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diff --git a/ghc/lib/concurrent/SampleVar.lhs b/ghc/lib/concurrent/SampleVar.lhs
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-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1995
-%
-\section[SampleVar]{Sample variables}
-
-Sample variables are slightly different from a normal @MVar@:
-
-\begin{itemize}
-\item Reading an empty @SampleVar@ causes the reader to block.
-    (same as @takeMVar@ on empty @MVar@)
-\item Reading a filled @SampleVar@ empties it and returns value.
-    (same as @takeMVar@)
-\item Writing to an empty @SampleVar@ fills it with a value, and
-potentially, wakes up a blocked reader  (same as for @putMVar@ on empty @MVar@).
-\item Writing to a filled @SampleVar@ overwrites the current value.
- (different from @putMVar@ on full @MVar@.)
-\end{itemize}
-
-\begin{code}
-module SampleVar
-       (
-         SampleVar,         -- :: type _ =
- 
-	 newEmptySampleVar, -- :: IO (SampleVar a)
-         newSampleVar,      -- :: a -> IO (SampleVar a)
-	 emptySampleVar,    -- :: SampleVar a -> IO ()
-	 readSampleVar,	    -- :: SampleVar a -> IO a
-	 writeSampleVar	    -- :: SampleVar a -> a -> IO ()
-
-       ) where
-
-import PrelConc
-
-
-type SampleVar a
- = MVar (Int,		-- 1  == full
-			-- 0  == empty
-			-- <0 no of readers blocked
-          MVar a)
-
--- Initally, a @SampleVar@ is empty/unfilled.
-
-newEmptySampleVar :: IO (SampleVar a)
-newEmptySampleVar = do
-   v <- newEmptyMVar
-   newMVar (0,v)
-
-newSampleVar :: a -> IO (SampleVar a)
-newSampleVar a = do
-   v <- newEmptyMVar
-   putMVar v a
-   newMVar (1,v)
-
-emptySampleVar :: SampleVar a -> IO ()
-emptySampleVar v = do
-   (readers, var) <- takeMVar v
-   if readers >= 0 then
-     putMVar v (0,var)
-    else
-     putMVar v (readers,var)
-
---
--- filled => make empty and grab sample
--- not filled => try to grab value, empty when read val.
---
-readSampleVar :: SampleVar a -> IO a
-readSampleVar svar = do
-   (readers,val) <- takeMVar svar
-   putMVar svar (readers-1,val)
-   takeMVar val
-
---
--- filled => overwrite
--- not filled => fill, write val
---
-writeSampleVar :: SampleVar a -> a -> IO ()
-writeSampleVar svar v = do
-   (readers,val) <- takeMVar svar
-   case readers of
-     1 -> 
-       swapMVar val v >> 
-       putMVar svar (1,val)
-     _ -> 
-       putMVar val v >> 
-       putMVar svar (min 1 (readers+1), val)
-\end{code}