On Fri, Jan 13, 2012 at 12:19:34PM -0800, Donn Cave wrote:

Quoth "Serge D. Mechveliani" , ...

...

Initially, I did the example by the Foreign Function Interface for C. But then, I thought "But this is unnatural! Use plainly the standard Haskell IO, it has everything".

So, your advice is "return to FFI" ?

Well, it turns out that the I/O system functions in System.Posix.IO may work for your purposes. I was able to get your example to work with these functions, which correspond to open(2), read(2), write(2).

I would also use these functions in C, as you did in your C program. Haskell I/O functions like hGetLine are analogous to C library I/O like fgets(3) - in particular, they're buffered, and I would guess that's why they don't work for you here.

Specifically, openFile "toA" WriteOnly Nothing defaultFileFlags openFile "fromA" ReadOnly Nothing defaultFileFlags

fdWrite toA str (str, len) <- fdRead fromA 64 return str

Great! Thank you very much. As I find, Posix.IO is not of the standard, but it is of GHC. Anyway, it fits my purpose. By openFile you, probably, mean openFd. Another point is the number of open files, for a long loop. I put toA_IO = openFd "toA" WriteOnly Nothing defaultFileFlags fromA_IO = openFd "fromA" ReadOnly Nothing defaultFileFlags axiomIO :: String -> IO String axiomIO str = do toA <- toA_IO fromA <- fromA_IO fdWrite toA str (str, _len) <- fdRead fromA 64 return str When applying axiomIO in a loop of 9000 strings, it breaks: "too many open files". I do not understand why it is so, because toA_IO and fromA_IO are global constants (I have not any experience with `do'). Anyway, I have changed this to toA = unsafePerformIO toA_IO fromA = unsafePerformIO fromA_IO axiomIO :: String -> IO String axiomIO str = do fdWrite toA str (str, _len) <- fdRead fromA 64 return str And now, it works in loong loops too (I need to understand further whether my usage of unsafePerformIO really damages the project). Its performance is 9/10 of the C <-> C performance (ghc -O, gcc -O, Linux Debian). It is still slow: 120000 small strings/second on a 2 GHz machine. But this is something to start with.

I was able to get your example to work with these functions, which correspond to open(2), read(2), write(2).

I would also use these functions in C, as you did in your C program. Haskell I/O functions like hGetLine are analogous to C library I/O like fgets(3) - in particular, they're buffered, and I would guess that's why they don't work for you here.

Indeed. Initially, I tried C <-> C, and used fgets, fputs, fflush. And it did not work, it required to open/close files inside a loop; I failed with attempts. Again, do not understand, why (do they wait till the buffer is full?). Then, I tried read/write, as it is in fifoFromA.c which I posted. And it works. Now, Haskell <-> C gives a hope. Nice. Thanks, ------ Sergei mechvel@botik.ru