PEG.js for numeric part of Metapolator's formula language

gistfile1.js

/*
 * Parser for Metapolator CPS formula language
 */

{
    var unaryOperators = {
        '-': 'negate'
    };

    function $_(operator, right) {
        var handler = unaryOperators[operator];
        if (right && right[handler])
            return right[handler]();
        switch (operator) {
        case '-': return -right;
        }
    }

    var binaryOperators = {
        '+': 'add',
        '-': 'subtract',
        '*': 'multiply',
        '/': 'divide',
        '^': 'exponent'
    };

    function _$_(left, operator, right) {
        var handler = binaryOperators[operator];
        if (left && left[handler])
            return left[handler](right);
        switch (operator) {
        case '+': return left + right;
        case '-': return left - right;
        case '*': return left * right;
        case '/': return left / right;
        case '^': return Math.pow(left, right);
        }
    }
}

start
  = sum

sum
  = left:factor s* "+" s* right:sum { return _$_(left, "+", right); }
  / left:factor s* "-" s* right:sum { return _$_(left, "-", right); }
  / factor

factor
  = left:exponent s* "*" s* right:factor { return _$_(left, "*", right); }
  / left:exponent s* "/" s* right:factor { return _$_(left, "/", right); }
  / exponent

exponent
  = left:negation s* "^" s* right:negation {return _$_(left, "^", right); }
  / negation

negation
  = "-" primary:primary { return $_("-", primary); }
  / primary

primary
  = number
  / "(" sum:sum ")" { return sum; }

digit
  = [0-9]

number "number"
  = digits:$((digit* "." digit+) / (digit+ "."?))(([eE][+\-]? digit+)?) { return parseFloat(digits, 10); }

s
  = [ \t\r\n\f]+