func evalArithmeticExp(s) {

    func evalExp(s) {

        func operate(s, op) {
           s.split(op).map{|c| Number(c) }.reduce(op)
        }

        func add(s) {
            operate(s.sub(/^\+/,'').sub(/\++/,'+'), '+')
        }

        func subtract(s) {
            s.gsub!(/(\+-|-\+)/,'-')

            if (s ~~ /--/) {
                return(add(s.sub(/--/,'+')))
            }

            var b = s.split('-')
            b.len == 3 ? (-1*Number(b[1]) - Number(b[2]))
                       : operate(s, '-')
        }

        s.gsub!(/[()]/,'').gsub!(/-\+/, '-')

        var reM  = /\*/
        var reMD = %r"(\d+\.?\d*\s*[*/]\s*[+-]?\d+\.?\d*)"

        var reA  = /\d\+/
        var reAS = /(-?\d+\.?\d*\s*[+-]\s*[+-]?\d+\.?\d*)/

        while (var match = reMD.match(s)) {
            match[0] ~~ reM
                ? s.sub!(reMD, operate(match[0], '*').to_s)
                : s.sub!(reMD, operate(match[0], '/').to_s)
        }

        while (var match = reAS.match(s)) {
            match[0] ~~ reA
                ? s.sub!(reAS,      add(match[0]).to_s)
                : s.sub!(reAS, subtract(match[0]).to_s)
        }

        return s
    }

    var rePara = /(\([^\(\)]*\))/
    s.split!.join!('').sub!(/^\+/,'')

    while (var match = s.match(rePara)) {
        s.sub!(rePara, evalExp(match[0]))
    }

    return Number(evalExp(s))
}