July 2010 - Libraries

Proposal #3339: Add (+>) as a synonym for mappend
by Bryan O'Sullivan 08 Nov '11

08 Nov '11

Ticket: http://hackage.haskell.org/trac/ghc/ticket/3339 >From the ticket: This proposal was, I think, originally suggested by Jules Bean. The idea is to add two functions to the Data.Monoid module, (+>) and (<+), corresponding to different uses of mappend. These should not be methods of the Monoidtypeclass, but top-level functions. I hope (but slightly doubt) that the visual nature of the two operators might help to counter the thought that monoids are just for gluing things together. (+>) :: (Monoid a) => a -> a -> a a +> b = a `mappend` b (<+) :: (Monoid a) => a -> a -> a a <+ b = b `mappend` a infixl 4 +> infixl 4 <+ Proposed deadline: two weeks. If this looks reasonable, I'll attach darcs patches.

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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

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[darcs patch] filepath: normalise trailing dot
by Conrad Parker 21 Dec '10

21 Dec '10

Hi, the attached darcs patch modifies the behaviour of normalise to handle trailing dots in a path. The previous behaviour yielded this: Prelude System.FilePath> normalise "../." "../." Prelude System.FilePath> normalise ".././" ".././" Prelude System.FilePath> normalise ".././.." "../.." This patch modifies dropDots such that the check for (".":[]) only occurs once for the path, after which a driver function dropDots' is used which skips this check. Hence "." can be removed from the end of a longer path, but a path of just "." is unchanged. (my trac account is pending verification, I'll reply with a trac ticket # later if needed) cheers, Conrad.

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Proposal: Add function to create new hash tables with a default size
by Jim Apple 18 Sep '10

18 Sep '10

In other some standard libraries (Java, OCaml), hash tables can be created with a user-supplied size. This avoids some resizing for users who know they will be inserting a lot of data. Data.HashTable does not expose a function to do this. This proposal changes that. For a dictionary of 5 million strings, this patch saves me about 33% of the total execution time. For 10 million strings, this patch saves me 50% of the total execution time. http://hackage.haskell.org/trac/ghc/ticket/4193

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xhtml maintainership?
by Ganesh Sittampalam 03 Aug '10

03 Aug '10

Hi, I believe the xhtml package is currently unmaintained. As it is something that used to be distributed with GHC, is it something that libraries@ could/should take on? Cheers, Ganesh

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Proposal: Make Permissions type abstract
by Ian Lynagh 03 Aug '10

03 Aug '10

Hi all, Proposal: Make Permissions type abstract Ticket: http://hackage.haskell.org/trac/ghc/ticket/4149 The Permissions type in System.Directory aims to be a lowest-common-denominator type. This makes it unsuitable for some tasks. For example, a copyPermissions primitive had to be implemented, as it is not possible to use the getPermissions and setPermissions functions to copy the permissions from one file to another: $ ls -l foo* -rwxr-x-wx 1 ian ian 0 Jun 23 21:27 foo1 ---------- 1 ian ian 0 Jun 23 21:27 foo2 ---------- 1 ian ian 0 Jun 23 21:27 foo3 $ hd -e 'System.Directory.copyPermissions "foo1" "foo2"' $ hd -e 'System.Directory.getPermissions "foo1" >>= System.Directory.setPermissions "foo3"' $ ls -l foo* -rwxr-x-wx 1 ian ian 0 Jun 23 21:27 foo1 -rwxr-x-wx 1 ian ian 0 Jun 23 21:27 foo2 -rwx------ 1 ian ian 0 Jun 23 21:27 foo3 I think we would be better served by the Permissions type being abstract in System.Directory, with the unix and Win32 packages providing the real definition, and some system-specific functions on it. This would allow the generic get/set functions to implement copyPermissions. This proposal just does the step which has most potential to cause problems for packages that use the type: It makes the type abstract in System.Directory (and adds explicit setter functions, so no functionality is lost). (patch is in the ticket) The type is also exported in Haskell 98's Directory module. I think this should get its own copy of the type. Suggested discussion deadline: 9 July 2010. Thanks Ian

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Error in Haddock documentation for process
by Ivan Lazar Miljenovic 30 Jul '10

30 Jul '10

I just spotted the following problem in the documentation for readProcess [1]. The documentation has the sample usage returning an "IO (Either a String)" action, yet the function only returns an "IO String". > readProcess "date" [] [] Right "Thu Feb 7 10:03:39 PST 2008\n" [1]: http://hackage.haskell.org/packages/archive/process/1.0.1.3/doc/html/System… -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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ANN: weighted-regexp-0.1.0.0
by Sebastian Fischer 28 Jul '10

28 Jul '10

Hello, this year's ICFP features A Play on Regular Expressions where two Haskell programmers and an automata theory guru develop an efficient purely functional algorithm for matching regular expressions. A Haskell library based on their ideas is now available from Hackage. For more information (and a link to the play) visit: http://sebfisch.github.com/haskell-regexp/ Cheers, Sebastian -- Underestimating the novelty of the future is a time-honored tradition. (D.G.)

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HTTP-4000.0.9
by Christian Maeder 28 Jul '10

28 Jul '10

Hi all, did someone hear from Sigbjorn, recently? I'm worried about the the maintainer of http://hackage.haskell.org/package/HTTP The issue tracker is terribly full of spam: http://trac.haskell.org/http/report/1 Cheers Christian -- original message Hi Sigbjorn, Under x86 solaris the attached example with simpleHTTP no longer works. The request blocks. It works with HTTP-4000.0.8! And it works under linux with HTTP-4000.0.9! What changed? Do you have an explanation? Thanks Christian <soapenv:Envelope encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"><soapenv:Body><ProveTPTPProblem><in0>%-------------------------------------------------------------------------- % File : No information % Domain : No information % Problem : asym.dfg % Version : No information % English : No information % Refs : No information % Source : No information % Name : [soapTest] % Status : unknown % Rating : ? % Syntax : No information % Comments : File generated by dfg2tptp Version 0.47a %-------------------------------------------------------------------------- fof('ga_non_empty_sort_Elem',axiom,( ? [U] : ssElem(U))). fof('trans',axiom,( ! [U,V,W] : ((ssElem(U) & ssElem(V) & ssElem(W)) => ((ssTilde__(U,V) & ssTilde__(V,W)) => ssTilde__(U,W))))). fof('irrefl',axiom,( ! [U] : (ssElem(U) => ~(ssTilde__(U,U))))). fof('asym',conjecture,( ! [U,V] : ((ssElem(U) & ssElem(V)) => (ssTilde__(V,U) => ~(ssTilde__(U,V)))))). %-------------------------------------------------------------------------- </in0><in1>10</in1></ProveTPTPProblem></soapenv:Body></soapenv:Envelope>

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can I indicate that an old version is not to be used, and some more questions
by S. Doaitse Swierstra 28 Jul '10

28 Jul '10

I uploaded a version of the uu-parsinglib to hackage. Only later I discovered that it depended on a verion of base >= 4.2, whereas I indicate > 4 in my .cabal file. I repaired this by uploading a new version in which only the cabal file has changed. This raises the following questions: - the Haskell code did not change, but I still had to bump the version number? - can I remove the incorrect version or indicate that it is superseded by the new version? - since I do not have a wide variety of Haskell installations and package versions on my machine, it would be very nice if the hackage server could test a package against the extremes of the indicated dependency ranges before installing. This would have prevented the mistake I made (and which undoubtedly others will make too) Doaitse

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