Re: [Haskell-cafe] GHC + interactive input/output
Hi Richard, On Mon, Feb 11, 2008 at 12:37:27PM +1300, Richard A. O'Keefe wrote: On 9 Feb 2008, at 2:29 pm, Philip Weaver wrote: GHC certain *could* do this, but it's arguably not the right thing to do. I have reminded the GHC maintainers before that the Haskell specification *REQUIRES* a Haskell system to support this; [this is flushing stdout when we read from stdin, if I have followed correctly] Can you please say where the report says this? I've just skimmed http://haskell.org/onlinereport/io.html and didn't see it mentioned. Also, if there's a GHC bug about this, can you please point me to it? A quick search didn't find anything. there is an example that makes no sense whatever without it. I'm not sure which example you're referring to, but the first example on the above page 21.10.1 Summing Two Numbers starts off by doing hSetBuffering stdout NoBuffering which implies to me that implementations are not expected to do the flushing hack. Thanks Ian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
On 9 Feb 2008, at 2:29 pm, Philip Weaver wrote: GHC certain *could* do this, but it's arguably not the right thing to do. I have reminded the GHC maintainers before that the Haskell specification *REQUIRES* a Haskell system to support this; there is an example that makes no sense whatever without it. (And the other Haskell systems I use get it right.) I note that David Bacon's SETL implementation has explicit support for tying an input stream and an output stream together so that any time input is done on the input stream the output stream is flushed; this is done automatically for sockets and is *seriously* useful in avoiding mistakes. Note that this should make essentially no difference to performance because (a) the flushing is only needed when the input buffer is exhausted, which happens once per line, (b) the kinds of streams where you want it (terminals, STREAMs, sockets, serial ports, c) generally have other costs so high you won't be able to measure this one, (c) it *only* applies to bidirectional streams or to explicitly coupled streams, so I/O to disc files or memory sticks or other high speed block devices should never be affected at all (unless someone chooses to do it explicitly, in which case it's still going to be faster than anything they could have done by hand). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GHC + interactive input/output
$ cat foo.c
#include stdio.h
int
main()
{
char s[1024];
printf(gsi );
gets(s);
printf(%s\n, s);
return 0;
}
$ make foo
cc gsi.c -o gsi
$ ./foo
warning: this program uses gets(), which is unsafe.
gsi hello
hello
$ cat foo.hs
main = do
putStr gsi
s - getLine
putStrLn s
$ ghc foo.hs -o foo
$ ./foo
hello
gsi hello
(This is on MacOS X). It strikes me that GHC is being
extraordinarily unhelpful here. Is there anyone on the planet who
ever actually wants this behavior?
jcc
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Re: [Haskell-cafe] GHC + interactive input/output
On Feb 8, 2008, at 19:41 , Philip Weaver wrote: Your gsi is buffered because there's no newline at the end. To flush the buffer and force it to be printed immediately, use 'hFlush' from the System.IO library, or use 'hSetBuffering' from that same library: http://haskell.org/ghc/docs/latest/html/ libraries/base/System-IO.html I believe you can observe the same behavior in C. Most C stdio libraries in my experience have extra code in the functions that read stdin to flush stdout first, specifically because of lazy people who don't pay attention to buffering. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
Your gsi is buffered because there's no newline at the end. To flush
the buffer and force it to be printed immediately, use 'hFlush' from the
System.IO library, or use 'hSetBuffering' from that same library:
http://haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html
I believe you can observe the same behavior in C.
- Phil
On Feb 8, 2008 4:14 PM, Jonathan Cast [EMAIL PROTECTED] wrote:
$ cat foo.c
#include stdio.h
int
main()
{
char s[1024];
printf(gsi );
gets(s);
printf(%s\n, s);
return 0;
}
$ make foo
cc gsi.c -o gsi
$ ./foo
warning: this program uses gets(), which is unsafe.
gsi hello
hello
$ cat foo.hs
main = do
putStr gsi
s - getLine
putStrLn s
$ ghc foo.hs -o foo
$ ./foo
hello
gsi hello
(This is on MacOS X). It strikes me that GHC is being
extraordinarily unhelpful here. Is there anyone on the planet who
ever actually wants this behavior?
jcc
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___
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Re: [Haskell-cafe] GHC + interactive input/output
On 8 Feb 2008, at 4:50 PM, Brandon S. Allbery KF8NH wrote: On Feb 8, 2008, at 19:41 , Philip Weaver wrote: Your gsi is buffered because there's no newline at the end. To flush the buffer and force it to be printed immediately, use 'hFlush' from the System.IO library, or use 'hSetBuffering' from that same library: http://haskell.org/ghc/docs/latest/html/ libraries/base/System-IO.html I believe you can observe the same behavior in C. Most C stdio libraries in my experience have extra code in the functions that read stdin to flush stdout first, specifically because of lazy people who don't pay attention to buffering. Why can't GHC implement the same thing? jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
On 8 Feb 2008, at 5:29 PM, Philip Weaver wrote: GHC certain *could* do this, but it's arguably not the right thing to do. For performance, the operating system buffers writes until it is ready to write large chunks at a time. If you do not want this behavior, change the buffering mode from its default. To what? BlockBuffering is worse, not better, and the docs *explicitly* say that switching to NoBuffering will break ^D (if it wasn't broken already...) My specification for a working program is `one that works exactly like every other program on my machine'. I don't see how to produce such a program with GHC.(1) jcc (1) Using readline might work (although I'm kind of sceptical given what's preceded it), but I haven't gotten it to link thus far... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
On 8 Feb 2008, at 6:34 PM, Ryan Ingram wrote: import System.IO myGetLine = hFlush stdout getLine That fixes this issue, certainly (although it's superfluous; my program really does contain only a single call to getLine)... Nevertheless, it would be nice to at least have it in the standard library; it's much more useful than any of the input functions that already exist. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
On 8 Feb 2008, at 6:50 PM, Jonathan Cast wrote: On 8 Feb 2008, at 6:34 PM, Ryan Ingram wrote: import System.IO myGetLine = hFlush stdout getLine That fixes this issue, certainly (although it's superfluous; my program really does contain only a single call to getLine)... Nevertheless, it would be nice to at least have it in the standard library; it's much more useful than any of the input functions that already exist. Also, for some reason, this doesn't seem to be necessary inside an Emacs buffer... Do we not care about performance in that case? jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
import System.IO myGetLine = hFlush stdout getLine -- ryan On 2/8/08, Jonathan Cast [EMAIL PROTECTED] wrote: On 8 Feb 2008, at 5:29 PM, Philip Weaver wrote: GHC certain *could* do this, but it's arguably not the right thing to do. For performance, the operating system buffers writes until it is ready to write large chunks at a time. If you do not want this behavior, change the buffering mode from its default. To what? BlockBuffering is worse, not better, and the docs *explicitly* say that switching to NoBuffering will break ^D (if it wasn't broken already...) My specification for a working program is `one that works exactly like every other program on my machine'. I don't see how to produce such a program with GHC.(1) jcc (1) Using readline might work (although I'm kind of sceptical given what's preceded it), but I haven't gotten it to link thus far... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
