So I basically start with a straight line from 0,0 to 0,10 (x,y space),and i need to add another line of that length,connected to the old one,but which slowly makes a curve,then another one....

The point is,I want the lines connected.

The bigger problem is doing this for infinite time.How would you go about it?

I just need to code random generated curves forever. For example,you start with 100 floats,representing points. With those 100 floats you have to create a random curve.When you move forward,you delete the first float,and create a new one,but that new one IS based on the 99th one.Basically each new float is somehow linked to the float behind it.

or look at it from this point,you always have 100 points.You first create a curve.Whenever the player moves forward,you create a new point where the player WAS last time,and that new point is creating a new curve.

So,if player is is on point 1,but moves to point 2,point 1 will equal to a new point.You do that untill all points have been recreated to form a new curve.

ok,the real problem is: " implement a road ,that has curves,and that goes one forever". When it says goes on forever,it means that when the player goes forward,the road will become longer.

its in 2d space btw

I may be misunderstanding, but you want a curve that you can add control points to? That should be straightforward enough. As long as you keep adding points to a spline, it will keep getting longer. A catmull rom spline, my go-to spline, only looks at 4 control points at a time, so you can remove points that are already off-screen, and add more on as they approach on-screen. (I also like catmull rom because all the control points are on the curve)