2. requires static typing in my personal opinion
If you really want static typing Clojure can probably do it. The community support isn't going to be as solid as for something like Haskell. But I'm pretty sure spec offers stronger control of the useful parts of a type system than something like, eg, C. Except the control over RAM; that isn't a Clojure competence.
Solving the problem doesn't require static typing.
Saying you've solved it, when your solution involves on dynamic typing, or even casts in an otherwise static language, is arguably akin to kicking the ball across the center field line and then claiming you've scored a goal.
(See: http://homepages.inf.ed.ac.uk/wadler/papers/expression/expre...)
See https://www.ibm.com/developerworks/library/j-clojure-protoco...
However, I learnt something. I didn't know that the definition of the expression problem required static typing. I prefer to think of it as adding static types to multiple dispatch.
Clojure does compile down to Java classes, but Java is only a partially statically typed language. It also permits run-time casting, which, in a language that even tries to be strongly typed, means run-time (to wit: dynamic) type checking. And Clojure relies heavily on that.
That's why I invoked Haskell. It's an example of a language that is truly statically typed, in that it doesn't (generally) permit any run-time type conversions. ALL type checks must be done statically.
I don’t think you should be writing off Clojure’s multimethods too quickly - they are quite nice, and I haven’t seen anything like them in other dynamic languages like Python.
By the way, I was also enticed by multi-methods in this area, but I ultimately don’t think multiple dispatch is necessary.