As someone alluded to, Interop can be frustrating with big frameworks.

Interop also relies heavily on reflection, and may require type hinting once it becomes a performance problem. Interop also implies the use of side-effects since we're relying on Java object. While a lot of Clojure's sequence and collection operations do work on Java sequences and Collections, it's not perfect and very easy to get bitten, requiring a Clojure.walk/postwalk and zipmap with coercion to get a good Java->Clojure container/sequence/collection.

If we used interop for everything mundane, Clojure would really just be an S-expression shaped husk over Java code. Not a very great solution imho.

I'll politely disagree. The mundane libraries I think you're talking about tend to be about IO, that's always going to be side-effectful in nature. Their APIs wouldn't be all that different even if implemented directly in Clojure.

Type hinting isn't hard or time consuming, literally you can take 10min and have everything type hinted.

Now I don't know about big frameworks, maybe I don't find a need for big frameworks? But even then, what kind of framework are you talking about? Using Spring MVC for example?

A problem I have run into (admittedly, having not written as much clojure code as I'd like) is that some java libraries in particular can make interop distinctly unpleasant. Anything around the Spring framework, for instance, made me tear my hair out. Yes it's possible, but by the time you've compensated for the impedance mismatch you might as well have done a rewrite.

Hum, I've used Spring with Clojure a lot, never had issues.

Things that are difficult to interop are java annotations based stuff, having to implement interfaces or subclass classes, and functional interfaces.

But you can use Spring without annotations, which is my preferred way anyways, because I favor explicit over implicit.

If you're using interop for mundane, everyday things, why use Clojure then? I imagine you would end up writing non-idiomatic Clojure code to do the interop (e.g. working with mutable objects and not immutable datastructures).

The recommended design for Clojure programs is imperative shell, functional core. You use Clojure as your functional core, and it interops with mundane libraries for the imperative shell, such as database clients, http clients, logging, http server, graphics, sound, etc.

It works beautifully, and the REPL helps with all of it.