Proposal for Symbols in Elm.

symbols.elm

-- life is a singleton. it acts as a symbol
-- In this case, we use the presence or absence of this symbol as a boolean flag.
mario = {
  position = {
    x = 0,
    y = 0
  },
  velocity = {
    x = 0,
    y = 0
  },
  Life
}

goomba = {
  position = {
    x = 0,
    y = 0
  },
  velocity = {
    x = 0,
    y = 0
  }
}

optional {Life} from entity
isAlive : entity -> Bool
isAlive entity = 
  if has Life entity
  then True
  else False