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


-- | A package for working with nullary type classes.
--   
--   Work with nullary type classes without orphan instances.
@package nullary
@version 0.1.0.0


-- | Provides a framework for defining and using nullary type classes
--   without needing orphan instances. To do this requires some evil to
--   locally generate a type class instances. This library encapsulates
--   that evil and provides a mechanism for safely defining new nullary
--   type classes.
--   
--   To define a nullary type class, you use the following pattern:
--   
--   <pre>
--   -- The following four extensions are necessary.
--   {-# LANGUAGE FlexibleContexts #-}
--   {-# LANGUAGE MultiParamTypeClasses #-}
--   {-# LANGUAGE Rank2Types #-}
--   {-# LANGUAGE UndecidableInstances #-}
--   
--   -- Not exported unless you want to allow users to opt out of
--   -- the checking by making an instance for Tag PartialTag.
--   data PartialTag
--   
--   -- The nullary type class. It can have members, but it's not
--   -- clear this accomplishes anything.
--   class Partial
--   
--   -- Enable this library.  Instances like this unfortunately
--   -- require UndecidableInstances.
--   instance Tag PartialTag =&gt; Partial
--   
--   -- Wrap unsafeTag for user convenience.
--   partial :: (Partial =&gt; a) -&gt; a
--   partial = unsafeTag (Proxy :: Proxy PartialTag)
--   {-# INLINE partial #-}
--   
--   -- Define your functions using the Partial class.
--   head :: Partial =&gt; [a] -&gt; a
--   head (x:xs) = x
--   </pre>
module Type.Class.Nullary

-- | Class for declaring tagged nullary instances. See module description.
class Tag t

-- | Unsafely cast off the Tag constraint. This should only be used at the
--   "top-level" of an application. In practice, specializations of this
--   should be provided, e.g. unsafeUnsafe. This uses the same evil as
--   Data.Reflect.
unsafeTag :: Proxy t -> (Tag t => r) -> r

-- | A concrete, poly-kinded proxy type
data Proxy (t :: k) :: k -> *
Proxy :: Proxy

module Type.Class.Partial

-- | Nullary type class to mark partial functions, e.g. head.
class Partial

-- | Prefer <a>partial</a>. However, if you want to disable Partial
--   wholesale, make an orphan instance of Tag for this type. NEVER put an
--   instance of this in a library.
data PartialTag

-- | Accept the possibility of partiality.
partial :: (Partial => a) -> a
instance Type.Class.Nullary.Tag Type.Class.Partial.PartialTag => Type.Class.Partial.Partial

module Type.Class.Unsafe

-- | Nullary type class to mark unsafe functions, like unsafePerformIO.
class Unsafe

-- | Unsafely ignore Unsafe marker.
unsafeUnsafe :: (Unsafe => a) -> a
instance Type.Class.Nullary.Tag Type.Class.Unsafe.UnsafeTag => Type.Class.Unsafe.Unsafe