invocable "newton_cooling" # needed to use the 'proc' procedure

procedure euler (f, y0, a, b, h)
  t := a
  y := y0
  until (t >= b) do {
    write (right(t, 4) || " " || left(y, 7))
    t +:= h
    y +:= h * (proc(f) (t, y)) # 'proc' applies procedure named in f to (t, y)
  }
  write ("DONE")
end

procedure newton_cooling (time, T)
  return -0.07 * (T - 20)
end

procedure main ()
  # generate data for all three step sizes [2, 5, 10]
  every (step_size := ![2,5,10]) do
    euler ("newton_cooling", 100, 0, 100,  step_size)
end