uses GraphABC;

type realFun= real -> real;

procedure DrawGraph(f:realFun; a, b, d:real);
begin
  var k:= (window.Width div 2) / (b - a);
  coordinate.SetOrigin(round(window.Width div 2 - (b + a)*k), window.Height div 2);
  Line(0, -300, 0, 300);
  Line(-600, 0, 600, 0);
  for var i:= floor(a) to ceil(b) do
    Line(round(i*k), -3, round(i*k), 3);
  var x:= a;
  var y:= f(x);
  pen.color:= Color.Red;
  while x < b do
  begin
    Line(round(x*k), round(y*k),
         round((x + d)*k), round((f(x + d))*k));
    x+=d;
    y:= f(x);
  end;
end;

begin
  DrawGraph(x -> x, -10, 5, 0.1);
end.