There's more to being a productive programmer than knowing the semantics of a language. Someone who has been programming for a while but is learning a new lang

There's more to being a productive programmer than knowing the semantics of a language. Someone who has been programming for a while but is learning a new language will have a ramp-up period when their code is ugly or unidiomatic, and they will take longer to write it, but it will capture the correct algorithms and abstractions. Compare that to someone who is inexperienced and writes a pile of exponential-time spaghetti that is slow and unmaintainable in any language.