[jerf]

"Jack of all trades, master of none" applies to situations where the trades are not terribly related to each other. Beyond a certain basic level of knowledge that applies to everything, being a good plumber isn't going to contribute to your being a good farmer, which won't contribute to your being a good therapist. To be sorta good at all those things and others besides requires that you can not have put in the time to master any of them.

Programming languages are different. For one, they all run on the same hardware. For another, the basics of logic and such are the same. And for the coup de grace, we have the well-known acecdata that learning a language of a significantly different paradigm than your "main" language generally improves your ability to program in your "main" language, to the point where I and others routinely recommend to people that they learn (or implement!) other language paradigms as a routine, expected part of their programming career. Learning Haskell to the point you can effectively use it can and will improve your PHP.

In the programming field, I don't think you can be a master programmer without being a fairly effective polyglot, as a bare minimum requirement. That is, if someone claims to be a master but they only have fluency in one language, even if that language is C++ or something, I would not consider them a "programming" master, only a C++ master.