Few hundred milliseconds? I played with clojure a month or so ago and invoking lein repl was ~7.5 seconds.

I never worked with Clojure, but a simple java "hello world" starts and finishes within a second. Same with a simple java Swing UI "hello world" sample. If some application is doing something slow during initialization - it is not the platform itself, but the specific code to blame.

Lein starts a JVM instance for itself, then loads plugins, checks dependencies etc. and starts a new JVM instance for the program if necessary.

Yes, I can confirm this.

Clojure seems like a good fit for tiny projects that are little more than scripts, but the start up time makes them kind of annoying to manually test. Fortunately Clojure does have a REPL.

The best cure to this problem is nREPL. It basically is an REPL server. There are plugins for Emacs (nrepl) and vim (vim-fireplace). With these tools, one may start a user repl and run tests within that. I have written a humble guide to set up Emacs for clojure here: http://gkayaalp.com/2014/01/28/taste-clojure.html#emacs My emacs configuration repository is gone thought; I'm using vim these days.

A JVM with smaller memory and cpu needs and faster startup would make me consider using Scala/Clojure again.

> There are plugins for Emacs (nrepl)

I think nrepl for emacs has been replaced by cider (which still uses nREPL)

AFAIK Cider is like SLIME, big and integrated. Emacs nrepl is just the repl connection, and is usually enough (at least, has been enough for me).

Ok, maybe I'm misunderstanding, but from [1]:

"CIDER (formerly nrepl.el) is the Clojure IDE and REPL for Emacs, built on top of nREPL, the Clojure networked REPL server."

That and the availability of the packages on melpa:

  cider              20140318.... available  Clojure Integrated Development Environment and REPL

And the fact that technomancy's git repository for nrepl.el hasn't been touched in 2 years leads me to believe that cider is the better nREPL choice ;) Be happy to hear that nrepl.el is still maintained and is better in some way than cider, but I don't see cider as being that heavy (at least as compared to SLIME).

[1] -- https://github.com/clojure-emacs/cider

Yes, but that's more of a Clojure problem than a JVM problem.

Practically any command line utility? eg. ls, cat, sort, uniq, ps, what have you.

I'm constantly amazed that make(1) can do successive recompiles of a 50k LOC project in less than a second, while gradle / maven / etc takes upwards of a minute.

Good example, but we have heaps of command-line utilities written in Java. Many complaints but never about performance or start-up time.

For some low-level programs executed hundreds of time per session (like "ls") I agree it adds up and might cause frustration. Java is a bad choice for this niche, but you are not going to write them in Python anyway, aren't you?

PS: Just tested "LS" in Java, less than a second run, I could personally live with that.

ls