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CStruct in haskell (example 1)
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE AllowAmbiguousTypes #-}
module Main where
import GHC.TypeLits
import Data.Proxy
import CStruct
-- this really should be Addr#
data Ptr (k :: Element) = Ptr Int
deriving (Show,Eq)
plusPtr :: Ptr k -> Integer -> Ptr v
plusPtr (Ptr p) i = Ptr (p + fromIntegral i)
accessor :: forall fields el child . (KnownNat (Offset 0 fields el), Resolv fields el ~ child)
=> Ptr el -> Ptr child
accessor p = p `plusPtr` (getOffset @el @fields)
type X = 'FStruct
'[ '("a", 'FInt64)
, '("b", 'FInt8)
, '("c", 'FWord32)
, '("byte", 'FArray 2 'FWord8)
, '("xyz", 'FArray 12 'FWord64)
]
type U = 'FUnion '[ '("w64", 'FWord64)
, '("w32", 'FStruct '[ '("high", 'FWord32), '("low", 'FWord32) ])
, '("x", X)
]
type Y = 'FStruct
'[ '("other", 'FInt64)
, '("myx", X)
, '("union", U)
]
(+>) :: Ptr x -> (Ptr x -> Ptr y) -> Ptr y
(+>) p access = access p
main :: IO ()
main = do
putStrLn $ "X: " ++ show (getSize @X)
putStrLn $ "U: " ++ show (getSize @U)
putStrLn $ "Y: " ++ show (getSize @Y)
putStrLn $ show (getOffset @X @('[ 'Field "a"]))
putStrLn $ show (getOffset @Y @('[ 'Field "myx", 'Field "c"]))
putStrLn $ show (getOffset @Y @('[ 'Field "union", 'Field "x", 'Field "c"]))
let p = Ptr 0 :: Ptr Y
p2 = (accessor @('[ 'Field "myx", 'Field "c"])) p
p4 = p +> accessor @('Field "myx" ': '[])
p5 = accessor @('Field "myx" ': '[]) p
p6 = p +> accessor @('Field "myx" ': 'Field "byte" ': '[ 'Index 0])
putStrLn $ show p
putStrLn $ show p2
putStrLn $ show p6
return ()
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