module Data.TimeVal (
  TimeVal(..)
  ) where

import Algebra

-- |A type wrapper that adds a Bounded instance for types that don't possess one.
data TimeVal t = Always | Since t | Never
                 deriving (Show,Eq,Ord)
instance Functor TimeVal where
  map f (Since a) = Since (f a)
  map _ Always = Always
  map _ Never = Never
instance Unit TimeVal where pure = Since
instance Applicative TimeVal
instance Monad TimeVal where
  join (Since b) = b
  join Always = Always
  join Never = Never
instance Foldable TimeVal where
  fold (Since t) = t
  fold _ = zero
instance Traversable TimeVal where
  sequence (Since t) = Since<$>t
  sequence Always = pure Always
  sequence Never = pure Never

instance Bounded (TimeVal t) where
  minBound = Always ; maxBound = Never