[Haskell-cafe] Win32 API
Hi guys. Last time I looked at the Win32 bindings, it covered a few basic file I/O things (e.g., special access modes, file permissions, etc.), registry editing, and that was about it. Yesterday I took another look, and was pleasently surprised to find that GDI is now covered. Suffice it to say, yesterday I wrote my very first ever program using the Win32 API directly. (Who'd have thought Haskell would be the place to do that?) This was complicated by a small glitch: Graphics.Win32.Window exposes SendMessage() but does not expose PostMessage(). Kind of an important difference there. Fortunately, it's not actually especially hard to fix this deficiency. (Basically few the source code for the module, copy and paste the line for SendMessage(), and edit it to say PostMessage(). The type signature just happens to be identical.) Is there a reason why this is missing to start with? What other functions are missing? (I didn't see PostQuitMessage() anywhere...) Still, 85 lines of code to make a working, native-looking Windows program isn't too shabby, really... (Not that any sane person writes nontrivial programs directly like this of course.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why the stack overflow?
Hi haskell-cafe,
Why does rlist 10 [] gives stack overflow in ghci?
rlist 0 l = return l
rlist n l = do {x - randomRIO (1,maxBound::Int); let nl = x:l in nl `seq`
rlist (n-1) nl}
I first uses replicateM then foldM and finally an explicit function. But
they give all stack overflow
I don't know why 10 is not absurd and it is tail recursive. Or is it
not, due to the monad structure?
greetings
Gerben
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Re: [Haskell-cafe] Why the stack overflow?
Am Samstag 19 September 2009 12:37:41 schrieb staafmeister:
Hi haskell-cafe,
Why does rlist 10 [] gives stack overflow in ghci?
rlist 0 l = return l
rlist n l = do {x - randomRIO (1,maxBound::Int); let nl = x:l in nl `seq`
rlist (n-1) nl}
I first uses replicateM then foldM and finally an explicit function. But
they give all stack overflow
I don't know why 10 is not absurd and it is tail recursive. Or is it
not, due to the monad structure?
Prelude System.Random :set -XBangPatterns
Prelude System.Random let rlist2 0 l = return l; rlist2 n l = do { !x -
randomRIO
(1,maxBound :: Int); let {nl = x:l}; nl `seq` rlist2 (n-1) nl }
Prelude System.Random rlist2 10 [] = \l - print (take 3 l) print (last l)
[800589677,541186119,1521221143]
1279766979
Prelude System.Random rlist2 1000 [] = \l - print (take 3 l) print (last
l)
[655069099,324945664,2137996923]
1108985638
Prelude System.Random rlist2 1 [] = \l - print (take 3 l) print
(last l)
[286279491,63955,2118785404]
315689721
Prelude System.Random rlist2 10 [] = \l - print (take 3 l) print
(last l)
[862262999,947331403,790576391]
1250271938
Prelude System.Random rlist2 100 [] = \l - print (take 3 l) print
(last l)
[681201080,627349875,484483111]
1048225698
Prelude System.Random rlist2 1000 [] = \l - print (take 3 l) print
(last l)
[1247387053,690485134,1924757191]
1637122415
The problem is that randomRIO doesn't evaluate its result, so you build a long
chain of
calls to randomR, which isn't evaluated until the count reaches 0, hence the
stack
overflow. Forcing x prevents the long chain from being built.
But better don't use randomRIO, make it a pure function with the PRNG as an
argument.
greetings
Gerben
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Re: [Haskell-cafe] Win32 API
On Sat, 2009-09-19 at 08:52 +0100, Andrew Coppin wrote: This was complicated by a small glitch: Graphics.Win32.Window exposes SendMessage() but does not expose PostMessage(). Kind of an important difference there. Fortunately, it's not actually especially hard to fix this deficiency. (Basically few the source code for the module, copy and paste the line for SendMessage(), and edit it to say PostMessage(). The type signature just happens to be identical.) Is there a reason why this is missing to start with? What other functions are missing? (I didn't see PostQuitMessage() anywhere...) I doubt there's any reason it was not bound except that it was not needed by the person who bound the related ones. Send in your patch. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggested additions to System.FilePath.Posix/Windows
On Thu, 2009-09-17 at 11:58 +0200, Marcus D. Gabriel wrote: -- | 'reduceFilePath' returns a pathname that is reduced to canonical -- form equivalent to that of ksh(1), that is, symbolic link names are -- treated literally when finding the directory name. See @cd -L@ of -- ksh(1). Specifically, extraneous separators @(\/\)@, dot -- @(\.\)@, and double-dot @(\..\)@ directories are removed. reduceFilePath :: FilePath - FilePath reduceFilePath = joinPath . filePathComponents So it's like the existing System.Directory.canonicalizePath but it's pure and it does not do anything with symlinks. On the other hand because it's pure it can do something with non-local paths. Is there anything POSIX-specific about this? I don't see it. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Hs-Generics] how to automatically create and install documentations of a package?
Hi Daneel, On Sat, Sep 19, 2009 at 13:58, Daneel Yaitskov wrote: Recently I've found wonderful thing cabal can install packages itself! It can even install those packages which need for final one. But I'm disturbed cabal doesn't create the documentation of a package by default. It manually makes runhaskell Setup haddock. Who knows? I believe you can do 'cabal haddock', but I don't know why it doesn't do it by default. BTW, the Haskell Café is typically more suitable for questions such as these. The Generics list is more specifically for generic programming discussions while the Haskell Café serves a broader audience. I've CC'd haskell-cafe@ to see if anybody there knows the answer to your question. Regards, Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Hs-Generics] how to automatically create and install documentations of a package?
On Sat, Sep 19, 2009 at 11:59 AM, Sean Leather leat...@cs.uu.nl wrote: Hi Daneel, On Sat, Sep 19, 2009 at 13:58, Daneel Yaitskov wrote: Recently I've found wonderful thing cabal can install packages itself! It can even install those packages which need for final one. But I'm disturbed cabal doesn't create the documentation of a package by default. It manually makes runhaskell Setup haddock. Who knows? I believe you can do 'cabal haddock', but I don't know why it doesn't do it by default. BTW, the Haskell Café is typically more suitable for questions such as these. The Generics list is more specifically for generic programming discussions while the Haskell Café serves a broader audience. I've CC'd haskell-cafe@ to see if anybody there knows the answer to your question. Regards, Sean If you use cabal-install (as you should!), you can have it build haddocks by customizing ~/.cabal/config and adding: documentation: True -- gwern ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Is it safe to use unsafePerformIO here?
Cristiano Paris wrote: Daniel Fischer wrote: I would separate the reading of headers and bodies, reopening the files whose body is needed, for some (maybe compelling) reason he wants to do it differently. Yes, that's the way Haskell forces you to do that as it's the only way for you to go safe. I don't think it has anything to do with Haskell. How would you do this in C? You'd pass a flag indicating whether to read the whole file or just the header. You can do the same in Haskell, of course, no lazy IO needed. The body remains undefined if the flag indicates header only. Even better wrap the body in a Maybe. But, if you know more about your code, you can use unsafe(Perform|Interleave)IO to assure the compiler that everything's right. I have a hard time believing this is possible, if you demand that the files should not stay opened indefinitely. How is the runtime supposed to know whether to close the file or not? What you /can/ do is use unsafePerformIO to lazily re-open, read the body, and close the file, as soon as the body gets demanded. However, this is ugly and not advised. Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 131 - September 19, 2009
Hopefully the line endings come out okay this week, I did a test before sending it to the list, please let me know if you notice anything awry. Just put a [HWN] in the subject line so my filter's will catch it. /metaeditorial --- Haskell Weekly News http://sequence.complete.org/hwn/20090918 Issue 131 - September 18, 2009 --- Welcome to issue 131 of HWN, a newsletter covering developments in the [1]Haskell community. Last week, I received an email from Mark Wotton about his project [2]Hubris. I totally forgot to put it in the HWN last week, too busy trying to figure out all the tools. So, I thought I'd make it up and give him some special editorial status this week. Hubris is a bridge between Ruby and Haskell, allowing you to call Haskell from Ruby. It's very cool, I highly suggest playing with it. Also, I've been posting a bit about the new HWN tools (dubbed HWN2) on my [3]blog, there is also a repo up at [4]patch-tag which will have all the code. If there is some interest in helping me, I'll try to come up with a TODO list/Trac. Announcements hssqlppp, sql parser and type checker, pre-alpha. Jake Wheat [5]announced his parser/type checker for SQL. It currently parses a subset of PostGreSQL and PL/pgSQL, and can type check some statements. LambdaINet-0.1.0, Graphical Interaction Net Evaluator for Optimal Evaluation. Paul L [6]announced a LambdaINet 0.1.0, available on [7]Hackage. LambdaINet implements an interaction net based optimal evaluator. With an interactive graphical interface allowing the user to view and directly manipulate the interaction net. arbtt-0.1. Joachim Breitner [8]announced the Automatic Rule-Based Time Tracking tool on hackage. he has an introduction available [9]here. A statistics library. Bryan O'Sullivan [10]announced the imaginatively named [11]statistics library. Which supports common discrete and continuous probability distributions, Kernel density estimation, Auto-correlation analysis, Functions over sample data, Quantile estimation, and Re-sampling techniques. CFP: JSC Special Issue on Automated Verification and Specification of Web Systems. [12]A Special Issue of the Journal of symbolic computation was announced. This issue is related to the topics of the Automated Specification and Verification of Web Systems Workshop (WWV'09). Read the announcement for more details. Haskeline 0.6.2. Judah Jacobson [13]announced the release of Haskeline 0.6.2, available [14]here. Improvements over the last version include, new emacs and vi bindings, a new preference to remove repeated history entries, recognition of page-up and page-down keys, and more. PEPM'10 - Last CFP (Submission: 6 Oct 09, Notification: 29 Oct 09). Janis Voigtlaender [15]announced the Last Call for Papers for PEPM'10, see the announcement for more details. Videos of HIW 2009. Malcolm Wallace [16]announced videos of all the presentations/discussions at the recent Haskell Implementers Workshop 2009, in Edinburgh, are now [17]online. The program of talks is available [18]here. Unification in a Commutative Monoid (cmu 1.1) and a new release of Abelian group unification and matching (agum 2.2). John D. Ramsdell [19]announced cmu 1.1, which provides unification in a commutative monoid, also know as ACU-unification. The core computation finds the minimal non-zero solutions to homogeneous linear Diophantine equations. The linear equation solver has been place in a separate module so it can be used for other applications. He also announced agum 2.2, which provides unification and matching in an Abelian group, also know as AG-unification and matching. graphviz-2999.5.1.0. Ivan Lazar Miljenovic [20]announced a bug-fix release of the GraphViz package, no major API changes occurred. levmar-0.2, bindings-levmar-0.1.1. Bas van Dijk and Roel van Dijk announced [21]new [22]versions of the levmar and bindings-levmar packages. New features include automatic calculation of the Jacobian via Conal Elliot's automatic differentiation from his vector-space library. CmdArgs - easy command line argument processing. Neil Mitchell [23]announced CmdArgs 0.1. CmdArgs is a library for parsing command-line arguments. It offers several improvements over GetOpts, namely that the Command Line Argument Processors are shorter and CmdArgs can support multiple-mode command lines such as those found in darcs, cabal, hpc, etc. OpenGL 2.4.0.1. Sven Panne [24]announced a new version of the OpenGL package, this version fixes a bug that didn't make it into the previous release. OpenGLRaw 1.1.0.0. Sven Panne [25]announced a new version of the
Re: [Haskell-cafe] Why the stack overflow?
On Sat, Sep 19, 2009 at 6:54 AM, Daniel Fischer
daniel.is.fisc...@web.de wrote:
Am Samstag 19 September 2009 12:37:41 schrieb staafmeister:
Hi haskell-cafe,
Why does rlist 10 [] gives stack overflow in ghci?
rlist 0 l = return l
rlist n l = do {x - randomRIO (1,maxBound::Int); let nl = x:l in nl `seq`
rlist (n-1) nl}
I first uses replicateM then foldM and finally an explicit function. But
they give all stack overflow
I don't know why 10 is not absurd and it is tail recursive. Or is it
not, due to the monad structure?
Prelude System.Random :set -XBangPatterns
Prelude System.Random let rlist2 0 l = return l; rlist2 n l = do { !x -
randomRIO
(1,maxBound :: Int); let {nl = x:l}; nl `seq` rlist2 (n-1) nl }
Prelude System.Random rlist2 10 [] = \l - print (take 3 l) print (last
l)
[800589677,541186119,1521221143]
1279766979
Prelude System.Random rlist2 1000 [] = \l - print (take 3 l) print
(last l)
[655069099,324945664,2137996923]
1108985638
Prelude System.Random rlist2 1 [] = \l - print (take 3 l) print
(last l)
[286279491,63955,2118785404]
315689721
Prelude System.Random rlist2 10 [] = \l - print (take 3 l) print
(last l)
[862262999,947331403,790576391]
1250271938
Prelude System.Random rlist2 100 [] = \l - print (take 3 l) print
(last l)
[681201080,627349875,484483111]
1048225698
Prelude System.Random rlist2 1000 [] = \l - print (take 3 l) print
(last l)
[1247387053,690485134,1924757191]
1637122415
The problem is that randomRIO doesn't evaluate its result, so you build a
long chain of
calls to randomR, which isn't evaluated until the count reaches 0, hence the
stack
overflow. Forcing x prevents the long chain from being built.
Incidentally, nl is already in head normal form so seq nl does
nothing. Leading to:
rlist 0 l = return l
rlist n l = do !x - randomRIO (1, maxBound :: Int); rlist (n-1) (x:l)
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Re: [Haskell-cafe] Suggested additions to System.FilePath.Posix/Windows
On Sep 19, 2009, at 07:45 , Duncan Coutts wrote: On Thu, 2009-09-17 at 11:58 +0200, Marcus D. Gabriel wrote: -- | 'reduceFilePath' returns a pathname that is reduced to canonical -- form equivalent to that of ksh(1), that is, symbolic link names are -- treated literally when finding the directory name. See @cd -L@ of -- ksh(1). Specifically, extraneous separators @(\/\)@, dot -- @(\.\)@, and double-dot @(\..\)@ directories are removed. So it's like the existing System.Directory.canonicalizePath but it's pure and it does not do anything with symlinks. On the other hand because it's pure it can do something with non-local paths. Is there anything POSIX-specific about this? I don't see it. It's making assumptions about the safety of eliding ... (What does \ \machine\share\..\ do?) On the other hand that's also unsafe on POSIX in the presence of symlinks. In general I consider path cleanup not involving validation against the filesystem to be risky. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ambiguous type variable with subclass instance (also: is there a better way to do this?)
On 17 Sep 2009, at 18:01, Ryan Ingram wrote: Here's a way that works more closely to your original version: instance Enumerated a = Target a where convert n | n = 0 n numConstrs = Just (constrs !! n) | otherwise = Nothing where constrs = constructors numConstrs = length constrs Aha - that's great, and it works without OverlappingInstances (but still with FlexibleInstances and UndecidableInstances - should that worry me?) Just making sure constructors is only referenced once is the key, it seems. Thanks! -Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ambiguous type variable with subclass instance (also: is there a better way to do this?)
Am Samstag 19 September 2009 20:55:10 schrieb Andy Gimblett: On 17 Sep 2009, at 18:01, Ryan Ingram wrote: Here's a way that works more closely to your original version: instance Enumerated a = Target a where convert n | n = 0 n numConstrs = Just (constrs !! n) | otherwise = Nothing where constrs = constructors numConstrs = length constrs Aha - that's great, and it works without OverlappingInstances (but still with FlexibleInstances and UndecidableInstances - should that worry me?) FlexibleInstances need not worry anybody. They just remove a fairly arbitrary restriction of Haskell98 for instance declarations. UndecidableInstances can be dangerous, but there are perfectly safe things which reauire UndecidableInstances, too. Just making sure constructors is only referenced once is the key, it seems. Just making sure that every time it is referenced, it is referenced at the correct type. Thanks! -Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Suggested additions to System.FilePath.Posix/Windows
Brandon S. Allbery KF8NH wrote: On Sep 19, 2009, at 07:45 , Duncan Coutts wrote: On Thu, 2009-09-17 at 11:58 +0200, Marcus D. Gabriel wrote: -- | 'reduceFilePath' returns a pathname that is reduced to canonical -- form equivalent to that of ksh(1), that is, symbolic link names are -- treated literally when finding the directory name. See @cd -L@ of -- ksh(1). Specifically, extraneous separators @(\/\)@, dot -- @(\.\)@, and double-dot @(\..\)@ directories are removed. So it's like the existing System.Directory.canonicalizePath but it's pure and it does not do anything with symlinks. On the other hand because it's pure it can do something with non-local paths. Is there anything POSIX-specific about this? I don't see it. It's making assumptions about the safety of eliding ... (What does \\machine\share\..\ do?) On the other hand that's also unsafe on POSIX in the presence of symlinks. In general I consider path cleanup not involving validation against the filesystem to be risky. I agree; this came up before during the design of System.FilePath, and it's why the current library doesn't have a way to remove ... The docs should probably explain this point, because it's non-obvious that you can't just clean up a path to remove the .. and end up with something that means the same thing. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ambiguous type variable with subclass instance (also: is there a better way to do this?)
A few issues, you can remove the overlapping instances by using a newtype
wrapper to disambiguate which instance you want.
A little alarm bell goes off in my head whenever I read 'instance Foo a'.
newtype Wrapped a = Wrapped a
instance Target Foo where ...
instance Enumerated a = Target (Wrapped a) where ...
is probably a better idea over all.
As for the use of constructors. your problem is that it is ambiguous which
constructors you want to take the list of.
Try replacing constructors with a local variable. The choice of constructors
then will be fixed by the use of the argument from the Just branch and the
monomorphism restriction constraining you so that the list you take the
length of has the same type.
instance (Enumerated a) = Target a where
convert n | n `elem` [0..len-1] = Just $ cons !! n
| otherwise = Nothing
where
len = length cons
cons = constructors
You could also do it with some sort of
asListOf :: [a] - a - [a]
asListOf = const
convert n = result where
...
len = length cons
...
cons = constructors `asListOf` result
if relying on the MR makes you feel dirty.
-Edward
On Thu, Sep 17, 2009 at 9:40 AM, Andy Gimblett hask...@gimbo.org.uk wrote:
Hi all. This email is in literate Haskell; you should be able to load
it into ghci and verify what I'm saying (nb: it won't compile without
alteration: see below).
I'm trying to do something which may anyway be stupid / not the best
approach to what I'm trying to achieve; however, it's not working and
I can't see why not. So I'm asking for help on two fronts:
1) Why is this failing?
2) Maybe more usefully, how should I actually be doing this? It seems
an ugly approach; a voice in my head is saying scrap your
boilerplate, but I've no idea yet if that's actually applicable
here; should I look at it?
On with the show...
I need these for subclass stuff later on...
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverlappingInstances #-}
{-# LANGUAGE UndecidableInstances #-}
module Ambig where
I wish to define a number of algebraic data types with the ability to
turn Int values into instances of those types. So I define a
typeclass saying this is possible. I use Maybe so I can encode the
existence of out-of-range Int values, which will vary from target type
to target type.
class Target a where
convert :: Int - Maybe a
E.g. here's a type Foo which only wants values between 1 and 10:
data Foo = Foo Int deriving (Show)
instance Target Foo where
convert n | n `elem` [1..10] = Just $ Foo n
| otherwise = Nothing
(That's a simple example; some are rather more complex. How to do
this isn't what I'm asking about, really.)
So we have, for example:
*Ambig (convert 1) :: Maybe Foo
Just (Foo 1)
*Ambig (convert 11) :: Maybe Foo
Nothing
Now, some of those algebraic data type types happen to be
enumerations; in this case, my idea is to list the constructors, with
the rule that each constructor's position in the list is the Int which
gets converted into that constructor.
class Enumerated a where
constructors :: [a]
E.g. here's a type Bar with three constructors:
data Bar = X | Y | Z deriving (Show)
instance Enumerated Bar where
constructors = [X, Y, Z]
(This is certainly ugly. Any suggestions?)
Now we get to the crux. If a type is an instance of Enumerated, it
should also be a Target, because we should be able to convert from Int
just by list lookup. But we include a bounds check, naturally...
instance (Enumerated a) = Target a where
convert n | n `elem` [0..len-1] = Just $ constructors !! n
| otherwise = Nothing
where len = length constructors
So I would _hope_ that then, e.g., we'd have:
*Ambig (convert 0) :: Maybe Bar
Just X
*Ambig (convert 1) :: Maybe Bar
Just Y
*Ambig (convert 3) :: Maybe Bar
Nothing
Sadly, this function doesn't compile, dying with an Ambiguous type
variable error:
Ambig.lhs:75:29:
Ambiguous type variable `a' in the constraint:
`Enumerated a'
arising from a use of `constructors' at Ambig.lhs:74:29-40
Probable fix: add a type signature that fixes these type variable(s)
If we replace length constructors with 3 (say), it compiles (but
is useless). Adding a type signature doesn't help: it's misplaced
in that context. If I break it out of the instance declaration so I
can add one, I still get the same problem:
convert' :: (Enumerated a, Target a) = Int - Maybe a
convert' n | n `elem` [0..len-1] = Just $ constructors !! n
| otherwise = Nothing
where len = length constructors
I guess I see roughly what's going on; the question is which
constructors instance is meant?, right? In the Just part it's OK,
because it can be inferred from the function's return type (right?).
But in the guard we don't have that help, so it could be any
Enumerated
Re: [Haskell-cafe] Re: [Hs-Generics] how to automatically create and install documentations of a package?
Gwern Branwen wrote: If you use cabal-install (as you should!), you can have it build haddocks by customizing ~/.cabal/config and adding: documentation: True Is there a way to make it automatically update a single contents page with links to the documentation of all installed packages? I have been doing this manually every time I cabal-install something, by running a little shell script which looks through all the packages directories for html directories and .haddock files and compiles them all into a call to haddock --gen-contents. Mike ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
