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Mutable List builder in the ST Monad
1{-# LANGUAGE MagicHash, UnboxedTuples, GHCForeignImportPrim, UnliftedFFITypes, BangPatterns #-}
2-- | This module allows for the (obviously unsafe) overwriting of one haskell value with another.
3module Data.ListBuilder.Unsafe (
4 unsafeSetField
5 , unsafeGetField
6 ) where
7
8import GHC.Prim
9import GHC.Exts
10
11foreign import prim "unsafeSetFieldzh" unsafeSetField# :: Int# -> Any -> Any -> (##)
12foreign import prim "unsafeGetFieldzh" unsafeGetField# :: Int# -> Any -> (# Any #)
13
14-- Set the value of a certain constructor field.
15-- You'd better be careful that it isn't being shared
16unsafeSetField :: Int -> a -> b -> IO ()
17unsafeSetField (I# i) !x y = case unsafeSetField# i (unsafeCoerce# x :: Any) (unsafeCoerce# y :: Any) of
18 (##) -> return ()
19{-# INLINE unsafeSetField #-}
20
21unsafeGetField :: Int -> a -> IO b
22unsafeGetField (I# i) !x = case unsafeGetField# i (unsafeCoerce# x :: Any) of
23 (# y #) -> return (unsafeCoerce# y)
24{-# INLINE unsafeGetField #-}