Name.hs

{-# LANGUAGE CPP #-}
#ifdef __GLASGOW_HASKELL__
{-# LANGUAGE DeriveDataTypeable #-}

# if __GLASGOW_HASKELL__ >= 704
{-# LANGUAGE DeriveGeneric #-}
# endif

#endif
-----------------------------------------------------------------------------
-- |
-- Module      :  Bound.Name
-- Copyright   :  (C) 2012 Edward Kmett
-- License     :  BSD-style (see the file LICENSE)
--
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  experimental
-- Portability :  portable
--
-- The problem with locally nameless approaches is that original names are
-- often useful for error reporting, or to allow for the user in an interactive
-- theorem prover to convey some hint about the domain. A @'Name' n b@ is a value
-- @b@ supplemented with a (discardable) name that may be useful for error
-- reporting purposes. In particular, this name does not participate in
-- comparisons for equality.
--
-- This module is /not/ exported from "Bound" by default. You need to explicitly
-- import it, due to the fact that 'Name' is a pretty common term in other
-- people's code.
----------------------------------------------------------------------------
module Bound.Name
  ( Name(..)
  , _Name
  , name
  , abstractName
  , abstract1Name
  , instantiateName
  , instantiate1Name
  ) where

import Bound.Scope
import Bound.Var
import Control.Applicative
import Control.Comonad
import Control.Monad (liftM, liftM2)
import Data.Foldable
import Data.Traversable
import Data.Monoid
import Data.Bifunctor
import Data.Bifoldable
import qualified Data.Binary as Binary
import Data.Binary (Binary)
import Data.Bitraversable
import Data.Bytes.Serial
#ifdef __GLASGOW_HASKELL__
import Data.Data
# if __GLASGOW_HASKELL__ >= 704
import GHC.Generics
# endif
#endif
import Data.Hashable
import Data.Hashable.Extras
import Data.Profunctor
import qualified Data.Serialize as Serialize
import Data.Serialize (Serialize)
import Prelude.Extras

-------------------------------------------------------------------------------
-- Names
-------------------------------------------------------------------------------

-- |
-- We track the choice of 'Name' @n@ as a forgettable property that does /not/ affect
-- the result of ('==') or 'compare'.
--
-- To compare names rather than values, use @('Data.Function.on' 'compare' 'name')@ instead.
data Name n b = Name n b deriving
  ( Show
  , Read
#ifdef __GLASGOW_HASKELL__
  , Typeable
  , Data
# if __GLASGOW_HASKELL__ >= 704
  , Generic
# endif
#endif
  )

-- | Extract the 'name'.
name :: Name n b -> n
name (Name n _) = n
{-# INLINE name #-}

-- |
--
-- This provides an 'Iso' that can be used to access the parts of a 'Name'.
--
-- @
-- '_Name' :: Iso ('Name' n a) ('Name' m b) (n, a) (m, b)
-- @
_Name :: (Profunctor p, Functor f) => p (n, a) (f (m,b)) -> p (Name n a) (f (Name m b))
_Name = dimap (\(Name n a) -> (n, a)) (fmap (uncurry Name))
{-# INLINE _Name #-}

-------------------------------------------------------------------------------
-- Instances
-------------------------------------------------------------------------------

instance Eq b => Eq (Name n b) where
  Name _ a == Name _ b = a == b
  {-# INLINE (==) #-}

instance Hashable2 Name where
  hashWithSalt2 m (Name _ a) = hashWithSalt m a
  {-# INLINE hashWithSalt2 #-}

instance Hashable1 (Name n) where
  hashWithSalt1 m (Name _ a) = hashWithSalt m a
  {-# INLINE hashWithSalt1 #-}

instance Hashable a => Hashable (Name n a) where
  hashWithSalt m (Name _ a) = hashWithSalt m a
  {-# INLINE hashWithSalt #-}

instance Ord b => Ord (Name n b) where
  Name _ a `compare` Name _ b = compare a b
  {-# INLINE compare #-}

instance Functor (Name n) where
  fmap f (Name n a) = Name n (f a)
  {-# INLINE fmap #-}

instance Foldable (Name n) where
  foldMap f (Name _ a) = f a
  {-# INLINE foldMap #-}

instance Traversable (Name n) where
  traverse f (Name n a) = Name n <$> f a
  {-# INLINE traverse #-}

instance Bifunctor Name where
  bimap f g (Name n a) = Name (f n) (g a)
  {-# INLINE bimap #-}

instance Bifoldable Name where
  bifoldMap f g (Name n a) = f n `mappend` g a
  {-# INLINE bifoldMap #-}

instance Bitraversable Name where
  bitraverse f g (Name n a) = Name <$> f n <*> g a
  {-# INLINE bitraverse #-}

instance Comonad (Name n) where
  extract (Name _ b) = b
  {-# INLINE extract #-}
  extend f w@(Name n _) = Name n (f w)
  {-# INLINE extend #-}

instance Eq1   (Name b) where
  (==#)      = (==)
  {-# INLINE (==#) #-}
instance Ord1  (Name b) where
  compare1   = compare
  {-# INLINE compare1 #-}
instance Show b => Show1 (Name b) where showsPrec1 = showsPrec
instance Read b => Read1 (Name b) where readsPrec1 = readsPrec

-- these are slightly too restrictive, but still safe
instance Eq2 Name   where
  (==##)     = (==)
  {-# INLINE (==##) #-}
instance Ord2 Name  where
  compare2   = compare
  {-# INLINE compare2 #-}
instance Show2 Name where showsPrec2 = showsPrec
instance Read2 Name where readsPrec2  = readsPrec

instance Serial2 Name where
  serializeWith2 pb pf (Name b a) = pb b >> pf a
  {-# INLINE serializeWith2 #-}

  deserializeWith2 gb gf = liftM2 Name gb gf
  {-# INLINE deserializeWith2 #-}

instance Serial b => Serial1 (Name b) where
  serializeWith = serializeWith2 serialize
  {-# INLINE serializeWith #-}
  deserializeWith = deserializeWith2 deserialize
  {-# INLINE deserializeWith #-}

instance (Serial b, Serial a) => Serial (Name b a) where
  serialize = serializeWith2 serialize serialize
  {-# INLINE serialize #-}
  deserialize = deserializeWith2 deserialize deserialize
  {-# INLINE deserialize #-}

instance (Binary b, Binary a) => Binary (Name b a) where
  put = serializeWith2 Binary.put Binary.put
  get = deserializeWith2 Binary.get Binary.get

instance (Serialize b, Serialize a) => Serialize (Name b a) where
  put = serializeWith2 Serialize.put Serialize.put
  get = deserializeWith2 Serialize.get Serialize.get

-------------------------------------------------------------------------------
-- Abstraction
-------------------------------------------------------------------------------

-- | Abstraction, capturing named bound variables.
abstractName :: Monad f => (a -> Maybe b) -> f a -> Scope (Name a b) f a
abstractName f t = Scope (liftM k t) where
  k a = case f a of
    Just b  -> B (Name a b)
    Nothing -> F (return a)
{-# INLINE abstractName #-}

-- | Abstract over a single variable
abstract1Name :: (Monad f, Eq a) => a -> f a -> Scope (Name a ()) f a
abstract1Name a = abstractName (\b -> if a == b then Just () else Nothing)
{-# INLINE abstract1Name #-}

-------------------------------------------------------------------------------
-- Instantiation
-------------------------------------------------------------------------------

-- | Enter a scope, instantiating all bound variables, but discarding (comonadic)
-- meta data, like its name
instantiateName :: (Monad f, Comonad n) => (b -> f a) -> Scope (n b) f a -> f a
instantiateName k e = unscope e >>= \v -> case v of
  B b -> k (extract b)
  F a -> a
{-# INLINE instantiateName #-}

-- | Enter a 'Scope' that binds one (named) variable, instantiating it.
--
-- @'instantiate1Name' = 'instantiate1'@
instantiate1Name :: Monad f => f a -> Scope n f a -> f a
instantiate1Name = instantiate1
{-# INLINE instantiate1Name #-}