[Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. -- Colin Adams Preston Lancashire ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
On Sun, Jun 21, 2009 at 11:12 PM, Colin Paul Adamsco...@colina.demon.co.uk wrote: I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. Use System.Directory.doesDirectoryExist/doesFileExist. -Judah ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
Colin Paul Adams wrote: I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. The first example in this chapter of Real World Haskell uses the doesDirectoryExist function : http://book.realworldhaskell.org/read/io-case-study-a-library-for-searching-the-filesystem.html HTH, Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
Hello Colin, Monday, June 22, 2009, 10:12:57 AM, you wrote: I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. isdir - withFileStatus isdir? filename isDirectory module System.Directory withFileStatus :: String - FilePath - (Ptr CStat - IO a) - IO a isDirectory :: Ptr CStat - IO Bool -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
Judah == Judah Jacobson judah.jacob...@gmail.com writes: Judah On Sun, Jun 21, 2009 at 11:12 PM, Colin Paul Judah Adamsco...@colina.demon.co.uk wrote: I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. Judah Use System.Directory.doesDirectoryExist/doesFileExist. Thanks. it seems it's time i went to the optician again. -- Colin Adams Preston Lancashire ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cross platform getProcessID
The short anser is...you need to make a ffi call to getCurrentProcessId unfortunately there is no binding to this function in System.Win32.Process which is the natural home for it. Perhaps you could submit a patch for Win32 package, once you have created the binding the signature for the function is quite simple, so there should be no problem with the ffi call DWORD GetCurrentProcessId(VOID) - Original Message - From: John Van Enk vane...@gmail.com To: Haskell Cafe haskell-cafe@haskell.org Sent: Monday, June 22, 2009 1:43 PM Subject: [Haskell-cafe] Cross platform getProcessID In the unix package, we have getProcessID. Is there a corresponding method for finding the process ID in Windows? /jve ___ 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
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
2009/6/22 Colin Paul Adams co...@colina.demon.co.uk: Judah == Judah Jacobson judah.jacob...@gmail.com writes: Judah On Sun, Jun 21, 2009 at 11:12 PM, Colin Paul Judah Adamsco...@colina.demon.co.uk wrote: I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. Judah Use System.Directory.doesDirectoryExist/doesFileExist. Thanks. it seems it's time i went to the optician again. I'm not surprised that anyone would make the mistake. I think that the two functions should be named isDirectory and isFile, but it seems that isDirectory was already taken by another function in System.Directory, which is quite unfortunate. does goes against the intuition one gets from pretty much everything else in Haskell, where is seems to be the convention. In fact, Hoogle only knows about three functions which start with does. -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestion for Network.Socket in regards to PortNumber
On Mon, Jun 22, 2009 at 1:22 AM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: I'm in favor of the entire Network library being reworked with an improved API that is higher level and type-safe instead of a direct translation/FFI of Berkeley sockets. I also would like the Network package to export Data instances for headers while taking advantage of pretty, prettyclass, and parsec. I started such work with network-data but never really got off the ground with it. I've given this some thought. There are a few different things that would be nice to have in a new API: * Use a binary type (e.g. ByteString) instead of Strings. (see network-bytestring) * Encoding more things in the type system, in particular the socket state (opened, closed, connected, etc). I would like to avoid a very heavyweight encoding though. * Allow folds over the input i.e. foldSocket :: (a - ByteString - a) - a - Socket - IO a I'm all for having a higher level API but I would like to keep the Berkeley socket interface. The reason is the following: If we provide a higher level API that does not expose the whole underlying OS API there will be some users who can't use the library and will have to resort to writing their own bindings. I've seen this problem in a few other libraries. The reasoning often goes something like this: This interface will cover 90% (or 95%) of all the use cases so its sufficient for most people. The problem with this kind of reasoning is that I have to write my own OS bindings for every ten libraries I use (on average). Perhaps we should start a wiki page where we can take some notes on things that could be improved in the style of Haskell' discussions (i.e. outlines of the problem together possible solutions together with their trade-offs. Python's PEPs are a good model here)? -- Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE fmlist
On Jun 19, 2009, at 7:12 PM, Sjoerd Visscher wrote: I see you did performance tests. How does your current version compare to f.e. one based on DiffLists? The current versions (0.4) of bfs and idfs based on FMList (0.5) use the same amount of memory and are about 10-15% slower than corresponding versions of breadth-first search and iterative deepening depth-first search based on CPS and DiffList when enumerating pythagorean triples without an upper bound (I didn't check other examples). I wonder though, aren't you worried that updated versions of FMList might use the monoid laws to rewrite certains bits, and your code would break? Essentially you are using FMLists as a tree structure, which isn't possible when you abide by the monoid laws. Manipulating w.r.t. monoid laws may change the order in which results are computed by bfs and idfs. However, I won't consider this breaking the code. The important property of bfs and idfs is that all results are eventually computed and I happily abstract from their order when enumerating results of non-deterministic computations. Other people may disagree though, so I should mention something about it in the docs. If rewriting FMList w.r.t. monoid laws would break the completeness of the strategies I would be concerned. But currently I have the impression that parametricity ensures that I will always be able to convert an FMList into the (implicit) tree structures that I use for complete search. I think you should be able to do the same thing in as many lines, using f.e. the ChoiceT type from MonadLib, where bfs and idfsBy are variations on runChoiceT. I think so too. With a monad instance for a tree structure one can implement both strategies as well. However, the continuation-based implementation of monadic bind is more efficient when nested left associatively [1]. One could regain the asymptotic improvement of monadic bind by wrapping ChoiceT under ContT but that seems inelegant as it uses more monads than necessary. By using a free representation of a pointed monoid one could use fmlists to generate the tree structure of a search space: data PMonoid a = Point a | Empty | Append (PMonoid a) (PMonoid a) instance Monoid PMonoid where mempty = Empty mappend = Append treeSearch :: FMList a - PMonoid a treeSearch l = unFM l Point Just like this monoid instance violates the monoid laws, the monad ChoiceT m violates corresponding laws of MonadPlus: mzero `mplus` return 42 = Choice NoAnswer (Answer 42) /= Answer 42 = return 42 a `mplus` (b `mplus` c) = Choice a (Choice b c) /= Choice (Choice a b) c = (a `mplus` b) `mplus` c So also w.r.t. laws there is no advantage in using a tree monad explicitly. Manipulating a non-deterministic computation w.r.t. these laws will change the order of computed results. Mike Spivey gets by without breaking these laws by introducing an additional combinator 'wrap' to increase the depth of the search [2]. However, this additional combinator prevents the use of (only) MonadPlus and whether all results of a non-deterministic computation are eventually enumerated depends on appropriate use of 'wrap'. Cheers, Sebastian [1]: J. Voigtländer, Asymptotic Improvement of Computations over Free Monads http://wwwtcs.inf.tu-dresden.de/~voigt/mpc08.pdf [2]: Michael Spivey, Algebras for Combinatorial Search http://spivey.oriel.ox.ac.uk/mike/search-jfp.pdf -- Underestimating the novelty of the future is a time-honored tradition. (D.G.) 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] Optimizing spelling correction program
Kamil Dworakowski ka...@dworakowski.name writes: Right... Python uses hashtables while here I have a tree with log n access time. I did not want to use the Data.HashTable, it would pervade my program with IO. The alternative is an ideal hashmap that never gets changed. This program creates a dictionary at start which then is only being used to read from: an ideal application for the Data.PerfectHash by Mark Wotton available on Hackage [3]. If you are considering alternative data structures, you might want to look at tries or Bloom filters, both have O(n) lookup, both have Haskell implementations. The latter is probably faster but probabilistic (i.e. it will occasionally fail to detect a misspelling - which you can of course check against a real dictionary). -k -- 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] coding standard question
Magnus Therning wrote: Also from experience, I get a good feeling about software that compiles without warnings. It suggests the author cares and is indicative of some level of quality. In contrast, I find almost all the GHC warnings to be useless, and therefore turn them off. I don't find they have a significant correlation with code quality. YMMV :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
I so don't want to be the one supporting your code... Jules Bean wrote on 22.06.2009 13:00: Magnus Therning wrote: Also from experience, I get a good feeling about software that compiles without warnings. It suggests the author cares and is indicative of some level of quality. In contrast, I find almost all the GHC warnings to be useless, and therefore turn them off. I don't find they have a significant correlation with code quality. YMMV :) ___ 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
Re: [Haskell-cafe] Optimizing spelling correction program
Hey, you're using String I/O! nWORDS - fmap (train . map B.pack . words) (readFile big.txt) This should be WORDS - fmap (train . B.words) (B.readFile big.txt) By the way, which exact file do you use as a misspellings file? The corpus linked to at Norvig's page has many. And do you have a driver program that I could run and obtain your timings? 2009/6/22 Kamil Dworakowski ka...@dworakowski.name: Hi all, I want to learn how to optimize Haskell code on the Norvig's spelling correction program [1]. Peter Norvig has written the program in Python, quite a literate translation to Haskell (thanks to Grzegorz Chrupala) [2] was also available. Both versions are about 23 LOCs, and Haskell version is four times slower, 2m25s versus 36s. All the numbers I give come from running the program on a list of 806 misspellings, Haskell version compiled with - O2 and -fforce-recomp flags. I started with trial and error approach. Just preventing a repetitive call to keysSet brought the running time down to 1m48s. I also restructured the edits1 function and dropped all uses of sets, which haven't been pulling their own weight. This brought the running time down to 55s. Not quite there yet but close. Reading the Profiling chapter in the RWH book enabled me to do some more informed optimizing. At this point the GC time was about 2% of the overall runnig time, Grzegorz has done a good job of using strict versions of functions where necessary. The timing per expression however showed something useful, 70% of the time was being spent around determining membership in the known words dictionary (Data.Map). There are about 30 000 items in the dictionary. Right... Python uses hashtables while here I have a tree with log n access time. I did not want to use the Data.HashTable, it would pervade my program with IO. The alternative is an ideal hashmap that never gets changed. This program creates a dictionary at start which then is only being used to read from: an ideal application for the Data.PerfectHash by Mark Wotton available on Hackage [3]. The PerfectHash is a dictionary keyed by ByteStrings, so I had to migrate the program to use these instead of Strings. Sadly it increased the running time to 59s. Adding PerfectHash brought the running time down to 39s. I have done some code restructuring with the view to publishing it, which brought the running time up to 45s. The code is available on patch-tag [4] for anyone to scrutinize and hopefully point out mistakes (it uses big.txt and misspellings file which are linked to from Norvig's page [1]). At this point [5] I don't know how to proceed. The program is still slower than Python. The -ddump-simpl dump does not give me any clues, there is too much of it and I don't understand most of it. The GC time is about 10% of the total, and according to the profiler almost half the time is spent in the member function, and almost all the rest in edits1. Shouldn't it run much faster than the interpreted Python? Frankly, I am not impressed with the PerfectHash performance; It looks as if it is only two times faster than Data.Map. Is this because of the number of elements? 1. http://www.norvig.com/spell-correct.html 2. http://pitekus.blogspot.com/2007/04/norvigs-spelling-corrector-in-haskell.html 3. http://hackage.haskell.org/package/PerfectHash 4. http://patch-tag.com/r/spellcorrect/ 5. http://patch-tag.com/r/spellcorrect/snapshot/hash/20090621192727-a99e5-fed48a7ccf07b79c572fddb0304648fe80d39904/content/pretty/SpellingCorrection.hs ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Eugene Kirpichov Web IR developer, market.yandex.ru ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
Magnus Therning wrote: Speaking from experience it's good to fix all warnings, This was may experience from the C programming language. since otherwise there will be enough of them to cause a few terminal pages to scroll by when you compile and then there's a real danger of not noticing real errors. I'd pass '-Wall -Werror' to ghc to force myself to do this :-) I usually add -fwarn-tabs to -Wall -Werror. Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
Miguel Mitrofanov wrote: I so don't want to be the one supporting your code... Well, that's lucky. Because you aren't. However, that's an easy arrow to fling. I say I don't find warnings useful so you suggest my code is unmaintainable. Is that based on any knowledge of my code, or the GHC warnings? I've been using GHC for years and my honest opinion is that the warnings very rarely flag an actual maintainability problem in the code I write, and very frequently annoying highlight something I knew I was doing, and did quite deliberately - most often inexhaustive patterns or shadowing. Maybe there are mistakes which you can make which the warnings usefully highlight, and maybe I just never make that kind of mistake. Jules ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] rewrite rules
Hi all,
I have a rewrite rule as follows:
{-# RULES
transform/transform forall (f::forall m. Monoid m = (a - m) - (b -
m))
(g::forall m. Monoid m = (b - m) - (c
- m))
(l::FMList c). transform f (transform g
l) = transform (g.f) l
#-}
It fires on this code:
print $ transform (. (*2)) (transform (. (+1)) (upto 10))
But it doesn't fire on this code:
print $ map (*2) (map (+1) (upto 10)))
with
map g x = transform (. g) x
and with or without {-# INLINE map #-}.
What am I doing wrong?
--
Sjoerd Visscher
sjo...@w3future.com
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Re: [Haskell-cafe] coding standard question
Jules Bean wrote on 22.06.2009 13:09: Miguel Mitrofanov wrote: I so don't want to be the one supporting your code... Well, that's lucky. Because you aren't. Exactly. However, that's an easy arrow to fling. I say I don't find warnings useful so you suggest my code is unmaintainable. Is that based on any knowledge of my code, or the GHC warnings? First of all, I never said that your code is unmaintainable. And, if it's not, i still don't want to maintain it, since we clearly have very different approaches to programming - which is, actually, a good thing (except that mine is obviously good and yours is obviously bad). I've been using GHC for years and my honest opinion is that the warnings very rarely flag an actual maintainability problem in the code I write, and very frequently annoying highlight something I knew I was doing, and did quite deliberately - most often inexhaustive patterns or shadowing. Maintainability is (mostly) NOT about how good are YOU in supporting your own code. Maybe there are mistakes which you can make which the warnings usefully highlight, and maybe I just never make that kind of mistake. It's a kind of mistakes that I can make maintaining your code, that's all. That doesn't imply that it's your fault (except that it certainly is). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Optimizing spelling correction program
Johan Tibell johan.tib...@gmail.com writes: Typo? Bloom filters have O(1) lookup and tries O(m) lookup where m is the number of characters in the string. Typically you need to examine the (whole) search string in order to compute the hash function, so I think it is fair to consider them both O(m). (Sorry about the alphabet confusion, I should of course have made it clear that I referred to search pattern size, not the data size.) -k -- 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] coding standard question
Erik de Castro Lopo mle...@mega-nerd.com wrote: Vasili I. Galchin wrote: where/let functions use the same name for function parameters as the outer function and hence there is a shadow warning from the compiler. In Haskell there is an easy way around this. Variables can be name a, a', a'' and so on. ... ... its a good idea to fix these warnings. I would _strongly_ advise not to do that. By trying to silence the spurious warning about shadowing, there is enormous potential to introduce new bugs that were not there before. Example: f a b = g (a+b) (b-a) where g a c = a*c ghc warns that g's parameter a shadows the parameter to f. So we introduce a primed identifier to eliminate the warning: f a b = g (a+b) (b-a) where g a' c = a*c Now, no warnings! But, oops, this function does not do the same thing. We forgot to add a prime to all occurrences of a on the right-hand-side. Particularly in larger examples, it can be remarkably easy to miss an occurrence of the variable whose name you are refactoring. The key point is that in this situation, unlike most refactorings, the compiler _cannot_ help you find the mistake with useful error messages or warnings. When I write code that shadows variable names, it is always deliberate. In fact, the language's lexical rules encourage shadowing, otherwise why have scopes at all? I think bug-introduction by the elimination of shadowing is much more common than bug-elimination by the same route. Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
Jules Bean wrote: I've been using GHC for years and my honest opinion is that the warnings very rarely flag an actual maintainability problem in the code I write, and very frequently annoying highlight something I knew I was doing, and did quite deliberately - most often inexhaustive patterns or shadowing. I would agree to a certain extent about the warnings. Name shadowing is not really a problem, and it's often hard to avoid shadowing names that already exist in an imported module (why shouldn't I have a variable named lines?). It's also usually the case that when I write inexhaustive pattern matches, it's because I know that the function (in a where clause) cannot be called with the missing pattern. Type defaulting and monomorphism bits may be useful to some, but I only usually fix them to get rid of the warning, not because they cause a problem. The ones I find useful are unused imports (handy for tidying up the import list), overlapping patterns, missing fields, warnings about tabs and a few others. Of course, you can easily customise which warnings are on and which are off, so we can all have different preferences. It would be nice to be able to set some warnings to be errors though, while leaving others as warnings, or turned off (don't think GHC can do this?). Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Creating a new Haskell mailing list
I'm interested in creating a list for iPhone development. While I also have an ongoing iPhone build target project, which I will be open-sourcing very soon, I'd like the list to be about Haskell on iPhone without regard to whether it has anything to do with my project. Ryan On Fri, Jun 19, 2009 at 03:06, Wolfgang Jeltsch g9ks1...@acme.softbase.orgwrote: Am Donnerstag, 18. Juni 2009 16:21 schrieb Henning Thielemann: Ryan Trinkle schrieb: Hi all, I'm interested in starting a mailing list on haskell.org http://haskell.org. Who should I talk to about such things? Is it a mailing list related to a project? Then you may request a project on community.haskell.org, then you can start a mailing list at yourproj...@project.haskell.org See http://community.haskell.org/. Best wishes, Wolfgang ___ 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] Re: Creating a new Haskell mailing list
On Wed, 17 Jun 2009 20:38:54 -0400, Ryan Trinkle ryant5...@gmail.com wrote: Hi all, I'm interested in starting a mailing list on haskell.org. Who should I talk to about such things? One way is to propose the mailing list on the Haskell mailing list (see the Haskell Info Page at http://www.haskell.org/mailman/listinfo/haskell and The Haskell Archives at http://www.haskell.org/pipermail/haskell/), and then move the discussion, after a few rounds, to this mailing list (the Haskell-Cafe mailing list). (Haskell-Beginners was created in this manner, for example.) -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Optimizing spelling correction program
On Mon, Jun 22, 2009 at 12:05 PM, Ketil Malde ke...@malde.org wrote: Johan Tibell johan.tib...@gmail.com writes: Typo? Bloom filters have O(1) lookup and tries O(m) lookup where m is the number of characters in the string. Typically you need to examine the (whole) search string in order to compute the hash function, so I think it is fair to consider them both O(m). Very true. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] STM/Data Invariant related Segfault with GHC 6.10.3
Hello,
I just discovered that programs compiled with GHC 6.10.3 segfault when
accessing a TVar created under certain conditions. This happens when
the TVar is created and a data invariant is added (using
alwaysSucceeds) in the same atomic block. The invariant does not
necessarily have to read the TVar in question, a mere
alwaysSucceeds (return ()) is enough.
It looks like by adding the invariant the TVar allocation is not kept
after the block. The appended code snippets show how to reproduce
this behaviour. IMHO the first version should work, too.
Is there anything one can do to (reliably) work around this problem?
Is there maybe an underlying problem that causes this?
Regards,
Jan
module Main where
import GHC.Conc
-- this segfaults:
main = do { t - atomically
(do { t1 - newTVar 0
; alwaysSucceeds (readTVar t1)
; return t1 })
; atomically $ readTVar t }
-- it works if written like this:
main2 = do { t - newTVarIO 0
; atomically $ alwaysSucceeds (readTVar t)
; atomically $ readTVar t }
-- works also if no invariant is added:
main3 = do { t - atomically
(do { t1 - newTVar 0
; return t1 })
; atomically $ readTVar t }
-- works also if invariant is added later:
main4 = do { t - atomically
(do { t1 - newTVar 0
; return t1 })
; atomically $ alwaysSucceeds (readTVar t)
; atomically $ readTVar t }
--
If you're happy and you know it, syntax error!
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Re: [Haskell-cafe] coding standard question
On Mon, Jun 22, 2009 at 12:06 PM, Malcolm Wallace malcolm.wall...@cs.york.ac.uk wrote: Erik de Castro Lopo mle...@mega-nerd.com mle%2...@mega-nerd.com wrote: Vasili I. Galchin wrote: where/let functions use the same name for function parameters as the outer function and hence there is a shadow warning from the compiler. In Haskell there is an easy way around this. Variables can be name a, a', a'' and so on. ... ... its a good idea to fix these warnings. I would _strongly_ advise not to do that. By trying to silence the spurious warning about shadowing, there is enormous potential to introduce new bugs that were not there before. Example: f a b = g (a+b) (b-a) where g a c = a*c ghc warns that g's parameter a shadows the parameter to f. So we introduce a primed identifier to eliminate the warning: f a b = g (a+b) (b-a) where g a' c = a*c Now, no warnings! But, oops, this function does not do the same thing. We forgot to add a prime to all occurrences of a on the right-hand-side. Actually there's a warning: ghci let f a b = g (a+b) (b-a) where g a' c = a*c interactive:1:34: Warning: Defined but not used: `a'' Cheers, Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
On Mon, 2009-06-22 at 08:53 +0200, Deniz Dogan wrote: 2009/6/22 Colin Paul Adams co...@colina.demon.co.uk: Judah == Judah Jacobson judah.jacob...@gmail.com writes: Judah On Sun, Jun 21, 2009 at 11:12 PM, Colin Paul Judah Adamsco...@colina.demon.co.uk wrote: I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. Judah Use System.Directory.doesDirectoryExist/doesFileExist. Thanks. it seems it's time i went to the optician again. I'm not surprised that anyone would make the mistake. I think that the two functions should be named isDirectory and isFile, but it seems that isDirectory was already taken by another function in System.Directory, which is quite unfortunate. does goes against the intuition one gets from pretty much everything else in Haskell, where is seems to be the convention. In fact, Hoogle only knows about three functions which start with does. One explanation is that isBlah asks is this thing a blah, but we're not asking that because there is an indirection via the filepath. We're asking does this filepath refer to a directory not is this filename a directory. The latter could be a function: isDirectory :: FileInfo - Bool along with a hypothetical getFileInfo :: FilePath - IO FileInfo Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Creating a new Haskell mailing list
Most likely, if you propose your new mailing list (on the Haskell mailing list), the discussion will focus on whether it will be likely to gather enough posts to stay reasonably active. While the definition of reasonably active differs depending on the individual, it is likely to mean somewhere between an average of several posts per week to one or two per day. Your proposal will be more likely to pass if you can demonstrate a reasonably strong demand for active discussion in the Haskell community. Alternatively, it is possible to create a Haskell-related mailing list that is not hosted at haskell.org. Haskell-Art (see the haskell-art Info Page at http://lists.lurk.org/mailman/listinfo/haskell-art and The haskell-art Archives at http://lists.lurk.org/pipermail/haskell-art/) is one example of such a list. You may wish to see the following sites for reference: haskell.org Mailing Lists http://haskell.org/mailman/listinfo Mailing lists - HaskellWiki http://haskell.org/haskellwiki/Mailing_lists -- Benjamin L. Russell On Mon, 22 Jun 2009 07:16:14 -0400, Ryan Trinkle ryant5...@gmail.com wrote: I'm interested in creating a list for iPhone development. While I also have an ongoing iPhone build target project, which I will be open-sourcing very soon, I'd like the list to be about Haskell on iPhone without regard to whether it has anything to do with my project. Ryan On Fri, Jun 19, 2009 at 03:06, Wolfgang Jeltsch g9ks1...@acme.softbase.orgwrote: Am Donnerstag, 18. Juni 2009 16:21 schrieb Henning Thielemann: Ryan Trinkle schrieb: Hi all, I'm interested in starting a mailing list on haskell.org http://haskell.org. Who should I talk to about such things? Is it a mailing list related to a project? Then you may request a project on community.haskell.org, then you can start a mailing list at yourproj...@project.haskell.org See http://community.haskell.org/. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
Malcolm Wallace wrote: When I write code that shadows variable names, it is always deliberate. In fact, the language's lexical rules encourage shadowing, otherwise why have scopes at all? I think bug-introduction by the elimination of shadowing is much more common than bug-elimination by the same route. I would almost agree that blindly eliminating shadowing will lead to bugs, but they will be shallow bugs detected almost immediately. The bugs I am particularly interested in avoiding are the difficult bugs that seem to be intermittent, that only hit in certain rare situations and that take ages to find. I will gladly trade you a hundred of the first for one of the second :-). Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cross platform getProcessID
Hi John, The short anser is...you need to make a ffi call to getCurrentProcessId unfortunately there is no binding to this function in System.Win32.Process which is the natural home for it. Perhaps you could submit a patch for Win32 package, once you have created the binding the signature for the function is quite simple, so there should be no problem with the ffi call DWORD GetCurrentProcessId(VOID) I think I'll do just that. Thanks. :) -- /jve ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Documentation on hackage
On Mon, 2009-06-15 at 06:49 -0700, Don Stewart wrote:
si:
Dear Haskellers,
who needs this kind of documentation?
http://hackage.haskell.org/packages/archive/tfp/0.2/doc/html/Types-Data-Num-Decimal-Literals.html
isn't this a kind of spam?
Seems like a good case for the haddock -hide option.
Note that this can be added to the module itself:
{-# OPTIONS_HADDOCK prune #-}
From the user guide[1]:
prune
Omit definitions that have no documentation annotations from the
generated documentation.
hide
Omit this module from the generated documentation, but
nevertheless propagate definitions and documentation from within
this module to modules that re-export those definitions.
Duncan
[1] http://haskell.org/haddock/doc/html/module-attributes.html
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Re: [Haskell-cafe] Suggestion for Network.Socket in regards to PortNumber
Johan - glad you chimed in! I'm all in favor of keeping a low level interface and don't have an issue with Network.Socket existing, I additionally really like the suggestion of moving from the ML to a wiki in the same style as Haskell'. I'll port these comments to the wiki if that is whats agreed on and hold off on other thoughts for now. * ByteStrings! Absolutely. The one issue is I feel network packets should be represented as strict bytestrings and any encode/decode issues resulting in a 'Left err' via binary-strict or some beefed up version of that package. * Avoiding a 'heavy weight' solution for socket state might get ugly fast with all the 'Either a b' results that we'll need - also a socket can close at any time so a socket in 'Connected' state might not actually be connected. I understand the attraction to a light solution using existential types but Tim Sheard sketched for me a reasonable alternative which I invite him to restate here, if he has the time. Thomas On Mon, Jun 22, 2009 at 12:16 AM, Johan Tibelljohan.tib...@gmail.com wrote: On Mon, Jun 22, 2009 at 1:22 AM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: I'm in favor of the entire Network library being reworked with an improved API that is higher level and type-safe instead of a direct translation/FFI of Berkeley sockets. I also would like the Network package to export Data instances for headers while taking advantage of pretty, prettyclass, and parsec. I started such work with network-data but never really got off the ground with it. I've given this some thought. There are a few different things that would be nice to have in a new API: * Use a binary type (e.g. ByteString) instead of Strings. (see network-bytestring) * Encoding more things in the type system, in particular the socket state (opened, closed, connected, etc). I would like to avoid a very heavyweight encoding though. * Allow folds over the input i.e. foldSocket :: (a - ByteString - a) - a - Socket - IO a I'm all for having a higher level API but I would like to keep the Berkeley socket interface. The reason is the following: If we provide a higher level API that does not expose the whole underlying OS API there will be some users who can't use the library and will have to resort to writing their own bindings. I've seen this problem in a few other libraries. The reasoning often goes something like this: This interface will cover 90% (or 95%) of all the use cases so its sufficient for most people. The problem with this kind of reasoning is that I have to write my own OS bindings for every ten libraries I use (on average). Perhaps we should start a wiki page where we can take some notes on things that could be improved in the style of Haskell' discussions (i.e. outlines of the problem together possible solutions together with their trade-offs. Python's PEPs are a good model here)? -- Johan ___ 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
Re: [Haskell-cafe] Suggestion for Network.Socket in regards to PortNumber
Moving off list to the Wiki has my vote. On Mon, Jun 22, 2009 at 7:52 AM, Thomas DuBuissonthomas.dubuis...@gmail.com wrote: Johan - glad you chimed in! I'm all in favor of keeping a low level interface and don't have an issue with Network.Socket existing, I additionally really like the suggestion of moving from the ML to a wiki in the same style as Haskell'. I'll port these comments to the wiki if that is whats agreed on and hold off on other thoughts for now. * ByteStrings! Absolutely. The one issue is I feel network packets should be represented as strict bytestrings and any encode/decode issues resulting in a 'Left err' via binary-strict or some beefed up version of that package. * Avoiding a 'heavy weight' solution for socket state might get ugly fast with all the 'Either a b' results that we'll need - also a socket can close at any time so a socket in 'Connected' state might not actually be connected. I understand the attraction to a light solution using existential types but Tim Sheard sketched for me a reasonable alternative which I invite him to restate here, if he has the time. Thomas On Mon, Jun 22, 2009 at 12:16 AM, Johan Tibelljohan.tib...@gmail.com wrote: On Mon, Jun 22, 2009 at 1:22 AM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: I'm in favor of the entire Network library being reworked with an improved API that is higher level and type-safe instead of a direct translation/FFI of Berkeley sockets. I also would like the Network package to export Data instances for headers while taking advantage of pretty, prettyclass, and parsec. I started such work with network-data but never really got off the ground with it. I've given this some thought. There are a few different things that would be nice to have in a new API: * Use a binary type (e.g. ByteString) instead of Strings. (see network-bytestring) * Encoding more things in the type system, in particular the socket state (opened, closed, connected, etc). I would like to avoid a very heavyweight encoding though. * Allow folds over the input i.e. foldSocket :: (a - ByteString - a) - a - Socket - IO a I'm all for having a higher level API but I would like to keep the Berkeley socket interface. The reason is the following: If we provide a higher level API that does not expose the whole underlying OS API there will be some users who can't use the library and will have to resort to writing their own bindings. I've seen this problem in a few other libraries. The reasoning often goes something like this: This interface will cover 90% (or 95%) of all the use cases so its sufficient for most people. The problem with this kind of reasoning is that I have to write my own OS bindings for every ten libraries I use (on average). Perhaps we should start a wiki page where we can take some notes on things that could be improved in the style of Haskell' discussions (i.e. outlines of the problem together possible solutions together with their trade-offs. Python's PEPs are a good model here)? -- Johan ___ 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 -- /jve ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestion for Network.Socket in regards to PortNumber
On Mon, Jun 22, 2009 at 1:52 PM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: Johan - glad you chimed in! I'm all in favor of keeping a low level interface and don't have an issue with Network.Socket existing, I additionally really like the suggestion of moving from the ML to a wiki in the same style as Haskell'. I'll port these comments to the wiki if that is whats agreed on and hold off on other thoughts for now. Yes, please start a new wiki page. We can still discuss issues here and add things to the wiki as different solutions materialize. * Avoiding a 'heavy weight' solution for socket state might get ugly fast with all the 'Either a b' results that we'll need - also a socket can close at any time so a socket in 'Connected' state might not actually be connected. I understand the attraction to a light solution using existential types but Tim Sheard sketched for me a reasonable alternative which I invite him to restate here, if he has the time. Good point. The encodings using existential types are not very lightweight in my opinion. I'd love to hear Tim's alternative. -- Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
2009/6/22 Duncan Coutts duncan.cou...@worc.ox.ac.uk: On Mon, 2009-06-22 at 08:53 +0200, Deniz Dogan wrote: 2009/6/22 Colin Paul Adams co...@colina.demon.co.uk: Judah == Judah Jacobson judah.jacob...@gmail.com writes: Judah On Sun, Jun 21, 2009 at 11:12 PM, Colin Paul Judah Adamsco...@colina.demon.co.uk wrote: I've been hoogling like bad to try to determine if a function like this exists. getDirectoryContents returns sub-directories as well as file names. I want only the latter, so I'm looking for a suitable filter. Judah Use System.Directory.doesDirectoryExist/doesFileExist. Thanks. it seems it's time i went to the optician again. I'm not surprised that anyone would make the mistake. I think that the two functions should be named isDirectory and isFile, but it seems that isDirectory was already taken by another function in System.Directory, which is quite unfortunate. does goes against the intuition one gets from pretty much everything else in Haskell, where is seems to be the convention. In fact, Hoogle only knows about three functions which start with does. One explanation is that isBlah asks is this thing a blah, but we're not asking that because there is an indirection via the filepath. We're asking does this filepath refer to a directory not is this filename a directory. The latter could be a function: isDirectory :: FileInfo - Bool along with a hypothetical getFileInfo :: FilePath - IO FileInfo Duncan I think see what you mean, but I find the argument more of an excuse to the poor naming than a solid argument for it. Following the convention and intuition that most users have should be more important than making the (sometimes unnecessary) distinction between a directory and the path to it. -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing spelling correction program
On Jun 22, 10:03 am, Eugene Kirpichov ekirpic...@gmail.com wrote: Hey, you're using String I/O! nWORDS - fmap (train . map B.pack . words) (readFile big.txt) This should be WORDS - fmap (train . B.words) (B.readFile big.txt) By the way, which exact file do you use as a misspellings file? The corpus linked to at Norvig's page has many. And do you have a driver program that I could run and obtain your timings? Yep, Don pointed that out and I have changed the program accordingly. It didn't make any difference though. The time spent on building the dictionary is a small portion of the overall run time. Please see the repository contents for the current version of the program: http://patch-tag.com/r/spellcorrect/snapshot/current/content/pretty The eval-bytestring.hs there is the program I used for timing. Inside of it you will find the name of the misspellings file needed. Thanks all for the suggestions. I'll try them when I get home tonight. -- Kamil Dworakowski ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
On Mon, Jun 22, 2009 at 2:09 PM, Deniz Dogandeniz.a.m.do...@gmail.com wrote: I think see what you mean, but I find the argument more of an excuse to the poor naming than a solid argument for it. Following the convention and intuition that most users have should be more important than making the (sometimes unnecessary) distinction between a directory and the path to it. I disagree. (isDirectory /no/such/directory/) should equal true: the given FilePath is a directory path (on Unix), since it ends with a slash. However (doesDirectoryExist /no/such/directory) should return false, since there is no such directory. -- Deniz Dogan --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
Johan Tibell johan.tib...@gmail.com wrote: Example: f a b = g (a+b) (b-a) where g a c = a*c f a b = g (a+b) (b-a) where g a' c = a*c Actually there's a warning: interactive:1:34: Warning: Defined but not used: `a'' Clearly I simplified the example too far. Try this, only slightly more complex, example instead. Remember, the larger the example, the more likely you are to miss an occurrence. f a b = g (a+b) (b-a) where g a c = a*(c-a) f a b = g (a+b) (b-a) where g a' c = a'*(c-a) Perhaps I should advocate for a new warning in GHC to cover this case: -fwarn-mixed-scopes, which could flag the use of the unprimed a, due to being bound at an outer scope. Because warn-mixed-scopes is almost the opposite of warn-name-shadowing, then the only way to avoid warnings would be to manually lambda-lift all functions. :-) Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Suggestion for Network.Socket in regards to PortNumber
All, I've started to add to the network trac [1] - its just framework for now. Please do add proposals, organized comments, and feel free to alter the framework. I'm not sure how formal we'd like to make this so I haven't even tried to make guidelines for proposals. I'll add proposals and perhaps try my hand at guidelines throughout this week. Thomas [1] http://trac.haskell.org/network/wiki/WikiStart Possible proposal guidelines: [2] http://hackage.haskell.org/trac/haskell-prime/wiki/CreateProposal [3] http://www.python.org/dev/peps/ On Mon, Jun 22, 2009 at 5:03 AM, Johan Tibelljohan.tib...@gmail.com wrote: On Mon, Jun 22, 2009 at 1:52 PM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: Johan - glad you chimed in! I'm all in favor of keeping a low level interface and don't have an issue with Network.Socket existing, I additionally really like the suggestion of moving from the ML to a wiki in the same style as Haskell'. I'll port these comments to the wiki if that is whats agreed on and hold off on other thoughts for now. Yes, please start a new wiki page. We can still discuss issues here and add things to the wiki as different solutions materialize. * Avoiding a 'heavy weight' solution for socket state might get ugly fast with all the 'Either a b' results that we'll need - also a socket can close at any time so a socket in 'Connected' state might not actually be connected. I understand the attraction to a light solution using existential types but Tim Sheard sketched for me a reasonable alternative which I invite him to restate here, if he has the time. Good point. The encodings using existential types are not very lightweight in my opinion. I'd love to hear Tim's alternative. -- Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
2009/6/22 Max Rabkin max.rab...@gmail.com: On Mon, Jun 22, 2009 at 2:09 PM, Deniz Dogandeniz.a.m.do...@gmail.com wrote: I think see what you mean, but I find the argument more of an excuse to the poor naming than a solid argument for it. Following the convention and intuition that most users have should be more important than making the (sometimes unnecessary) distinction between a directory and the path to it. I disagree. (isDirectory /no/such/directory/) should equal true: the given FilePath is a directory path (on Unix), since it ends with a slash. However (doesDirectoryExist /no/such/directory) should return false, since there is no such directory. Are you saying that when a function is named isDirectory you expect it to only check for a trailing forward slash character? -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: coding standard question
Malcolm Wallace wrote: Johan Tibell johan.tib...@gmail.com wrote: Example: f a b = g (a+b) (b-a) where g a c = a*c The proper way to avoid shadowing in this simple case would be to make g global (and don't export it). f a b = g (a+b) (b-a) g a c = a*c f a b = g (a+b) (b-a) where g a' c = a*c Actually there's a warning: interactive:1:34: Warning: Defined but not used: `a'' Clearly I simplified the example too far. Try this, only slightly more complex, example instead. Remember, the larger the example, the more likely you are to miss an occurrence. f a b = g (a+b) (b-a) where g a c = a*(c-a) f a b = g (a+b) (b-a) where g a' c = a'*(c-a) Perhaps I should advocate for a new warning in GHC to cover this case: -fwarn-mixed-scopes, which could flag the use of the unprimed a, due to being bound at an outer scope. The main reason for let and where are such mixed scopes. (And maybe you should get a warning if the scope is not mixed, as in the initial example.) In any case I think, it does make sense to avoid name shadowing in the same way as it make sense to avoid shadowing of imported (or declared) global names by local variables (i.e. by using pi or id as variables). Surely, it may be convenient to reuse names in local scopes, but it is as hard to read such code as it is to replace shadowed variables consistently by hand. (A refactoring tool could rename shadowed variables as reliable as the compiler treats them.) Surely there's no help against mixing up names with the same type. Cheers Christian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to determine if a FilePath is a directory name or regular file?
Deniz Dogan deniz.a.m.do...@gmail.com writes: One explanation is that isBlah asks is this thing a blah, but we're not asking that because there is an indirection via the filepath. We're asking does this filepath refer to a directory not is this filename a directory. I think see what you mean, but I find the argument more of an excuse to the poor naming than a solid argument for it. Following the convention and intuition that most users have should be more important than making the (sometimes unnecessary) distinction between a directory and the path to it. It is more important to be consistent and logical than to follow conventions and intuitions. And at any rate, convention is that 'isFoo' is a pure function with the type 'FooType - Bool', clearly different from 'doesDirectoryExist', which returns an IO action. So IMO 'isDirectory /foo/bar/' should always return false, since it is a string, not a directory. -k -- 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] How to determine if a FilePath is a directory name or regular file?
On Mon, Jun 22, 2009 at 2:54 PM, Deniz Dogandeniz.a.m.do...@gmail.com wrote: Are you saying that when a function is named isDirectory you expect it to only check for a trailing forward slash character? No. I'm saying that *if* isDirectory existed, then (isDirectory /no/such/directory/) should equal true on Unix. I'm saying isDirectory should not *exist*, because it cannot do what it says on Unix or Windows. There are OSes where it can do what it says (i.e., it is possible to tell whether a path points at a directory or a file). -- Deniz Dogan --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
Jules Bean wrote: Magnus Therning wrote: Also from experience, I get a good feeling about software that compiles without warnings. It suggests the author cares and is indicative of some level of quality. In contrast, I find almost all the GHC warnings to be useless, and therefore turn them off. I don't find they have a significant correlation with code quality. YMMV :) I strongly disagree with this. There is a huge difference between f (x:xs) = ... and f (x:xs) = ... f [] = error f: we expect a nonempty list The reason for this is that in the second case you express to somebody who reads your code (including yourself) that this omission was intentional. The same holds for other warnings (although I sometimes am annoyed by the shadowing warnings, I agree :). My default is to start developing, then adding -Wall -Werror and make it compile again. Regards, -- Jochem Berndsen | joc...@functor.nl GPG: 0xE6FABFAB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: haskelldb + sqlite problem.
Hi Cloud,
this often occurs when the path to the database includes a non-ascii
character.
In my dev environment, the path to the database deliberately contains an
umlaut and the original code base of hdbc.sqlite3 from John Goerzen,
version 2.0 version 2.1 thus does not work.
John Goerzen, the author of HDBC has considerably rewritten some parts
of his hdbc package to use utf8-string wrapping, which includes wrapping
the connection string, and in my case caused considerable problems, it
just wouldn't work. So my solution was to rollback all these changes
where he used the utf8-wrapping, which was quite a lot of work. I did
communicate this to John, but he insists that his current solution is
correct, and I'm not going to argue with him.
Anyway what you can do, for now, is to put your sqlite3 database file
into a location where the path contains no non-ascii characters, that
should fix the problem.
You may experience other, utf8-wrapping related problems, for instance
when you want to insert non-ascii strings into varchar columns. They may
not come back as you put them in.
HTH
Günther
Magicloud Magiclouds schrieb:
Hi,
I am using haskelldb and haskelldb-hdbc-sqlite3. Well, I finally got
the source compiled and ran, I got this error:
App: user error (SQL error: SqlError {seState = , seNativeError =
21, seErrorMsg = prepare 74: SELECT subject,\n timestamp\nFROM
notes as T1\nORDER BY timestamp DESC: library routine called out of
sequence})
Any clue what I should check? Thanks.
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Re: [Haskell-cafe] Suggestion for Network.Socket in regards to PortNumber
On Mon, Jun 22, 2009 at 2:46 PM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: All, I've started to add to the network trac [1] - its just framework for now. Please do add proposals, organized comments, and feel free to alter the framework. I'm not sure how formal we'd like to make this so I haven't even tried to make guidelines for proposals. I'll add proposals and perhaps try my hand at guidelines throughout this week. Lets just get some concrete proposals up there and see if we need some kind of guidelines and what those guidelines should be. FWIW I like the PEP style. -- Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ICFP09 Call for Participation
= Call for Participation The 14th ACM SIGPLAN International Conference on Functional Programming (ICFP 2009) http://www.cs.nott.ac.uk/~gmh/icfp09.html Edinburgh, Scotland, 31 August - 2 September 2009 = ICFP 2009 provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. Preliminary program: * Accepted papers: + http://web.cecs.pdx.edu/~apt/icfp09_accepted_papers/accepted.html * Invited speakers: + Guy Steele -- Organizing Functional Code for Parallel Execution: or, foldl and foldr Considered Slightly Harmful + Benjamin Pierce -- Lambda, the Ultimate TA: Using a Proof Assistant to Teach Programming Language Foundations +Dan Piponi -- Commutative Monads, Diagrams and Knots Schedule including related workshops: * Aug 30: ACM SIGPLAN Workshop on ML * Aug 30: ACM SIGPLAN Workshop on Generic Programming * Aug 31-Sep 2: ICFP09 * Sep 3: ACM SIGPLAN Haskell Symposium * Sep 3: ACM SIGPLAN Developer Tracks on Functional Programming * Sep 4: Commercial Users of Functional Programming * Sep 4: ACM SIGPLAN Workshop on Mechanizing Metatheory * Sep 4: ACM SIGPLAN Workshop on Approaches and Applications of Inductive Programming * Sep 5: ACM SIGPLAN Erlang Workshop * Sep 5: ACM SIGPLAN Developer Tracks on Functional Programming * Sep 5: ACM SIGPLAN Haskell Implementors Workshop Registration information: * http://www.regmaster.com/conf/icfp2009.html * Early registration deadline: July 30, 2009 Local arrangements (including travel and accommodation): * http://www.haskell.org/haskellwiki/ICFP_2009_Local_Arrangements * Conference reservation/rate deadline: July 20, 2009 * ICFP09 coincides with the final week of the Edinburgh International Festival, one of the premier arts and cultural festivals in the world. The opportunity to attend the Festival is a plus! Due to the popularity of Edinburgh during the festival period, we strongly recommend booking accommodation early. Conference organizers: * General Chair: Graham Hutton (University of Nottingham) * Program Chair: Andrew Tolmach (Portland State University) * Local Arrangements Chairs: Philip Wadler (University of Edinburgh), Kevin Hammond (University of St Andrews), and Gregory Michaelson (Heriot-Watt University) * Workshop Co-Chairs: Christopher Stone (Harvey Mudd College), and Michael Sperber (DeinProgramm) * Programming Contest Chair: Andrew Gill (University of Kansas) * Publicity Chair: Matthew Fluet (Toyota Technological Institute at Chicago) = = And, don't forget about the ICFP Programming Contest this weekend!! * http://www.icfpcontest.org * Friday, June 26 to Monday, June 29 * Organizers: Computer Systems Design Laboratory (University of Kansas) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type system trickery
On Sun, Jun 21, 2009 at 09:16:12PM +0100, Andrew Coppin wrote: Niklas Broberg wrote: That's what GADTs are for: data Flag = HasZoo | NoZoo data Foobar a where Foo :: Foobar a - Foobar a Bar :: Foobar a - Foobar a Zoo :: Foobar a - Foobar HasZoo Ouch #1: This appears to instantly disable deriving the Eq, Ord and Show instances I want. :-/ Ah, yes, that is a pain. Maybe try playing around with tools like Data.Derive? I haven't played with them much myself so I don't know if they will help. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] rewrite rules
Hi Sjoerd,
I don't know the cause of the problem, but if I add this rule, it works:
{-# RULES
inline_map forall g x. map g x = transform (. g) x
-#}
maybe, for whatever reason, the 'map' is inlined too late for the
transform/transform rule to see it?
Greetings,
Daniel
On Monday 22 June 2009 11:41:33 Sjoerd Visscher wrote:
Hi all,
I have a rewrite rule as follows:
{-# RULES
transform/transform forall (f::forall m. Monoid m = (a - m) - (b -
m))
(g::forall m. Monoid m = (b - m) - (c
- m))
(l::FMList c). transform f (transform g
l) = transform (g.f) l
#-}
It fires on this code:
print $ transform (. (*2)) (transform (. (+1)) (upto 10))
But it doesn't fire on this code:
print $ map (*2) (map (+1) (upto 10)))
with
map g x = transform (. g) x
and with or without {-# INLINE map #-}.
What am I doing wrong?
--
Sjoerd Visscher
sjo...@w3future.com
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Re: [Haskell-cafe] rewrite rules
On Jun 22, 2009, at 6:38 PM, Ryan Ingram wrote:
Not 100% sure (especially without source/core), but my guess is that
the higher-rank types make the rule unlikely to fire.
Try -ddump-simpl to see the core output, and look for places where you
expect the rule to fire. I suspect you will find that the types of f
and g are not forall at that point in the code, but have already
been specialized.
Is there a reason you cannot use this simpler rule?
{-# RULES transform/tranform forall f g l. transform f (transform g
l) = transform (g.f) l #-}
Yes, this is the reason:
Inferred type is less polymorphic than expected
Quantified type variable `m' is mentioned in the environment:
f :: (a - m) - b - m (bound at Data/FMList.hs:124:29)
In the first argument of `transform', namely `f'
In the expression: transform f (transform g l)
When checking the transformation rule transform/transform
This is the function:
transform :: (forall m. Monoid m = (a - m) - (b - m)) - FMList b -
FMList a
transform t l = FM $ \f - unFM l (t f)
I'll have to clean things up before the core output becomes manageable.
Sjoerd
-- ryan
On Mon, Jun 22, 2009 at 2:41 AM, Sjoerd
Visschersjo...@w3future.com wrote:
Hi all,
I have a rewrite rule as follows:
{-# RULES
transform/transform forall (f::forall m. Monoid m = (a - m) -
(b - m))
(g::forall m. Monoid m = (b - m) -
(c - m))
(l::FMList c). transform f (transform g
l) =
transform (g.f) l
#-}
It fires on this code:
print $ transform (. (*2)) (transform (. (+1)) (upto 10))
But it doesn't fire on this code:
print $ map (*2) (map (+1) (upto 10)))
with
map g x = transform (. g) x
and with or without {-# INLINE map #-}.
What am I doing wrong?
--
Sjoerd Visscher
sjo...@w3future.com
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--
Sjoerd Visscher
sjo...@w3future.com
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Re: [Haskell-cafe] Getting my mind around UArray - STUArray conversion
On Fri, Jun 19, 2009 at 7:08 PM, Dan Doeldan.d...@gmail.com wrote:
Oops, I replied too hastily.
What I wrote in my first mail is a problem, as witnessed by the ix and ix1
in the error message. However, it isn't the main error. The main error is that
you have a monadic expression, with type something like:
ST s (UArray ix e)
but the return type of your function is:
UArray ix e
To make a no-op you need to add a runST, something like:
runST (unsafeThaw mem = unsafeFreeze)
Actually, I probably wanted runSTUArray. :-)
But even then, I can't manage to get wombat to compile correctly. I'm
starting to think that MArray is itself a WOMBAT (waste of money,
brains and time), for three reasons:
a) Overly restrictive Monads in which implementation is supported
(i.e., ST and IO)
b) The triviality of the examples gives no insight as to how they
could be used, other than a create array, do something completely
trivial and freeze.
c) They are evidently very hard to use in a general sense.
Even google-ing for examples just comes up with trivial examples of
MArray usage.
You might ask why I might need a MArray? I'm investigating the
feasibility of building a cycle accurate PPC750 emulator. Memory
emulates better as a mutable array. I'd like to be somewhat more
general because the various systems with which I deal aren't
necessarily 32-bit, sometimes they are 16-bit and sometimes they
aren't PPC750 (different systems hooked to a common bus.) Classes with
rank-n types looked like a good approach to solving this particular
design problem, with a default implementation.
I did try out your suggestions and here's what the code looks like now.
{-# LANGUAGE FlexibleContexts, RankNTypes, ScopedTypeVariables #-}
module Wombat where
import Control.Monad.ST;
import Data.Array.ST;
import Data.Array.Unboxed;
import Data.Array.MArray;
wombat :: forall e ix s. (IArray UArray e, Ix ix, MArray (STUArray s)
e (ST s)) = e - ix - UArray ix e - UArray ix e
wombat val idx mem = runSTUArray (unsafeThaw mem = return)
GHCi says:
[1 of 1] Compiling Wombat ( wombat.hs, interpreted )
wombat.hs:11:34:
Could not deduce (MArray (STUArray s1) e (ST s1))
from the context ()
arising from a use of `unsafeThaw'
at wombat.hs:11:34-47
Possible fix:
add (MArray (STUArray s1) e (ST s1)) to the context of
the polymorphic type `forall s. ST s (STUArray s ix e)'
or add an instance declaration for (MArray (STUArray s1) e (ST s1))
In the first argument of `(=)', namely `unsafeThaw mem'
In the first argument of `runSTUArray', namely
`(unsafeThaw mem = return)'
In the expression: runSTUArray (unsafeThaw mem = return)
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Re: [Haskell-cafe] rewrite rules
Not 100% sure (especially without source/core), but my guess is that
the higher-rank types make the rule unlikely to fire.
Try -ddump-simpl to see the core output, and look for places where you
expect the rule to fire. I suspect you will find that the types of f
and g are not forall at that point in the code, but have already
been specialized.
Is there a reason you cannot use this simpler rule?
{-# RULES transform/tranform forall f g l. transform f (transform g
l) = transform (g.f) l #-}
-- ryan
On Mon, Jun 22, 2009 at 2:41 AM, Sjoerd Visschersjo...@w3future.com wrote:
Hi all,
I have a rewrite rule as follows:
{-# RULES
transform/transform forall (f::forall m. Monoid m = (a - m) - (b - m))
(g::forall m. Monoid m = (b - m) - (c - m))
(l::FMList c). transform f (transform g l) =
transform (g.f) l
#-}
It fires on this code:
print $ transform (. (*2)) (transform (. (+1)) (upto 10))
But it doesn't fire on this code:
print $ map (*2) (map (+1) (upto 10)))
with
map g x = transform (. g) x
and with or without {-# INLINE map #-}.
What am I doing wrong?
--
Sjoerd Visscher
sjo...@w3future.com
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Re: [Haskell-cafe] Type system trickery
Brent Yorgey wrote: On Sun, Jun 21, 2009 at 09:16:12PM +0100, Andrew Coppin wrote: Niklas Broberg wrote: That's what GADTs are for: data Flag = HasZoo | NoZoo data Foobar a where Foo :: Foobar a - Foobar a Bar :: Foobar a - Foobar a Zoo :: Foobar a - Foobar HasZoo Ouch #1: This appears to instantly disable deriving the Eq, Ord and Show instances I want. :-/ Ah, yes, that is a pain. Maybe try playing around with tools like Data.Derive? I haven't played with them much myself so I don't know if they will help. Not nearly as annoying as this: data Foobar a where Foo :: X - Y - Foobar NoZoo Bar :: X - Y - Foobar NoZoo Zoo :: Foobar NoZoo - Foobar Zoo For some reason, if I do this I get endless type check errors. I have to change the top two back to Foobar a before it will work. *sigh* ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Getting my mind around UArray - STUArray conversion
scooter.phd: On Fri, Jun 19, 2009 at 7:08 PM, Dan Doeldan.d...@gmail.com wrote: Oops, I replied too hastily. What I wrote in my first mail is a problem, as witnessed by the ix and ix1 in the error message. However, it isn't the main error. The main error is that you have a monadic expression, with type something like: ST s (UArray ix e) but the return type of your function is: UArray ix e To make a no-op you need to add a runST, something like: runST (unsafeThaw mem = unsafeFreeze) Actually, I probably wanted runSTUArray. :-) But even then, I can't manage to get wombat to compile correctly. I'm starting to think that MArray is itself a WOMBAT (waste of money, brains and time), for three reasons: a) Overly restrictive Monads in which implementation is supported (i.e., ST and IO) b) The triviality of the examples gives no insight as to how they could be used, other than a create array, do something completely trivial and freeze. c) They are evidently very hard to use in a general sense. Even google-ing for examples just comes up with trivial examples of MArray usage. Can you just use STUArrays directly without worrying about MArray overloading? writeArray/readArray on ST is just type safe raw memory access, so should be easy. wombat :: forall e ix s. (IArray UArray e, Ix ix, MArray (STUArray s) e (ST s)) = e - ix - UArray ix e - UArray ix e wombat val idx mem = runSTUArray (unsafeThaw mem = return) Argh. That type is scary overloaded. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type system trickery
Not nearly as annoying as this: data Foobar a where Foo :: X - Y - Foobar NoZoo Bar :: X - Y - Foobar NoZoo Zoo :: Foobar NoZoo - Foobar Zoo For some reason, if I do this I get endless type check errors. I have to change the top two back to Foobar a before it will work. *sigh* Well, that means something very different obviously. It means Zoo constructors can never take Zoo arguments, so you could only have at most one Zoo constructor at the outermost level, having either a Foo or a Bar inside it. Why would that give you type check errors? If it does, you're doing something else wrong. Cheers, /Niklas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type system trickery
Andrew Coppin said:
data Foobar a where
Foo :: X - Y - Foobar NoZoo
Bar :: X - Y - Foobar NoZoo
Zoo :: Foobar NoZoo - Foobar Zoo
For some reason, if I do this I get endless type check errors. I have to
change the top two back to Foobar a before it will work. *sigh*
That code snippet works for me, so I think you're doing something else
wrong or I transcribed wrong
My code in full:
-
{-# LANGUAGE GADTs, EmptyDataDecls #-}
data NoZoo
data Zoo
data Place a where
Office :: String - Int - Place NoZoo
Home :: String - Int - Place NoZoo
Zoo:: Place NoZoo - Place Zoo
-
It works fine (but I absolutely agree the lack of deriving is frustrating):
-
*Main let x = Zoo (Office 9th street 3342)
*Main let y = Home Friends House 4422
*Main :t x
x :: Place Zoo
*Main :t y
y :: Place NoZoo
*Main
And if you want to change it wrt Niklas's comments:
---
{-# LANGUAGE GADTs, EmptyDataDecls #-}
data NoZoo
data Zoo
data Place a where
Office :: String - Int - Place NoZoo
Home :: String - Int - Place NoZoo
Zoo:: Place a - Place Zoo
---
Which works:
---
*Main let x = Zoo (Zoo (Office 9th street 3342))
*Main let y = Home Friends House 4422
*Main :t x
x :: Place Zoo
*Main :t y
y :: Place NoZoo
-
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[Haskell-cafe] ANN: hledger 0.6.1 released
I have released hledger 0.6.1 which fixes a build problem with ghc 6.8. You can ignore this release if you use a newer ghc or if one of the http://hledger.org/binaries works for you. Thanks to Andreas Reuleaux for the report. More reports welcome on irc, list or http://code.google.com/p/hledger/issues . Best, -Simon (sm) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Getting my mind around UArray - STUArray conversion
Hello Scott, Monday, June 22, 2009, 10:23:42 PM, you wrote: wombat :: forall e ix s. (IArray UArray e, Ix ix, MArray (STUArray s) e (ST s)) = e - ix - UArray ix e - UArray ix e http://haskell.org/haskellwiki/Library/ArrayRef#Reimplemented_Arrays_library Unboxed arrays now can be used in polymorphic functions... -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing spelling correction program
On Jun 22, 6:46 am, Bulat Ziganshin bulat.zigans...@gmail.com wrote: Hello Kamil, Monday, June 22, 2009, 12:01:40 AM, you wrote: Right... Python uses hashtables while here I have a tree with log n you can try this pure hashtable approach: import Prelude hiding (lookup) import qualified Data.HashTable import Data.Array import qualified Data.List as List data HT a b = HT (a-Int) (Array Int [(a,b)]) -- size is the size of array (we implent closed hash) -- hash is the hash function (a-Int) -- list is assoclist of items to put in hash create size hash list = HT hashfunc (accumArray (flip (:)) [] (0, arrsize-1) (map (\(a,b) - (hashfunc a,b)) list) ) where arrsize = head$ filter (size)$ iterate (\x-3*x+1) 1 hashfunc a = hash a `mod` arrsize lookup a (HT hash arr) = List.lookup a (arr!hash a) main = do let assoclist = [(one, 1), (two, 2), (three, 3)] hash = create 10 (fromEnum . Data.HashTable.hashString) assoclist print (lookup one hash) print (lookup zero hash) It does not compile: No instance for (Num (String, b)) arising from the literal `3' at foo.hs:23:61 Possible fix: add an instance declaration for (Num (String, b)) In the expression: 3 In the expression: (three, 3) In the expression: [(one, 1), (two, 2), (three, 3)] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type system trickery
Niklas Broberg wrote: Not nearly as annoying as this: data Foobar a where Foo :: X - Y - Foobar NoZoo Bar :: X - Y - Foobar NoZoo Zoo :: Foobar NoZoo - Foobar Zoo For some reason, if I do this I get endless type check errors. I have to change the top two back to Foobar a before it will work. *sigh* Well, that means something very different obviously. It means Zoo constructors can never take Zoo arguments. ...which would be precisely what I want, yes. :-) Why would that give you type check errors? If it does, you're doing something else wrong. I think (I'm not sure) it's because of stuff like this: foobar :: Foobar a - X foobar f = case f of Foo x y - ... Zoo g - foobar g The first case implies that f :: Foobar NoZoo, while the second implies that f :: Foobar Zoo. Apparently this seemingly reasonable construct does not type-check... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type system trickery
This works for me:
{-# LANGUAGE EmptyDataDecls, GADTs #-}
module Main where
data NoZoo
data Zoo
newtype X = X Int deriving (Show)
newtype Y = Y Char deriving (Show)
data Foobar a where
Foo :: X - Y - Foobar NoZoo
Bar :: X - Y - Foobar NoZoo
Zoo :: Foobar NoZoo - Foobar Zoo
foobar :: Foobar a - X
foobar f = case f of
Foo x _ - x
Zoo g - foobar g
main :: IO ()
main = putStrLn . show $ foobar (Zoo $ Foo (X 1) (Y 'a'))
Could you post a test case?
On Jun 22, 2009, at 3:34 PM, Andrew Coppin wrote:
Niklas Broberg wrote:
Not nearly as annoying as this:
data Foobar a where
Foo :: X - Y - Foobar NoZoo
Bar :: X - Y - Foobar NoZoo
Zoo :: Foobar NoZoo - Foobar Zoo
For some reason, if I do this I get endless type check errors. I
have to
change the top two back to Foobar a before it will work. *sigh*
Well, that means something very different obviously. It means Zoo
constructors can never take Zoo arguments.
...which would be precisely what I want, yes. :-)
Why would that give you type check errors? If it
does, you're doing something else wrong.
I think (I'm not sure) it's because of stuff like this:
foobar :: Foobar a - X
foobar f = case f of
Foo x y - ...
Zoo g - foobar g
The first case implies that f :: Foobar NoZoo, while the second
implies that f :: Foobar Zoo. Apparently this seemingly reasonable
construct does not type-check...
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Re: [Haskell-cafe] Re: Optimizing spelling correction program
Am Montag 22 Juni 2009 21:31:50 schrieb Kamil Dworakowski: On Jun 22, 6:46 am, Bulat Ziganshin bulat.zigans...@gmail.com wrote: Hello Kamil, Monday, June 22, 2009, 12:01:40 AM, you wrote: Right... Python uses hashtables while here I have a tree with log n you can try this pure hashtable approach: import Prelude hiding (lookup) import qualified Data.HashTable import Data.Array import qualified Data.List as List data HT a b = HT (a-Int) (Array Int [(a,b)]) -- size is the size of array (we implent closed hash) -- hash is the hash function (a-Int) -- list is assoclist of items to put in hash create size hash list = HT hashfunc (accumArray (flip (:)) [] (0, arrsize-1) (map (\(a,b) - (hashfunc a,b)) Typo: should be map (\(a,b) - (hashfunc a, (a,b)) list) ) where arrsize = head$ filter (size)$ iterate (\x-3*x+1) 1 hashfunc a = hash a `mod` arrsize lookup a (HT hash arr) = List.lookup a (arr!hash a) main = do let assoclist = [(one, 1), (two, 2), (three, 3)] hash = create 10 (fromEnum . Data.HashTable.hashString) assoclist print (lookup one hash) print (lookup zero hash) It does not compile: No instance for (Num (String, b)) arising from the literal `3' at foo.hs:23:61 Possible fix: add an instance declaration for (Num (String, b)) In the expression: 3 In the expression: (three, 3) In the expression: [(one, 1), (two, 2), (three, 3)] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing spelling correction program
On Jun 22, 9:10 am, Ketil Malde ke...@malde.org wrote: Kamil Dworakowski ka...@dworakowski.name writes: Right... Python uses hashtables while here I have a tree with log n access time. I did not want to use the Data.HashTable, it would pervade my program with IO. The alternative is an ideal hashmap that never gets changed. This program creates a dictionary at start which then is only being used to read from: an ideal application for the Data.PerfectHash by Mark Wotton available on Hackage [3]. If you are considering alternative data structures, you might want to look at tries or Bloom filters, both have O(n) lookup, both have Haskell implementations. The latter is probably faster but probabilistic (i.e. it will occasionally fail to detect a misspelling - which you can of course check against a real dictionary). Using Bryan O'Sullivan's fantastic BloomFilter I got it down below Python's run time! Now it is 35.56s, 28% of the time is spent on GC, which I think means there is still some room for improvement. Do you say that PerfectHash runs with a penalty of calling into c library? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing spelling correction program
On Jun 22, 9:06 pm, Daniel Fischer daniel.is.fisc...@web.de wrote: Am Montag 22 Juni 2009 21:31:50 schrieb Kamil Dworakowski: On Jun 22, 6:46 am, Bulat Ziganshin bulat.zigans...@gmail.com wrote: Hello Kamil, Monday, June 22, 2009, 12:01:40 AM, you wrote: Right... Python uses hashtables while here I have a tree with log n you can try this pure hashtable approach: import Prelude hiding (lookup) import qualified Data.HashTable import Data.Array import qualified Data.List as List data HT a b = HT (a-Int) (Array Int [(a,b)]) -- size is the size of array (we implent closed hash) -- hash is the hash function (a-Int) -- list is assoclist of items to put in hash create size hash list = HT hashfunc (accumArray (flip (:)) [] (0, arrsize-1) (map (\(a,b) - (hashfunc a,b)) Typo: should be map (\(a,b) - (hashfunc a, (a,b)) Wait! Have you typed that definition into the msg off the top of your head? :) I went back to using Strings instead of ByteStrings and with that hashtable the program finishes in 31.5s! w00t! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskelldb + sqlite problem.
Magicloud Magiclouds wrote:
Hi,
I am using haskelldb and haskelldb-hdbc-sqlite3. Well, I finally got
the source compiled and ran, I got this error:
App: user error (SQL error: SqlError {seState = , seNativeError =
21, seErrorMsg = prepare 74: SELECT subject,\n timestamp\nFROM
notes as T1\nORDER BY timestamp DESC: library routine called out of
sequence})
Any clue what I should check? Thanks.
At the HDBC level, I would say:
I suspect that you have used a function that returns results lazily, but
haven't completely read them before calling back into the database with
something else. As an example, you should probably use quickQuery'
instead of quickQuery, unless you are fully prepared to accept the
consequences of reading data lazily from a database.
I am not very familiar with HaskellDB, and can't really comment on what
it's doing under the hood. If it is returning results to you lazily,
make sure you have completely consumed them before sending more queries
to the database.
If you can post some example code, it would likely help.
-- John
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Re: [Haskell-cafe] Re: Optimizing spelling correction program
Hello Kamil, Tuesday, June 23, 2009, 12:54:49 AM, you wrote: I went back to using Strings instead of ByteStrings and with that hashtable the program finishes in 31.5s! w00t! and GC times are? also, try ByteString+HT, it should be pretty easy to write hashByteString -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: haskelldb + sqlite problem.
Günther Schmidt wrote: Hi Cloud, this often occurs when the path to the database includes a non-ascii character. In my dev environment, the path to the database deliberately contains an umlaut and the original code base of hdbc.sqlite3 from John Goerzen, version 2.0 version 2.1 thus does not work. This is conflating many issues. I do recall some discussion about data within a database; I don't recall one about the filename of it, which would certainly be a separate discussion. I can see why a connectRaw or some such function could be useful if you want to pass a raw binary string as the file path to Sqlite3. (I don't think any other DB would have a use for such a thing). John Goerzen, the author of HDBC has considerably rewritten some parts of his hdbc package to use utf8-string wrapping, which includes wrapping the connection string, and in my case caused considerable problems, it just wouldn't work. So my solution was to rollback all these changes where he used the utf8-wrapping, which was quite a lot of work. I did And unnecessary work at that, if all you cared about was the filename. I see your point on the filename, and tweaking that would have been a one-line fix for you. The mess we had before was this huge cloud of **UNDEFINED BEHAVIOR** when dealing with anything other than 7-bit ASCII. Databases could have some encodings, systems could have encodings, and it was all a huge fiasco. So with HDBC 2, what we have is: * If you want to communicate with the database in a raw manner, use ByteStrings. If you want a String out of it, convert it yourself. * If you want to use Strings to communicate with the databases, these will automatically be converted to the appropriate Unicode representation by the library. For all current database backends, that means converting them to a UTF-8 CStringLen type of thing, and back. Anyway what you can do, for now, is to put your sqlite3 database file into a location where the path contains no non-ascii characters, that should fix the problem. His problem is not caused by non-ASCII characters. You may experience other, utf8-wrapping related problems, for instance when you want to insert non-ascii strings into varchar columns. They may not come back as you put them in. They will, unless you are doing something weird like putting Latin1 8-bit text into a String and passing it to HDBC as a String, when the documentation specifically states that Strings are expected to be in the Unicode space. As I recall, that is specifically what you were doing. That doesn't mean I haven't provided an outlet for you to do deal with things in the Latin1 space (see the ByteString discussion above.) But in truth, HDBC is not a character set conversion library, nor should it be. If you have more complex needs than Unicode Strings, use one of the many quality encoding libraries available for Haskell, and combine it with the ByteString features in HDBC. Every popular database that I am aware of can either speak UTF-8 directly, or convert transparently to and from it. So, to summarize: 1) This is not the original poster's problem. 2) HDBC 2 is simpler than HDBC 1, and actually defines behavior in terms of character sets rather than leaving it completely undefined. 3) HDBC 2 standardizes character sets around UTF-8, the most common global standard, and structures its API in a way that this is transparent when you want it to be, and available for manual processing when you want that. 4) Nothing requires you to use UTF-8, which is why the ByteString API is there. 5) A one-line patch would have fixed your filename connection issue. 6) If memory serves, your not getting things back is because you are storing non-Unicode data in your Strings, and then using an improper API to store it. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Optimizing spelling correction program
Am Montag 22 Juni 2009 22:54:49 schrieb Kamil Dworakowski: Wait! Have you typed that definition into the msg off the top of your head? :) No, took a bit of looking. I went back to using Strings instead of ByteStrings and with that hashtable the program finishes in 31.5s! w00t! Nice :D ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Optimizing spelling correction program
kamil: On Jun 22, 9:10 am, Ketil Malde ke...@malde.org wrote: Kamil Dworakowski ka...@dworakowski.name writes: Right... Python uses hashtables while here I have a tree with log n access time. I did not want to use the Data.HashTable, it would pervade my program with IO. The alternative is an ideal hashmap that never gets changed. This program creates a dictionary at start which then is only being used to read from: an ideal application for the Data.PerfectHash by Mark Wotton available on Hackage [3]. If you are considering alternative data structures, you might want to look at tries or Bloom filters, both have O(n) lookup, both have Haskell implementations. The latter is probably faster but probabilistic (i.e. it will occasionally fail to detect a misspelling - which you can of course check against a real dictionary). Using Bryan O'Sullivan's fantastic BloomFilter I got it down below Python's run time! Now it is 35.56s, 28% of the time is spent on GC, which I think means there is still some room for improvement. One easy way to fix the GC time is to increase the default heap size. ./a.out +RTS -A200M for example. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: haskelldb + sqlite problem.
John Goerzen wrote: I do recall some discussion about data within a database; I don't recall one about the filename of it, which would certainly be a separate discussion. I can see why a connectRaw or some such function could be I have just pushed a patch to my git repo that adds connectSqlite3Raw to help in these cases. You can grab the diff directly here: http://git.complete.org/hdbc-sqlite3?a=commitdiff_plain;h=0ef5df694d74cfaea7da3fcfc97037411d3f13bb -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
On Mon, 22 Jun 2009, Jules Bean wrote: Miguel Mitrofanov wrote: I so don't want to be the one supporting your code... Well, that's lucky. Because you aren't. I think the most frequent warning which denotes actually an error for me, is the 'unused identifier' warning, since there are often identifiers that I planned to use but forgot to use. The shadowing problem is less often a problem for me. When I refer to the wrong identifier this usually spotted by the type system, but the type system cannot find out the reason for the problem, namely two identifiers with the same name in the same scope. Sometimes I wish warnings would be emitted before (type) errors. For reading the code however it is a clear advantage to have separate names for separate things. The prime is not enough for me. Even more in a GHC error message, I often think identifier `bar'' refers to bar not bar'. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
On Mon, 22 Jun 2009, Malcolm Wallace wrote: Example: f a b = g (a+b) (b-a) where g a c = a*c ghc warns that g's parameter a shadows the parameter to f. So we introduce a primed identifier to eliminate the warning: f a b = g (a+b) (b-a) where g a' c = a*c Now, no warnings! But, oops, this function does not do the same thing. We forgot to add a prime to all occurrences of a on the right-hand-side. Actually there will be the warning, that a' is unused. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: Optimizing spelling correction program
Hello Don, Tuesday, June 23, 2009, 1:22:46 AM, you wrote: One easy way to fix the GC time is to increase the default heap size. ./a.out +RTS -A200M to be exact, -A isn't a heap size - it's frequency of generation-1 collections. by default, collection perfromed every 512kbytes, tied to L2 cache of CPUs -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: haskelldb + sqlite problem.
Hi John,
let me first of all apologize, I didn't mean to criticize you, I'm sure
you had good reasons for those changes, I'm merely mean to state how
they did affect me after switching to HDBC 2.1.
Since after the rollback they no longer occurred I surmise that there is
a connection.
The error that Magicloud describes I recall only occurring when an
umlaut in the path to the database file, that may or may not be due to
the utf8-wrapping or it may just be a problem of the sqlite3.dll. No
harm in trying if it can be solved this way by just moving the database
file to one without any non-ascii characters. While I don't think that
umlauts actually cause Magiclouds problem I did notice that he signs his
emails with Chinese symbols, quite possible thus, that he has paths on
his machine with non-ascii characters.
Günther
John Goerzen schrieb:
Magicloud Magiclouds wrote:
Hi,
I am using haskelldb and haskelldb-hdbc-sqlite3. Well, I finally got
the source compiled and ran, I got this error:
App: user error (SQL error: SqlError {seState = , seNativeError =
21, seErrorMsg = prepare 74: SELECT subject,\n timestamp\nFROM
notes as T1\nORDER BY timestamp DESC: library routine called out of
sequence})
Any clue what I should check? Thanks.
At the HDBC level, I would say:
I suspect that you have used a function that returns results lazily, but
haven't completely read them before calling back into the database with
something else. As an example, you should probably use quickQuery'
instead of quickQuery, unless you are fully prepared to accept the
consequences of reading data lazily from a database.
I am not very familiar with HaskellDB, and can't really comment on what
it's doing under the hood. If it is returning results to you lazily,
make sure you have completely consumed them before sending more queries
to the database.
If you can post some example code, it would likely help.
-- John
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Re: [Haskell-cafe] Re: haskelldb + sqlite problem.
Günther Schmidt wrote: Hi John, let me first of all apologize, I didn't mean to criticize you, I'm sure you had good reasons for those changes, I'm merely mean to state how they did affect me after switching to HDBC 2.1. No, I completely understand and I'm not offended; but I didn't want people reading this message to get the wrong idea about the state of Unicode support in HBDC. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell on the iPhone
Dear Haskellers, Recently, there's been a groundswell of activity in the Haskell community regarding the Haskell's use in developing iPhone games. The iPhone is a powerful, innovative platform (with a great monetization scheme, to boot), and it's not surprising that many of us would want to develop apps for it in our favorite language. I am proud to announce today that my company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. As the first (to my knowledge) Haskell-based game studio, iPwn Studios is committed to giving back to the Haskell community through open source - contributing to a rising tide that lifts us all. I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. Best wishes, Ryan Trinkle President, iPwn Studios Inc. P.S.: If you wish to be involved in the preparation of the GHC patch or in the creation of iPwn Studios' first game, don't hesitate to contact me by email (ryant5...@gmail.com), AIM (RyanT5000), or IRC (RyanT5000 on irc.freenode.net). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] FFI and heap memory usage limit
Hello, Recently I've come across a certain GC/FFI-related problem. I've googled a bit, but didn't find anything specific. I'm running certain simulations, which tend to allocate a lot of garbage in memory. Since this causes the OOM-killer to kill my simulation at 98% completion, I used the -M switch, and all was well. But because my simulation results are fairly big, I needed to compress them with bz2 before sending them over the network. So I used bzlib. Now this took an odd turn, because the simulation started crashing with out-of-memory errors _after_ completing (during bz2 compression). I'm fairly certain this is a GC/FFI bug, because increasing the max heap didn't help. Moving the bz2 compression to a separate process provided a reasonable solution. What I think is happening is that after the simulation completes, almost all of the available memory (within the -M limit) is filled with garbage. Then I run bzlib which tries to allocate more memory (from behind FFI?) to compress the results, which in turn causes an out-of-memory error instead of triggering a GC collection. I'm writing to ask if this is a known/fixed issue. I'm using ghc 6.10.3, bzlib 0.5.0.0. If this is something new then I'll try to come up with a small program which demonstrates the problem. -- Marcin Kosiba ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on the iPhone
On Mon, Jun 22, 2009 at 3:30 PM, Ryan Trinkle ryant5...@gmail.com wrote: Dear Haskellers, Recently, there's been a groundswell of activity in the Haskell community regarding the Haskell's use in developing iPhone games. The iPhone is a powerful, innovative platform (with a great monetization scheme, to boot), and it's not surprising that many of us would want to develop apps for it in our favorite language. I am proud to announce today that my company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. As the first (to my knowledge) Haskell-based game studio, iPwn Studios is committed to giving back to the Haskell community through open source - contributing to a rising tide that lifts us all. Hi Ryan, This is great news! Thanks! Does iPwn have any up coming titles? Perhaps a blog where we could read about them so the advertising doesn't hit the list. I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. Sounds good to me. Please post back here if it gets created. Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on the iPhone
Jason, iPwn is currently in pre-production for its first title, which will be an action-RPG reminiscent of Diablo and Fallout. I'll try to keep the shameless plugging on Haskell-cafe to a minimum, but I make no promises :P I will definitely let people know when our website is put together in some useful way. Ryan On Mon, Jun 22, 2009 at 18:34, Jason Dagit da...@codersbase.com wrote: On Mon, Jun 22, 2009 at 3:30 PM, Ryan Trinkle ryant5...@gmail.com wrote: Dear Haskellers, Recently, there's been a groundswell of activity in the Haskell community regarding the Haskell's use in developing iPhone games. The iPhone is a powerful, innovative platform (with a great monetization scheme, to boot), and it's not surprising that many of us would want to develop apps for it in our favorite language. I am proud to announce today that my company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. As the first (to my knowledge) Haskell-based game studio, iPwn Studios is committed to giving back to the Haskell community through open source - contributing to a rising tide that lifts us all. Hi Ryan, This is great news! Thanks! Does iPwn have any up coming titles? Perhaps a blog where we could read about them so the advertising doesn't hit the list. I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. Sounds good to me. Please post back here if it gets created. Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on the iPhone
If you're doing it in Haskell, please feel free to keep plugging. A new market for Haskell apps is highly welcome. ryant5000: Jason, iPwn is currently in pre-production for its first title, which will be an action-RPG reminiscent of Diablo and Fallout. I'll try to keep the shameless plugging on Haskell-cafe to a minimum, but I make no promises :P I will definitely let people know when our website is put together in some useful way. Ryan On Mon, Jun 22, 2009 at 18:34, Jason Dagit da...@codersbase.com wrote: On Mon, Jun 22, 2009 at 3:30 PM, Ryan Trinkle ryant5...@gmail.com wrote: Dear Haskellers, Recently, there's been a groundswell of activity in the Haskell community regarding the Haskell's use in developing iPhone games. The iPhone is a powerful, innovative platform (with a great monetization scheme, to boot), and it's not surprising that many of us would want to develop apps for it in our favorite language. I am proud to announce today that my company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. As the first (to my knowledge) Haskell-based game studio, iPwn Studios is committed to giving back to the Haskell community through open source - contributing to a rising tide that lifts us all. Hi Ryan, This is great news! Thanks! Does iPwn have any up coming titles? Perhaps a blog where we could read about them so the advertising doesn't hit the list. I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. Sounds good to me. Please post back here if it gets created. Jason ___ 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
Re: [Haskell-cafe] FFI and heap memory usage limit
Hello Marcin, Tuesday, June 23, 2009, 2:31:13 AM, you wrote: Now this took an odd turn, because the simulation started crashing with out-of-memory errors _after_ completing (during bz2 compression). I'm fairly certain this is a GC/FFI bug, because increasing the max heap didn't help. Moving the bz2 compression to a separate process provided a reasonable solution. What I think is happening is that after the simulation completes, almost all of the available memory (within the -M limit) is filled with garbage. Then I run bzlib which tries to allocate more memory (from behind FFI?) to compress the results, which in turn causes an out-of-memory error instead of triggering a GC collection. i can propose a quick fix - alloc 10 mb using allocBytes before starting your algorithm, and free it just before starting bzlib. it may help i agree that this looks like a deficiency of memory allocator. it's better to write at ghc-users maillist (or at least make a copy to Simon Marlow) to attract attention to your message -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HaRe (the Haskell Refactorer) in action - short screencast
I've heard that many Haskellers know HaRe only as a rumour. It has been many years since the original project finished, and HaRe hasn't been maintained for quite some time, so just pointing to the sources isn't quite the right answer. The sources are still available, and build with GHC 6.8.3 (I had to fix one lineending issue on windows, iirc, and copy one old bug fix that hadn't made it into the latest release), but there is currently noone with the time or funding for maintenance, fixing bugs, making releases, or ironing out practical issues. If anyone would provide funding, people to do the work could be found, but the effort would probably be better spent on reimplementing the ideas in a GHC / Cabal environment (instead of the Haskell'98 environment targetted by our Refactoring Functional Programs project). If you've got the funding, please get in touch - even a three month run could get something started at least!-) In principle, the project experiences and lessons learned are quite well documented at the project site http://www.cs.kent.ac.uk/projects/refactor-fp/ but that doesn't give anyone an idea of what working with HaRe was like. With the recent interest in screencasts, I thought I'd make a little demo, for archival purposes. Nothing fancy, using only features that were already present in HaRe 0.3 (end of 2004), and not all of those, on a tiny 2-module example (screenspace is a bit crowded to keep the text readable on YouTube). I hope it might give a rough idea of what the papers, slides and reports are talking about, for Haskellers who weren't around at the time: http://www.youtube.com/watch?v=4I7VZV7elnY For the old HaRe team, Claus --- YouTube video description: HaRe - the Haskell Refactorer (a mini demo) [4:10] The Haskell Refactorer HaRe was developed in our EPSRC project Refactoring Functional Programs http://www.cs.kent.ac.uk/projects/refactor-fp/ Building on Programatica's Haskell-in-Haskell frontend and Strafunski's generic programming library, it supported module-aware refactorings over the full Haskell'98 language standard. Interfaces to the refactoring engine were provided for both Vim and Emacs (this demo uses HaRe via GVim on Windows). While HaRe has continued to see occasional contributions by students and researchers, who use its Haskell program transformation API as a platform for their own work, it is not currently maintained. As the Haskell environment marches on, this demo is meant to record a snapshot of what working with HaRe could be like when it still built (here with GHC 6.8.3). The lessons learned (note, eg, the preservation of comments, and the limited use of pretty-printing, to minimize layout changes) are well documented at the project site, and should be taken into account when porting the ideas to the GHC Api, or other Haskell frontends. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on the iPhone
How exciting! I fully support the creation of a new mailing list about iphone+haskell :) On Mon, Jun 22, 2009 at 6:30 PM, Ryan Trinkleryant5...@gmail.com wrote: Dear Haskellers, Recently, there's been a groundswell of activity in the Haskell community regarding the Haskell's use in developing iPhone games. The iPhone is a powerful, innovative platform (with a great monetization scheme, to boot), and it's not surprising that many of us would want to develop apps for it in our favorite language. I am proud to announce today that my company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. As the first (to my knowledge) Haskell-based game studio, iPwn Studios is committed to giving back to the Haskell community through open source - contributing to a rising tide that lifts us all. I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. Best wishes, Ryan Trinkle President, iPwn Studios Inc. P.S.: If you wish to be involved in the preparation of the GHC patch or in the creation of iPwn Studios' first game, don't hesitate to contact me by email (ryant5...@gmail.com), AIM (RyanT5000), or IRC (RyanT5000 on irc.freenode.net). ___ 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] GHCi infers a type but refuses it as type signature
Hi haskell helpers, I am new to haskell (but enthusiast). I have begun to play with State and StateT, but this very simple exercice has led me to a strange situation where GHCi recognises and accepts the type of a function but GHC won't allow it as a type signature. Here is the example (which is also a try at literate haskell). import Control.Monad.State type Play = Char type Game = [Play] -- a game is a series of plays Now, you play by issuing a char, and you win if you have played an already played char. That was my first play function, returning True if you win. play :: Play - State Game Bool play p = do ps - get put (p:ps) return $ p `elem` ps I tested this one this way: play_abc :: State Game Bool play_abc = do play 'a' play 'b' play 'c' play_abca :: State Game Bool play_abca = play_abc play 'a' Now in GHCi, runState play_abc [] yields (False, cba) runState play_abca [] yields (True, acba) Good! I was happy, now trying StateT to add IO to get console input: type IOGame = StateT Game IO run_io :: IOGame Bool - IO (Bool, Game) run_io x = runStateT x [] Now I wanted a version of play that reads a char, on the following model: play_once :: IOGame Bool play_once = do x - liftIO getChar play' x Of course I first tried to express play' using play, and failed. Eventually I copied-and-pasted play, only changing the type signature, and it worked: play' :: Play - IOGame Bool play' x = do xs - get put (x:xs) return $ x `elem` xs Now, on GHCi I was happy to type: run_io $ play_once or even run_io $ play_once play_once play_once However, how to avoid the code duplication? I just tried to remove the type signature, and yes, play2 suddenly works in both State Game and StateT Game IO: play2 x = do xs - get put (x:xs) return $ x `elem` xs play2_abc :: State Game Bool play2_abc = play2 'a' play2 'b' play2 'c' play2_once :: IOGame Bool play2_once = do x - liftIO getChar play2 x So what's the type of play2? :t play2 yields: (MonadState [a] m, Eq a) = a - m Bool Wow, nice, I get it now! However if I try to add that type signature, or even the second, more specific one below, ghci fails (signatures commented out because of that): -- play3 :: (MonadState [a] m, Eq a) = a - m Bool -- play3 :: (MonadState Game m) = Play - m Bool play3 x = do xs - get put (x:xs) return $ x `elem` xs It seems that an extension is required: Non type-variable argument in the constraint: MonadState [a] m (Use -XFlexibleContexts to permit this) In the type signature for `play3': play3 :: (MonadState [a] m, Eq a) = a - m Bool So how is it possible that GHCi can infer (and use) a type that you cannot use as signature? And is it really non standard to avoid such code duplication? I was a bit surprised that such simple example should require a compiler extension. Thanks! Eric ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHCi infers a type but refuses it as type signature
On Tue, Jun 23, 2009 at 02:02:25AM +0200, Eric wrote: It seems that an extension is required: Non type-variable argument in the constraint: MonadState [a] m (Use -XFlexibleContexts to permit this) In the type signature for `play3': play3 :: (MonadState [a] m, Eq a) = a - m Bool So how is it possible that GHCi can infer (and use) a type that you cannot use as signature? Simple: the definition of MonadState uses those extensions. If the library was part of your code you would have had to turn on some extensions, but you could have used them only on some files (e.g. using LANGUAGE pragma). Here the same thing is happening, but the library is not part of your code. Errr, not a great explanation, but I HTH anyway. :) -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: haskell-src-exts-1.0.0
Fellow Haskelleers, It is with great pleasure I hereby announce the first stable release of the haskell-src-exts package, version 1.0.0! haskell-src-exts is a package for Haskell source code manipulation. In particular it defines an abstract syntax tree representation, and a parser and pretty-printer to convert between this representation and String. It handles (almost(*)) all syntactic extensions to the Haskell 98 standard implemented by GHC, and the parsing can be parametrised on what extensions to recognise. I wish to thank the glorious Haskell community, for giving me the chance to work on this project as part of Haskell.org's GSoC programme, but also for simply being such a nice place to be! Special thanks to everyone who helped me with testing and bug reports during the final stretch of release candidates, in particular the many excellent reports from Ganesh Sittampalam, Sebastian Fischer, and Neil Mitchell who is also mentoring the project. You're all awesome! haskell-src-exts-1.0.0: = Via cabal: cabal install haskell-src-exts-1.0.0 Via darcs: darcs get http://code.haskell.org/haskell-src-exts On hackage: http://hackage.haskell.org/package/haskell-src-exts-1.0.0 Changes from 0.5.7, the last release candidate: == * CPP lines are no longer ignored, which means haskell-src-exts will now invariably give a parse error on files with CPP pragmas in them. CPP is not supported by haskell-src-exts, and this is more intuitive than parsing e.g. all branches of an #if pragma, which is invariably give unintended results. * Fixed a stupid introduced bug where extensions passed int he parse mode were ignored. * fromParseOk is now exported, not just defined (doh). * ScopedTypeVariables now implies TypeOperators, as per GHC. I'm sure there are more implications that are missing from haskell-src-exts, I will add them as I find out about them. Thanks once again, and Happy Haskell Hacking to all! Cheers, /Niklas (*) The only two exceptions are NewQualifiedOperators and UnicodeSyntax. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] STM/Data Invariant related Segfault with GHC 6.10.3
Jan Schaumlöffel wrote: I just discovered that programs compiled with GHC 6.10.3 segfault when accessing a TVar created under certain conditions. This is a known bug, but it hasn't gotten much attention: http://hackage.haskell.org/trac/ghc/ticket/3049 Bertram ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: haskell-src-exts-1.0.0
It is with great pleasure I hereby announce the first stable release of the haskell-src-exts package, version 1.0.0! There's a kind of programming work that have great intelectual impact, as it lets you see your code in diferent ways. Yours, however, is of a special kind, as it has a physical impact on those who use it. With haskell-src-exts, all the time I'm typing Haskell I feel less pain in my fingers, since now I can get beautifull pretty-printed code with no thumb pain. Haskell is now a more pleasant experience. It handles (almost(*)) all syntactic extensions to the Haskell 98 standard implemented by GHC, (...) (*) The only two exceptions are NewQualifiedOperators and UnicodeSyntax. How far is Unicode from beeing parsed? It doesn't seem to be a huge step (from my ill-informed viewpoint), and it would not let behind those who are happy to be able to declare names in their own native language. (Oh, and sorry for resorting to politically correct blackmail...) Best, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] IMO ghc 6.8.2 misleading warning messages
Hello, For: parseOptional = Parse.parseOptional I got warning messages: Swish/HaskellUtils/ParseURI.hs:77:4: Warning: Defined but not used: `parseOptional' Swish/HaskellUtils/ParseURI.hs:77:4: Warning: Definition but no type signature for `parseOptional' Inferred type: parseOptional :: forall a b. Parse.Parser a [b] - [a] - [([b], [a])] IMO the warning messages should be reversed! (parseOptional was never used .. called ... but I would strongly prefer the type signature warning first. Kind regards, Vasili ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Haskell on the iPhone
On Mon, 22 Jun 2009 18:30:50 -0400, Ryan Trinkle ryant5...@gmail.com wrote: [...] I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. This sounds like a great idea. Please count my vote in favor of this new mailing list. -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on the iPhone
Rick, I know some work has been done on JVM - iirc, Don Stewart did some work back in the day, www.cse.unsw.edu.au/~pls/thesis/dons-thesis.ps.gz, but I'm not sure how comprehensive it is. Is anyone else interested in JVM-based Haskell targets? Ryan On Mon, Jun 22, 2009 at 20:42, Rick R rick.richard...@gmail.com wrote: This is definitely good news! So... who's doing the Android/JVM target? ;) On Mon, Jun 22, 2009 at 7:37 PM, Daniel Peebles pumpkin...@gmail.comwrote: How exciting! I fully support the creation of a new mailing list about iphone+haskell :) On Mon, Jun 22, 2009 at 6:30 PM, Ryan Trinkleryant5...@gmail.com wrote: Dear Haskellers, Recently, there's been a groundswell of activity in the Haskell community regarding the Haskell's use in developing iPhone games. The iPhone is a powerful, innovative platform (with a great monetization scheme, to boot), and it's not surprising that many of us would want to develop apps for it in our favorite language. I am proud to announce today that my company, iPwn Studios Inc., is currently preparing to release an open source patch to GHC that allows it to output binaries for iPhone OS. The patch will be released under a BSD license as soon as possible and hopefully integrated into the GHC main-line in the near future. As the first (to my knowledge) Haskell-based game studio, iPwn Studios is committed to giving back to the Haskell community through open source - contributing to a rising tide that lifts us all. I would like to take this opportunity to propose the creation of a haskell-iphone mailing list, so that all Haskellers working with the iPhone - whether for profit or for pleasure - can come together to make Haskell a force to be reckoned with in the burgeoning iPhone App marketplace. Best wishes, Ryan Trinkle President, iPwn Studios Inc. P.S.: If you wish to be involved in the preparation of the GHC patch or in the creation of iPwn Studios' first game, don't hesitate to contact me by email (ryant5...@gmail.com), AIM (RyanT5000), or IRC (RyanT5000 on irc.freenode.net). ___ 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 -- The greatest obstacle to discovering the shape of the earth, the continents, and the oceans was not ignorance but the illusion of knowledge. - Daniel J. Boorstin ___ 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
