LookAt function and module

Rotate an object towards a waypoint.
Uses angle+vector format of openSCADs native rotate operand.
Usage:

Lookatpoint=[rnd(-20,20),rnd(-20,20),rnd(-20,20)];
Origin=[rnd(-20,20),rnd(-20,20),rnd(-20,20)];
translate(Lookatpoint)color("red")sphere(2);
translate(Origin)color("blue")sphere(2);
translate(Origin)look_at(Lookatpoint ,Origin ){
translate([0,0,5])cylinder(7,2,0);
translate([0,0,-3])cylinder(9,1,1);
}
module look_at(lookpoint,origin=[0,0,0],rotatefrom=[0,0,1]){
rotations=look_at(lookpoint,origin ,rotatefrom);
rotate(rotations[0],rotations[1]) children();
}

function look_at(p,o=[0,0,0],up=[0,0,1])=
let(
a=up,
b=p-o,
c=cross(a,b) ,
d=angle(a,b))
[d,c];

function angle (a,b)=
atan2(
sqrt((cross(a, b)*cross(a, b))), 
(a* b)
);


function rnd(a = 1, b = 0, s = []) =
s == [] ?
  (rands(min(a, b), max(
    a, b), 1)[0]) :
  (rands(min(a, b), max(a, b), 1, s)[0]);