I think that there's a bug in dupChan in Chan.lhs

I tried the following program.

main = do
chan <- newChan
ch <- dupChan chan
writeChan chan "done"
x <- readChan chan
y <- readChan ch
prnt ("Got "++x ++" "++y)

Now if I remember correctly this should print "Got done done".

Instead it exits with

C:\Test\test.exe: no threads to run: infinite loop or deadlock?

I looked for the code for dupChan in hslibs and it says

dupChan :: Chan a -> IO (Chan a)
dupChan (Chan _read write) = do
   new_read <- newEmptyMVar
   hole     <- readMVar write
   putMVar new_read hole
   return (Chan new_read write)

Shouldn't this instead be

dupChan :: Chan a -> IO (Chan a)
dupChan (Chan _read write) = do
   new_read <- newEmptyMVar
   hole     <- readMVar write
   putMVar new_read hole

** putMVar write hole **
return (Chan new_read write)

That's at least what the Concurrent haskell paper says.

Hugs 98 seems to have the same bug with its library.

Meurig