> I wonder if there is a generally accepted quantifiable definition of programming language expressiveness. Here the author seems to equate it to closeness to natural languages.

I was going to make a similar comment -- it seems there might not be well agreed definitions of "expressiveness" here. I write most of my own projects in Haskell, precisely because I find Haskell to be extremely expressive, but I mean something different to "reads like English" (for which I think AppleScript is the closest example I can think of): to me, the expressiveness of the language is "how accurately can I describe my problem domain to the computer in a way that lets me naturally reason about it in code". I think this is mostly a function of the type system, not the particular syntax (e.g. allowing "?" in a method).

I am really interested in what other people consider "expressiveness" to mean, however.