Simit

element Point
  x : float;
  v : float;
  m : float;
end

element Spring
  k : float;
  l : float;
end

extern points : set{Point};
extern springs : set{Spring}(points,points);

func compute_forces(s : Spring, p : (Point*2)) -> (f : (float*2))
  var dx = p(1).x - p(0).x;
  var stretch = dx - s.l;
  var force = s.k * stretch;
  f(0) = force;
  f(1) = -force;
end

export func main()
  forces = map compute_forces to springs reduce +;
  points.v = points.v + (forces / points.m) * 0.01;
  points.x = points.x + points.v * 0.01;
end