Readit Newshuahaiy commented on Ask HN: Share your personal website · Posted by u/susam
https://yyhh.org
Yes, plan is there but didn't have time yet. Most likely will be available next week
Wonderful. Looking forward to it.
Very nice. Is there a plan to have an EDN writer in C as well?
The whole premise of static typing is that type errors can be caught at compile time. Java type system allows for kinds of errors to be caught at compile time that will not be caught by using protocols in Clojure. Yes, you can run the compiler at run time, but that's entirely besides the point here.
These libraries aren't using protocols for type safety though, they're using them as a performance optimization. That's certainly a perfectly fine reason to use protocols, and I agree that it's a completely legitimate use case. It's the whole right tool for the job thing. If you're writing something where performance is the top concern, then that's what protocols are for.
I very much agree with you that that there are people who focus on low level code, and those who focus on application level code. The style of coding will be different depending on the type of problem you're solving. You're right that I failed to qualify my original statement regarding protocols being an anti-pattern.
You're absolutely correct that we should take a pragmatic approach towards using language features. Hence why the context of whether protocols are the right tool to each for lies in the type of code you're writing. And of course, some people find it easier to have more structure to help with their reasoning. Although, I'd argue tools like Malli work better there.
To sum up, I'm not arguing against protocols being useful or that there's no place for them. We started this discussion talking about whether protocols provide equivalent guarantees to Java's type system. I disagree regarding that. However, I also don't think that this is a real problem. Otherwise, use of something like core.typed would've become prevalent by now.
I wrote my library this way for both performance AND type checking reasons. You cannot tell me the reasons why I wrote my code my way. That is just absurd.
In any case, it is possible to write Clojure in a way that is type checked at compile time. And it is an acceptable way to write Clojure. I just want to clear the air.
Of course Clojure has to ultimately be compiled into a native format for the host platform, bytecode in the case of the JVM implementation, but that doesn't require type checking in the same way Java does.
Clojure functions are compiled into implementations of clojure.lang.IFn - you can see from https://clojure.github.io/clojure/javadoc/clojure/lang/IFn.h... that this interface simply has a number of overloads of an invoke method taking variable numbers of Object parameters. Since all values can be converted to Object, either directly for reference types or via a boxing conversion, no type checking is required to dispatch a call. With a form like
(some-fn 1, "abc", (Object.))
Protocol methods just get compiled into an implementation of IFn which searches for the implementation to dispatch to based on the runtime type of the first argument, so it doesn't introduce static type checking in any way.
But if you add type hint in the signature, it does check the type. Basically, if you specify the type, it will check type. Just like any language that is not automatically inferring types, e.g. Java. So it is the same as Java.
You guys make it out like Clojure is doing something extra to hide Java types, but it doesn’t. What Clojure does is really minimal on top of Java. It barely hides anything.
If you give it type, it will check type. If you don’t give a type, it falls back to a default type, Object, which IS a TYPE. The fact that Clojure compiler cannot deal with GraalVM SVM Pointer type tells you that it’s checking type, because Pointer is not an Object! I found this out the hard way: https://yyhh.org/blog/2021/02/writing-c-code-in-javaclojure-...
“One limitation that one needs to be aware of when writing native image related Clojure code, is that most things in the GraalVM SDK inherit from org.graalvm.word.WordBase, not from java.lang.Object, which breaks the hidden assumption of a lot of Clojure constructs.”
Even if you did, that wouldn't solve the problem because many checks are still done at runtime. Also, if you started doing that then you might as well just write Java at that point. I've worked on code bases structured in this way and it's absolutely terrible to work with. For one, protocols completely break any sort of REPL driven development.
Most libraries are absolutely not written in this way either. Please point me to a single library that's actually written in the style you describe. The use of protocols in actual popular libraries like Ring tends to be minimal.
The reality is that dynamic typing has never been a real problem in Clojure. I've worked with the language almost exclusively for over a decade now, and I maintain a number of popular libraries, like Selmer, with millions of users.
That has nothing to do with types. You are now talking about when a compiler is run.
Clojure gives you the option to run the compiler at runtime, so that's what people normally do. However, you can also run the compiler at compile time. Right?
For people who want type checking, they can opt to write Clojure in this defprotocol everywhere style, and turn on AOT. Then they basically get the same thing as what Java gives them.
As to example of libraries that are defprotocols everywhere, you should look at any of the low level performance minded libraries in the Clojure ecosystem, they are either written in this defprotocols everywhere style, such as nippy, neanderthal, dtype-next, and so on, or mostly in Java, such as http-kit, fast-edn, etc. I noticed this phenomenon, because my own libraries, editscript and datalevin, are written in this way. I take comfort that my fellow performance minded library authors are doing the same. Finally, isn't Clojurescript entirely driven by protocols?
So really, there are two kind of Clojure programmers. One type writes application code or high level libraries, and they write normal Clojure code all the time. However, there are also those who write primarily low level library code, which are used by the first camp, and their code is full of defprotocol and deftypes. So defprotocol everywhere is not anti-pattern. It's anti-pattern only in the mind of the first camp of programmers, and that's a narrow minded way of looking at things. Even the first version of Clojure Programming book by the core team members, are written in a way that's full of defrecord. Remember?
This "everything is a map" orthodoxy is turning people away from Clojure. Just let people write the code that suits their own needs. We can use more people who are pragmatic instead of dogmatic in the Clojure world. If you trust Rich Hickey's judgment, then you should trust him put in the features Clojure has for good reasons. Macros and protocols are part of the Clojure language, and you should be using them when the use case calls for them. Stop the "anti-pattern" nonsense.
Protocols do not work like Java interfaces or classes. Their methods are compiled into regular functions which lookup the implementation to use at runtime based on the runtime type of the receiver. Compilation will check for the named function but doesn't do any further checking. Given the following protocol and implementation:
(defprotocol P
(method [this ^Integer i]))
(extend-protocol P
String
(method [s i] (.substring s i)))
Of course there's no requirement for Clojure code to be AOT compiled anyway so in that case any name errors will still only be caught at runtime when the compilation happens.
Type hinted bindings are only converted into a cast and are not checked at compilation time either e.g.
(defn hinted [^String s] (.length s))
(hinted 3)
deftype is only used for Java interop an is also not a form of type checking. The methods will be compiled into Java classes and interfaces, but the implementations defer to regular Clojure functions which are not type checked. You can only make use of the type information by referencing the compiled class files in Java or another statically typed language, using them from Clojure will not perform type checking.
deftype IS a Java class, it's not compiled into something else. What is a Clojure function? A Clojure function is a Java class. Clojure is a compiled language, so it does check types, just like Java check types.
So if you use defprotocol and deftype for every domain objects in your code, your code won't compile if there's a type error. Try it.
BTW, that's the way many Clojure libraries are implemented. These libraries rely on dispatch on type to work, so they are taking advantage of the type checking.
Of course, you will say, "oh, clojure is not normally AOT, so it's not dong the checks.", but that's another issue. The issue at hand is this: can you write Clojure such that types are checked at compile time. The answer is YES.
The compiler may run only when you run the program, that's a different issue. You are confusing these two issues.
If you want a separate compile stage, then basically you are already excluding runtime compilation, i.e. you are arguing against runtime compilation. So it's not really about typing, but about how you want to run the program. Isn't it? You want AOT for everything, you don't want runtime compilation. That's it. It has nothing to do with types.
That's not quite true though. Java tracks types in the signatures of the functions, defprotocol does not. If I make a protocol and then pass a wrong type as a parameter to it then I'll get a runtime error. It's not going to tell me that I passed in a wrong type at compile time.
I find using defprotocol in Clojure tends to be an antipattern because it just makes code harder to read by introducing indirection. The libraries using defprotocol use it to solve a specific problem of creating a contract for how the API looks.
Then you are not writing in defprotocol everywhere style. The keyword is everywhere. All the domain objects are deftype or defrecord. Try that. It is the same as Java, basically.
It is not an anti pattern, it is the way most low level libraries and clojure itself are written.
Clojure is a tool, not a cult. This core team worship is turning people away. The core team made plenty of mistakes, and got called out, rightfully.