ometa IndirectLeftRecursion <: Parser {
  digit    = char:d ?(d >= '0' && d <= '9') -> d.digitValue(),
  number   = number:n digit:d               -> (10*n + d)
           | digit,

  d = char:d ?(d == '1') -> 1,

  x        = term, 
  term     = x:t1 "+" d:f              -> ['Add', t1, f]
           | d
}
IndirectLeftRecursion.matchAll('1+1+1+1', 'term')