Move some catch definitions around to avoid an import loop

[ghc-base.git] / System / IO / Error.hs

diff --git a/System/IO/Error.hs b/System/IO/Error.hs
index 132af61..372bb15 100644 (file)
--- a/System/IO/Error.hs
+++ b/System/IO/Error.hs
@@ -90,18 +90,23 @@ module System.IO.Error (
 #endif
   ) where
 
+#ifndef __HUGS__
+import qualified Control.Exception.Base as New (catch)
+#endif
+
+#ifndef __HUGS__
 import Data.Either
+#endif
 import Data.Maybe
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Base
 import GHC.IOBase
-import GHC.Exception
 import Text.Show
 #endif
 
 #ifdef __HUGS__
-import Hugs.Prelude(Handle, IOException(..), IOErrorType(..))
+import Hugs.Prelude(Handle, IOException(..), IOErrorType(..), IO)
 #endif
 
 #ifdef __NHC__
@@ -152,6 +157,9 @@ mkIOError t location maybe_hdl maybe_filename =
                IOError{ ioe_type = t, 
                         ioe_location = location,
                         ioe_description = "",
+#if defined(__GLASGOW_HASKELL__)
+                        ioe_errno = Nothing,
+#endif
                         ioe_handle = maybe_hdl, 
                         ioe_filename = maybe_filename
                         }
@@ -367,8 +375,9 @@ annotateIOError :: IOError
               -> Maybe Handle 
               -> Maybe FilePath 
               -> IOError 
-annotateIOError (IOError ohdl errTy _ str opath) loc hdl path = 
-  IOError (hdl `mplus` ohdl) errTy loc str (path `mplus` opath)
+annotateIOError ioe loc hdl path = 
+  ioe{ ioe_handle = hdl `mplus` ioe_handle ioe,
+       ioe_location = loc, ioe_filename = path `mplus` ioe_filename ioe }
   where
     Nothing `mplus` ys = ys
     xs      `mplus` _  = xs
@@ -384,3 +393,26 @@ annotateIOError (UserError loc msg) msg' file' hdl' =
 annotateIOError (PatternError loc) msg' file' hdl' =
     PatternError (loc++'\n':msg')
 #endif
+
+#ifndef __HUGS__
+-- | The 'catch' function establishes a handler that receives any 'IOError'
+-- raised in the action protected by 'catch'.  An 'IOError' is caught by
+-- the most recent handler established by 'catch'.  These handlers are
+-- not selective: all 'IOError's are caught.  Exception propagation
+-- must be explicitly provided in a handler by re-raising any unwanted
+-- exceptions.  For example, in
+--
+-- > f = catch g (\e -> if IO.isEOFError e then return [] else ioError e)
+--
+-- the function @f@ returns @[]@ when an end-of-file exception
+-- (cf. 'System.IO.Error.isEOFError') occurs in @g@; otherwise, the
+-- exception is propagated to the next outer handler.
+--
+-- When an exception propagates outside the main program, the Haskell
+-- system prints the associated 'IOError' value and exits the program.
+--
+-- Non-I\/O exceptions are not caught by this variant; to catch all
+-- exceptions, use 'Control.Exception.catch' from "Control.Exception".
+catch :: IO a -> (IOError -> IO a) -> IO a
+catch = New.catch
+#endif /* !__HUGS__ */