+-- v_InitDynFlags
+-- is the "baseline" dynamic flags, initialised from
+-- the defaults and command line options, and updated by the
+-- ':s' command in GHCi.
+--
+-- v_DynFlags
+-- is the dynamic flags for the current compilation. It is reset
+-- to the value of v_InitDynFlags before each compilation, then
+-- updated by reading any OPTIONS pragma in the current module.
+
+\begin{code}
+GLOBAL_VAR(v_InitDynFlags, defaultDynFlags, DynFlags)
+GLOBAL_VAR(v_DynFlags, defaultDynFlags, DynFlags)
+
+setDynFlags :: DynFlags -> IO ()
+setDynFlags dfs = writeIORef v_DynFlags dfs
+
+saveDynFlags :: IO ()
+saveDynFlags = do dfs <- readIORef v_DynFlags
+ writeIORef v_InitDynFlags dfs
+
+restoreDynFlags :: IO DynFlags
+restoreDynFlags = do dfs <- readIORef v_InitDynFlags
+ writeIORef v_DynFlags dfs
+ return dfs
+
+getDynFlags :: IO DynFlags
+getDynFlags = readIORef v_DynFlags
+
+updDynFlags :: (DynFlags -> DynFlags) -> IO ()
+updDynFlags f = do dfs <- readIORef v_DynFlags
+ writeIORef v_DynFlags (f dfs)
+
+dynFlag :: (DynFlags -> a) -> IO a
+dynFlag f = do dflags <- readIORef v_DynFlags; return (f dflags)
+
+setDynFlag, unSetDynFlag :: DynFlag -> IO ()
+setDynFlag f = updDynFlags (\dfs -> dopt_set dfs f)
+unSetDynFlag f = updDynFlags (\dfs -> dopt_unset dfs f)