[brandonbloom]

The Haskell REPL is pretty good for a static language, but the experience is dramatically different to how a Clojure programmer would use want to use it. To be fair, Node and Python also have totally not usable REPLs for this style.

[bad_user]

GHC's repl is completely fine.

The thing with dynamic languages is that the development style is basically println-driven.

It goes like this: because you can't keep anything longer than a 1-page script in your head and because you can't remember the APIs of other people and hence you can't trust anything you write, in order to keep some sanity, you have to execute every freaking line of code that you write in order to verify that what you wrote actually works — and the sooner you execute, the better, because if your program crashes, the triggered error can happen far away from where the mistake is actually made.

This happens for every dynamic language, not just Clojure. This is why the read–eval–print loop is so important.

However the development experience changes dramatically in a good static language (no, not talking of Java or Go), because you can write more than one line of code before feeling the need to verify it — when compiler type checks a piece of code, at the very least you can be sure that the APIs you used, or the shape of the data you're interacting with are correct.

Refactoring is also painless. Ever done refactoring of projects built on dynamic languages? It's a freaking nightmare and no, the tests don't help that much, the tests actually become part of the problem.

This is also why dynamic languages folks complaining about long compile times are missing the point — those long compile times are necessary to give you guarantees that in a dynamic language you don't get at all, changing the experience, because in turn you don't have to run your code that often.

[didibus]

Since your specific about your statically typed language, which I'm assuming you mean Haskell. Are you also specific about your dynamically typed language? Are you talking specifically of Clojure?

Its unfair to club Clojure and imperative object oriented dynamic languages together. The same way its unfair to club Java and Haskell together.

You're right about the print-ln style. You do run your code everytime you touch a single line. That's what I like about it. But its a personal preference, like some people prefer to compose music on a sheet, others rather have their instrument in hand.

And you're forgetting the trade offs. With haskell, you wrestle the compiler, and every line you write has a compile error at first, until you get it right. This takes as much time if not more, at least for me, then it does running each of my lines of code in my REPL.

I guess I fall in that category where I kind of enjoy the beauty of both, though at the end of the day, I find myself having more fun coding when writing Clojure.

I've never suffered from a Clojure refactoring. You have to be a little more careful, but its never been that painful to me. Again, could be how I perceive "coding pain" is different from others.

[brandonbloom]

These are old tired arguments.

I prefer being forced to keep my program simple by making complexity intolerable over encapsulating it. Your preference may differ.

I find I have to refactor my dynamically typed programs less frequently than my statically typed ones. Your mileage may vary.

No amount of type safety will prove my game is fun, or that my user can understand the UI. I want fast iteration times, since I can’t wait on the compiler to test a new enemy behavior or GUI layout.

[wz1000]

> No amount of type safety will prove my game is fun, or that my user can understand the UI

No, but what it can ensure to some extent is that your game runs, and doesn't crash randomly. If the game crashes constantly, no one is going to play it no matter how fun it is.

[didibus]

to some extent

That's the keyword here. Maybe I'm missing critical data, but I've never perceived the reduction in defect from Clojure to Haskell. I've looked for studies on it, and they all point to either no difference or incredibly close. Never I've been shown a case where the reduction in defects would have an impact on the business I work for. Enterprise software is a domain that isn't that sensitive to defect. Anything less then 5% difference would go unnoticed, and affect in no way sales.

My conclusion, it comes down to your own enjoyment. Which one do you have more fun using and are the most productive in, that's the one you should be using.

I allow muself to change my mind if Haskell really proves to be 10% to 30% or more lower defect, maybe in a later version, with some GHC extension, maybe liquid haskell, I'm not closing my mind to it if it happens I'll be there.

[tome]

> since I can’t wait on the compiler to test a new enemy behavior or GUI layout.

Clojure is compiled, isn't it?

[brandonbloom]

Yes, but it’s fast!

[tome]

If no other language has any functionality similar to how Clojure does things then I think we'll need references to explanations or videos before we can even begin to understand your claims!

[brandonbloom]

Clojure is following in the tradition of lisps that do this right. The important bit is the extra indirection on top-level names. I wrote more about it here a long time ago: https://www.brandonbloom.name/blog/2012/12/21/the-nodejs-rep...

Also interesting is the other end of the spectrum: Forth. Instead of mutation, offers snapshots and restores of the “dictionary”. See this video: https://youtu.be/mvrE2ZGe-rs

[tome]

I don't fully understand what you're getting at. It would have been nice to see no examples with code entered at a REPL and the results, in both JS and Clojure, say.

Are you saying that you want to be able to make bindings that are refreshed on REPL reload? For example if I have a file that contains

    x = 1

and in my REPL I write

    y = x + 1

then I change my file to say

    x = 10

and reload the REPL then y is 11?

[didibus]

Well, the three key aspects, in my preference order, are:

1. Server repl with editor integrated clients. So your text buffers in your favorite editor is the repl. Look at the gifs here https://atom.io/packages/proto-repl to give you an idea for it.

2. Reifed language constructs. You can read about it here http://www.lispcast.com/reification . An easy example is if you have fn A depend on B. If you change B and call A, A will use new B. That's because the information is still availaible at runtime for A to figure out the latest version of B when calling it.

3. Functional programming / emphasis on small independent code blocks that compose. This is where you hear things like immutability, functions that take functions, purity, side effect free, managed references, etc. Basicly state in Clojure is hard to corrupt. That means if you alter state in your repl, it rarely messes up the full state, allowing you to keep working long sessions with your app state still being valid and usable.

I don't have a link for #3. So I'll give an example. Say you have a map you want to add data too. Say this map is read by something else, but you want to try adding something deeply nested to it. In Clojure, you can try as much as you want, experiment until you succeed to mold the map the way you wanted. The other thing reading the map never saw any of your changes, because it sees an immutable view of it. So after your done, if you use that other thing, it'll still work, because you didn't mess up the state it was depending on.

[tome]

Thanks, that's very helpful.

As a Haskell programmer I already know the benefits of 3! 1 and 2 are things that I don't take advantage of so I have a couple more questions.

1. Is this like a Jupyter notebook or some different sort of functionality?

2. Does it work for integer values, say, as well as functions? Suppose my source code says

    x = 1

and in my REPL I write

    y = 10 + x

and then I change my source code to

    x = 2

and reload the REPL. Then is y 11 or will y be updated to 12?

[didibus]

Is this like a Jupyter notebook or some different sort of functionality?

Its similar in some ways, but not quite exactly the same thing. The repl is a server, and doesn't have an interface. So it reads over a socket port, and prints a response back over the socket using a common protocol. So you can build any client you want for it. What is most common is to take an existing editor, like emacs, vim, eclipse, atom, etc. And write a plugin for them which interacts with the server repl. So say your in eclipse, you have a Clojure project open, you can have eclipse send your project code to the repl for you. In practice that means you just work on your code files directly, and just sync them to the repl as you go. Some clients try to be even fancier, creating visual representation of code output like graphs, or gui controls like drilling into a nested map.

Does it work for integer values, say, as well as functions? Suppose my source code says

Y would be 12.

(let [x 1 y (+ 10 x)] y)

If you load this it'll return 11. If you change x to 2 and reload this, it will return 12.

Globally you'd do:

(def x 1) (def y (+ 10 x)

Now y is equal to 11. If you change x to 2, and only reload x, y would still be equal to 11. You'd have to reload y also if you want it to be 12 now.

That's because y is bound to the value of the expression, not to the expression itself. And the value is calculated at load time.

Now you could bind it to the expression by using a function.

(def x 1) (def y #(+ 10 x)

#() is Clojure's shorthand for lambda.

So now the caller is in charge of deciding when to evaluate y.

Calling: (y)

Would return 11 and if you change x to 2, calling it again would return 12.

You can also use reactive constructs instead. So when setting x to 2, an event is published, so you can listen to it and have it reset y to the new value of evaluating (+ 10 x).

[brandonbloom]

    (require '[foo :refer [f]])
    ; edit f in foo.clj
    (require '[foo :reload])
    (f 1) ; should call NEW f.

Node doesn’t have a reload construct. If you hack it in by mucking with the module cache, you still won’t get the new f in your module’s local copy of it.

[tome]

But doesn't the same apply for integer too, as in my example? After reloading y should refer to the NEW x?

And what should happen in your example if f were deleted?

[brandonbloom]

If f were deleted, it would still be in memory unless you explicitly call ns-remove to clean it up. In practice, this is rarely an issue, but I do wish the experience was a little cleaner there.

The same things do apply to integers, but if you use them at the top level (outside a function) then they will be dereferenced immediately (there is no delayed function body to wait for) and so you will get the initial value only once. If you want to enforce a delay, you can use (var x) or the shorthand #’x and later derefence that with @

[didibus]

Other languages do, like Common Lisp, Racket, and most other Lisps. I hear dylan and smalltalk do to, but I don't have first hand experience.

This page https://clojure.org/about/dynamic explains it well.

The difference basically is that the mindset is to work within a running environment, swaping things out as its running. Its closer to a Jupyter notebook, or an excel sheet in some ways, if that helps you visualize it.