Probably Erlang, but potentially Ocaml. I'll probably catch some flack for this (from both sides): You can (and should) use Ocaml as a Lisp where you lose the

Probably Erlang, but potentially Ocaml. I'll probably catch some flack for this (from both sides): You can (and should) use Ocaml as a Lisp where you lose the easy macros but gain strict typing. It's brilliant. The only downside is emacs; it's the only sensible IDE. Haskell (and friends) are fantastic, but in my experience you have to be reasonably smart and work full-time with it, since every medium sized project gets turned into its own DSL (more so than with other languages). Maybe it's not ideal for consulting.