November 2008 - Libraries

There are too many error handling conventions used in library code!
by dons＠cse.unsw.edu.au 13 Aug '11

13 Aug '11

This article on the 8 different error handling strategies various common Haskell libs use: http://www.randomhacks.net/articles/2007/03/10/haskell-8-ways-to-report-err… got me thinking: we need to standardise/recommend a small set of methods for library error handling. The lack of consistent error reporting between libs results in verbose code, as we're not able to use a single error handling technique when gluing together code from different libs (i.e. we can't just use Maybe or Either/ErrorT). (It's always nice when you *can* use, say, a Maybe monad to glue code from a number of sources, but eventually you reach code with a different error system, and the Maybe monad breaks down). So, some questions I think we can tackle: * can we identify error handling strategies from the list that should not be used anymore? (throwDyn?) * can we move some of the outlying libraries to a more consistent error framework? * do we need more support for gluing together our different error systems? (it should be easier to glue code using , say, Maybe/Either). * what role does MonadError play here, as a generic error handler? * can we make precise recommendations about which error strategies to use? -- Don

11 16

Proposal #2629: Data.List: Replace nub; add nubOrd, nubInt, nubWith
by Bart Massey 24 Feb '10

24 Feb '10

http://hackage.haskell.org/trac/ghc/ticket/2629 Everyone always complains about nub, but nobody ever does anything about it except (map head . group . sort), which isn't lazy and isn't always faster. :-) I've implemented a new function nubWith that takes a "stop list" as an argument and filters its target list against the stop list. I've then re-implemented nub and implemented nubOrd and nubInt in terms of nubWith: the stop list is a typeclass, so these implementations are trivial and new implementations are easily added. nubBy is left alone, since there's nothing obvious to be done about it. All of the nubs are still fully lazy. Basic QuickCheck tests are provided, and pass. Performance benchmarking code is provided. The performance of my nub implementation is quite comparable to that of the standard one. My nubOrd and nubInt implementations are dramatically faster, since they use a Set and IntSet respectively for the stop list. In particular, they are performant on long lists with long nubs, unlike the basic nub. My implementation is available via git at git://svcs.cs.pdx.edu/git/nub.git or can be browsed at http://svcs.cs.pdx.edu/gitweb?p=nub.git;a=tree and has a maybe-outdated tarball at http://svcs.cs.pdx.edu/haskell/nub.tar.gz The Nub.hs file itself is attached to the proposal. If the proposal is accepted, I will prepare a patch against current GHC library top-of-tree, but for now it seems easier for everyone to just look at the bits in their current natural habitat.

15 31

export toDescList from Data.Map
by Evan Laforge 25 Nov '09

25 Nov '09

So, I mentioned this a long time ago but didn't get any responses and then I got distracted. So this time I added a ticket and patch and everything: 2580 Here's the text: It's even implemented, but not exported. Without this, there's apparently no way to iterate over a map from high to low, since foldl is also not exported. Also, I implemented a toDescList for IntMap, and could do the same for Set, and could add those patches, if people agree it's a good idea. In addition, is there any problem with exporting foldl aka descending for the three modules? I implemented a foldl for IntMap and it seems to work, but I'd want someone smarter to look for problems with it. In addition, Set and Map are inconsistent with folds: Set exports 'fold' and says "no order is guaranteed", but it's just defined to foldr, which is in ascending order. Set.foldr itself is not exported. Meanwhile, Map also exports fold, but heavily implies from the doc that it's guaranteed to be ascending. Would it restrict implementation changes too much to export a descending fold for all three? Other languages that have tree oriented general purpose maps all let you start anywhere and iterate in either direction. Anyway, is 2-3 weeks ok for discussion period? The library submission wiki doesn't say how long.

6 13

template-haskell depends on packedstring
by Gwern Branwen 18 May '09

18 May '09

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 So I was trying to compile lambdabot with cabal-install. Lambdabot uses Template Haskell for generating some boilerplate, and it was a failed dependency. Template Haskell uses packedstring for... something... and packedstring was a failed dependency: Data/PackedString.hs:83:7: Could not find module `Data.Data': it is a member of package base, which is hidden Now this is a problem, but it's not the problem I am interested in. I am interested in: why is template-haskell using packedstring? Wasn't packedstring obsoleted years ago? I downloaded the TH tarball to see what fascinating things it was using packedstring for, and I found that it's hardly doing anything - it apparently is just encoding module (ModName) and OccName (whatever that is), and then the other functions shift back from PackedString/ModName-OccName to String. (This is all in Language/Haskell/TH/Syntax.hs) I replaced all the PackedString stuff with normal ol' String and compiled fine, and indeed seems to work fine at Template-Haskelly stuff. So here's my suggestions: 1) Remove the packedstring dep and calls from the TH code. It is useless, it shackles the package to a long obsolete one, and so on. Even if we assume that the packedstring code is still faster than native String, and that there's no performance penalty for the conversions back and forth from String to PackedString, and that the possible size increase from linking in PackedString code is not worth worrying about, and we also assume that PackedString is being used on Names large enough to make up for any overhead - even if we assume all that, TH is a compile-time process and so it doesn't matter all that much if we shave a few microseconds off one small part of the compilation process. Installability and cleaner code would be worth that price. 2) If just String is not acceptable, then I understand from dons that the reason we can't use just plain ol' ByteString is because the Names may well be in UTF-8, and ByteString's [Word8]s apparently don't treat that well. Given that, we need some sort of UTF8 bytestring. As it happens, we do in fact have such a thing: Data.ByteString.UTF8 . It looks a bit incomplete, but utf8-string in general is pretty widely-used and reliable (also builds on 6.10): just about every XMonad user uses XMonadContrib which uses utf8-string, and I can count the number of complaints because utf8-string on one hand. Thoughts? I searched thoroughly through various bug-trackers and mailing lists, but this doesn't seem to've come up before. - -- gwern -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEAREKAAYFAkkqJTsACgkQvpDo5Pfl1oLYoQCgjRSqno+DtyZiLbAS5Pk4l8Ao sqkAn15sBq+alBy5ZVLHIMthjZ6eU6E6 =N8Qj -----END PGP SIGNATURE-----

3 6

Generics
by Simon Peyton-Jones 11 Dec '08

11 Dec '08

Jose As part of your work on the SYB library, could you spare the time to look into these two library bug reports? http://hackage.haskell.org/trac/ghc/ticket/2759 http://hackage.haskell.org/trac/ghc/ticket/2760 Many thanks Simon

3 8

More on Proposal #2717: Add nubWith, nubOrd
by Bart Massey 08 Dec '08

08 Dec '08

As those who follow this list know, the consensus after discussion of Proposal #2717 was to just add nubOrd to Data.Set. Final question: should we add nubInt to Data.IntSet as well? It seems to me like the right thing to do, given the existence of Data.IntSet in the first place. Once this last question is answered, I will start a new proposal round with a "final" set of proposed patches. Bart Massey bart <at> cs.pdx.edu

7 11

Building haddock when accessing data files from package code
by Hugo Pacheco 03 Dec '08

03 Dec '08

Hi all, When creating a cabal package that contains module that import Paths_<mybraryname> (as tutored in http://www.haskell.org/cabal/release/latest/doc/users-guide/authors.html#pa…) haddock complains that it cannot find such module, since it is generated automatically by cabal: $ runhaskell Setup.lhs haddock ... Setup.lhs: can't find source for module Paths_GHood How do I tell haddock to ignore such module? Should this be handled in the Setup.lhs file? I am using the default Simple file. Thanks in advance, hugo -- www.di.uminho.pt/~hpacheco

2 6

How to expose cabal-generated installation paths?
by Peter Simons 01 Dec '08

01 Dec '08

Hi, please pardon me if this question is not appropriate for this forum or if there is a document that answers my question already. I had no better idea but to ask here and I'd be happy to receive pointers into the right direction. Recently, I received a patch for the FuncMP package [1] that exposes the Cabal-generated "Paths_funcmp" module. It appears, however, that Cabal doesn't find that module when running the 'haddock' target: | Creating dist/doc/html/funcmp (and its parents) | Preprocessing library funcmp-1.2... | Running hscolour for funcmp-1.2... | Creating dist/doc/html/funcmp/src (and its parents) | /usr/local/bin/HsColour -print-css -odist/doc/html/funcmp/src/hscolour.css | cabal-setup: can't find source for module Paths_funcmp The complete log is available at [2]. Does anyone know, by any chance, a simple way to remedy that problem? Peter [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funcmp [2] http://hackage.haskell.org/packages/archive/funcmp/1.2/logs/failure/ghc-6.10

2 2

darcs patch: Fix typo (or out of date reference) in throwTo documen...
by shelarcy 30 Nov '08

30 Nov '08

DarcsURL: http://darcs.haskell.org/packages/base MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="=_" --=_ Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Sat Nov 29 11:46:39 =93=8C=8B=9E (=95W=8F=80=8E=9E) 2008 shelarcy <shelarc= y(a)gmail.com> * Fix typo (or out of date reference) in throwTo documentation. --=_ Content-Type: text/x-darcs-patch; name="fix-typo-_or-out-of-date-reference_-in-throwto-documentation_.dpatch" Content-Transfer-Encoding: quoted-printable Content-Description: A darcs patch for your repository! New patches: [Fix typo (or out of date reference) in throwTo documentation. shelarcy <shelarcy(a)gmail.com>**20081129024639] hunk ./GHC/Conc.lhs 304 (<http://research.microsoft.com/~simonpj/Papers/asynch-exns.htm>). In the paper, 'throwTo' is non-blocking; but the library implementation ad= opts a more synchronous design in which 'throwTo' does not return until the exc= eption -is received by the target thread. The trade-off is discussed in Section 8= of the paper. -Like any blocking operation, 'throwTo' is therefore interruptible (see Sec= tion 4.3 of +is received by the target thread. The trade-off is discussed in Section 9= of the paper. +Like any blocking operation, 'throwTo' is therefore interruptible (see Sec= tion 5.3 of the paper). = There is currently no guarantee that the exception delivered by 'throwTo' = will be Context: [Add more description of what "round" does, from the H98 report Ian Lynagh <igloo(a)earth.li>**20081119143131] = [re-instate the gcd/Integer and lcm/Integer RULES Simon Marlow <marlowsd(a)gmail.com>**20081120101826 Fixes a performance regression between 6.8.3 and 6.10.1 ] = [Change an "undefined" into a more informative error; trac #2782 Ian Lynagh <igloo(a)earth.li>**20081116160228] = [updating Haddock documentation jpm(a)cs.uu.nl**20081111095023 = Fixed the broken link from Data.Generics to Data.Data. ] = [add GHC.Conc.runSparks (required by GHC patch "Run sparks in batches") Simon Marlow <marlowsd(a)gmail.com>**20081106095419] = [FIX #2722: update RULES for the Category/Arrow split Ross Paterson <ross(a)soi.city.ac.uk>**20081104144515 = The rule = arr id =3D id = interacts unpleasantly with the advice to define = id =3D arr id = in instances of Category that are also instances of Arrow (#2722). = Also changed a couple of >>>'s to .'s in later rules. ] = [Add AnnotationWrapper type so GHC can capture annotation dictionaries duri= ng compilation Max Bolingbroke <batterseapower(a)hotmail.com>**20081016122608] = [docs about how exceptions are handled by forkIO'd threads (#2651) Simon Marlow <marlowsd(a)gmail.com>**20081016100410] = [Import n_capabilities via import symbol when linking dynamically Clemens Fruhwirth <clemens(a)endorphin.org>**20081013161220] = [add link to the new syb wiki jpm(a)cs.uu.nl**20081013111605] = [changing haddock links jpm(a)cs.uu.nl**20081010095434] = [add readTVarIO :: TVar a -> IO a Simon Marlow <marlowsd(a)gmail.com>**20081010113835] = [removed (->) instance from Data.Data jpm(a)cs.uu.nl**20081006075254] = [non-GHC: delete unnecessary imports Ross Paterson <ross(a)soi.city.ac.uk>**20081007134809] = [added new module Data.Data 'Jose Pedro Magalhaes <jpm(a)cs.uu.nl>'**20081002140535 = The new Data.Data module contains all of Data.Generics.Basics = and most of Data.Generics.Instances. The missing instances were = deemed dubious and moved to the syb package. ] = [add new Data.Data module 'Jose Pedro Magalhaes <jpm(a)cs.uu.nl>'**20081002082735] = [restore Complex's derived Data instance 'Jose Pedro Magalhaes <jpm(a)cs.uu.nl>'**20081002082655] = [update Data.Generics import 'Jose Pedro Magalhaes <jpm(a)cs.uu.nl>'**20081002082604] = [Don't use ^(2::Int) in Data.Complex.magnitude; partially fixes trac #2450 Ian Lynagh <igloo(a)earth.li>**20081004142651 We still might want to make a RULE for this, so the bug is not fully fixed= . ] = [Restore the Haskell 98 behaviour of Show Ratio (#1920) Simon Marlow <simonmarhaskell(a)gmail.com>**20080923134949] = [Pad version number to 4.0.0.0 Ian Lynagh <igloo(a)earth.li>**20080920155801] = [TAG 6.10 branch has been forked Ian Lynagh <igloo(a)earth.li>**20080919123437] = [In nhc98, Word is a type synonym, so class instance is not possible. Malcolm.Wallace(a)cs.york.ac.uk**20080917075326] = [Fix bugs in Text.Printf (#1548) Simon Marlow <marlowsd(a)gmail.com>**20080916133505] = [We should be including Rts.h here, not Stg.h Simon Marlow <marlowsd(a)gmail.com>**20080912134901 Stg.h is for .hc files only, and it sets up various global register variables. ] = [Generic functions that take integral arguments should work the same way as= their prelude counterparts **20080822022755 = The Prelude functions drop, take, and splitAt are unfailing (never call er= ror). This patch changes the Data.List generic versions to behave the same = way. At present, they call error on negative arguments. = ] = [Don't define __hscore_s_issock on Windows Ian Lynagh <igloo(a)earth.li>**20080904202845] = [Unbreak the GHC build with older versions of gcc Ian Lynagh <igloo(a)earth.li>**20080904185122 Patch from kili(a)outback.escape.de, who says: Stg.h must be included before HsBase.h, because the latter contains function definitions causing older versions of gcc (3.3.5 in my case) to bail out with "error: global register variable follows a function definition" on Regs.h, which is included by Stg.h. ] = [Don't make S_ISSOCK use conditional Ian Lynagh <igloo(a)earth.li>**20080904164234 We were conditionally defining the C wrapper, but unconditionally using it. So if it didn't exist then things would have broken anyway. ] = [Add missing files Ian Lynagh <igloo(a)earth.li>**20080904100951] = [Remerge concurrent,unique,timeout,st,getopt into base Ian Lynagh <igloo(a)earth.li>**20080903201908] = [remove 'pure' method from Arrow class (#2517) Ross Paterson <ross(a)soi.city.ac.uk>**20080903144436] = [make Typeable instances for larger tuples available to non-GHC Ross Paterson <ross(a)soi.city.ac.uk>**20080903113543] = [Don't look for actual OldException.Exception exceptions Ian Lynagh <igloo(a)earth.li>**20080902224730 We don't actually throw them (we throw the new Exception equivalents instead), and looking for them was causing an infinite loop ] = [add include/CTypes.h to extra-source-files Ross Paterson <ross(a)soi.city.ac.uk>**20080902153029] = [avoid relying on the implementation of SomeException Ross Paterson <ross(a)soi.city.ac.uk>**20080902080113 = This is because Hugs uses a different implementation. No semantic change. ] = [non-GHC: leave out Belch functions Ross Paterson <ross(a)soi.city.ac.uk>**20080831180227] = [non-GHC: add Typeable instance for ForeignPtr Ross Paterson <ross(a)soi.city.ac.uk>**20080831180048] = [docs: mention that killThread on a completed thread is a no-op Simon Marlow <marlowsd(a)gmail.com>**20080902093126] = [#2528: reverse the order of args to (=3D=3D) in nubBy to match nub Simon Marlow <marlowsd(a)gmail.com>**20080902092950 This only makes a difference when the (=3D=3D) definition is not reflexive, but strictly speaking it does violate the report definition of nubBy, so we should fix it. ] = [System.Timeout is no longer part of base Malcolm.Wallace(a)cs.york.ac.uk**20080901145738] = [getopt is no longer part of base Malcolm.Wallace(a)cs.york.ac.uk**20080827145336] = [Split syb off into its own package Ian Lynagh <igloo(a)earth.li>**20080825214144 I've also moved the Data (Complex a) instance into it, and made it portable rather than GHC-only in the process. ] = [add extra-source-files field Ross Paterson <ross(a)soi.city.ac.uk>**20080825231317] = [Fix warnings in PrelIOUtils.c Ian Lynagh <igloo(a)earth.li>**20080825141841] = [Windows-only fixes for moving concurrent out of base Ian Lynagh <igloo(a)earth.li>**20080824164146] = [Split off the concurrent hierarchy (concurrent, unique, timeout) Ian Lynagh <igloo(a)earth.li>**20080824123956] = [Split getopt off into its own package Ian Lynagh <igloo(a)earth.li>**20080824020213] = [Remove ST stuff that is now in the new st package Ian Lynagh <igloo(a)earth.li>**20080823223014] = [Fix Windows-only warnings Ian Lynagh <igloo(a)earth.li>**20080823002249] = [Fix Windows-only warnings in GHC.Conc Ian Lynagh <igloo(a)earth.li>**20080822234837] = [Suppress some warnings that are hard to fix because of ifdefs Ian Lynagh <igloo(a)earth.li>**20080822233951] = [Provide blockedOnDeadMVar, blockedIndefinitely for the RTS Ian Lynagh <igloo(a)earth.li>**20080821110723] = [Fix more warnings Ian Lynagh <igloo(a)earth.li>**20080820233958] = [Suppress a couple of warnings in GHC.PArr Ian Lynagh <igloo(a)earth.li>**20080820232018 The fix isn't immediately obvious to me ] = [Fix more warnings Ian Lynagh <igloo(a)earth.li>**20080820231937] = [Fix warnings in Data.Generics.* Ian Lynagh <igloo(a)earth.li>**20080820230437] = [Fix some more warnings Ian Lynagh <igloo(a)earth.li>**20080820223252] = [Ignore some orphan warnings Ian Lynagh <igloo(a)earth.li>**20080820211901] = [remove some functions that aren't used in base Simon Marlow <marlowsd(a)gmail.com>**20080821142339] = [remove __hscore_renameFile, it is no longer uesd Simon Marlow <marlowsd(a)gmail.com>**20080818155950 System.Directory implements renameFile using unix/Win32 now. ] = [Rewrite the documentation for forkOS again Simon Marlow <marlowsd(a)gmail.com>**20080818132856 Try to make it clearer that forkOS is only necessary when calling foreing libraries that use thread-local state, and it has nothing to do with scheduling behaviour between Haskell threads. I also added something about the performance impact of forkOS, and mentioned that the main thread is a bound thread. ] = [nhc only: expose Foldable and Traversable instances of Array Ross Paterson <ross(a)soi.city.ac.uk>**20080817002719 = These were turned off as a side-effect of a previous nhc-only fix for #2176 that is no longer needed. They should be fine for nhc now. ] = [Fix hReady (trac #1063) Ian Lynagh <igloo(a)earth.li>**20080816182715 We now throw an EOF exception when appropriate ] = [Fix oversight in Control.OldException Bertram Felgenhauer <int-e(a)gmx.de>**20080816132631 The NonTermination constructor slipped through in the Exception instance. ] = [Eliminate orphan rules and instances in the array package Ian Lynagh <igloo(a)earth.li>**20080816122253] = [Control.OldException: Map exceptions to old exceptions and back properly. Ian Lynagh <igloo(a)earth.li>**20080814210219 * Control.OldException: Map exceptions to old exceptions and back proper= ly. = It's really necessary to map them back as well, or the RTS and base librar= y will not recognize exceptions that got caught and rethrown. (See #2508) = Patch from Bertram Felgenhauer <int-e(a)gmx.de> ] = [add Traversable generalizations of mapAccumL and mapAccumR (#2461) Ross Paterson <ross(a)soi.city.ac.uk>**20080814162617] = [simplify definition of Prelude.catch Ross Paterson <ross(a)soi.city.ac.uk>**20080814143650] = [remove returns from void functions Ross Paterson <ross(a)soi.city.ac.uk>**20080814110841] = [No reason for Handler and catches to exclude nhc98. Malcolm.Wallace(a)cs.york.ac.uk**20080813125850] = [Must import ExitCode for its instance to be re-exported. Malcolm.Wallace(a)cs.york.ac.uk**20080813125710 The Cabal library depends on "instance Exception ExitCode", and expects to import it from Control.Exception, not Control.Exception.Base. ] = [use New.catch instead of catchException in OldException Ross Paterson <ross(a)soi.city.ac.uk>**20080813071307] = [use the Haskell 98 module Control.Exception.Base in the Concurrent modules Ross Paterson <ross(a)soi.city.ac.uk>**20080813000219] = [export Control.Exception.Base Ross Paterson <ross(a)soi.city.ac.uk>**20080812233640] = [use dummy implementation of timeout for all non-GHCs Ross Paterson <ross(a)soi.city.ac.uk>**20080812151602] = [Hugs only: fix imports Ross Paterson <ross(a)soi.city.ac.uk>**20080812145654] = [non-GHC: hide Prelude.catch Ross Paterson <ross(a)soi.city.ac.uk>**20080812145622] = [add Control.Exception.Base to nhc98 build Malcolm.Wallace(a)cs.york.ac.uk**20080812174300] = [bump to version 4.0 Simon Marlow <marlowsd(a)gmail.com>**20080805153354] = [Hugs only: don't import exception types -- their instances are now in Cont= rol.Exception.Base Ross Paterson <ross(a)soi.city.ac.uk>**20080812140433] = [split most of Control.Exception into new Control.Exception.Base Ross Paterson <ross(a)soi.city.ac.uk>**20080812124912 = Move everything but catches/Handler into a new internal module. This was needed to get the new exceptions working with Hugs, because Hugs has the constraint that all Haskell 98 library modules, and everything they include, must be Haskell 98. This also involves a different representation of SomeException for Hugs, so that type is exported opaquely for Hugs. Then Control.Exception.Base is Haskell 98 as far as Hugs is concerned, but Control.Exception needs the extensions turned on. = Control.Exception re-exports everything from Control.Exception.Base except the functions used by the GHC runtime. ] = [remove kludges, now that Control.Exception is imported Ross Paterson <ross(a)soi.city.ac.uk>**20080811180328] = [threadDelay and friends are GHC-only Ross Paterson <ross(a)soi.city.ac.uk>**20080811175039] = [fix imports for non-GHC Malcolm.Wallace(a)cs.york.ac.uk**20080808092017] = [Eq and Ord have moved into GHC.Classes Ian Lynagh <igloo(a)earth.li>**20080807095352] = [Use the proper CInt type in GHC.Unicode Ian Lynagh <igloo(a)earth.li>**20080806232948] = [Import wibbles Ian Lynagh <igloo(a)earth.li>**20080806232055] = [Remove unnecessary Data/Dynamic.hs-boot Ian Lynagh <igloo(a)earth.li>**20080806230623] = [Remove more redundant GHC.Float imports Ian Lynagh <igloo(a)earth.li>**20080806225411] = [Remove an unnecessary import Ian Lynagh <igloo(a)earth.li>**20080806224742] = [Move Int, Float and Double into ghc-prim:GHC.Types Ian Lynagh <igloo(a)earth.li>**20080806191554] = [Put some explicit import lists in Data.Typeable Ian Lynagh <igloo(a)earth.li>**20080806190353] = [Fix a couple of imports Ian Lynagh <igloo(a)earth.li>**20080806165549] = [Remove unused conditional import Ian Lynagh <igloo(a)earth.li>**20080806124930] = [Swap imports around to get GHC.ForeignPtr out of the base knot Ian Lynagh <igloo(a)earth.li>**20080806121313] = [Move some bits around to stop Data.Either being in the base import knot Ian Lynagh <igloo(a)earth.li>**20080806120504] = [Tweak an import Ian Lynagh <igloo(a)earth.li>**20080806000440] = [Remove the DynIOError constructor of IOErrorType Ian Lynagh <igloo(a)earth.li>**20080805234720 As far as I can see it is never used or exported ] = [Move some internals around to simplify the import graph a bit Ian Lynagh <igloo(a)earth.li>**20080805221341] = [Move the Char datatype into ghc-prim Ian Lynagh <igloo(a)earth.li>**20080805204009] = [Remove an unnecessary import Ian Lynagh <igloo(a)earth.li>**20080805182336] = [The [] definition has moved to ghc-prim Ian Lynagh <igloo(a)earth.li>**20080805182332] = [Fix warnings Ian Lynagh <igloo(a)earth.li>**20080805150250] = [Add a missing case to Show AsyncException Ian Lynagh <igloo(a)earth.li>**20080805142811] = [Remove GHC.Dotnet Ian Lynagh <igloo(a)earth.li>**20080804215840] = [Hide standalone deriving clauses from haddock Ian Lynagh <igloo(a)earth.li>**20080804211617] = [Control.Exception doesn't need to export assertError Ian Lynagh <igloo(a)earth.li>**20080804161838] = [Generalise the type of mapException; pointed out by Isaac Dupree Ian Lynagh <igloo(a)earth.li>**20080804160941] = [Remove some unnecessary Data.Tuple imports Ian Lynagh <igloo(a)earth.li>**20080804155956] = [The tuple datatype definitions have moved to ghc-prim Ian Lynagh <igloo(a)earth.li>**20080804155420] = [make ExitCode an instance of Exception for nhc98 Malcolm.Wallace(a)cs.york.ac.uk**20080805160330] = [poke and peek come from Foreign.Storable Malcolm.Wallace(a)cs.york.ac.uk**20080804160616] = [zipWithM_ comes from Control.Monad Malcolm.Wallace(a)cs.york.ac.uk**20080804160319] = [Fix nhc98 code variations to use the extensible exception API. Malcolm.Wallace(a)cs.york.ac.uk**20080804155842 There is still only one real exception type in nhc98, so it is not truly extensible. But this is enough to get the base package building again. ] = [nhc98 needs the Prelude for this module Malcolm.Wallace(a)cs.york.ac.uk**20080804133853] = [Change some imports and derive Show (Either a b) Ian Lynagh <igloo(a)earth.li>**20080804004147 rather than writing it by hand in GHC.Show ] = [Windows fixes Ian Lynagh <igloo(a)earth.li>**20080803180345] = [Remove the duplicate definition of throwTo in Control.Exception Ian Lynagh <igloo(a)earth.li>**20080803141703 It now imports GHC.Conc, so it is no longer necessary ] = [Remove the only import of GHC.Exts Ian Lynagh <igloo(a)earth.li>**20080803141944] = [Move assertError into GHC.IOBase Ian Lynagh <igloo(a)earth.li>**20080803141040] = [Use onException rather than catchAny Ian Lynagh <igloo(a)earth.li>**20080803114104] = [Generalise the type of onException Ian Lynagh <igloo(a)earth.li>**20080803003001 The type of the thing to do on an exception is now IO b rather than IO () which better matches functions like bracket. ] = [Remove the dangerous Exception functions Ian Lynagh <igloo(a)earth.li>**20080802231358 Removed: catchAny, handleAny, ignoreExceptions These make it easy to eat /any/ exception, which is rarely what you want. Normally you either want to: * only catch exceptions in a certain part of the hierarchy, e.g. "file not found", in which case you should only catch exceptions of the appropriate type, or * you want to do some cleanup when an exception happens, and then rethrow the exception, in which case you should use onException, or one of the bracketing functions. ] = [Remove an unused import Ian Lynagh <igloo(a)earth.li>**20080801230343] = [Remove unused imports Ian Lynagh <igloo(a)earth.li>**20080801230059] = [Remove unused imports in Control.Exception Ian Lynagh <igloo(a)earth.li>**20080801225847] = [Get rid of some duplicate imports Ian Lynagh <igloo(a)earth.li>**20080801214933] = [Remove the now-unused GHC/Conc.lhs-boot Ian Lynagh <igloo(a)earth.li>**20080801214707] = [Make some more imports non-recursive Ian Lynagh <igloo(a)earth.li>**20080801214546] = [Rejig some code so Control.Exception and GHC.Conc don't need recursive imp= orts Ian Lynagh <igloo(a)earth.li>**20080801214208] = [Remove the now-unused GHC/TopHandler.lhs-boot Ian Lynagh <igloo(a)earth.li>**20080801212105] = [Reshuffle GHC.Conc/GHC.TopHandler a bit to remove a recursive import Ian Lynagh <igloo(a)earth.li>**20080801211801] = [Don't import Control.Concurrent.MVar in GHC.TopHandler Ian Lynagh <igloo(a)earth.li>**20080801200123] = [Export assertError from Control.Exception to make GHC happy Ian Lynagh <igloo(a)earth.li>**20080801111716 It's a wired-in name in GHC. We should possibly move it to another module. ] = [TopHandler now uses the new extensible exceptions Ian Lynagh <igloo(a)earth.li>**20080731153553] = [Comment wibble Ian Lynagh <igloo(a)earth.li>**20080730202127] = [Make numericEnumFrom more efficient Ian Lynagh <igloo(a)earth.li>**20080730202049] = [Put in some parens to clarify how things parse Ian Lynagh <igloo(a)earth.li>**20080730201934] = [applied patches to make enumFrom and friends strict in arguments as per th= e Report; closes ticket #1997 Bart Massey <bart(a)cs.pdx.edu>**20080726080444] = [Don't use "deriving Typeable" (for portability reasons) Ian Lynagh <igloo(a)earth.li>**20080730194434] = [Add onException Ian Lynagh <igloo(a)earth.li>**20080730172014] = [Fix whitespace Ian Lynagh <igloo(a)earth.li>**20080730171951 The space after "\begin{code}" was confusing haddock ] = [Re-add blocked; it got lost in the extensible exceptions patches Ian Lynagh <igloo(a)earth.li>**20080730145614] = [Start to actually use extensible exceptions Ian Lynagh <igloo(a)earth.li>**20080730145115] = [Rejig the extensible exceptions so there is less circular importing Ian Lynagh <igloo(a)earth.li>**20080730122539] = [Define nonTermination for the RTS to use Ian Lynagh <igloo(a)earth.li>**20080621144420 We'll probably need to do the same for some other exceptions too ] = [Use extensible exceptions at the lowest level Ian Lynagh <igloo(a)earth.li>**20080621121501 Everything above is largely unchanged; just the type of catch and throw. ] = [add comment Simon Marlow <marlowsd(a)gmail.com>**20080730114559] = [add some big warnings to the docs for unsafeIOToSTM (#2401) Simon Marlow <marlowsd(a)gmail.com>**20080730114554] = [FIX #2376: inline shiftR Simon Marlow <marlowsd(a)gmail.com>**20080730103539 Duplicating the default definition for shiftR doesn't seem quite right to me, but it gets the right results when compiling the example program, and I couldn't find a better way to do it. ] = [Add instance Show Control.Exception.Exception for nhc98. Malcolm.Wallace(a)cs.york.ac.uk**20080728164537] = [Extend nhc98's Exception type to resemble ghc's more closely Malcolm.Wallace(a)cs.york.ac.uk**20080728163445] = [fix dummy async implementations for non-GHC Ross Paterson <ross(a)soi.city.ac.uk>**20080715125521] = [Fix haddocking with older haddocks Ian Lynagh <igloo(a)earth.li>**20080710190855] = [Add threadStatus :: ThreadId -> IO ThreadStatus Simon Marlow <marlowsd(a)gmail.com>**20080710151711 = -- | The current status of a thread data ThreadStatus =3D ThreadRunning -- ^the thread is currently runnable or running | ThreadFinished -- ^the thread has finished | ThreadBlocked BlockReason -- ^the thread is blocked on some resource | ThreadDied -- ^the thread received an uncaught exception deriving (Eq,Ord,Show) = data BlockReason =3D BlockedOnMVar -- ^blocked on on 'MVar' | BlockedOnBlackHole -- ^blocked on a computation in progress by another thread | BlockedOnException -- ^blocked in 'throwTo' | BlockedOnSTM -- ^blocked in 'retry' in an STM transaction | BlockedOnForeignCall -- ^currently in a foreign call | BlockedOnOther -- ^blocked on some other resource. Without @-threaded@, -- I/O and 'threadDelay' show up as 'BlockedOnOther', with @-threa= ded@ -- they show up as 'BlockedOnMVar'. deriving (Eq,Ord,Show) = This is useful for concurrency debugging. I've left threadStatus in GHC.Conc for now, since the ThreadStatus type is somewhat GHC-specific. ] = [forkOS: start the new thread in blocked mode iff the parent was (#1048) Simon Marlow <marlowsd(a)gmail.com>**20080709135558 This matches the behaviour of forkIO ] = [Add Control.Exception.blocked :: IO Bool Simon Marlow <marlowsd(a)gmail.com>**20080709133139 Tells you whether async exceptions are currently blocked or not. ] = [FIX BUILD (on Windows) Simon Marlow <marlowsd(a)gmail.com>**20080709123110] = [check CONST_SIGINT Simon Marlow <marlowsd(a)gmail.com>**20080709122527] = [Make threadWaitRead/threadWaitWrite partially useable on Windows Simon Marlow <marlowsd(a)gmail.com>**20080709111008 = They work with -threaded by calling fdReady() in a separate thread. = "threadWaitRead 0" also works without -threaded (because we happen to know it's virtually equivalent to "hWaitForInput stdin (-1)"). ] = [FIX #1198: hWaitForInput on Windows Simon Marlow <marlowsd(a)gmail.com>**20080708134254 Now we do the appropriate magic in fdReady() to detect when there is real input available, as opposed to uninteresting console events. ] = [FIX part of #2301 Simon Marlow <marlowsd(a)gmail.com>**20080709094437 = Control-C now causes the new exception (AsyncException UserInterrupt) to be raised in the main thread. The signal handler is set up by GHC.TopHandler.runMainIO, and can be overriden in the usual way by installing a new signal handler. The advantage is that now all programs will get a chance to clean up on ^C. = When UserInterrupt is caught by the topmost handler, we now exit the program via kill(getpid(),SIGINT), which tells the parent process that we exited as a result of ^C, so the parent can take appropriate action (it might want to exit too, for example). = One subtlety is that we have to use a weak reference to the ThreadId for the main thread, so that the signal handler doesn't prevent the main thread from being subject to deadlock detection. ] = [() has moved to ghc-prim:GHC.Unit, and the Eq and Ord instances to Data.Tu= ple Ian Lynagh <igloo(a)earth.li>**20080624144932] = [Add GHC.Exts.maxTupleSize :: Int, the size of the largest tuple supported Ian Lynagh <igloo(a)earth.li>**20080622141559] = [Remove code for older GHC versions Ian Lynagh <igloo(a)earth.li>**20080620194521] = [Make the macros in Typeable.h add type signatures Ian Lynagh <igloo(a)earth.li>**20080619235808] = [Fix #2363: getChar cannot be interrupted with -threaded Simon Marlow <marlowsd(a)gmail.com>**20080619141911 Now in -threaded mode, instead of just making a blocking call to read(), we call select() first to make sure the read() won't block, and if it would block, then we use threadWaitRead. = The idea is that the current thread must be interruptible while it blocks. This is a little slower than before, but the overhead only applies to blocking Handles (stdin/stdout/stderr, and those created by System.Process). ] = [Remove -fglasgow-exts from pragmas and comments Ian Lynagh <igloo(a)earth.li>**20080616230727] = [Avoid using deprecated flags Ian Lynagh <igloo(a)earth.li>**20080616145207] = [delete __hscore_{mkstemp,getrlimit,setrlimit} (moved to unix) Ross Paterson <ross(a)soi.city.ac.uk>**20080615224413] = [Update WCsubst.c for Unicode 5.1.0, and add a README.Unicode Ian Lynagh <igloo(a)earth.li>**20080613201754 README.Unicode describes how to do updates in the future. ] = [Fix ubconfc Ian Lynagh <igloo(a)earth.li>**20080613201456 The current code doesn't seem to be what was used to generate WCsubst.c, so I'm not sure if it never worked, or if my tools work slightly differently to those of the previous user. ] = ['permutations' is now more lazy and also faster Twan van Laarhoven <twanvl(a)gmail.com>**20080102231712] = ['subsequences' is now more lazy and also faster Twan van Laarhoven <twanvl(a)gmail.com>**20080102231629] = [Add 'subsequences' and 'permutations' to Data.List Twan van Laarhoven <twanvl(a)gmail.com>**20071218154950] = [Tweak the definition of (^) again Ian Lynagh <igloo(a)earth.li>**20080601120759 This fixes trac #2306 (do the minimum number of (*)s), and also means that we don't use the value of (1 :: a) which causes problems if the Num a definition isn't complete. ] = [note about evaluation affecting StableNames Simon Marlow <marlowsd(a)gmail.com>**20080527110549] = [TAG 2008-05-28 Ian Lynagh <igloo(a)earth.li>**20080528003830] = Patch bundle hash: 525406fd5ead4fca8b9b099f3b4b649c8a09ec66 --=_-- .

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arrows-0.4/0.4.1 + Stream: Monoid instances
by Marc A. Ziegert 29 Nov '08

29 Nov '08

hi i've just had serious problems with too many (or too strange) Monoid instances in the arrows library. {- i tried to install/patch Conal Elliott's bot package, which reinterprets some arrow types, i.e. type StreamBot = StreamArrow (->) and then tries to derive the Monoid instance with deriving instance Monoid o => Monoid (StreamBot i o). -} the main problem is the circumstance, that the instance of StreamArrow as Monoid depends strangely on ArrowPlus, but (->) is no instance of the ArrowPlus class. instance ArrowPlus a => Monoid (StreamArrow a b c) instance ArrowPlus a => Monoid (XyzArrow a b c) (->) makes only sense to be in MonadPlus, iff (a->b) is a Monoid -- which is, iff b is a Monoid; and that dependency does not work: instance Monoid b => ArrowPlus (->) where...?! INHO it does not make any sense at all to derive the Monoid instance from ArrowPlus instead of other Monoids. so, is it possible to remove them? anyway, they are only copies of MonadPlus. additionally, if it is possible and does not cause too many problems in other packages, i suggest to generalize the Monoid instance for (->), which is located at Data.Monoid. i.e. like this: instance (Arrow (~>),Monoid c) => Monoid ((~>) b c) where mempty = arr (const mempty) mappend f g = (f &&& g) >>> arr (uncurry mappend) besides that, i miss a Monoid instance for Streams, which should be located in the corresponding library: instance Monoid x => Monoid (Stream x) where mempty = Cons mempty mempty mappend (Cons a as) (Cons b bs) = mappend a b `Cons` mappend as bs greetings - marc

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