-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Class of data structures that can be unfolded from a seed value.
--   
--   Class of data structures that can be unfolded from a seed value.
@package unfoldable
@version 0.2.0

module Data.Splittable

-- | Splittable datatypes are datatypes that can be used as seeds for
--   unfolds.
class Splittable s
split :: Splittable s => Int -> s -> [s]
choose :: Splittable s => [s -> x] -> s -> x
getInt :: Splittable s => s -> Int

-- | If a datatype is bounded and enumerable, we can use <a>getInt</a> to
--   produce a value from a seed.
boundedEnum :: (Splittable s, Bounded a, Enum a) => s -> a
data Left
L :: Left
data Right
R :: Right
instance Splittable s => Splittable (Dual s)
instance (Splittable a, Splittable b) => Splittable (Either a b)
instance (Splittable a, Splittable b) => Splittable (a, b)
instance Splittable Integer
instance Splittable StdGen
instance Splittable Right
instance Splittable Left

module Data.Unfoldable

-- | Data structures that can be unfolded.
--   
--   For example, given a data type
--   
--   <pre>
--   data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
--   </pre>
--   
--   a suitable instance would be
--   
--   <pre>
--   instance Unfoldable Tree where
--     unfoldMap f = choose
--       [ spread $ pure Empty
--       , spread $ Leaf &lt;$&gt; to f
--       , spread $ Node &lt;$&gt; to (unfoldMap f) &lt;*&gt; to f &lt;*&gt; to (unfoldMap f)
--       ]
--   </pre>
--   
--   i.e. it follows closely the instance for <tt>Traversable</tt>, with
--   the addition of <a>choose</a>, <a>spread</a> and <a>to</a>.
--   
--   The instance can be simplified to:
--   
--   <pre>
--   instance Unfoldable Tree where
--     unfoldMap f = choose
--       [ const Empty
--       , Leaf . f
--       , spread $ Node &lt;$&gt; to (unfoldMap f) &lt;*&gt; to f &lt;*&gt; to (unfoldMap f)
--       ]
--   </pre>
class Unfoldable f
unfoldMap :: (Unfoldable f, Splittable s) => (s -> a) -> s -> f a

-- | The same as <tt>unfoldMap id</tt>.
unfold :: (Unfoldable f, Splittable s) => s -> f s

-- | Always choose the first constructor.
leftMost :: Unfoldable f => f ()

-- | Always choose the last constructor.
rightMost :: Unfoldable f => f ()

-- | Count the number of times <a>to</a> is used, and split the seed in
--   that many parts.
spread :: Splittable s => State ([s], Int) a -> s -> a

-- | Signal to <a>spread</a> that this is a subpart that needs a seed.
to :: (s -> a) -> State ([s], Int) a
instance Unfoldable f => Unfoldable (Reverse f)
instance (Unfoldable p, Unfoldable q) => Unfoldable (Compose p q)
instance (Unfoldable p, Unfoldable q) => Unfoldable (Product p q)
instance (Bounded a, Enum a) => Unfoldable (Constant a)
instance Unfoldable Identity
instance (Bounded a, Enum a) => Unfoldable ((,) a)
instance (Bounded a, Enum a) => Unfoldable (Either a)
instance Unfoldable Maybe
instance Unfoldable []