Safe Heterogeneous Lists through meta-annotations

heterogeneousLists.elm

-- We could use meta-annotations to have heterogeneous lists
mario = {
  position = { x = 0, y = 0 },
  velocity = { x = 0, y = 0 },
  Life,
  Controllability,
  Groundedness
}

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


lakituCloud = {
  position = { x = 0, y = 100 },
  velocity = { x = 0, y = 0 },
  Flight,
  Life
}

-- One way to have heterogeneous lists is to require a set number of fields
-- Anything else would be optional
require {position : {x : Float, y : Float}, velocity : {x : Float, y : Float}} from entity
entities : List entity
entities = [mario, goomba, lakituCloud]


-- Another way is to state all of the optional stuff
type alias Entity = {
  position : {x : Float, y : Float},
  velocity : {x : Float, y : Float}
}

optional {Life, Controllability, Groundedness, Flight} from Entity
entities2 : List Entity
entities2 = [mario, goomba, lakituCloud]