I never really "learned" lisp (I read a library book about it as a teenager but I didn't have access to a computer that ran it.) But I did learn Haskell later,

I never really "learned" lisp (I read a library book about it as a teenager but I didn't have access to a computer that ran it.) But I did learn Haskell later, and I think that made me worse at the job (C++) I was doing at the time, because it gave me the habit of trying to write C++ in a functional style and made me more frustrated with C++'s type system.