August 2010 - Haskell-Cafe

Fwd: Searching for Haskell (was: [Haskell-cafe] Slightly humorous: Headhunters toolbox (example for Germany))
by Alberto G. Corona 07 Sep '10

07 Sep '10

Ooops Just after sending this I relized that it is possible to narrow the search using categories. Using the category programming: http://www.google.com/insights/search/?hl=en-US#&cat=31&q=haskell&cmpt=q <http://www.google.com/insights/search/?hl=en-US#&cat=31&q=haskell&cmpt=q>it is even possible to compare the evolution of the term against the whole category. Both go down with time (because technical people dominate less and less the wen searches) . But the slope of "Haskell" is lesser than the one of "programming". By the way, it is possible to compare two or more search terms. Within the category programming, monad, and "type class" are scarce compared with "object" but the slope of the former ones are clearly up while object is down. (press "growth compared with the programing category"). What happened in the first half of 2006? monads were high there!. An further example is lazy versus strict. Both are comparable in percentage, but lazy is scandalously up while strict is down at the same rate. http://www.google.com/insights/search/?hl=en-US#cat=31&q=lazy%2Cstrict%2C&c… By the way, the term "tired" has increasing share in the programming category ;) 2010/8/31 Henk-Jan van Tuyl <hjgtuyl(a)chello.nl> On Tue, 31 Aug 2010 13:57:42 +0200, Alberto G. Corona <agocorona(a)gmail.com> > wrote: > > Entering "haskell language" instead of "haskell" the ambiguity >> dissapears. Then, Jamaica no longer appears in the crude reality . The >> weigth of USA is hides all other country here. >> >> I think that a more appropriate term to look for haskell interest is >> "monad" although it may catch some crazy philosophers too. The result is >> interesting, >> >> > You can still get things like a page titled "Ben Haskell - Language > Technologies Institute - Carnegie Mellon", and of course, not all pages > about the programming language contain the word "language". To get proper > results you would need a good semantic search engine, but these search > engines seem to be in early research stage. > > Regards, > Henk-Jan van Tuyl > > > -- > http://Van.Tuyl.eu/ > http://members.chello.nl/hjgtuyl/tourdemonad.html > -- >

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Projects that could use student contributions?
by Brent Yorgey 06 Sep '10

06 Sep '10

Hi all, This fall I'll be teaching a half-credit introduction to Haskell to some undergrads. As a final project I am thinking of giving them the option of (instead of developing some program/project of their own) contributing to an existing open-source Haskell project. Of course, this requires the existence of projects they could contribute to. I'm sure they exist, but need your help to figure out what they are. So, do you maintain, or know of, any projects with the following characteristics? * might conceivably be interesting to undergraduate CS majors * simple enough that someone could make some non-trivial contributions in the space of 3 or 4 weeks * could use some help! This is a little non-traditional, so we'll see how it goes! -Brent

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Crypto-API is stabilizing
by Thomas DuBuisson 05 Sep '10

05 Sep '10

All, Crypto-API - a unified interface to which I hope hash and cipher algorithms will adhere - has recently gotten a reasonable amount of polish work. I continue to welcome all comments! A blog on its current interface is online [1] as are darcs repositories of the crypto-api package [2]. Recent changes includes added block cipher modes, platform-independent RNG, tests, a simplistic benchmark framework, and minor tweaks of the classes. I've made experimental hash, block cipher and stream cipher instances. Almost no optimizations have been made as of yet! Thanks to everyone for their past comments! I have made numerous changes based on input received. If you feel I didn't respond properly to your suggestion then please ping me again - this is purely a spare time effort and things do fall through the cracks. Cheers, Thomas [1] http://tommd.wordpress.com/2010/08/23/a-haskell-api-for-cryptographic-algor… [2] http://community.haskell.org/~tommd/crypto/ (If you're wondering why you're BCCed its probably because you worked on a crypto-related Haskell package)

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Haddock: Documentation of instances with un-documentable type arguments
by Alexander McPhail 04 Sep '10

04 Sep '10

Hi, Here, http://hackage.haskell.org/packages/archive/graphviz/2999.10.0.1/doc/html/D…, there is an example of the internal implementation leaking. I was taught to separate interface from implementation. For example, header versus c/cc/cpp files. The privacy of typeclasses of GeneralNewTypedDeriving'ed variety, such as MonadReader and MonadState, should be hidable. I may want the programmer to know my operations, as provided in the interface, are monadic (and thus sequencable, temporally deterministic operations) but not allow them to set/get, ask, tell, fetch, push, throw, or pass my implementational details. Perhaps Haddock could exclude class instance reporting when it cannot find a documentable link to a parameter? Vivian -- --- yolar et elver. --- DISCLAIMER This transmission contains information that may be confidential. It is intended for the named addressee only. Unless you are the named addressee you may not copy or use it or disclose it to anyone else.

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On to applicative
by michael rice 02 Sep '10

02 Sep '10

"Learn You a Haskell ..." says that (->) is a type just like Either. Where can I find its type definition? Michael

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Statically tracking "validity" - suggestions?
by strejon 01 Sep '10

01 Sep '10

Hello. I'm using Haskell to write a specification for some software. The software uses certificates (standard X.509 certificates) and stores user name information in the Subject's CommonName field. The X.509 standard doesn't actually require the presence of a CommonName field so the contents of the Subject section (with the rest of the fields omitted) are just represented by a Maybe User_Name. > import Data.List (find, concat) > import Data.Maybe (fromJust, isJust) > > type User_Name = String > type Public_Key = Integer > data Subject_Name = Subject_Name (Maybe User_Name) deriving (Show, Eq) > > data Certificate = Certificate { > certificate_subject :: Subject_Name, > certificate_key :: Public_Key, > certificate_issuer :: String, > certificate_serial :: Integer > } deriving (Show, Eq) This is all well and good, but the problem is that the validity of certificates isn't tracked statically and I have to use the following as guards on all functions that only expect valid certificates (and inevitably handle cases that I know can't actually happen but have to be handled in pattern matching and the like, bloating the specification): > user_name :: Subject_Name -> Maybe User_Name > user_name (Subject_Name name) = name > > is_valid :: Certificate -> Bool > is_valid = isJust . user_name . certificate_subject I'm aware of phantom types and the like, but I've been unable to work out how to use them (or another type system extension) to properly track "validity" on the type level. I'd want something like: validate :: Certificate Possibly_Valid -> Maybe (Certificate Valid) With later functions only accepting values of type "Certificate Valid". Is there a simple way to do this? -- View this message in context: http://old.nabble.com/Statically-tracking-%22validity%22---suggestions--tp2… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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open and closed
by Gábor Lehel 01 Sep '10

01 Sep '10

This is pure speculation, inspired in part by Brent Yorgey's blog post[1] from a few weeks ago. I'm wondering if it might be possible, in theory, to have both open and closed variants for each of value-level functions, type functions, and classes, in a fairly analogous way. (Maybe you could even have open (G)ADTs, which you would then need open functions to match on; or maybe a closed one with a case for _ to ensure exhaustiveness.) In each case you'd have the closed variant requiring you to keep all the definitions in the same module, permitting overlap, and trying to match definitions in the order they're listed; whereas the open variant would let you have definitions across modules, would forbid overlap (or would require definitions to be equivalent where they overlap, as with type families), and would always select the uniquely matching definition. Open value-level functions with this scheme would be inherently partial, which is bad. (It's not a problem at the type level because you just get a compile error if nothing matches, but an exception at runtime isn't so nice.) As a solution, perhaps it might be possible to allow a limited form of overlap (or don't even call it overlap) for the open variants: a default "use this is if nothing else matches" definition (which would need to be in the same module as the original class / type family declaration, or whatever ends up being analogous for open value-level functions, maybe the type signature). That way you could use Maybe for open value-level functions and make the default Nothing, among other options. Overlap in type functions allegedly makes typechecking unsound; I don't know if that would also hold in this more limited case. This would definitely break the property where adding or removing an import can't change the behaviour of a program other than whether it compiles, which is considered very important by many [2], so maybe it's not a good solution. (Possibly you could add explicit import/export control for instances/other-open-things to alleviate this, in a way so that definitions for open thingies with default definitions (at least) would always have to imported explicitly, thereby acknowledging that it might change behaviour... or maybe that would be a bandaid too far, I dunno.) (I think this would also cover most (if not all?) of the use cases for OverlappingInstances, which permits overlap and selects the most specific instance in a more general fashion; but maybe that doesn't matter if the two are equally bad, I don't know. I'm not 100% clear on peoples' opinion of OverlappingInstances, but I as far as I know the problems are twofold: both import-unsafeness, and the matter of how you would actually define "most specific" in a way that's both rigorous and intuitive; this would remove at least the latter.) Anyway, thoughts? Is this all completely crazy and way out there? [1] http://byorgey.wordpress.com/2010/08/05/typed-type-level-programming-in-has… [2] http://hackage.haskell.org/trac/haskell-prime/wiki/LanguageQualities -- Work is punishment for failing to procrastinate effectively.

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ICFP Hotel Room
by Michael D. Adams 01 Sep '10

01 Sep '10

Hi all, I'm a graduate student (male) and am looking for a (male) roommate to split the cost of a hotel room at ICFP. If anyone is interested in splitting a room, please drop me a line. I will be attending the workshops collocated with ICFP so I currently have a reservation at the conference hotel (at the conference rate) with check-in on September 24 (the day before the first workshop) and check-out on October 3 (the day after the last workshop). Michael D. Adams Ph.D. Student, Indiana University

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Announce: Significant performance improvements for Data.Map
by Don Stewart 01 Sep '10

01 Sep '10

http://hackage.haskell.org/trac/ghc/ticket/4277 Proposal: Significant performance improvements for Data.Map Description Milan Straka's recent [52] Haskell Symposium paper (PDF) shed light on the containers:Data.Map library, indicating there were both algorithmic and stylistic performance improvements to be made. 52. http://research.microsoft.com/~simonpj/papers/containers/containers.pdf This proposal provides a patch that [53] dramatically improves performance across the API. Three standard techniques are applied to the code: * [54] Worker/Wrapper transformations of recursive functions with constant arguments (aka. the [55] static argument transformation). * Explicit inlining of wrapper functions. * Explicit strictness of keys to functions. 53. http://is.gd/eJHIE 54. http://www.workerwrapper.com/ 55. http://hackage.haskell.org/trac/ghc/ticket/888 Three complementary, but orthogonal patches are provided. 1. Add a testsuite, [56] with coverage data (currently 91% of top level functions, and all core functions). 2. Add a micro-benchmark suite based on [57] Criterion, for empirical evidence of improvements to each function. 3. The optimization patch itself. All 3 patches should be applied, under this proposal. 56. http://code.haskell.org/~dons/tests/containers/hpc_index.html 57. http://hackage.haskell.org/package/criterion The [58] benchmark results are very strong: * An average speedup across the core api of 47% (on intel i7 / linux 64 bit), and; * 36% on Mac / intel core 2 duo 32 bit). http://i.imgur.com/05BWe.png 58. http://is.gd/eJHIE No bugs were identified in the development of the comprehensive testsuite, which includes a large set of unit tests from [60] Kazu Yamamoto 60. http://twitter.com/kazu_yamamoto/status/22351727559 A fork of the containers package, with the 3 patches (and a version bump to make it easier to test out) is available: darcs get http://code.haskell.org/~dons/code/containers/ Separately, the patches are attached to this ticket. The consideration period is 3 weeks (before ICFP). __________________________________________________________________ Work carried out over 28/29th August, 2010 in Utrecht, NL, by Johan Tibell and Don Stewart.

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:Trace has no history
by Steve 01 Sep '10

01 Sep '10

I am trying to debug a problem in GHCI. I invoke my method with trace but when it breaks on exception i can't get this history. Output is below. Thanks. relude Symbols> :set -fbreak-on-exception Prelude Symbols> :trace myMethod Loading package HUnit-1.2.2.1 ... linking ... done. Loading package syb-0.1.0.2 ... linking ... done. Loading package base-3.0.3.2 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package time-1.1.4 ... linking ... done. Loading package random-1.0.0.2 ... linking ... done. Loading package QuickCheck-1.2.0.0 ... linking ... done. Loading package Decimal-0.1.0 ... linking ... done. Loading package array-0.3.0.0 ... linking ... done. Loading package Diff-0.1.2 ... linking ... done. Loading package bytestring-0.9.1.5 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-time-1.0.0.3 ... linking ... done. Loading package convertible-1.0.9 ... linking ... done. Loading package utf8-string-0.3.4 ... linking ... done. Loading package HDBC-2.2.6 ... linking ... done. Loading package HDBC-mysql-0.6.3 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package network-2.2.1.7 ... linking ... done. Loading package HTTP-4000.0.9 ... linking ... done. Loading package binary-0.5.0.2 ... linking ... done. Loading package digest-0.0.0.8 ... linking ... done. Loading package filepath-1.1.0.3 ... linking ... done. Loading package unix-2.4.0.0 ... linking ... done. Loading package directory-1.0.1.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package zlib-0.5.2.0 ... linking ... done. Loading package zip-archive-0.1.1.6 ... linking ... done. Loading package Core-0.0.1 ... linking ... done. Beginning Update Stopped at <exception thrown> _exception :: e = GHC.Exception.SomeException (GHC.Exception.D:Exception _ (GHC.Show.D:Show ...) ....) (GHC.IO.Exception.IOError Nothing GHC.IO.Exception.UserError ....) [<exception thrown>] Prelude Symbols> :history Empty history. Perhaps you forgot to use :trace?

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