[Haskell-cafe] named pipe interface

[Serge D. Mechveliani]

To my question about safety of

>> toA_IO   = openFd "toA"   WriteOnly Nothing defaultFileFlags
>> fromA_IO = openFd "fromA" ReadOnly  Nothing defaultFileFlags
>> toA   = unsafePerformIO toA_IO
>> fromA = unsafePerformIO fromA_IO
>>
>> axiomIO :: String -> IO String
>> axiomIO str = do
>>               fdWrite toA str
>>               (str, _) <- fdRead fromA 64
>>               return str


Jean-Marie Gaillourdet wrote on  Jan 16, 2012 

> [..]
> 
> I'd say this use of unsafePerformIO is *not* safe. E.g. a Haskell 
> compiler is allowed to evaluate the right hand side of toA and fromA 
> multiple times. If you aren't 100% sure that it is ok to use 
> unsafePerformIO, don't use it!
> [..]

For example, consider  in the above context  the program

  main = do
         (str1, _) <- fdRead fromA 64
         (str2, _) <- fdRead fromA 64
         putStr (str1 ++ str2)

Is this possible that  str1  and  str2  are input from different file
descriptors?
Does this effect depend on  in-lining  of  fromA_IO  by the compiler ?
Will   {-# NOTINLINE "fromA_IO" #-}   make it safe?

Please, copy the respond to  mechvel at botik.ru

Regards,

------
Sergei
mechvel at botik.ru