From c497471bb7fc204afb546f3116ad116f8569e452 Mon Sep 17 00:00:00 2001 From: Simon Marlow Date: Tue, 20 Jul 2010 08:28:19 +0000 Subject: [PATCH] add unsafeLocalState from Haskell 2010, and docs --- Foreign/Marshal.hs | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/Foreign/Marshal.hs b/Foreign/Marshal.hs index 1daf8ef..b815122 100644 --- a/Foreign/Marshal.hs +++ b/Foreign/Marshal.hs @@ -14,11 +14,16 @@ ----------------------------------------------------------------------------- module Foreign.Marshal - ( module Foreign.Marshal.Alloc + ( + -- | The module "Foreign.Marshal" re-exports the other modules in the + -- @Foreign.Marshal@ hierarchy: + module Foreign.Marshal.Alloc , module Foreign.Marshal.Array , module Foreign.Marshal.Error , module Foreign.Marshal.Pool , module Foreign.Marshal.Utils + -- | and provides one function: + , unsafeLocalState ) where import Foreign.Marshal.Alloc @@ -26,3 +31,26 @@ import Foreign.Marshal.Array import Foreign.Marshal.Error import Foreign.Marshal.Pool import Foreign.Marshal.Utils + +import GHC.IO + +{- | +Sometimes an external entity is a pure function, except that it passes +arguments and/or results via pointers. The function +@unsafeLocalState@ permits the packaging of such entities as pure +functions. + +The only IO operations allowed in the IO action passed to +@unsafeLocalState@ are (a) local allocation (@alloca@, @allocaBytes@ +and derived operations such as @withArray@ and @withCString@), and (b) +pointer operations (@Foreign.Storable@ and @Foreign.Ptr@) on the +pointers to local storage, and (c) foreign functions whose only +observable effect is to read and/or write the locally allocated +memory. Passing an IO operation that does not obey these rules +results in undefined behaviour. + +It is expected that this operation will be +replaced in a future revision of Haskell. +-} +unsafeLocalState :: IO a -> a +unsafeLocalState = unsafePerformIO -- 1.7.10.4