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 fcbffad..372bb15 100644 (file)
--- a/System/IO/Error.hs
+++ b/System/IO/Error.hs
@@ -91,13 +91,15 @@ module System.IO.Error (
   ) 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 {-# SOURCE #-} Prelude (catch)
-
 import GHC.Base
 import GHC.IOBase
 import Text.Show
@@ -391,3 +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__ */