Using Heterogeneous lists in Proposal in Elm

usingHeterogeneousLists.elm

mario = {
  position = {x = 0, y = 0},
  velocity = {x = 0, y = 0},
  mass = 10,
  Life,
  Groundedness,
  Controllability
}

goomba = {
  position = {x = 20, y = 0},
  velocity = {x = -1, y = 0},
  mass = 10,
  Life,
  Groundedness
}

lakituCloud = {
  position = {x = 0, y = 0},
  velocity = {x = -2, y = 0},
  Life
}


optional {mass : Float, velocity : {x : Float, y : Float}} from entity
applyGravity : {x : Float, y : Float } -> entity -> entity
applyGravity force entity = 
  if has {mass : Float, velocity : {x : Float, y : Float}} entity
  then
    {entity | 
      velocity.x <- entity.velocity.x + force.x / entity.mass,
      velocity.y <- entity.velocity.y + force.y / entity.mass
    }
  else
    entity
    
    
optional {position : {x : Float, y : Float}, velocity : {x : Float, y : Float}} from entity
move : entity -> entity
move entity = 
  if has {position : {x : Float, y : Float}, velocity : {x : Float, y : Float}} entity
  then
    {entity | 
      position.x <- entity.position.x + entity.velocity.x,
      position.y <- entity.position.y + entity.velocity.y
    }
  else
    entity
    
    
update = move << applyGravity {x = 0, y = -9.81}
  

-- The list of entities. Note how all entities do not have the same fields
entities = [mario, goomba, lakituCloud]  

-- The entities after calling update on every entity
-- In this case, mario, goomba, and lakituCloud have moved
-- But only mario and goomba were affected by gravity
updatedEntities = map update entities