Just jump straight to Haskell. The learning curve is substantial, but it will guarantee that you learn functional concepts correctly and not in the hackneyed wa

Just jump straight to Haskell. The learning curve is substantial, but it will guarantee that you learn functional concepts correctly and not in the hackneyed way most "functional" js or Java code is written. If you end up not liking Haskell, every other popular functional language (e.g. Scala) has some subset of haskell's features, so you'll already be equipped to use them.