Actually I think we basically agree, it's just a matter of degree. When I read "write your own language" I'm mostly thinking of the kinds of work you might do i

Actually I think we basically agree, it's just a matter of degree. When I read "write your own language" I'm mostly thinking of the kinds of work you might do in an undergrad PL class, which I think works well as a kind of antidote to the Java monoculture. I agree that inventing and designing a custom language with no reference, in a vacuum, would probably not be helpful. As for parsing, that was almost exactly my point, learning about parsing, and realizing what kind of work is involved, is just the experience you need to reject being assigned the writing of a custom XML parser by a clueless manager (true story).