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" ar

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.