+-- ^ A value of type @'FunPtr' a@ is a pointer to a function callable
+-- from foreign code. The type @a@ will normally be a /foreign type/,
+-- a function type with zero or more arguments where
+--
+-- * the argument types are /marshallable foreign types/,
+-- i.e. 'Char', 'Int', 'Prelude.Double', 'Prelude.Float',
+-- 'Bool', 'Data.Int.Int8', 'Data.Int.Int16', 'Data.Int.Int32',
+-- 'Data.Int.Int64', 'Data.Word.Word8', 'Data.Word.Word16',
+-- 'Data.Word.Word32', 'Data.Word.Word64', @'Ptr' a@, @'FunPtr' a@,
+-- @'Foreign.StablePtr.StablePtr' a@ or a renaming of any of these
+-- using @newtype@.
+--
+-- * the return type is either a marshallable foreign type or has the form
+-- @'Prelude.IO' t@ where @t@ is a marshallable foreign type or @()@.
+--
+-- A value of type @'FunPtr' a@ may be a pointer to a foreign function,
+-- either returned by another foreign function or imported with a
+-- a static address import like
+--
+-- > foreign import ccall "stdlib.h &free"
+-- > p_free :: FunPtr (Ptr a -> IO ())
+--
+-- or a pointer to a Haskell function created using a /wrapper/ stub
+-- declared to produce a 'FunPtr' of the correct type. For example:
+--
+-- > type Compare = Int -> Int -> Bool
+-- > foreign import ccall "wrapper"
+-- > mkCompare :: Compare -> IO (FunPtr Compare)
+--
+-- Calls to wrapper stubs like @mkCompare@ allocate storage, which
+-- should be released with 'Foreign.Ptr.freeHaskellFunPtr' when no
+-- longer required.
+--
+-- To convert 'FunPtr' values to corresponding Haskell functions, one
+-- can define a /dynamic/ stub for the specific foreign type, e.g.
+--
+-- > type IntFunction = CInt -> IO ()
+-- > foreign import ccall "dynamic"
+-- > mkFun :: FunPtr IntFunction -> IntFunction