defint.js

var defint = function(symbol, dx, from, to) {
    var vars = core.Utils.variables(symbol),
        integral = __.integrate(symbol, dx),
        retval;
    if(!integral.hasIntegral()) {
        var upper = {},
            lower = {};
        upper[dx] = to;
        lower[dx] = from;
        retval = _.subtract(_.parse(integral, upper), _.parse(integral, lower));
    }
    else if(vars.length === 1) {
        retval = 0;
        var step = 0.005,
            f = core.Utils.build(symbol),
            n = Math.floor((to - from)/step),
            c = from, e;
        //we'll stop around 1e6;
        if(n > 1e6)
            retval = _.symfunction('defint', [symbol, dx, from , to]);
        else {
            while(true) {
                e = c + step;
                if(e > to)
                    e = to;
                try {
                    retval += (e-c)*(f(c)+f(e))/2;
                }
                catch(e){
                   return _.symfunction('defint', [symbol, dx, from , to]); //exit. Not continuous 
                }
                c += step;
                if(c >= to)
                    break;
            }
        }
    }
    else 
        retval = _.symfunction('defint', [symbol, dx, from , to]);
    return retval;
}