At one point I wrote Clojure for my day job. I think having a REPL is actually more useful for untyped languages, especially Clojure, where most data "types" are maps/lists. By exploring in the REPL, you can get a good feel for what kinds of data a function works with.

In a statically typed language, a REPL can still be useful, but the gains from it are less than you'd get with an untyped language. It's easy to see what kinds of data a function works with by just looking at the types. There are exceptions of course, like when the type is very complicated, it can be helpful to see some examples of actual values of the type. And I suppose that's why languages like Haskell and OCaml have REPLs.

That's hardly fair. Clojure is unusable without having a REPL already loaded.

    $ time lein run 
    Hello, World!

    real	0m5.683s
    user	0m5.981s
    sys	0m0.557s

I have.

That's not even the beginnings of a useful reply. :)

Give me a highlight of your normal day-to-day with the language. What, exactly, does the REPL offer you that provides significant productivity gains that can't be had any other way?

Because clearly I've missed it.

And it should be pretty easy for you to describe if it's that common and/or obvious.