A Self-Referential Script

This code is in the object's position expression box. As far as I can tell, this code should make the object accelerate. It is instead making the object move at a steady rate. Also, it's not starting from 50,50 like it should, but instead, at frame 1, it's jumping to 360,240. Can anyone tell me what I am doing wrong?

if(time==0) {[50,50]} //this is to give the object a starting position
else{

offsetx = time;
offsety = time;

transform.position + [offsetx, offsety]

}

//Thanks in advance!