Louden, Figure 7.11.

program chain;

procedure p;
var x : integer;

  procedure q;
    procedure r;
    begin
        x = 2;
        ...
      if ... then p;
    end; (* r *)
  begin
    r;
  end; (* q *)

begin
  q;
end; (* p *)

begin (* chain *)
  p;
end.