That looks not like a 2-pole lowpass filter, but like a Butterworth filter.

However it illustrates good the coding overhead of MQL4, even though it's also based on C. A 3rd order Butterworth filter in lite-C looks like this:

Code:
var Butterworth(var *Data,int Cutoff)
{
	var a = exp(-PI / Cutoff);
	var b = 2*a*cos(1.738*PI / Cutoff);
	var c = a*a;
	var c1 = b + c;
	var c2 = -(c + b*c);
	var c3 = c*c;
	var c0 = 1 - c1 - c2 - c3;

	var* Filt = series(*Data,4);
	return Filt[0] = c0*Data[0] + c1*Filt[1] + c2*Filt[2] + c3*Filt[3];
}