types.elm

type alias TimesClicked = Int
type alias Count = Int

updateCount : Msg -> TimesClicked -> TimesClicked
updateCount msg count =
  case msg of
    Increment ->
      if count < maxCount then count + 1 else count

    Decrement ->
      if count > minCount then count - 1 else count

-- Unfortunately, due to how type aliases work, 
-- we could as well write the updateCount type annotation like this…
updateCount : Msg -> Count -> TimesClicked
-- …and it'd still compile.



-- We can fix this by introducing a completely new type instead of an alias:

type Count = Count Int
type TimesClicked = TimesClicked Int

updateCount : Msg -> TimesClicked Int -> TimesClicked Int
updateCount msg count =
  case msg of
    Increment ->
      if count < maxCount then TimesClicked count + 1 else TimesClicked count

    Decrement ->
      if count > minCount then TimesClicked count - 1 else TimesClicked count

-- With this implementation, we can't mismatch the types,
-- but we have to re-wrap every integer inside updateCount.