- Libraries - Haskell.org

Readline readHistory & writeHistory API broken
by Krasimir Angelov 11 Jun '08

11 Jun '08

The current readHistory and writeHistory bindings are defined as: -- |Read in a history file. Returns 'False' on failure -- (for example, if the file does not exist). readHistory :: FilePath -- ^ The file to read (if null, read ~\/.history) -> IO Bool readHistory fp = do ok <- withCString fp read_history return (ok==0) foreign import ccall unsafe read_history :: Ptr CChar -> IO CInt -- |Write out a history file. Returns 'False' if there was a problem writing the file. writeHistory :: FilePath -- ^ The file to write (if null, write ~\/.history) -> IO Bool writeHistory fp = do ok <- withCString fp write_history return (ok==0) foreign import ccall unsafe write_history :: Ptr CChar -> IO CInt Note the comments "(if null, write ~/.history)"! This is supported in the original C API but in Haskell the filepath cannot be null. In the best case it can be empty string. Either the type signatures have to be changed to accept (Maybe FilePath) or the comments have to be changed because the Haskell binding currently doesn't support this functionality. Comments? I hope that this will not start another endless discussion. Regards, Krasimir

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Feature request: more transparency for Data.Graph.Inductive.NodeMap
by Misha Aizatulin 11 Jun '08

11 Jun '08

hello, would it be possible to add functions to NodeMap for inspecting the contents of the map? I would be particularly interested in a function like toList :: NodeMap a -> [LNode a] If I use a node map m to construct a graph g, then of course (labNodes g) would achieve the same as (toList m), but if I later transform the labels of the graph, say using nmap, then I cannot do it anymore - the connection between old label values and nodes is still a valuable piece of information, but I cannot access it. Cheers, Misha

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Fwd: [Haskell-cafe] Data.Tree.Zipper in the standard libraries
by Krasimir Angelov 09 Jun '08

09 Jun '08

Ups! According to the library submission procedure this message should have been sent to libraries(a)haskell.org. I appologise for the multiple copies. ---------- Forwarded message ---------- From: Krasimir Angelov <kr.angelov(a)gmail.com> Date: Sat, May 31, 2008 at 10:42 AM Subject: Re: [Haskell-cafe] Data.Tree.Zipper in the standard libraries To: Haskell-cafe <haskell-cafe(a)haskell.org> Hi again, I was silent for some time but in this time I created QuickCheck tests for Data.Tree.Zipper which achieve 100% coverage with HPC. I also created a ticket for it: Ticket #2324 http://hackage.haskell.org/trac/ghc/ticket/2324 The attached file is the current implementation and it contains the version updated from Iavor Diatchki. It has the advantage that it also works with forests, not just with trees. Initially I thought that complete testsuite for such a simple module might be overkill but actually I found a bug :-) in the splitChildren function which is now fixed. The dead line for further considerations is one week. Regards, Krasimir On Sun, May 25, 2008 at 1:09 AM, Iavor Diatchki <iavor.diatchki(a)gmail.com> wrote: > Hello, > I think that the modified API (no state monad, and using Maybe) is > quite nice! I implemented a version of the the suggested API using a > slightly different data structure, which makes the code a bit simpler, > I think. I put the code in the Haskell wiki: > http://www.haskell.org/sitewiki/images/2/2d/RoseZipper.hs > I also added a couple of extra functions that seemed useful, and > renamed a few of the functions to be more consistent. > > As for how to distribute the code, it seems that Zipper should live in > the same place as Data.Tree. I think that Data.Tree is part of the > "containers" package, so it would make sense to add the Zipper there > as well. > > -Iavor > > > > On Sat, May 24, 2008 at 1:24 AM, Neil Mitchell <ndmitchell(a)gmail.com> wrote: >> Hi, >> >>> It doesn't use State monad anymore and it returns Maybe. This seems to >>> be the common preference, is it? Feel free to vote against. Should we >>> change Data.Map also? There is another proposal for changes in >>> findMin/findMax so it is better to make this two breaking changes >>> together rather than in a later release. >> >> The standard libraries proposal thingy is to go via the libraries >> list, create tickets etc. What reason is there to make this part of >> the base libraries, rather than a separate package on hackage? I can't >> see much reason to make Data.Tree part of the base libraries, other >> than the fact it already is, and it could easily get moved out at a >> future date. >> >> We've seen there is some advantage in leaving the implementation >> outside the base library, as its already changed several times in the >> past few days. >> >> Thnanks >> >> Neil >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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hackage, package list, trac, some suggestions/questions
by Claus Reinke 06 Jun '08

06 Jun '08

hope this is the right list for hackage issues?-) 1. hackage trac does not seem to have a "register" option (compare hackage trac with ghc trac). individual logins are nice because: - gives individual rather than anonymous reporters - one place less to support spam email harvesters (account name instead of full email address) - "register" is always there, hence easy to find, unlike the hint hidden on the trac home page that hackage is still abusing the haskell' trac.. (i had started this email before i found that hint;-) 2. the hackage package list ought to have a link to an alphabetical index (i often know the package name, but not the likely categories, so i tend to 'search' on that page..). 3. the hackage package list ought to list successful and failed builds (simply a list of compiler versions, each one green or red, depending on success, with direct link to build/ failure log; this would fit into the one-line-per-package format) for each entry, and report them to package authors. build failures currently seem to be created automatically where package authors may not notice them? at least, that would explain things like (just examples of things i happened to have looked at, no offence intended;-) - hint: advertised to work with ghc 6.8.x on the same package page that lists a build failure for ghc-6.8 - haskell-src-exts: lists a build failure for ghc-6.8 the first is probably a too optimistic cabal version spec, the second is a haddock issue. but that makes two out of two for package i looked up recently.. 4. is there an cross-package index of builds/failures, so that one might see trends (cabal issues, base package issues, bytestring issues, next big thing issues,..) and statistics (how many hackage packages fail/build, which compiler/ cabal/haddock versions are successful for the largest number of packages, etc.)? 5. generally, i've always thought that hackage works the wrong way round; instead of yet another push-based place for people to put and forget copies of things, it should work as a pull-based cache: - author registers package, with author/maintainer email and package url - hackage retrieves package, tries to build, and either accepts or not, reporting all to author - occasionally, hackage scans for new versions to be retrieved, again notifying authors of uploads and problem reports - the maintainer email on each hackage package page ought to be (a) protected, not plain text (b) annotated with last successful contact date if i understand #243, authors are not even notified when someone uploads their packages? claus

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type-level integers using type families
by Peter Gavin 03 Jun '08

03 Jun '08

Has anyone else tried implementing type-level integers using type families? I tried using a couple of other type level arithmetic libraries (including type-level on Hackage) and they felt a bit clumsy to use. I started looking at type families and realized I could pretty much build an entire Scheme-like language based on them. In short, I've got addition, subtraction, & multiplication working after just a days worth of hacking. I'm going to post the darcs archive sometime, sooner if anyone's interested. I really like the type-families based approach to this, it's a lot easier to understand, and you can think about things functionally instead of relationally. (Switching back and forth between Prolog-ish thinking and Haskell gets old quick.) Plus you can do type arithmetic directly in place, instead of using type classes everywhere. One thing that I'd like to be able to do is lazy unification on type instances, so that things like data True data False type family Cond x y z type instance Cond True y z = y type instance Cond False y z = z will work if the non-taken branch can't be unified with anything. Is this planned? Is it even feasible? I'm pretty sure it would be possible to implement a Lambda like this, but I'm not seeing it yet. Any ideas? Pete

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Re: type-level integers using type families
by Peter Gavin 31 May '08

31 May '08

Benedikt Huber wrote: >> data True >> data False >> >> type family Cond x y z >> type instance Cond True y z = y >> type instance Cond False y z = z > > I'm not sure if this is what you had in mind, but I also found that e.g. > > > type instance Mod x y = Cond (y :>: x) x (Mod (Sub x y) y) > > won't terminate, as > > > Mod D0 D1 ==> Cond True D0 (Mod (Sub D0 D1) D0) ==> <loop> Right, because it always tries to infer the (Mod (Sub x y) y) part no matter what the result of (y :>: x) is. > > rather than > > > Mod D0 D1 ==> Cond True D0 ? ==> D0 > > For Mod, I used the following (usual) encoding: > > > type family Mod' x y x_gt_y > > type instance Mod' x y False = x > > type instance Mod' x y True = Mod' (Sub x y) y ((Sub x y) :>=: y) > > type family Mod x y > > type instance Mod x y = Mod' x y (x :>=: y) > Yes, it's possible to terminate a loop by matching the type argument directly. > 1) One cannot define type equality (unless total type families become > available), i.e. use the overlapping instances trick: >> instance Eq e e True >> instance Eq e e' False I didn't want to mix type classes and families in my implementation. All the predicates are implemented like so: > type family Eq x y > type instance Eq D0 D0 = True > type instance Eq D1 D1 = True ... > type instance Eq (xh :* xl) (yh :* yl) = And (Eq xl yl) (Eq xh yh) then I've added a single type-class > class Require b > instance Require True so you can do stuff like > f :: (Require (Eq (x :+: y) z)) => x -> y -> z or whatever. I haven't yet tested it (but I think it should work) :) Pete > > Consequently, all type-level functions which depend on type equality > (see HList) need to be encoded using type classes. > > 2) One cannot use superclass contexts to derive instances e.g. to define >> instance Succ (s,s') => Pred (s',s) > > In constrast, when using MPTC + FD, one can establish more than one TL > function in one definition > > > class Succ x x' | x -> x', x' -> x > > 3) Not sure if this is a problem in general, but I think you cannot > restrict the set of type family instances easily. > > E.g., if you have an instance > > > type instance Mod10 (x :* D0) = D0 > > then you also have > > > Mod10 (FooBar :* D0) ~ D0 > > What would be nice is something like > > > type instance (IsPos x) => Mod10 (x :* D0) = D0 > > though > > > type family AssertThen b x > > type instance AssertThen True x = x > > type instance Mod10 (x :* D0) = AssertThen (IsPos x) D0 > > seems to work as well. > > 4) Not really a limitation, but if you want to use instance methods of > Nat or Bool (e.g. toBool) on the callee site, you have to provide > context that the type level functions are closed w.r.t. to the type class: > >> test_1a :: forall a b b1 b2 b3. >> (b1 ~ And a b, >> b2 ~ Not (Or a b), >> b3 ~ Or b1 b2, >> Bool b3) => a -> b -> Prelude.Bool >> test_1a a b = toBool (undefined :: b3) > > Actually, I think the 'a ~ b' syntax is very nice. > > I'm really looking forward to type families. > > best regards, > > benedikt

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System.Posix.Temp
by Peter Gammie 30 May '08

30 May '08

The docs for mkstemp are somewhat short. (One must add XXXXXX to the end of the template for things to go, and probably prepend a path as well.) Apparently it is better to use tmpfile(3) now. How difficult would it be to provide that function as well? (Note the return type is FILE *.) cheers pete -- http://peteg.org/

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Proposal #2316: Add Applicative instances for all MTL Monads
by Spencer Janssen 29 May '08

29 May '08

This proposal is very straightforward: add Applicative instances for all the Monads in the MTL. Deadline for discussion is two weeks from today, June 12 2008. Cheers, Spencer Janssen

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darcs patch: Better handling of the vararg el_get function
by Judah Jacobson 29 May '08

29 May '08

The following patch fixes the issue reported today in: http://www.haskell.org/pipermail/glasgow-haskell-users/2008-May/014801.html Mon May 26 11:01:19 PDT 2008 Judah Jacobson <judah.jacobson(a)gmail.com> * Better handling of the vararg el_get function. M ./System/Console/Editline.hsc -2 +2 M ./cbits/HsEditline.c +4 M ./include/HsEditline.h -2 +1

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Re: [Haskell-cafe] library for drawing charts
by Peter Gammie 29 May '08

29 May '08

Tim, Thanks for the pointer. Just to clarify: On 26/05/2008, at 9:09 AM, Tim Docker wrote: >> I'd like 2D pie charts, bar charts and something like a google-o- >> meter. > > An the moment it does line charts and a few variants of these. I'll > add > pie and bar charts when I need them - patches in the meantime > gratefully > accepted. So the library itself supports drawing these other types of charts? Can you steer me towards some sample outputs? One thing I was most unhappy to discover was the lack of Unicode support in Google charts. Another is the lack of control over some colours (the arrow in the google-o-meter, e.g.) and labelling. When one wants to build an accessible website, these things end up breaking the deal. BTW Bjorn has written a binding to libgd. Does Cairo have similar functionality, e.g. quizzing an image file for geometry info? cheers peter

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