The ML family (SML, Ocaml, F#) is also pretty good with the mixture of functional and imperative constructs.

Having a part of the program known to be pure at compile-time, but another part effectful is something you see in the language F* (http://fstar-lang.org) - here you get monads, dependent types, a proof system, and the ML module system neatly packed into a general-purpose programming language.

Not as widely popular as O'Caml, F# or Haskell, but both as practical as Ocaml and as researchy as Haskell.

Also there's a free tutorial/book on the website.