So I decided to sit down finally and write the line parser for the new Decl, and since it was parsing, I decided not to unearth my old HOP-inspired parsing code but rather take the plunge and try Marpa, to avoid getting bogged down in parser issues.
I am in love.
It basically looks like Marpa can do anything related to parsing. It can even handle ambiguous parses! One of the test cases is literally "time flies like an arrow"!
But what doesn't yet exist (there's a partial beginning) is a tutorial set, a "Gentle Guide to Marpa". I think I'll write one.