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Comment by shivekkhurana | Hacker News Reader

REPL is a killer Clojure feature that nobody (outside the ecosystem) talks about.

Probably it's hard to comprehend what developing in a REPL feels like, majorly because no other commercial language has a REPL as powerful as Clojure.

I gave a talk[1] explaining the REPL and most people in the audience (including senior Java, C# and Python developers) had never seen something like that before.

REPL is the reason why I (and perhaps other Clojure devs) endure the pain around Clojure tooling, demand, supply and ecosystem in general.

[1] https://www.youtube.com/watch?v=Bs44qdAX5yo

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Everytime I've singled out the REPL as why I like Clojure so much when explaining why Clojure so great to my friends they seem to mention that other languages have repls too. Like F# or JavaScript. When I counter that Clojure's REPL is connected to the running app instance they are developing I don't think they really understand. Perhaps this is one of those things that you just have to try out to grok.

As is javascript. Have you ever tried debugging an application with Chrome ?

I frequently use the "pause on exception" feature of the debugger or also place breakpoints strategically and then use the console as REPL for further debugging.

I think the "_running_ app instance" is the key distinction here.

Breakpoints require halting your system, so while you can inspect the system's state, you can't meaningfully alter it as you could with the kinds of Clojure REPL workflows talked about here.

Another limitation is that you can't really inspect parts of your system outside the context of the currently running function where the breakpoint was triggered.

I think debugging with state-preserving hot reloading in UI development is probably the closest analogue I've encountered to debugging workflows with a Clojure REPL, though it's still nowhere near as flexible.

> Breakpoints require halting your system, so while you can inspect the system's state, you can't meaningfully alter it as you could with the kinds of Clojure REPL workflows talked about here.

Fix and continue. Various language implementations provide that.

That's altering the _code_ as opposed to altering the _state_ of the system.

Just change the state, too. Many languages/implementations provide that.

One difference is that you might then be debugging compiled, possibly even modified JS. The Lisp REPL deals in the original Lisp source code.

When I started learning/using Clojure, I didn't use the REPL much and kept on working in the traditional way: Write code, compile, test. Repeat until it works.

It took some time to break my old habits and start using the REPL. It's unfortunately made me a bit lazier writing unit tests :), as I can hammer on a piece of code until I know it works - and small, deterministic functions tend to not break once you get them working. So much of my test code is integration tests.

Nowadays, when I have to work in Java (or Scala, Javascript, Python, etc), I seriously miss the Clojure REPL. Though Clojure (and Lisp in general) has definitely affected the way I write code in other languages.

> I gave a talk[1] explaining the REPL and most people in the audience (including senior Java, C# and Python developers) had never seen something like that before.

I find that quite surprising, as I use the REPL a lot when coding in Python.

There are big differences in capabilities between the Python REPL and a Lisp REPL.

Even then the Python REPL can be quite useful but I do not expect most Python developers to use it. (This is from personal observations as a Common Lisp enthousiast.)

> no other commercial language has a REPL as powerful as Clojure Except for other Lisps like CL

Smalltalk.

My use of the word "commercial" is not apt. I meant to say "mainstream" languages.

That would exclude Clojure, too.

Seeing how Clojure is actively used at places like Apple, Amazon, Atlassian, and even Walmart where software development isn't even their primary business, I think it's pretty safe to call it mainstream.

I would call languages like Java, Javascript, Python, C++, C# 'mainstream'. But not niche languages which have 1/100ths or less of open positions.

Monster lists 68000 positions after a search for 'Java', and 180 for 'Clojure'.

I would call any language that's actively used in the industry with a large and active community mainstream. Restricting the term mainstream to a handful of most used languages is pretty silly in my opinion.

It's just that the community is not large. It's small. To think that 'a few thousand people' is large among millions of other programmers is 'silly' (to quote you).

I'd love to know where your numbers come from

Do you have other numbers?

The last Clojure survey has ~2500 people responding. Which is basically the same for several years now. I we assume that 10 times more people are actively using Clojure, then that would be 25000. Still a lot less than the probably 7 million Java programmers and 8 million Python developers. https://www.zdnet.com/article/programming-languages-python-d...

I'm not arguing that Clojure is as widely used as Java or Python, which are two most popular languages in the world. I'm saying that it's a ridiculous bar to set for calling something mainstream.

However, there are some other metrics we can look at. For example, if we look at downloads for popular libraries, we can see that Ring's been downloaded 9,058,741 times, and obviously there are repeat downloads for the same users, but even accounting for that it indicates a much bigger user base than you're suggesting. https://clojars.org/ring/ring-core

Other data points would be commercial tooling like Cursive and commercial funding for projects with organizations like Clojurists Together indicates that there is a critical mass of commercial users who are willing to fund projects

https://lambdaisland.com/blog/2020-02-03-open-collective-lam...

https://www.clojuriststogether.org/

Finally, Clojure usage is growing for new projects both in enterprise and government sectors in countries like Finalnd

https://twitter.com/autiomaa/status/1235944730267193345

https://docs.google.com/presentation/d/1nCZ-GmWLcH8Dcz3XJHY0...

This is a very different picture from a tiny isolated community of a few thousand developers that you seem to be painting.

> 9,058,741 times,

This says nothing about the number of human users.

> This is a very different picture from a tiny isolated community of a few thousand developers that you seem to be painting.

https://opencollective.com/lambda-island#section-contributor...

They have 13 contributors.

>This says nothing about the number of human users.

It obviously does because people are using these libraries in their projects. As I noted, it's an indirect measure, but it still gives an idea of the usage. And Open Collective was just announced last month, so not sure what point you were trying to make there. Wonder why you didn't mention anything about Clojurists Together, doesn't fit your narrative? https://www.clojuriststogether.org/members/

> It obviously does because people are using these libraries in their projects.

Obviously it says nothing about the number. If we look at the number of downloads of the current version, it's ~40000. Now many systems may download it multiple times. So the number is not an indicator for a large user community.

> Wonder why you didn't mention anything about Clojurists Together, doesn't fit your narrative? https://www.clojuriststogether.org/members/

It 'fits my narrative' well. Just count the number of the members.

Don't get me wrong, that's all fine and useful in a small community, but to claim a handful of companies and a few hundred people is an indicator of a mainstream popularity is just massive overselling and looks 'silly' (to quote you again, sorry).

If commercial usage of the language by companies big and small around the world along with funding of the ecosystem is not an indication of mainstream usage, then I guess we'll have to disagree on what constitutes mainstream.

Right, a few users don't make something mainstream. Big companies have thousands of developers - even non IT companies - that someone inside some big company uses a programming language doesn't make it an indicator for widespread (most people use something -> mainstream) usage.

Mainstream: large relative and absolute numbers of users.

For example the Porsche Taycan (-> Microsoft) is not a mainstream car, even though Bill Gates has one and Porsche is an incredible profitable company. https://www.economist.com/business/2019/09/12/porsche-is-sma...

well fair enough then

9 millions downloads in 10 years, expressjs has 12 millions download per week (if you want to go by that metric).

My whole point is that languages like like Js or Java are not a good metric, and you don't have to be as popular as the top handful of languages to be mainstream.

> you don't have to be as popular as the top handful of languages to be mainstream.

I thought being in the top is the definition of 'mainstream': 'most people use it, know it, learn it, ...'.

Mainstream is typically taken to be known and widely used which Clojure is. You seem to have a personal much more restrictive definition which only includes the top few languages for reasons unstated.

> Mainstream is typically taken to be known and widely used which Clojure is.

But Clojure is neither widely known nor widely used. The last Clojure survey was done by just 2500 people.

> You seem to have a personal much more restrictive definition which only includes the top few languages for reasons unstated.

The top ten languages are all two orders of magnitude more used than Clojure. They are mainstream. Literally they have millions of users. That's the definition of mainstream. Mainstream pop: the music most people hear and which dominates the charts. No one would claim that free jazz is mainstream, even though it has some stable fan group.

For a language that's not widely known it's weird how Clojure features in Stack Overflow and JVM surveys. Meanwhile, it's also strange that a language that's not widely used finds its ways into all kinds of well known companies.

The only project at Amazon that uses Clojure is one legacy project in maintenance mode.

I'll take your word on that. However, that doesn't change my point that Clojure is used at lost of large companies, and the recent developer survey showed that it's becoming more widely used at large companies.

A good REPL is nice, but its hardly a killer feature or a big productivity boost. If Clojure didn't have a REPL it would have been completely dead by now cause its startup time is really bad. Clojure needs to have a REPL in order to survive (which is barely doing).

Programmers are equally productive[0] (or way more because of their big ecosystems) in languages that have a fast code-run cycle.

[0] https://groups.google.com/forum/#!topic/comp.lang.lisp/L5dZ-...

REPL driven workflow allows me to put the application in a specific state, and then continue developing features against that state. If you have to restart the application each time you make a code change then you have to rebuild that state each time. This creates a much slower feedback loop, especially when you're working on large applications. Furthermore, the REPL is a fantastic tool for troubleshooting live systems in production, and in some cases even patching them with zero downtime.

I don't know a single person who's worked with this workflow on a serious project and would want to go back to compile/run cycle afterwards.

Meanwhile, Clojure leverages host ecosystem getting all the same benefits as any other language running on it.

>Programmers are equally productive[0] (or way more because of their big ecosystems) in languages that have a fast code-run cycle.

I would disagree with this. I feel much more productive in Lisp than, e.g. go or C or C++. In Smalltalk, the productivity was so great that I was dead tired after 8 hours, as it was all thinking and effectively zero compiling.

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