Allow trailing comma in clauses

[trilis]

It would be nice to allow trailing commas in clauses, e.g.

Elpi Accumulate lp:{{
   C1,
   C2,
   C3, % <-- 
   .
}}

This would allow to delete or comment the last line without a syntax error.

[gares]

Indeed.

This is already the case in the very frequent, in my code at least, case where one uses std.do! and list notation.
Eg

foo :- std.do! [
  a,
  b,
  c,
].

parses fine.

Anyway I don't see anbiguities in the grammar you propose, so I'm favorable to this change.

[gares]

@trilis in your example you talk about clauses, but I think you meant premises. Did I get your comment right?
(because clauses are . terminated, if they are just one line you can comment them independently)