojure.spec[1] in 1.9 and core.typed[2] adds an optional type system as well.

[1]: http://clojure.org/about/spec [1]: https://github.com/clojure/core.typed

The REPL-driven development of Lisps makes types not as important because everything is interactively tested as you write it. Having an optional type system makes it much easier to start with dynamic types and gradually add type annotations as your architecture stabilizes.

[yogthos]

Conversely, lack of mutability makes dynamic typing much easier to reason about. Since variables typically can't be changed via side effects, you can do local reasoning about your code vast majority of the time.

[rkrzr]

> Conversely, lack of mutability makes dynamic typing much easier to reason about.

Dynamic typing does not imply lack of mutability. Those are unrelated concepts.

Python and Ruby are dynamically typed but both are certainly mutable.

Conversely static typing actually makes it easier to reason (locally or not) about things, since you always know the type of everything.

[jeremiep]

I think he meant it in the context of Clojure, which has immutable values.

I don't feel static typing makes it easier to reason about, at all. Reasoning about values and their transformations is more important to me than reasoning about types, and since values carry types you're actually working with more information. Most of the time the types I'm interested in are closer to concepts (sequences, mappings) than concrete classes.

Thats where having immutable dynamically typed values is better than having statically typed mutable ones.

[rkrzr]

> since values carry types you're actually working with more information.

Only for the specific value that you are reasoning about. If you want to reason about all possible values, then you are de-facto reasoning about their types.

> Most of the time the types I'm interested in are closer to concepts (sequences, mappings) than concrete classes.

But sequences and mapping are also types, right? You can abstract types to type classes (i.e. whole classes of types, e.g. all types that can be iterated over, or all types that are ordered etc.) and also reason about them.

> Thats where having immutable dynamically typed values is better than having statically typed mutable ones.

Sure, ideally you want to have immutable statically typed functions and values, since you can then do some equational reasoning and prove certain properties of your program.

[jeremiep]

> If you want to reason about all possible values, then you are de-facto reasoning about their types.

True, but a variable can only ever have one value at any given time; knowing a variable is an int is good, knowing a variable is the same int value throughout its extent is better :)

> But sequences and mapping are also types, right?

Yes, but they're not concrete types and don't map to a single interface either. When they do these interfaces are compositions of smaller interfaces anyways and I prefer to reason about these smaller parts.

Which means I'm reasoning more about the shape of the data than the actual type implementing it, and that to me is closer to a value than a type. Its the same with type-classes, you're reasoning about the features of a value rather than the specific type implementing said features.

> ideally you want to have immutable statically typed functions and values

For functions we're talking about purity rather than immutability (which qualifies variables). Type systems also are very leaky abstractions; null pointer exceptions, can't limit the range of value, requiring more code which introduces its own bugs and complexity and more.

From experience I prefer a smaller dynamically typed codebase that has tests for the trickier parts over a statically typed codebase (even if tested). The productivity difference is startling and the resulting quality is about the same.

[yogthos]

I never said dynamic typing implied lack of mutability. What I meant is that Clojure defaults to immutability, so reasoning about types becomes easier than in a language with mutable data.

In a language like Ruby or Python, it's possible for a side effect to change the type of the variable you're looking at externally. This cannot happen when you're writing idiomatic Clojure.

Static typing comes at a cost however. You have to figure out how to encode the problem using types. Effectively, you have to prove to the compiler that your code is self-consistent. Proving something is often much harder than stating it.

At the same time, static typing doesn't guarantee semantic correctness. So, it doesn't actually tell you that your code is correct in any meaningful sense.

I think that Clojure Spec packaged with the 1.9 release, provides a much better way to catch errors than types. The main reason being that it focuses on ensuring semantic correctness.

For example, consider a sort function. The types can tell me that I passed in a collection of a particular type and I got a collection of the same type back. However, what I really want to know is that the collection contains the same elements, and that they're in order. This is difficult to express using most type systems out there. However, with Spec I can just write:

    (s/def ::sortable (s/coll-of number?))

    (s/def ::sorted #(or (empty? %) (apply <= %)))

    (s/fdef mysort
            :args (s/cat :s ::sortable)
            :ret  ::sorted
            :fn   (fn [{:keys [args ret]}]
                    (and (= (count ret)
                            (-> args :s count))
                         (empty?
                          (difference
                           (-> args :s set)
                           (set ret))))))

The specification will check that the arguments follow the expected pattern, and that the result is sorted, and I can do an arbitrary runtime check using the arguments and the result. In this case it can verify that the returned items match the input.

[yawaramin]

> ... you have to prove to the compiler that your code is self-consistent. Proving something is often much harder than stating it.

Not really. When you learn the properties of your type system, you can 'prove' your way through most day-to-day programming tasks fairly easily. And when you can't prove something to the compiler, you can just fall back to telling it using its 'dynamic' escape hatch. You're certainly no worse off than you are with pure dynamic typing.

> ... Clojure Spec ... focuses on ensuring semantic correctness.

Nothing in a static type system precludes something like Clojure Spec, or at least something very much like it. You can still fall back to runtime tests that your function works according to spec. In fact that's what Haskell's QuickCheck and related generative testing systems are all about.

[groovy2shoes]

Indeed, they are distinct concepts. However, in Clojure, only a small handful of datatypes allow mutation (sorta like refs in ML, but thread-safe and with various semantics depending on how that thread-safety should be handled). All of the usual datatypes are immutable (lists, vectors, hashmaps, sets, strings, etc.). If you need mutation, you need to wrap your object up in a "mutable box".

[mindcrash]

Typed data was already possible with schema [1], which is now maintained by the plumatic (former prismatic) team. Which also says something about the way Clojure is awesome. Everything is optional, you arent forced to use anything to get to a working solution. Stuart Halloway and Rich Hickey also have some great talks on this subject. If you are interested you might want to check out "Radical Simplicity" [1] by Stuart and "Simple Made Easy" [2] by Rich to see why Clojure wipes the floor with almost any other programming language, especially the likes of C# and Java.

I am not surprised at all Bob Martin loves it. Any principled software engineer would.

[1] https://skillsmatter.com/skillscasts/2302-radical-simplicity

[2] https://www.infoq.com/presentations/Simple-Made-Easy

[sdegutis]

> "the feeling you get with OCaml is that once your program compiles, it most likely also runs correctly"

The feeling you get with Clojure is that, when you write and test each function (using CIDER) and get live feedback to make sure they work, you can combine them into bigger functions that most likely also run correctly.

[justinhj]

"baroquesque abomination" is a very colourful but somewhat unfair description of Scala. I've been using it in production for a few years now and I find it can be quite pretty if you're careful, and is quite readable once learned. Not only that but after years of Common Lisp and Clojure programming (at hobby level) I never really satisfactorily lived the dream of the programmable programming language that lisp offers. With Scala I find it has capable facilities for writing DSL's without even resorting to compile type macros. I do agree the syntax can be terrible especially when people go crazy making DSL's for libraries or make their code too dense and unreadable.