This effect is even more pronounced with erlang, which has had several waves of popularity, going back to at least 2007. Because the language is harder to lear

This effect is even more pronounced with erlang, which has had several waves of popularity, going back to at least 2007. Because the language is harder to learn than most other languages due to the syntax being perceived as "difficult" (and it is for a week or two before you see its elegance) the barrier for entry is actually higher than many other languages. Someone coming from Java has to learn both FP and the erlang syntax at the same time.