Rejig the extensible exceptions so there is less circular importing

12 files changed, 125 insertions, 171 deletions

diff --git a/libraries/base/Control/Exception.hs b/libraries/base/Control/Exception.hs
index 3a92b156c7..769bf1fcad 100644
--- a/libraries/base/Control/Exception.hs
+++ b/libraries/base/Control/Exception.hs
@@ -128,9 +128,8 @@ module Control.Exception (
   ) where
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.Base         ( assert )
-import GHC.IOBase
-import GHC.Exception    as ExceptionBase hiding (Exception, catch)
+import GHC.IOBase as ExceptionBase hiding ( catch )
+import GHC.Exception hiding ( Exception )
 import GHC.Conc         ( throwTo, ThreadId )
 import Data.IORef       ( IORef, newIORef, readIORef, writeIORef )
 import Foreign.C.String ( CString, withCString )
diff --git a/libraries/base/Data/Typeable.hs b/libraries/base/Data/Typeable.hs
index 4614ab54f1..293564e858 100644
--- a/libraries/base/Data/Typeable.hs
+++ b/libraries/base/Data/Typeable.hs
@@ -101,8 +101,8 @@ import GHC.IOBase       (IORef,newIORef,unsafePerformIO)
 -- These imports are so we can define Typeable instances
 -- It'd be better to give Typeable instances in the modules themselves
 -- but they all have to be compiled before Typeable
-import GHC.IOBase       ( IO, MVar, Exception, ArithException, IOException, 
-                          ArrayException, AsyncException, Handle )
+import GHC.IOBase       ( IO, MVar, Exception, ArithException, IOException,
+                          ArrayException, AsyncException, Handle, block )
 import GHC.ST           ( ST )
 import GHC.STRef        ( STRef )
 import GHC.Ptr          ( Ptr, FunPtr )
@@ -110,7 +110,6 @@ import GHC.ForeignPtr   ( ForeignPtr )
 import GHC.Stable       ( StablePtr, newStablePtr, freeStablePtr,
                           deRefStablePtr, castStablePtrToPtr,
                           castPtrToStablePtr )
-import GHC.Exception    ( block )
 import GHC.Arr          ( Array, STArray )
 
 #endif
diff --git a/libraries/base/Foreign/Marshal/Pool.hs b/libraries/base/Foreign/Marshal/Pool.hs
index 445b786778..754b48419c 100644
--- a/libraries/base/Foreign/Marshal/Pool.hs
+++ b/libraries/base/Foreign/Marshal/Pool.hs
@@ -47,8 +47,9 @@ module Foreign.Marshal.Pool (
 #ifdef __GLASGOW_HASKELL__
 import GHC.Base              ( Int, Monad(..), (.), not )
 import GHC.Err               ( undefined )
-import GHC.Exception         ( block, unblock, throw, catchException, catchAny )
-import GHC.IOBase            ( IO, IORef, newIORef, readIORef, writeIORef, )
+import GHC.Exception         ( throw )
+import GHC.IOBase            ( IO, IORef, newIORef, readIORef, writeIORef
+                               block, unblock, catchAny )
 import GHC.List              ( elem, length )
 import GHC.Num               ( Num(..) )
 #else
diff --git a/libraries/base/GHC/Conc.lhs b/libraries/base/GHC/Conc.lhs
index d1158dd32d..50ebab7e45 100644
--- a/libraries/base/GHC/Conc.lhs
+++ b/libraries/base/GHC/Conc.lhs
@@ -121,7 +121,7 @@ import GHC.Base         ( Int(..) )
 import GHC.Read         ( Read )
 import GHC.Enum         ( Enum )
 #endif
-import GHC.Exception    ( catchException, catchAny, throw, block, unblock )
+import GHC.Exception    ( throw )
 import GHC.Pack         ( packCString# )
 import GHC.Ptr          ( Ptr(..), plusPtr, FunPtr(..) )
 import GHC.STRef
diff --git a/libraries/base/GHC/Exception.lhs b/libraries/base/GHC/Exception.lhs
index b4c511fecb..a28554222d 100644
--- a/libraries/base/GHC/Exception.lhs
+++ b/libraries/base/GHC/Exception.lhs
@@ -16,16 +16,11 @@
 -----------------------------------------------------------------------------
 
 -- #hide
-module GHC.Exception
-        ( module GHC.Exception,
-          throwIO, ioError )
-  where
+module GHC.Exception where
 
 import Data.Maybe
 import {-# SOURCE #-} Data.Typeable
 import GHC.Base
-import GHC.IOBase hiding (Exception)
-import qualified GHC.IOBase
 import GHC.Show
 \end{code}
 
@@ -54,146 +49,16 @@ instance Exception SomeException where
     fromException = Just
 \end{code}
 
-For now at least, make the monolithic Exception type an instance.
-
-\begin{code}
-instance Exception GHC.IOBase.Exception
-\end{code}
-
 %*********************************************************
 %*                                                      *
-\subsection{Primitive catch and throw}
+\subsection{Primitive throw}
 %*                                                      *
 %*********************************************************
 
-catchException used to handle the passing around of the state to the
-action and the handler.  This turned out to be a bad idea - it meant
-that we had to wrap both arguments in thunks so they could be entered
-as normal (remember IO returns an unboxed pair...).
-
-Now catch# has type
-
-    catch# :: IO a -> (b -> IO a) -> IO a
-
-(well almost; the compiler doesn't know about the IO newtype so we
-have to work around that in the definition of catchException below).
-
 \begin{code}
-catchException :: Exception e => IO a -> (e -> IO a) -> IO a
-catchException (IO io) handler = IO $ catch# io handler'
-    where handler' e = case fromException e of
-                       Just e' -> unIO (handler e')
-                       Nothing -> raise# e
-
-catchAny :: IO a -> (forall e . Exception e => e -> IO a) -> IO a
-catchAny (IO io) handler = IO $ catch# io handler'
-    where handler' (SomeException e) = unIO (handler e)
-
--- | 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 m k       =  catchException m handler
-  where handler (IOException err)   = k err
-        handler other               = throw other
-
 -- | Throw an exception.  Exceptions may be thrown from purely
 -- functional code, but may only be caught within the 'IO' monad.
 throw :: Exception e => e -> a
 throw e = raise# (toException e)
-
--- | A variant of 'throw' that can be used within the 'IO' monad.
---
--- Although 'throwIO' has a type that is an instance of the type of 'throw', the
--- two functions are subtly different:
---
--- > throw e   `seq` x  ===> throw e
--- > throwIO e `seq` x  ===> x
---
--- The first example will cause the exception @e@ to be raised,
--- whereas the second one won\'t.  In fact, 'throwIO' will only cause
--- an exception to be raised when it is used within the 'IO' monad.
--- The 'throwIO' variant should be used in preference to 'throw' to
--- raise an exception within the 'IO' monad because it guarantees
--- ordering with respect to other 'IO' operations, whereas 'throw'
--- does not.
-throwIO :: Exception e => e -> IO a
-throwIO e = IO (raiseIO# (toException e))
 \end{code}
 
-
-%*********************************************************
-%*                                                      *
-\subsection{Controlling asynchronous exception delivery}
-%*                                                      *
-%*********************************************************
-
-\begin{code}
--- | Applying 'block' to a computation will
--- execute that computation with asynchronous exceptions
--- /blocked/.  That is, any thread which
--- attempts to raise an exception in the current thread with 'Control.Exception.throwTo' will be
--- blocked until asynchronous exceptions are enabled again.  There\'s
--- no need to worry about re-enabling asynchronous exceptions; that is
--- done automatically on exiting the scope of
--- 'block'.
---
--- Threads created by 'Control.Concurrent.forkIO' inherit the blocked
--- state from the parent; that is, to start a thread in blocked mode,
--- use @block $ forkIO ...@.  This is particularly useful if you need to
--- establish an exception handler in the forked thread before any
--- asynchronous exceptions are received.
-block :: IO a -> IO a
-
--- | To re-enable asynchronous exceptions inside the scope of
--- 'block', 'unblock' can be
--- used.  It scopes in exactly the same way, so on exit from
--- 'unblock' asynchronous exception delivery will
--- be disabled again.
-unblock :: IO a -> IO a
-
-block (IO io) = IO $ blockAsyncExceptions# io
-unblock (IO io) = IO $ unblockAsyncExceptions# io
-
--- | returns True if asynchronous exceptions are blocked in the
--- current thread.
-blocked :: IO Bool
-blocked = IO $ \s -> case asyncExceptionsBlocked# s of
-                        (# s', i #) -> (# s', i /=# 0# #)
-\end{code}
-
-\begin{code}
--- | Forces its argument to be evaluated when the resultant 'IO' action
--- is executed.  It can be used to order evaluation with respect to
--- other 'IO' operations; its semantics are given by
---
--- >   evaluate x `seq` y    ==>  y
--- >   evaluate x `catch` f  ==>  (return $! x) `catch` f
--- >   evaluate x >>= f      ==>  (return $! x) >>= f
---
--- /Note:/ the first equation implies that @(evaluate x)@ is /not/ the
--- same as @(return $! x)@.  A correct definition is
---
--- >   evaluate x = (return $! x) >>= return
---
-evaluate :: a -> IO a
-evaluate a = IO $ \s -> case a `seq` () of () -> (# s, a #)
-        -- NB. can't write  
-        --      a `seq` (# s, a #)
-        -- because we can't have an unboxed tuple as a function argument
-\end{code}
diff --git a/libraries/base/GHC/Exception.lhs-boot b/libraries/base/GHC/Exception.lhs-boot
deleted file mode 100644
index dfd80131ad..0000000000
--- a/libraries/base/GHC/Exception.lhs-boot
+++ /dev/null
@@ -1,19 +0,0 @@
-
-\begin{code}
-{-# OPTIONS_GHC -XNoImplicitPrelude #-}
-
-module GHC.Exception where
-
-import {-# SOURCE #-} qualified GHC.IOBase as IOB
-
-class Exception e
-
-data SomeException
-
-instance Exception IOB.Exception
-
-throwIO :: Exception e => e -> IOB.IO a
-
-toException :: Exception e => e -> SomeException
-\end{code}
-
diff --git a/libraries/base/GHC/Handle.hs b/libraries/base/GHC/Handle.hs
index 1d8445e428..3421502c64 100644
--- a/libraries/base/GHC/Handle.hs
+++ b/libraries/base/GHC/Handle.hs
@@ -73,7 +73,7 @@ import GHC.Base
 import GHC.Read         ( Read )
 import GHC.List
 import GHC.IOBase
-import GHC.Exception    ( block, catchException, catchAny, throw, throwIO )
+import GHC.Exception    ( throw )
 import GHC.Enum
 import GHC.Num          ( Integer(..), Num(..) )
 import GHC.Show
diff --git a/libraries/base/GHC/IO.hs b/libraries/base/GHC/IO.hs
index 14c2b3d1f8..7ca3e6ecd5 100644
--- a/libraries/base/GHC/IO.hs
+++ b/libraries/base/GHC/IO.hs
@@ -45,7 +45,6 @@ import GHC.Real
 import GHC.Num
 import GHC.Show
 import GHC.List
-import GHC.Exception    ( ioError, catch )
 
 #ifdef mingw32_HOST_OS
 import GHC.Conc
diff --git a/libraries/base/GHC/IOBase.lhs b/libraries/base/GHC/IOBase.lhs
index 378237dfe7..ac7d0a43ae 100644
--- a/libraries/base/GHC/IOBase.lhs
+++ b/libraries/base/GHC/IOBase.lhs
@@ -44,6 +44,8 @@ module GHC.IOBase(
     stackOverflow, heapOverflow, ioException, 
     IOError, IOException(..), IOErrorType(..), ioError, userError,
     ExitCode(..),
+    throwIO, block, unblock, catch, catchAny, catchException,
+    evaluate,
     -- The RTS calls this
     nonTermination,
   ) where
@@ -59,7 +61,8 @@ import GHC.Show
 import GHC.List
 import GHC.Read
 import Foreign.C.Types (CInt)
-import {-# SOURCE #-} GHC.Exception ( SomeException, toException, throwIO )
+import GHC.Exception hiding (Exception)
+import qualified GHC.Exception as Exc
 
 #ifndef __HADDOCK__
 import {-# SOURCE #-} Data.Typeable     ( showsTypeRep )
@@ -717,6 +720,10 @@ data Exception
 nonTermination :: SomeException
 nonTermination = toException NonTermination
 
+-- For now at least, make the monolithic Exception type an instance of
+-- the Exception class
+instance Exc.Exception Exception
+
 -- |The type of arithmetic exceptions
 data ArithException
   = Overflow
@@ -972,3 +979,108 @@ instance Show IOException where
 data IOMode      =  ReadMode | WriteMode | AppendMode | ReadWriteMode
                     deriving (Eq, Ord, Ix, Enum, Read, Show)
 \end{code}
+
+%*********************************************************
+%*                                                      *
+\subsection{Primitive catch and throwIO}
+%*                                                      *
+%*********************************************************
+
+catchException used to handle the passing around of the state to the
+action and the handler.  This turned out to be a bad idea - it meant
+that we had to wrap both arguments in thunks so they could be entered
+as normal (remember IO returns an unboxed pair...).
+
+Now catch# has type
+
+    catch# :: IO a -> (b -> IO a) -> IO a
+
+(well almost; the compiler doesn't know about the IO newtype so we
+have to work around that in the definition of catchException below).
+
+\begin{code} 
+catchException :: Exception e => IO a -> (e -> IO a) -> IO a
+catchException (IO io) handler = IO $ catch# io handler'
+    where handler' e = case fromException e of
+                       Just e' -> unIO (handler e')
+                       Nothing -> raise# e
+
+catchAny :: IO a -> (forall e . Exception e => e -> IO a) -> IO a
+catchAny (IO io) handler = IO $ catch# io handler'
+    where handler' (SomeException e) = unIO (handler e)
+
+-- | A variant of 'throw' that can be used within the 'IO' monad.
+--
+-- Although 'throwIO' has a type that is an instance of the type of 'throw', the
+-- two functions are subtly different:
+--
+-- > throw e   `seq` x  ===> throw e
+-- > throwIO e `seq` x  ===> x
+--
+-- The first example will cause the exception @e@ to be raised,
+-- whereas the second one won\'t.  In fact, 'throwIO' will only cause
+-- an exception to be raised when it is used within the 'IO' monad.
+-- The 'throwIO' variant should be used in preference to 'throw' to
+-- raise an exception within the 'IO' monad because it guarantees
+-- ordering with respect to other 'IO' operations, whereas 'throw'
+-- does not.
+throwIO :: Exception e => e -> IO a
+throwIO e = IO (raiseIO# (toException e))
+\end{code}
+
+
+%*********************************************************
+%*                                                      *
+\subsection{Controlling asynchronous exception delivery}
+%*                                                      *
+%*********************************************************
+
+\begin{code}
+-- | Applying 'block' to a computation will
+-- execute that computation with asynchronous exceptions
+-- /blocked/.  That is, any thread which
+-- attempts to raise an exception in the current thread with 'Control.Exception.throwTo' will be
+-- blocked until asynchronous exceptions are enabled again.  There\'s
+-- no need to worry about re-enabling asynchronous exceptions; that is
+-- done automatically on exiting the scope of
+-- 'block'.
+--
+-- Threads created by 'Control.Concurrent.forkIO' inherit the blocked
+-- state from the parent; that is, to start a thread in blocked mode,
+-- use @block $ forkIO ...@.  This is particularly useful if you need to
+-- establish an exception handler in the forked thread before any
+-- asynchronous exceptions are received.
+block :: IO a -> IO a
+
+-- | To re-enable asynchronous exceptions inside the scope of
+-- 'block', 'unblock' can be
+-- used.  It scopes in exactly the same way, so on exit from
+-- 'unblock' asynchronous exception delivery will
+-- be disabled again.
+unblock :: IO a -> IO a
+
+block (IO io) = IO $ blockAsyncExceptions# io
+unblock (IO io) = IO $ unblockAsyncExceptions# io
+\end{code}
+
+\begin{code}
+-- | Forces its argument to be evaluated when the resultant 'IO' action
+-- is executed.  It can be used to order evaluation with respect to
+-- other 'IO' operations; its semantics are given by
+--
+-- >   evaluate x `seq` y    ==>  y
+-- >   evaluate x `catch` f  ==>  (return $! x) `catch` f
+-- >   evaluate x >>= f      ==>  (return $! x) >>= f
+--
+-- /Note:/ the first equation implies that @(evaluate x)@ is /not/ the
+-- same as @(return $! x)@.  A correct definition is
+--
+-- >   evaluate x = (return $! x) >>= return
+--
+evaluate :: a -> IO a
+evaluate a = IO $ \s -> case a `seq` () of () -> (# s, a #)
+        -- NB. can't write
+        --      a `seq` (# s, a #)
+        -- because we can't have an unboxed tuple as a function argument
+\end{code}
+
diff --git a/libraries/base/GHC/IOBase.lhs-boot b/libraries/base/GHC/IOBase.lhs-boot
index 3ddd211d06..fb0b9fe7e8 100644
--- a/libraries/base/GHC/IOBase.lhs-boot
+++ b/libraries/base/GHC/IOBase.lhs-boot
@@ -5,6 +5,5 @@
 module GHC.IOBase where
 
 data Exception
-data IO a
 \end{code}
 
diff --git a/libraries/base/GHC/TopHandler.lhs b/libraries/base/GHC/TopHandler.lhs
index c0fcd6b130..867c2891f8 100644
--- a/libraries/base/GHC/TopHandler.lhs
+++ b/libraries/base/GHC/TopHandler.lhs
@@ -33,7 +33,6 @@ import Control.Concurrent.MVar
 import Foreign
 import Foreign.C
 import GHC.IOBase
-import GHC.Exception    ( catchException )
 import GHC.Prim
 import GHC.Conc
 import GHC.Weak
diff --git a/libraries/base/System/IO.hs b/libraries/base/System/IO.hs
index a2edaec751..a47e7bd95e 100644
--- a/libraries/base/System/IO.hs
+++ b/libraries/base/System/IO.hs
@@ -171,7 +171,7 @@ import System.Posix.Internals
 #endif
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.Exception    as ExceptionBase hiding (catch)
+import GHC.IOBase       as ExceptionBase
 #endif
 #ifdef __HUGS__
 import Hugs.Exception   as ExceptionBase