ghc-mod/Data/Binary/Generic.hs
2016-05-22 02:53:51 +02:00

134 lines
4.4 KiB
Haskell

{-# LANGUAGE BangPatterns, CPP, FlexibleInstances, KindSignatures,
ScopedTypeVariables, TypeOperators, TypeSynonymInstances #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
-----------------------------------------------------------------------------
-- |
-- Module : Data.Binary.Generic
-- Copyright : Bryan O'Sullivan
-- License : BSD3-style (see LICENSE)
--
-- Maintainer : Bryan O'Sullivan <bos@serpentine.com>
-- Stability : unstable
-- Portability : Only works with GHC 7.2 and newer
--
-- Instances for supporting GHC generics.
--
-----------------------------------------------------------------------------
module Data.Binary.Generic where
import Control.Applicative
import Data.Binary
import Data.Bits
import GHC.Generics
import Prelude
class GGBinary f where
ggput :: f t -> Put
ggget :: Get (f t)
-- Type without constructors
instance GGBinary V1 where
ggput _ = return ()
ggget = return undefined
-- Constructor without arguments
instance GGBinary U1 where
ggput U1 = return ()
ggget = return U1
-- Product: constructor with parameters
instance (GGBinary a, GGBinary b) => GGBinary (a :*: b) where
ggput (x :*: y) = ggput x >> ggput y
ggget = (:*:) <$> ggget <*> ggget
-- Metadata (constructor name, etc)
instance GGBinary a => GGBinary (M1 i c a) where
ggput = ggput . unM1
ggget = M1 <$> ggget
-- Constants, additional parameters, and rank-1 recursion
instance Binary a => GGBinary (K1 i a) where
ggput = put . unK1
ggget = K1 <$> get
-- Borrowed from the cereal package.
-- The following GGBinary instance for sums has support for serializing
-- types with up to 2^64-1 constructors. It will use the minimal
-- number of bytes needed to encode the constructor. For example when
-- a type has 2^8 constructors or less it will use a single byte to
-- encode the constructor. If it has 2^16 constructors or less it will
-- use two bytes, and so on till 2^64-1.
#define GUARD(WORD) (size - 1) <= fromIntegral (maxBound :: WORD)
#define PUTSUM(WORD) GUARD(WORD) = putSum (0 :: WORD) (fromIntegral size)
#define GETSUM(WORD) GUARD(WORD) = (get :: Get WORD) >>= checkGetSum (fromIntegral size)
instance ( GSum a, GSum b
, SumSize a, SumSize b) => GGBinary (a :+: b) where
ggput | PUTSUM(Word8) | PUTSUM(Word16) | PUTSUM(Word32) | PUTSUM(Word64)
| otherwise = sizeError "encode" size
where
size = unTagged (sumSize :: Tagged (a :+: b) Word64)
{-# INLINE ggput #-}
ggget | GETSUM(Word8) | GETSUM(Word16) | GETSUM(Word32) | GETSUM(Word64)
| otherwise = sizeError "decode" size
where
size = unTagged (sumSize :: Tagged (a :+: b) Word64)
{-# INLINE ggget #-}
sizeError :: Show size => String -> size -> error
sizeError s size =
error $ "Can't " ++ s ++ " a type with " ++ show size ++ " constructors"
------------------------------------------------------------------------
checkGetSum :: (Ord word, Num word, Bits word, GSum f)
=> word -> word -> Get (f a)
checkGetSum size code | code < size = getSum code size
| otherwise = fail "Unknown encoding for constructor"
{-# INLINE checkGetSum #-}
class GSum f where
getSum :: (Ord word, Num word, Bits word) => word -> word -> Get (f a)
putSum :: (Num w, Bits w, Binary w) => w -> w -> f a -> Put
instance (GSum a, GSum b) => GSum (a :+: b) where
getSum !code !size | code < sizeL = L1 <$> getSum code sizeL
| otherwise = R1 <$> getSum (code - sizeL) sizeR
where
sizeL = size `shiftR` 1
sizeR = size - sizeL
{-# INLINE getSum #-}
putSum !code !size s = case s of
L1 x -> putSum code sizeL x
R1 x -> putSum (code + sizeL) sizeR x
where
sizeL = size `shiftR` 1
sizeR = size - sizeL
{-# INLINE putSum #-}
instance GGBinary a => GSum (C1 c a) where
getSum _ _ = ggget
{-# INLINE getSum #-}
putSum !code _ x = put code *> ggput x
{-# INLINE putSum #-}
------------------------------------------------------------------------
class SumSize f where
sumSize :: Tagged f Word64
newtype Tagged (s :: * -> *) b = Tagged {unTagged :: b}
instance (SumSize a, SumSize b) => SumSize (a :+: b) where
sumSize = Tagged $ unTagged (sumSize :: Tagged a Word64) +
unTagged (sumSize :: Tagged b Word64)
instance SumSize (C1 c a) where
sumSize = Tagged 1