signature INPUT_MESSAGE =
sig
  datatype t =
    MOUSE_MOVE of {x: Real32.real, y: Real32.real}
  | MOUSE_LEFT_CLICK
  | MOUSE_LEFT_RELEASE
end

structure InputMessage :> INPUT_MESSAGE =
struct
  datatype t =
    MOUSE_MOVE of {x: Real32.real, y: Real32.real}
  | MOUSE_LEFT_CLICK
  | MOUSE_LEFT_RELEASE
end