Syntax change: tolerating trailing comma

[burakemir]

A new year, a new announcement - happy new year everyone!

Did you ever have to edit a large file with structured data definitions and had to "hunt" for syntax errors that came from trailing commas caused by refactorsing like reordering lines?

To do away with such productivity losses, Mangle now tolerates a trailing comma in lists, maps, structs etc.,. similar to what you might be used to from python and go.

You can now write something like this:

person_address(/aliya, {
    /street: "800 W El Camino Real",
    /city: "Mountain View",
    /zip: 94040,
    /state: /ca,   # <-- trailing comma is permitted
}).

See the commit for changes to the grammar.