Quickly? Perhaps. But being productive is a whole different story. You may pick Scheme or Forth in maybe half a day; but being productive with them implies know

Quickly? Perhaps. But being productive is a whole different story. You may pick Scheme or Forth in maybe half a day; but being productive with them implies knowing their common idioms, their standard libraries by heart and their ecosystem well. That's the meaning of the "Looking for ..." job offers.