Ask HN: A month to learn a new programming language

I find myself with one month of free time between jobs and I've decided that I want to learn a new programming language and implement a small ray tracer in this.

I'm familiar with imperative and OO programming models, so I was thinking to dive into something completely new to me like Standard ML, Ocaml or Haskell.

I would love to hear your suggestions about what new programming language to learn (as long as it is not a paradigm that I'm already familiar with).

Thanks