Window
  -> Text
  -> Button
  -> Input

Component
  # Properties
  coords: vec<x,y>
  size: vec<w,h>
  children: [Component]
  # Methods
  inbounds(x,y): -> boolean
  # Implemented by subclasses.
  onclick(x,y): -> halt | cont
  onkey(key): -> halt | cont

Text extends Component
  # Properties
  content: string
  children: nil
  # Implementations
  onclick(_,_): -> cont
  onkey(_) -> cont

Image extends Component
  # Properties
  data: binary
  children: nil
  # Implementations
  onclick(_,_): -> cont
  onkey(_): -> cont

Button extends Component
  # Properties
  mousedown: function
  keydown: function
  children: [Text|Image]
  # Implementations
  onclick(x,y) -> inbounds(x,y) ? call mousedown; halt : cont
  onkey(key) -> call keydown ? halt : cont

Input extends Component
  # Properties
  value: string
  focus: boolean
  children: nil
  # Implementations
  onclick(x,y): -> inbounds(x,y) ? focus = true; halt : cont
  onkey(key): -> focus ? value += key; halt : cont