[COFF] What languges would you like to learn?

A recent thread makes me wonder which languages would people like to learn? (I confess to trying, as Dave does, but time prevents anything more that learing syntax and writing toy programmes. One must write something substantial -- not synonomous with large -- to really learn a language.) Erlang, Smalltalk, Prolog, Haskell, and Scheme come to mind... N.