ometa StatefulCalculator <: Parser {
  var           = spaces letter:x      -> x,
  num           = num:n digit:d        -> (n*10 + d*1)
                | digit:d              -> (d*1),
  primaryExpr   = spaces var:x         -> self.vars[x]
                | spaces num:n         -> n
                | "(" expr:r ")"       -> r,
  mulExpr       = mulExpr:x "*" primaryExpr:y -> ( x * y )
                | mulExpr:x "/" primaryExpr:y -> ( x / y )
                | primaryExpr,
  addExpr       = addExpr:x "+" mulExpr:y     -> ( x + y )
                | addExpr:x "-" mulExpr:y     -> ( x - y )
                | mulExpr,
  expr          = var:x  "=" expr:r           -> (self.vars[x] = r)
                | addExpr,
  doit          = (expr:r)* spaces end        -> r                                                       
}
StatefulCalculator.initialize = function() {  this.vars = {}; }

StatefulCalculator.matchAll("x = 1
x + x", "doit")