Expression freezes After Effects

Hey guys. Maybe a silly question, but I want to make an expression that is gonna calculate object's position every frame. But for some reason with this loop After Effects freezes compeletly. What may actually cause this problem?

gravity = thisComp.layer("controller").effect("gravity")("Slider");
projectile = transform.position;
	px = projectile[0];
	py = projectile[1];
anchor = thisComp.layer("anchor").transform.position;
	ax = anchor[0];
	ay = anchor[1];
currentFrame = 	Math.round((time - inPoint) / thisComp.frameDuration);
for(i = 0; i = currentFrame; i++){
	px += 5
}
[px,py]