For use here; http://mause.me/blog/2014/04/08/lists-with-lemon.html

list.y

list(A) ::= LIST_ITEM(B). { A=B; }
list(A) ::= LIST_ITEM(B) list_clause(C). {
    A=B;
    append_contents of C to B
}
list_clause(A) ::= COMMA list(B). { A=B; }