Comment by brabel

11 hours ago

Yes but I don’t know how someone familiar with a Jetbrains IDE can claim that only Lisp has that feature. I love Common Lisp and SLIME, but most of what it can do, I can also do in Java with the IDE. Change a method definition while it’s running and then restart the method? No problem. Run any code within the context of the running method? Yes, Java can do it. Change local variables values in the middle of a method? Easy!

The Lisp REPLcis still superior because it comes with more stuff, like DECOMPILE, INSPECT and so on that can only exist because the language is essentially a compiler even at runtime, which can also be a problem for sensitive domains… but in Java you can do all those things using the IDE so the distance between what is possible in Lisp and a language with good IDE support like Java and Kotlin is now negligible in my opinion.

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brabel

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Jach  7 hours ago

I've frequently said that Java + JRebel gets the closest to the Common Lisp + slime experience (closer than Python) but as you say the Lisp experience is still superior, the Java ecosystem has yet to close the gap*. The widest part of that gap I'd mention is in not having the condition system built-in to Java (though I'm aware people have tried to make a comparable one as a library), lacking it degrades the debugging experience considerably (even though simple step-debugging is typically more pleasant than in Lisp). IntelliJ's drop frame feature isn't good enough. The other problem is needing Java + something. What you get with just a regular JVM running under your IDE is no better than what other languages offer (if they offer anything) as their cute hotswap/hotpatch feature and comes with big limitations. (Like no changing method signatures or no adding/removing methods or properties, or only applying changes to new objects.) Once you're doing something non-trivial, especially if you're trying to incrementally develop your program rather than just debug one specific problem, you'll have to restart. In contrast Common Lisp's got its disassemble, describe, inspect, compile, fmakunbound, ... all being functions callable at runtime, and update-instance-for-redefined-class is part of the standard language too. Support for live reloading of everything is baked into the language rather than a hack on top, slime is just a convenient way of working with it. It's still convenient to restart the program occasionally, but few things force you to.

Unfortunately JRebel has killed their free tier, so I'd now point unwilling-to-pay programmers to something like https://github.com/JetBrains/JetBrainsRuntime which is IntelliJ/Eclipse/whatever-independent. I haven't tried it myself yet though... Given they only address the biggest class reloading concerns, I doubt it's actually comparable to JRebel for business-world Java. JRebel handles among other things dynamic reloading from XML changes and reinitializing autowired Spring beans that other classes use for dependencies.

*Caveat, I've been out of the professional Java grind for a while, I'd be pleasantly surprised if some new version that's come out contradicts me.