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

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

ExpTranslator.trans('44')

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

Calc.expr(3+2);