Re: [Haskell-cafe] Re: I/O interface
Marcin 'Qrczak' Kowalczyk wrote: Ben Rudiak-Gould [EMAIL PROTECTED] writes: is there *any* way to get, without an exploitable race condition, two filehandles to the same file which don't share a file pointer? In unix the traditional way to do this is to use a directory. Each process/thread opens its own file... and you have some kind of master index/ordering file to keep track of which file is doing what (for example Highly parallel mail software). At the end of the day IO is serial by nature (to one device anyway), so the way to do this into one file is to have one thread that reads and writes, and to 'send' read and write requests over channels from the threads that need the work done... Effectively the channels serialise the requests. This has the added advantage that is guarantees the transactional itegrity of the IO (for example database software) Keean. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: I/O interface
Keean Schupke [EMAIL PROTECTED] writes: At the end of the day IO is serial by nature (to one device anyway), so the way to do this into one file is to have one thread that reads and writes, and to 'send' read and write requests over channels from the threads that need the work done Would the stream proposal make this possible and easy? I.e. could the IO thread provide (say) output streams to the other threads, and pass writes on to its own output stream? -kzm -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: I/O interface
No I meant Channels (from Data.Concurrent)... you can use a structure like: data Command = Read FileAddr (MVar MyData) | Write FileAddr MyData So to write you just do: writeChan iochan (Write address data) -- returns immediately -- write happens asynchronously later and to read: data - newEmptyMVar writeChan iochan (Read address data) -- read not happend yet. myData - readMVar data -- blocks until read completes. The forked thread (with forkIO) just reads the commands form the iochan and processes them one at a time. Keean Ketil Malde wrote: Keean Schupke [EMAIL PROTECTED] writes: At the end of the day IO is serial by nature (to one device anyway), so the way to do this into one file is to have one thread that reads and writes, and to 'send' read and write requests over channels from the threads that need the work done Would the stream proposal make this possible and easy? I.e. could the IO thread provide (say) output streams to the other threads, and pass writes on to its own output stream? -kzm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
package readline unknown symbol problem on GHCi 6.2.2 Windows binary (Was: [Haskell-cafe] Problem with wxHaskell
On Wed, 12 Jan 2005 12:03:44 -0800, John Velman [EMAIL PROTECTED] wrote: Your code works fine on Linux. :-) Oh, by the way, I compiled my wxHaskell with GHC 6.2.2 On Wed, Jan 12, 2005 at 04:16:33PM +0100, Dmitri Pissarenko wrote: I've downloaded wxHaskell, ran the wxhaskell-register.bat file and now try to build a minimal wxHaskell program. For this purpose, I tried to start GHCi using following command ghci -package wx GuiTest.hs Hmm. I think this problem is specially on Windows binary by using GHCi. If you use GHC, programm may be compiled without following error message. GHCi crashed with following error messages: error-messages GHC Interactive, version 6.2.2, for Haskell 98. http://www.haskell.org/ghc/ Type :? for help. Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. Loading package lang ... linking ... done. Loading package concurrent ... linking ... done. Loading package QuickCheck ... linking ... done. Loading package readline ... linking ... C:/ghc/ghc-6.2.2/HSreadline.o: unknown symbol `_rl_redisplay_function' ghc.exe: unable to load package `readline' /error-messages I saw this error message in other programs what GHCi on Windows call readline package automaticly. ex. HaXml program. (So I don't want to use HaXml program on windows.) This is GHCi bug. -- shelarcy shelarcy capella.freemail.ne.jp http://page.freett.com/shelarcy/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: I/O interface
Ketil Malde wrote: Keean Schupke [EMAIL PROTECTED] writes: No I meant Channels (from Data.Concurrent)... you can use a structure like: Yes, I realize that (although I haven't yet used Data.Concurrent). It seemed to me, though, that streams are related to channels, and that it may be possible to use the same (or a slightly more generalized) abstraction? (I should perhasp experiment a bit with concurrent programming and streams, and it'll surely become apparent how and why I'm mistaken :-) -kzm I don't necessarily think you are mistaken, but why re-invent the wheel when channels are almost ideal for the job (inter-thread FIFO's)... At the end of the day streams between processes are channels... in effect (non seekable) streams are extending channels to IO. Keean. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Signature of a function
Hi folks The main thing I like about type signatures is that they help the computer write the boring bits of my programs for me. I've said it before and I'll say it again, no doubt: when we talk about 'type inference', we should distinguish two aspects: (1) the machine doesn't know your plan and tries to guess it (let-rule style, ie finding the abstraction) (2) the machine does know your plan and is fleshing out the details (var-rule style, ie finding the instantiation) You can only make (1) fully automatic at the cost of compulsory ignorance, dumbing down the collection of possible plans to those which are guessable by a machine. I find this unpleasantly restrictive. I at least want a manual override, which Haskell pretty much provides. But as types get more expressive, it's often the case that you can give your programs much more useful types than the machine is ever going to guess. Possibly even a type which explains what a function's output has to do with its input. You can make (2) very powerful indeed. Even in the conventional batch mode of edit-then-compile, you can use overloading to shift the burden of programming from a large amount of tedious plumbing in the program text to a smaller class constraint in the signature. I often find myself using newtypes to explain which structure of my data I want to exploit, then leaving instance inference to exploit it in the 'obvious' way. There are better reasons to write type signatures than that the compiler is too dumb or that the nuns will whip us if we don't. Type signatures enable chunks of program inference, which is much more useful than aspect (1) of type inference. Types can be seen as a highly expressive and compact language of design statements for both humans and machines to read: this design statement determines the space of essential choices for the programmer, and programming can, if we choose, consist of navigating that space. Machines can map that space out for us, and they can fill in all the no-choice bits and pieces once we decide which way to go. I'm not advocating compulsory refinement editing. I'm saying that type signatures currently feel ephemeral only because today's program-construction tools fail to take positive advantage of the fact that machines can manipulate programs in a typed way. Cheers Conor -- http://www.cs.nott.ac.uk/~ctm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: I/O interface
Ketil Malde [EMAIL PROTECTED] writes: It seemed to me, though, that streams are related to channels, I'm not sure what exactly do you mean by streams (because they are only being designed), but differences are: - A stream is either an input stream or an output stream, while a single channel supports reading from one end and writing to the other end. - A stream passes around bytes, which are usually grouped in blocks for efficiency. A channel is polymorphic wrt. the element type and elements are always processed one by one. - A stream may be backed by an OS file, pipe, socket etc., while a channel exists purely in Haskell. - A channel is never closed. Reading more data than have been put blocks until someone puts more data. A stream can reach its end, which is a condition a reader can detect. A stream backed by a pipe is similar to a channel of bytes in that the reader blocks until someone puts more data, but it can be closed too, which causes the reader to observe end of file. A writer to a stream can block too when the internal buffer in the kernel is full. - A stream can be inherited by child processes, and it generally continues to work by being linked to the same data sink or source as before. A channel is inherited as a whole: there is no communication between the two versions of the channel in the two processes. -- __( Marcin Kowalczyk \__/ [EMAIL PROTECTED] ^^ http://qrnik.knm.org.pl/~qrczak/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Signature of a function
Conor McBride wrote: Types can be seen as a highly expressive and compact language of design statements for both humans and machines to read: this design statement determines the space of essential choices for the programmer, and programming can, if we choose, consist of navigating that space. Machines can map that space out for us, and they can fill in all the no-choice bits and pieces once we decide which way to go. For me this is the most important aspect. As programs become more complex, and as optimisation techniques are applied (or algorithms changed), Types can act as 'contracts'. Infact I would like to see type expressiveness expanded... Imagine for examle (and this can be done in Haskell with the HList library) adding a static constraint requiring proof at compile time that a list was ordered (according to some criteria: mysort :: (HList a, HOrderedList b) = a - b Now the definition of the constraint for orderedness is quite simple, and easy to understand (as as it plays no part in the final program efficiency is not an issue) - we are now free to write a heap sort or whatever, knowing it will only compile if it obeys the constraint. Obviously the above only works when the input list is statically determined at compile time... We can easily insert run-time checks in code - but it would be much better to have the compiler proove that the code obeys the criteria under all circumstances. In other words rather than saying for a specific list the result should be ordered, it should be ordered forall a. Keean. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: I/O interface
Marcin 'Qrczak' Kowalczyk [EMAIL PROTECTED] writes: Ketil Malde [EMAIL PROTECTED] writes: It seemed to me, though, that streams are related to channels, I'm not sure what exactly do you mean by streams (because they are only being designed), but differences are: Sorry for being unclear, I was thinking in relation to the new-io proposal Simon M. recently posted on the lists (I put all Haskell mail in the same folder, it could have been a ghc list or haskell@). - A stream passes around bytes, which are usually grouped in blocks for efficiency. A channel is polymorphic wrt. the element type and elements are always processed one by one. Perhaps I'm confused, but while Stream.StreamInputStream is a stream of Word8, Text.TextInputStream provides a stream of Chars. Thanks for the explanation! -kzm -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with wxHaskell
Hello! Thanks for your answer! I solved the problem by using GHC 6.2.1 instead of GHC 6.2.2 (under Windows). Best regards Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with wxHaskell
Is someone aware of how to make it work with 6.2.2? Thanks, Michael On Thu, 13 Jan 2005 18:09:20 +0100, Dmitri Pissarenko [EMAIL PROTECTED] wrote: Hello! Thanks for your answer! I solved the problem by using GHC 6.2.1 instead of GHC 6.2.2 (under Windows). Best regards Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com ___ 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
[Haskell-cafe] Parsec and type (IO t) error
This is probably an easy question, but I'm having a problem with parsec in the IO monad. The essential parts of my program looks like this... import Text.ParserCombinators.Parsec main = do input - getContents putStr $ show $ parse_text shape_parse input --(cam, sh) - parse_text shape_parse input --putStr $ (show cam) ++ \n ++ (show sh) putStr \n parse_text p input = case (parse p input) of Left err - error $ Invalid input++(show err) Right x - x shape_parse = do cam - camera_parse shapes - many1 (sphere_parse | plane_parse) return (cam, shapes) -- blah, blah, blah, etc. This works fine in GHC. The types for parse_text and shape_parse are... *Main :t parse_text parse_text :: forall a tok. GenParser tok () a - [tok] - a *Main :t shape_parse shape_parse :: forall st. GenParser Char st (Camera, [Shape]) *Main Now when I change main to... main = do input - getContents --putStr $ show $ parse_text shape_parse input (cam, sh) - parse_text shape_parse input putStr $ (show cam) ++ \n ++ (show sh) putStr \n I get the following message from GHCi... p2.hs:38: Couldn't match `IO t' against `(Camera, [Shape])' Expected type: GenParser Char () (IO t) Inferred type: GenParser Char () (Camera, [Shape]) In the first argument of `parse_text', namely `shape_parse' In a 'do' expression: (cam, sh) - parse_text shape_parse input I'm probably missing something silly. Any hint would be appreciated. Thanks, Greg Buchholz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsec and type (IO t) error
Mike Gunter wrote: I'd guess that let (cam, sh) = parse_text shape_parse input is what you want? (Completely untested ...) Yep. That did it. Thanks, Greg Buchholz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Question about instance
Instance with a context doesn't seem to work as I expect.
Here's the story:
I define an data type, Relation, and I want to make it an instance of
Show, partly so I can debug and tinker with things interactively and have
ghci print something.
Here is my first try:
import Data.Set
type EN = String -- element name
type RN = String -- relation name
instance Show a = Show (Set a) where
show s = mkSet ++ show (setToList s)
data Relation = Relation {name::RN, arity::Int, members::(Set [EN])}
instance (Show a, Show i, Show b) = Show (Relation a i b)
where
show (Relation a i b) =
a ++ / ++ (show i) ++
++ (show b)
When I try to load this into ghci, I get:
---GHCI:
*Main :l test.hs
Compiling Main ( test.hs, interpreted )
test.hs:14:
Kind error: `Relation' is applied to too many type arguments
When checking kinds in `Relation a i b'
When checking kinds in `Show (Relation a i b)'
In the instance declaration for `Show (Relation a i b)'
Failed, modules loaded: none.
Prelude
---END GHCI
But, when I define showRelation separately, then leave the context out of
the instance declaration with show = showRelation it works:
---(Everything down to the instance declaration is the same)
instance Show Relation
where
show = showRelation
showRelation:: Relation - String
showRelation (Relation a i b) =
a ++ / ++ (show i) ++
++ (show b)
---
Now I get:
--- GHCI output:
Prelude :l test.hs
Compiling Main ( test.hs, interpreted )
Ok, modules loaded: Main.
*Main mkRelation1 test 2 [[one,two], [three,four]]
test/2 mkSet [[one,two],[three,four]]
*Main
-- End GHCI
Why does the original instance declaration result in failure and the
message Kind error: `Relation' is applied to too many type arguments (I
confess to not understanding 'kinds' too well.)
I've done a bit of tinkering with the original version, and have tried the
second version with a context in the instance declaration, but none of my
attmepts work. The only one that worked was the one shown, with no context
in the instance declaration. Needless to say (?), I've tried to
understand this from reading in the Haskell 98 report, `Haskell school of
Expression', and any place else I can think of, but I'm missing the point
somewhere.
Thanks,
John Velman
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Re: package readline unknown symbol problem on GHCi 6.2.2 Windows binary (Was: [Haskell-cafe] Problem with wxHaskell
You can remove that error message by including following in package.conf
file.
Package
{name = readline,
auto = True,
import_dirs = [$libdir/imports],
source_dirs = [],
library_dirs = [$libdir],
hs_libraries = [HSreadline],
extra_libraries = [readline, advapi32],
include_dirs = [],
c_includes = [HsReadline.h],
package_deps = [base],
extra_ghc_opts = [],
extra_cc_opts = [],
extra_ld_opts = [],
framework_dirs = [],
extra_frameworks = []},
Jinwoo Lee
Always remember that you are unique. Just like everyone else.
[EMAIL PROTECTED]
shelarcy wrote:
On Wed, 12 Jan 2005 12:03:44 -0800, John Velman [EMAIL PROTECTED] wrote:
Your code works fine on Linux. :-)
Oh, by the way, I compiled my wxHaskell with GHC 6.2.2
On Wed, Jan 12, 2005 at 04:16:33PM +0100, Dmitri Pissarenko wrote:
I've downloaded wxHaskell, ran the wxhaskell-register.bat file and
now try to build a minimal wxHaskell program.
For this purpose, I tried to start GHCi using following command
ghci -package wx GuiTest.hs
Hmm. I think this problem is specially on Windows binary by using GHCi.
If you use GHC, programm may be compiled without following error message.
GHCi crashed with following error messages:
error-messages
GHC Interactive, version 6.2.2, for Haskell 98.
http://www.haskell.org/ghc/
Type :? for help.
Loading package base ... linking ... done.
Loading package haskell98 ... linking ... done.
Loading package lang ... linking ... done.
Loading package concurrent ... linking ... done.
Loading package QuickCheck ... linking ... done.
Loading package readline ... linking ...
C:/ghc/ghc-6.2.2/HSreadline.o: unknown symbol `_rl_redisplay_function'
ghc.exe: unable to load package `readline'
/error-messages
I saw this error message in other programs what GHCi on Windows call
readline
package automaticly. ex. HaXml program. (So I don't want to use HaXml
program
on windows.)
This is GHCi bug.
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Re: [Haskell-cafe] Problem with wxHaskell
You can remove that error message by including following in package.conf
file.
Package
{name = readline,
auto = True,
import_dirs = [$libdir/imports],
source_dirs = [],
library_dirs = [$libdir],
hs_libraries = [HSreadline],
extra_libraries = [readline, advapi32],
include_dirs = [],
c_includes = [HsReadline.h],
package_deps = [base],
extra_ghc_opts = [],
extra_cc_opts = [],
extra_ld_opts = [],
framework_dirs = [],
extra_frameworks = []},
Jinwoo Lee
Always remember that you are unique. Just like everyone else.
[EMAIL PROTECTED]
Michael Walter wrote:
Is someone aware of how to make it work with 6.2.2?
Thanks,
Michael
On Thu, 13 Jan 2005 18:09:20 +0100, Dmitri Pissarenko
[EMAIL PROTECTED] wrote:
Hello!
Thanks for your answer!
I solved the problem by using GHC 6.2.1 instead of GHC 6.2.2 (under Windows).
Best regards
Dmitri Pissarenko
--
Dmitri Pissarenko
Software Engineer
http://dapissarenko.com
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Re: [Haskell-cafe] Question about instance
Thanks, Andreas. Your example still left me without context in the show
statement itself, but your message set me to look in the right place.
Now I have
--- Code
data Relation a i b = Rel {name::RN, arity::Int, members::(Set [EN])}
instance (Show a, Show i, Show b) = Show (Relation a i b)
where
show (Rel a i b) =
a ++ / ++ (show i) ++
++ (show b)
---
with result:
---GHCI
Prelude :l test.hs
Compiling Main ( test.hs, interpreted )
Ok, modules loaded: Main.
*Main mkRelation1 test 2 [[one,two], [three,four]]
test/2 mkSet [[one,two],[three,four]]
*Main
---End GHCI
It's hard to find examples like this, and the fact that it is fairly
standard practice for the type name and constructor names to be the same
in, for example, Gentle Haskell, and Haskell School of Expression make it
more difficult for the novice to see when each is used!
Best,
John Velman
On Fri, Jan 14, 2005 at 01:49:57AM +0100, Andreas Marth wrote:
If you replace
data Relation = Relation {name::RN, arity::Int, members::(Set [EN])}
with
data Relation = Rel {name::RN, arity::Int, members::(Set [EN])}
you will easy find out what is wrong and come to:
import Data.Set
type EN = String -- element name
type RN = String -- relation name
instance Show a = Show (Set a) where
show s = mkSet ++ show (setToList s)
data Relation = Rel {name::RN, arity::Int, members::(Set [EN])}
instance Show (Relation)
where
show (Rel a i b) = a ++ / ++ (show i) ++ ++ (show b)
Of course you can now change Rel back to Relation. But because of the
problems you just experienced I don't like it to name a type and its
constructor the same.
Happy coding,
Andreas
- Original Message -
From: John Velman [EMAIL PROTECTED]
To: haskell-cafe@haskell.org
Sent: Friday, January 14, 2005 1:29 AM
Subject: [Haskell-cafe] Question about instance
Instance with a context doesn't seem to work as I expect.
Here's the story:
I define an data type, Relation, and I want to make it an instance of
Show, partly so I can debug and tinker with things interactively and
have
ghci print something.
Here is my first try:
import Data.Set
type EN = String -- element name
type RN = String -- relation name
instance Show a = Show (Set a) where
show s = mkSet ++ show (setToList s)
data Relation = Relation {name::RN, arity::Int, members::(Set [EN])}
instance (Show a, Show i, Show b) = Show (Relation a i b)
where
show (Relation a i b) =
a ++ / ++ (show i) ++
++ (show b)
When I try to load this into ghci, I get:
---GHCI:
*Main :l test.hs
Compiling Main ( test.hs, interpreted )
test.hs:14:
Kind error: `Relation' is applied to too many type arguments
When checking kinds in `Relation a i b'
When checking kinds in `Show (Relation a i b)'
In the instance declaration for `Show (Relation a i b)'
Failed, modules loaded: none.
Prelude
---END GHCI
But, when I define showRelation separately, then leave the context out of
the instance declaration with show = showRelation it works:
---(Everything down to the instance declaration is the same)
instance Show Relation
where
show = showRelation
showRelation:: Relation - String
showRelation (Relation a i b) =
a ++ / ++ (show i) ++
++ (show b)
---
Now I get:
--- GHCI output:
Prelude :l test.hs
Compiling Main ( test.hs, interpreted )
Ok, modules loaded: Main.
*Main mkRelation1 test 2 [[one,two], [three,four]]
test/2 mkSet [[one,two],[three,four]]
*Main
-- End GHCI
Why does the original instance declaration result in failure and the
message Kind error: `Relation' is applied to too many type arguments (I
confess to not understanding 'kinds' too well.)
I've done a bit of tinkering with the original version, and have tried the
second version with a context in the instance declaration, but none of my
attmepts work. The only one that worked was the one shown, with no
context
in the instance declaration. Needless to say (?), I've tried to
understand this from reading in the Haskell 98 report, `Haskell school of
Expression', and any place else I can think of, but I'm missing the point
somewhere.
Thanks,
John Velman
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