Meanwhile this alternative query seems to do the job:
====
select name || ' ::=' || group_concat(
case when hasOr == 1 then ' (' || trim(rtxt) || ')'
else
case when length(rtxt) == 0 then ' /* empty */' else rtxt end
end, '
|')
from (
select lhs, name, substr(txt, instr(txt, tbl.sep) + length(tbl.sep)) rtxt, (instr(txt, '|') > 0) hasOr
from rule left join symbol on lhs=id, (select '::=' as sep) tbl
) as t
group by lhs;
====
Partial output:
====
input ::= cmdlist
cmdlist ::= cmdlist ecmd
| ecmd
ecmd ::= SEMI
| cmdx SEMI
| explain cmdx SEMI
cmdx ::= cmd
explain ::= EXPLAIN
| EXPLAIN QUERY PLAN
cmd ::= BEGIN transtype trans_opt
| (COMMIT|END trans_opt)
| ROLLBACK trans_opt
| SAVEPOINT nm
====