Created
March 30, 2017 03:11
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{-# LANGUAGE ScopedTypeVariables #-} | |
module ADTStorable where | |
import Foreign.Storable | |
import Foreign.Ptr | |
import Data.Word (Word8) | |
instance forall a . Storable a => Storable (Maybe a) where | |
sizeOf x = alignment x + sizeOf (undefined :: a) | |
alignment _ = alignment (undefined :: a) | |
peek ptr = do | |
tag <- peek (castPtr ptr :: Ptr Word8) | |
case tag of | |
0 -> return Nothing | |
1 -> do | |
let ptr' = ptr `plusPtr` alignment (undefined :: Maybe a) | |
value <- peek (castPtr ptr' :: Ptr a) | |
return (Just value) | |
poke ptr Nothing = do | |
poke (castPtr ptr :: Ptr Word8) 0 | |
poke ptr (Just v) = do | |
poke (castPtr ptr :: Ptr Word8) 1 | |
let ptr' = ptr `plusPtr` alignment (undefined :: a) | |
poke (castPtr ptr' :: Ptr a) v | |
instance forall a b . (Storable a, Storable b) => Storable (Either a b) where | |
sizeOf x = alignment x + max (sizeOf (undefined :: a)) (sizeOf (undefined :: b)) | |
alignment _ = lcm (alignment (undefined :: a)) (alignment (undefined :: b)) | |
peek ptr = do | |
tag <- peek (castPtr ptr :: Ptr Word8) | |
case tag of | |
0 -> do | |
let ptr' = ptr `plusPtr` alignment (undefined :: Either a b) | |
value <- peek (castPtr ptr' :: Ptr a) | |
return (Left value) | |
1 -> do | |
let ptr' = ptr `plusPtr` alignment (undefined :: Either a b) | |
value <- peek (castPtr ptr' :: Ptr b) | |
return (Right value) | |
poke ptr (Left x) = do | |
poke (castPtr ptr :: Ptr Word8) 0 | |
let ptr' = ptr `plusPtr` alignment (undefined :: Either a b) | |
poke (castPtr ptr' :: Ptr a) x | |
poke ptr (Right x) = do | |
poke (castPtr ptr :: Ptr Word8) 1 | |
let ptr' = ptr `plusPtr` alignment (undefined :: Either a b) | |
poke (castPtr ptr' :: Ptr b) x |
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