ometa CalcParser {
  digit    = ^digit:d                 -> d.digitValue(),
  number   = number:n digit:d         -> (n * 10 + d)
           | digit,
  addExpr  = addExpr:x '+' mulExpr:y  -> ['add', x, y]
           | addExpr:x '-' mulExpr:y  -> ['sub', x, y]
           | mulExpr,
  mulExpr  = mulExpr:x '*' primExpr:y -> ['mul', x, y]
           | mulExpr:x '/' primExpr:y -> ['div', x, y]
           | primExpr,
  primExpr = '(' expr:x ')'           -> x
           | number:n                 -> ['num', n],
  expr     = addExpr
}

tree = CalcParser.matchAll('6*(4+3)', 'expr') 

// we can write a "compiler" instead

ometa CalcCompiler {
  comp    = ['num' anything:x]    -> x.toString()
          | ['add' comp:x comp:y] -> ('(' + x + '+' + y + ')')
          | ['sub' comp:x comp:y] -> ('(' + x + '-' + y + ')')
          | ['mul' comp:x comp:y] -> ('(' + x + '*' + y + ')')
          | ['div' comp:x comp:y] -> ('(' + x + '/' + y + ')')
}

code = CalcCompiler.match(tree, 'comp')
eval(code)