14.4.2 The angle implementation file

Module: angle-implementation
define abstract class <angle> (<sixty-unit>)
end class <angle>;

define method say (angle :: <angle>) => ()
  let(degrees, minutes, seconds) = decode-total-seconds(angle);
  format-out("%d degrees %d minutes %d seconds",
             degrees, minutes, seconds);
end method say; 

define class <relative-angle> (<angle>)
end class <relative-angle>; 

define method say (angle :: <relative-angle>) => ()
  format-out(" %d degrees", decode-total-seconds(angle));
end method say; 

define abstract class <directed-angle> (<angle>)
  virtual slot direction :: <symbol>;
  slot internal-direction :: <symbol>;
  keyword direction:;
end class <directed-angle>; 

define method initialize (angle :: <directed-angle>, #key direction: dir)
  next-method();
  angle.direction := dir;
end method initialize;

define method direction (angle :: <directed-angle>) => (dir :: <symbol>)
  angle.internal-direction;
end method direction;

define method direction-setter 
    (dir :: <symbol>, angle :: <directed-angle>) => (new-dir :: <symbol>)
  angle.internal-direction := dir;
end method direction-setter; 

define method say (angle :: <directed-angle>) => ()
  next-method();
  format-out(" %s", angle.direction);
end method say; 

define class <latitude> (<directed-angle>)
end class <latitude>;

define method say (latitude :: <latitude>) => ()
  next-method();
  format-out(" latitude\n");
end method say;

define method direction-setter 
    (dir :: <symbol>, latitude :: <latitude>) => (new-dir :: <symbol>)
  if (dir == #"north" | dir == #"south")
    next-method();
  else
    error("%= is not north or south", dir);
  end if;
end method direction-setter; 

define class <longitude> (<directed-angle>)
end class <longitude>;

define method say (longitude :: <longitude>) => ()
  next-method();
  format-out(" longitude\n");
end method say;

define method direction-setter 
    (dir :: <symbol>, longitude :: <longitude>) => (new-dir :: <symbol>)
  if (dir == #"east" | dir == #"west")
    next-method();
  else
    error("%= is not east or west", dir);
  end if;
end method direction-setter;