disambiguate uses of foldr for nhc98 to compile without errors

[haskell-directory.git] / GHC / IOBase.lhs

diff --git a/GHC/IOBase.lhs b/GHC/IOBase.lhs
index 0a3cfca..499899a 100644 (file)
--- a/GHC/IOBase.lhs
+++ b/GHC/IOBase.lhs
@@ -20,7 +20,7 @@ module GHC.IOBase(
     unsafePerformIO, unsafeInterleaveIO,
   
        -- To and from from ST
-    stToIO, ioToST, unsafeIOToST,
+    stToIO, ioToST, unsafeIOToST, unsafeSTToIO,
 
        -- References
     IORef(..), newIORef, readIORef, writeIORef, 
@@ -30,7 +30,7 @@ module GHC.IOBase(
        -- Handles, file descriptors,
     FilePath,  
     Handle(..), Handle__(..), HandleType(..), IOMode(..), FD, 
-    isReadableHandleType, isWritableHandleType, showHandle,
+    isReadableHandleType, isWritableHandleType, isReadWriteHandleType, showHandle,
   
        -- Buffers
     Buffer(..), RawBuffer, BufferState(..), BufferList(..), BufferMode(..),
@@ -55,7 +55,7 @@ import GHC.List
 import GHC.Read
 
 #ifndef __HADDOCK__
-import {-# SOURCE #-} Data.Dynamic
+import {-# SOURCE #-} GHC.Dynamic
 #endif
 
 -- ---------------------------------------------------------------------------
@@ -155,6 +155,9 @@ ioToST (IO m) = (ST m)
 unsafeIOToST        :: IO a -> ST s a
 unsafeIOToST (IO io) = ST $ \ s -> (unsafeCoerce# io) s
 
+unsafeSTToIO :: ST s a -> IO a
+unsafeSTToIO (ST m) = IO (unsafeCoerce# m)
+
 -- ---------------------------------------------------------------------------
 -- Unsafe IO operations
 
@@ -212,7 +215,7 @@ help of 'unsafePerformIO'.  So be careful!
 -}
 {-# NOINLINE unsafePerformIO #-}
 unsafePerformIO        :: IO a -> a
-unsafePerformIO (IO m) = case m realWorld# of (# _, r #)   -> r
+unsafePerformIO (IO m) = lazy (case m realWorld# of (# _, r #) -> r)
 
 -- Why do we NOINLINE unsafePerformIO?  See the comment with
 -- GHC.ST.runST.  Essentially the issue is that the IO computation
@@ -220,6 +223,22 @@ unsafePerformIO (IO m) = case m realWorld# of (# _, r #)   -> r
 -- not at all.  If we let the compiler see the application of the IO
 -- to realWorld#, it might float out part of the IO.
 
+-- Why is there a call to 'lazy' in unsafePerformIO?
+-- If we don't have it, the demand analyser discovers the following strictness
+-- for unsafePerformIO:  C(U(AV))
+-- But then consider
+--     unsafePerformIO (\s -> let r = f x in 
+--                            case writeIORef v r s of (# s1, _ #) ->
+--                            (# s1, r #)
+-- The strictness analyser will find that the binding for r is strict,
+-- (becuase of uPIO's strictness sig), and so it'll evaluate it before 
+-- doing the writeIORef.  This actually makes tests/lib/should_run/memo002
+-- get a deadlock!  
+--
+-- Solution: don't expose the strictness of unsafePerformIO,
+--          by hiding it with 'lazy'
+
+
 {-|
 'unsafeInterleaveIO' allows 'IO' computation to be deferred lazily.
 When passed a value of type @IO a@, the 'IO' will only be performed
@@ -423,6 +442,9 @@ isWritableHandleType WriteHandle     = True
 isWritableHandleType ReadWriteHandle = True
 isWritableHandleType _              = False
 
+isReadWriteHandleType ReadWriteHandle{} = True
+isReadWriteHandleType _                 = False
+
 -- | File and directory names are values of type 'String', whose precise
 -- meaning is operating system dependent. Files can be opened, yielding a
 -- handle which can then be used to operate on the contents of that file.
@@ -599,6 +621,10 @@ data Exception
        -- ^The current thread was waiting to retry an atomic memory transaction
        -- that could never become possible to complete because there are no other
        -- threads referring to any of teh TVars involved.
+  | NestedAtomically
+       -- ^The runtime detected an attempt to nest one STM transaction
+       -- inside another one, presumably due to the use of 
+       -- 'unsafePeformIO' with 'atomically'.
   | Deadlock
        -- ^There are no runnable threads, so the program is
        -- deadlocked.  The 'Deadlock' exception is
@@ -733,10 +759,11 @@ instance Show Exception where
   showsPrec _ (RecConError err)                 = showString err
   showsPrec _ (RecUpdError err)                 = showString err
   showsPrec _ (AssertionFailed err)      = showString err
-  showsPrec _ (DynException _err)        = showString "unknown exception"
+  showsPrec _ (DynException err)         = showString "exception :: " . showsTypeRep (dynTypeRep err)
   showsPrec _ (AsyncException e)        = shows e
   showsPrec _ (BlockedOnDeadMVar)       = showString "thread blocked indefinitely"
   showsPrec _ (BlockedIndefinitely)     = showString "thread blocked indefinitely"
+  showsPrec _ (NestedAtomically)        = showString "Control.Concurrent.STM.atomically was nested"
   showsPrec _ (NonTermination)           = showString "<<loop>>"
   showsPrec _ (Deadlock)                 = showString "<<deadlock>>"
 
@@ -756,6 +783,7 @@ instance Eq Exception where
   AsyncException e1   == AsyncException e2   = e1 == e2
   BlockedOnDeadMVar   == BlockedOnDeadMVar   = True
   NonTermination      == NonTermination      = True
+  NestedAtomically    == NestedAtomically    = True
   Deadlock            == Deadlock            = True
   _                   == _                   = False