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ANN: improve-0.2.2
by Tom Hawkins 12 Dec '10

12 Dec '10

ImProve [1] is an imperative DSL for high assurance, embedded applications. This release includes a new compositional proof framework where users can leverage previously proved theorems to aid the proof of new theorems. This new addition was inspired from discussions with Lee Pike [2]. Lee also recommended the strategy of building disjunctive invariants to reduce, if not eliminate the need for multi step induction, thus dramatically reducing proof time. Using these new strategies with ImProve, we where able to verify several realtime safety properties of an Eaton Hybrid Hydraulic program. -Tom [1] http://hackage.haskell.org/package/improve [2] http://groups.google.com/group/fp-embedded/browse_thread/thread/63cd023e8f1…

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Contexts for type family instances
by Stephen Tetley 12 Dec '10

12 Dec '10

Hello all I've a type family DUnit that I use to allow the unit type, usually a Double, of geometric things (points, vectors...) to be parametric: > type family DUnit a :: * E.g for Points > data Point u = P2 u u > type instance (Point u) = u I can make an type instance for Maybe like this, using DUnit on the right hand side: > type instance DUnit (Maybe a) = DUnit a But pair is a problem. Is there a way to assert both parts of a pair should have the same DUnit? The code below won't compile but it should illustrate what I'm trying to do. > type instance (DUnit a ~ DUnit b) => DUnit (a,b) = DUnit a I don't want to pick an arbitrary side, e.g: > type instance DUnit (a,b) = DUnit a or > type instance DUnit (a,b) = DUnit b Thanks Best wishes Stephen

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How can i insert graphic into a haddock document?
by Poprádi Árpád 12 Dec '10

12 Dec '10

Hi, I have found nothing about this topic in the haddock documentation. Is there a light way to do that? Best regards, Árpád

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haskell2010 and state question.
by Magicloud Magiclouds 12 Dec '10

12 Dec '10

Hi, Formerly, I had IORef and some state monad to do the task of keeping states. Now in haskell 2010, I cannot find anything about it. Do I have to use ghc base package for this function? -- 竹密岂妨流水过山高哪阻野云飞

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dot-ghci files
by Tony Morris 12 Dec '10

12 Dec '10

I teach haskell quite a lot. I recommend using .ghci files in projects. Today I received complaints about the fact that ghci will reject .ghci if it is group-writeable. I didn't offer an opinion on the matter. I am wondering if these complaints have legitimate grounds i.e. maybe you want to have group write on that file for some reason. I'd appreciate some comments on this issue. Thanks. -- Tony Morris http://tmorris.net/

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haskell-2010 binary IO
by Permjacov Evgeniy 12 Dec '10

12 Dec '10

Does haskell 2010 include binary IO? If no, what was the reason?

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Issues Installing Vacuum-Cairo 0.4.1, gtk-0.12.0, GHC 6.12.3, Cairo 0.12.0
by aditya siram 12 Dec '10

12 Dec '10

Hi all, When I try to cabal install vacuum-cairo, I get the following error message : Resolving dependencies... Configuring vacuum-cairo-0.4.1... Preprocessing library vacuum-cairo-0.4.1... Building vacuum-cairo-0.4.1... [1 of 1] Compiling System.Vacuum.Cairo ( System/Vacuum/Cairo.hs, dist/build/System/Vacuum/Cairo.o ) System/Vacuum/Cairo.hs:239:17: Ambiguous occurrence `G.eventKeyName' It could refer to either `G.eventKeyName', imported from Graphics.UI.Gtk at System/Vacuum/Cairo.hs:21:0-36 or `G.eventKeyName', imported from Graphics.UI.Gtk.Gdk.Events at System/Vacuum/Cairo.hs:22:0-47 System/Vacuum/Cairo.hs:261:16: Ambiguous occurrence `G.eventKeyName' It could refer to either `G.eventKeyName', imported from Graphics.UI.Gtk at System/Vacuum/Cairo.hs:21:0-36 or `G.eventKeyName', imported from Graphics.UI.Gtk.Gdk.Events at System/Vacuum/Cairo.hs:22:0-47 cabal: Error: some packages failed to install: vacuum-cairo-0.4.1 failed during the building phase. The exception was: exit: ExitFailure 1 Can anyone shed some light? -deech

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: genprog-0.1
by Alberto G. Corona 12 Dec '10

12 Dec '10

DNK? I think you mean DNA. the genotype program that develips the fenotype is much more smooth and granular than a computer program. A chante un a gen does not make you to have a extra bone. It can make you to have your hand slighltly longer. or shorter. In fact there are metalevels of selection that discard abrupt changes. For example, when females ovulate there are a strong selection where thounsands of candidate cell ovules are tested and discarded. This is one of the reasons why anomalous mutations are scarce. > > 2010/12/8 Mitar <mmitar(a)gmail.com> > > Hi! >> >> On Wed, Dec 8, 2010 at 12:33 PM, Alberto G. Corona <agocorona(a)gmail.com> >> wrote: >> > But programs are non lineal. >> >> And DNK is? I doubt. ;-) >> >> I think the approach is valid, it simulates what is happening in >> nature (random insertions, deletions, changes, translations, copies, >> etc, without any "higher" meaning and guiding). Only problem is that >> people often do not want to wait millions of years for evolution of >> programs to achieve their goal. >> >> Of course mutations are only part of the story. Also combining >> different parents' genes in a way to get functional offsprings is also >> a question how to do with programs. >> >> >> Mitar >> > >

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Recent Package Updates on Haskell.org
by Gabríel A. Pétursson 11 Dec '10

11 Dec '10

Is it just me or has the list of recent package updates, as seen on the front page of haskell.org, not changed since the migration?

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Help with lhs2TeX
by Dominic Steintiz 11 Dec '10

11 Dec '10

Hi, I wonder if someone could point out what I am doing wrong. My understanding was that I should be able to create a .lhs file and run it e.g. with ghci and then use lhs2TeX to create a nice .pdf file, all from the same source. I can produce nice slides but unfortunately the .lhs does compile because of the special symbols I wish to use. So presumably I need to pre-process my file before submitting to ghci. However, I was unable to find any information about this in the excellent guide. For example: > \documentclass{beamer} > > %include polycode.fmt > %format m_ = "\mu" > %format ^ = " " > %format inv(a) = a^"^\circ" > %format in_ = "in" > > \begin{document} > > \title{Some Notes on Category Theory with Some Applications to Computer > Science} > > \author{Dominic Steinitz} > > \begin{frame} > \frametitle{Haskell Example: Total} > Initial algebras can be defined as follows: > \begin{code} > newtype m_^f = In {inv(in_) :: f (m_^f )} > \end{code} > \end{frame} > > > \end{document} produces a nice slide but does not compile. If I change the offending line to > newtype Mu f = In {in_ :: f (Mu f)} then all is well but the slide does not look as nice

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Re: [Haskell-cafe] [Haskell] haskell.org migration complete
by Henning Thielemann 11 Dec '10

11 Dec '10

It seems that the new Wiki interprets a line-feed as beginning of a new paragraph. Before only two LFs where interpreted as paragraph separators. I liked the former interpretation because it allowed to split a paragraph into lines, where each sentence or each part of a sentence is on an individual line. This is better for all the line-oriented Diff-tools. Also code like <haskell> class C a where method :: a instance C Int where method = bla </haskell> is formatted with strange indentation as class C a where method :: a instance C Int where method = bla

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Monads in the 'hood
by Greg Meredith 11 Dec '10

11 Dec '10

Dear Haskellians, Keepin' it light. For your amusement this weekend: monads in the hood<http://www.youtube.com/watch?v=rYANU61J5eY> . Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 1219 NW 83rd St Seattle, WA 98117 +1 206.650.3740 http://biosimilarity.blogspot.com

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Re: [Haskell-cafe] A home-brew iteration-alike library: some extension quiestions
by Antoine Latter 11 Dec '10

11 Dec '10

Also, one thing that tripped me up is that your "Stream" type is fundamentally different from the "Stream" types in the iteratee/enumerator libraries - yours is more of a monadic list in the inner monad, with explicit errors. How does this change the operation of the Iterator type? I hope I am not pestering you too much :-) I think it is really fascinating how many different approaches people have to the left-fold-enumerator idea, and it is hard for me to grasp which differences are fundamental and what the differences mean. Also, in what way are the other libraries not Haskell-2010 compliant? I haven't experimented too much with this sort of thing, since Cabal defaults to the Haskell '98 language, and that's how I install most things. Thanks for your response, Antoine On Thu, Dec 9, 2010 at 2:07 PM, Permjacov Evgeniy <permeakra(a)gmail.com> wrote: > On 12/09/2010 10:54 PM, Antoine Latter wrote: >> I only have some surface level questions/comments - >> >> What existing packages is this similar to? How is it different from >> any previous work in the area? >> > Main idea was taken from Iteratees invented by Oleg Kiselev (there are > two packages on hackage implementing this ideas: data-iteraties and > enumerator packages) > The difference is, that I wished haskell-2010 compilant package for > left-foldable streams, including support for easy builing, transcoding, > merging and folding of streams relying on do-notation (see > Data.Iteration.Unicode.* for examples of transcoding streams: it is > quite clean and easily understandable) and ability to specify easily > monadic actions in stream processors. >> Also, likes looks like you don't need the 'Monad m' constraint on your >> various Monad and Functor instances in Data.Iteration.Types, which I >> think is one of the nicest properties of the continuation-based >> approach to something like this. > Errgh. That may be true, but I did not consider non-monadic context at > all, so I enforced this constrain mindlessly >> It's a mater of taste which way to go, but I prefer importing modules >> qualified rather than have type-suffixes on functions - so I would >> rather use 'I.next' and 'A.next' instead of 'nextI' and 'nextA'. But >> reasonable people can disagree on this. >> >> Take care, >> Antoine > Thanks! >> On Thu, Dec 9, 2010 at 1:42 PM, Permjacov Evgeniy <permeakra(a)gmail.com> wrote: >>> Hi. I Wrote a simple iteration library. It was not intensively tested, >>> so it MAY contatin bugs, but it is very unlikely. The library is >>> currently on github: https://github.com/permeakra/iteration >>> >>> I'm not ready to upload it to hackage, as some testing and extension is >>> really needed. However, I'd like to know about possible flaws. >>> >>> Current goal is addition of byte-stream (de)compression and IO functions >>> extenstion. After this package will be cabalized and uploaded to >>> hackage. So, while design is not frozen yet, I'm interested in criticism -)/ >>> >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> > >

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ANN: archiver 0.1 and 0.2
by Gwern Branwen 11 Dec '10

11 Dec '10

I'd like to announce a small utility and library which builds on my WebArchive plugin for gitit: archiver http://hackage.haskell.org/package/archiver Source is available via `darcs get http://community.haskell.org/~gwern/archiver/`. The library half is a simple wrapper around the appropriate HTTP requests; the executable half reads a text file and loops as it (slowly) fires off requests and deletes the appropriate URL. That is, 'archiver' is a daemon which will process a specified text file, each line of which is a URL, and will one by one request that the URLs be archived or spidered by http://www.webcitation.org * and http://www.archive.org ** for future reference. That is, WebCite and the IA will store a copy of the HTML and hopefully all the non-dynamic resources the web pages need. (An example would be http://bits.blogs.nytimes.com/2010/12/07/palm-is-far-from-game-over-says-fo… and http://webcitation.org/5ur7ifr12) Usage of archiver might look like `while true; do archiver ~/.urls.txt gwern0(a)gmail.com; done`***. There are a number of ways to populate the source text file. For example, I have a script `firefox-urls` which is called in my crontab every hour, and which looks like this: #!/bin/sh set -e cp `find ~/.mozilla/ -name "places.sqlite"` ~/ sqlite3 places.sqlite "SELECT url FROM moz_places, moz_historyvisits \ WHERE moz_places.id = moz_historyvisits.place_id and visit_date > strftime('%s','now','-1 day')*1000000 ORDER by \ visit_date;" >> ~/.urls.txt rm ~/places.sqlite This gets all visited URLs in the last time period and prints them out to the file for archiver to process. Hence, everything I browse is backed-up. More useful perhaps is a script to extract external links from Markdown files and print them to stdout: import System.Environment (getArgs) import Text.Pandoc (defaultParserState, processWithM, readMarkdown, Inline(Link), Pandoc) main = getArgs >>= mapM readFile >>= mapM_ analyzePage analyzePage x = processWithM printLinks (readMarkdown defaultParserState x) printLinks (Link _ (x, _)) = putStrLn x >> return undefined printLinks x = return x So now I can take `find . -name "*.page"`, pass the 100 or so Markdown files in my wiki as arguments, and add the thousand or so external links to the archiver queue (eg. `find . -name "*.page" | xargs runhaskell link-extractor.hs >> ~/.urls.txt`); they will eventually be archived/backed up and when combined with a tool like link-checker**** means that there never need be any broken links since one can either find a live link or use the archived version. General comments: I've used archiver for a number of weeks now. It has never caught up with my Firefox-generated backlog since WebCite seems to have IP-based throttling so you can't request more often than once per 20 seconds, according to my experiments, so I removed the hinotify 'watch file' functionality. It may be I was too hasty in removing it. * http://en.wikipedia.org/wiki/WebCite ** http://en.wikipedia.org/wiki/Internet_Archive *** There are sporadic exceptions from somewhere in the network or HTTP libraries, I think **** http://linkchecker.sourceforge.net/ -- gwern http://www.gwern.net

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ANN: Digestive functors 0.0.2.0
by Jasper Van der Jeugt 10 Dec '10

10 Dec '10

Hello all, I'm very glad to announce the 0.0.2.0 release of the digestive functors library. The library provides a general API to input consumption, and is an upgrade of formlets. I've written an announcing blogpost and tutorial with more information here: http://jaspervdj.be/posts/2010-12-09-digestive-functors-0.0.2.html You can get it on hackage here: http://hackage.haskell.org/package/digestive-functors As always, all feedback is welcome. Kindest regards, Jasper Van der Jeugt

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Haskell and javascript
by jean-christophe mincke 10 Dec '10

10 Dec '10

Hello, I have just discovered WebSharp, a .Net product for web development that allows you to write client code in F# and have it translated into javascript. Does anyone know about somethig similar in Haskell? Thank you Regards J-C

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haskell flickr bindings: "invalid signature" when uploading
by Dougal Stanton 10 Dec '10

10 Dec '10

I've mailed the maintainer of the flickr api package but thought I would see if other people had this experience too. Google doesn't reveal many people using this package as far as I can tell. In short, authentication works fine but uploading images fails with this message. This happens with the included examples/Uploader.hs as well as my own code. toRequest: POST request contains 1 files; unable to represent as query string Defaulting to multiform/form-data instead Flickr error: Code: 96 Type: Flickr API error Details: Invalid signature I haven't had a chance to dive deeper into this yet, but any advice gratefully received. Cheers, D -- Dougal Stanton dougal(a)dougalstanton.net // http://www.dougalstanton.net

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Setting runtime memory limits on GHC programs to avoid thrashing
by John D. Ramsdell 10 Dec '10

10 Dec '10

Enclosed is a simple script that sets GHCRTS and provides a reasonable memory limit on systems that have /proc/meminfo. By default, the GHC runtime will grow to a size that can cause thrashing. John

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Missing Functor instances in GHC 7?
by Sebastian Fischer 10 Dec '10

10 Dec '10

Hello, according to http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Monad.ht… Control.Monad exports 20 Functor instance declarations in base-4.3.0.0. However: bash# ghc-pkg list | grep base base-4.3.0.0 bash# ghci --version The Glorious Glasgow Haskell Compilation System, version 7.0.1 bash# ghci Prelude> import Control.Monad Prelude Control.Monad> :i Functor class Functor f where fmap :: (a -> b) -> f a -> f b (GHC.Base.<$) :: a -> f b -> f a -- Defined in GHC.Base instance Functor Maybe -- Defined in Data.Maybe instance Functor [] -- Defined in GHC.Base instance Functor IO -- Defined in GHC.Base There are only 3 instances instead of 20. Importing Control.Applicative gives 3 more instances but for example the instance for ((->) r) is still missing. Is my installation broken? Or has anybody similar problems finding Functor instances in GHC 7? Sebastian

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ANNOUNCE: mime-mail 0.1.0
by Michael Snoyman 10 Dec '10

10 Dec '10

Hi all (again), I'm happy to announce the second major release of the mime-mail[1] package. mime-mail is a package providing support for rendering multipart emails. This new release introduces: * A partHeaders record, allowing you to place arbitrary headers on individual parts of a message. This is especially useful for ContentID * Support for quoted-printable. There are two new Encoding constructors added: QuotedPrintableText and QuotedPrintableBinary. They differ in how they treat newline characters: the latter outputs CRs and LFs in an escaped form, while the former strips all CRs and outputs LFs as the ASCII codes for "\r\n". * Support for encoded-word for header values. This is a completely transparent change: now if you use non-ASCII characters in your header values, mime-mail will automatically encode appropriately. Enjoy! Michael [1] http://hackage.haskell.org/package/mime-mail

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: genprog-0.1
by Alberto G. Corona 10 Dec '10

10 Dec '10

Hi ;) 2010/12/8 Mitar <mmitar(a)gmail.com> > Hi! > > On Wed, Dec 8, 2010 at 3:39 PM, Alberto G. Corona <agocorona(a)gmail.com> > wrote: > > DNK? I think you mean DNA. > > Sorry. In my native language it is DNK. ;-) > > > the genotype program that develips the fenotype is much more smooth and > > granular than a computer program. A chante un a gen does not make you to > > have a extra bone. It can make you to have your hand slighltly longer. or > > shorter. > > Because we are using very small programs. A change of one constant in > a Linux kernel would also be a very small change in general. Maybe > some esoteric device would not function anymore, but this is it. Of > course there would be also changes which would make whole kernel > dysfunctional. > > Of course there are smooth zones in the fitness landscape of any code. what is necessary is to direct the process by avoiding absurd replacements (mutations that goes straight to dead zones) and rules for changing from a smooth to another smooth area once the local maximum is not satisfactory. Or to detect them as early as possible (that is, rules again). That is what I mentioned before. > > In fact there are metalevels of selection that discard abrupt changes. > For > > example, when females ovulate there are a strong selection where > thounsands > > of candidate cell ovules are tested and discarded. This is one of the > > reasons why anomalous mutations are scarce. > > I doubt that. Aren't female eggs made while she is still a fetus? And > they do not divide anymore later on? > This selection of candidate eggs happens each month within each ovulation period. It is mentioned in this superb conference series by Yale university. It is a very good introduction. I don´t remember the exact chapter. sorry: http://www.youtube.com/watch?v=VjgHd6HKtvE Moreover, the genetic code has evolved to evolve. For many reasons. Neither Haskell nor any conventional language has. One of the safety measures of the genetic code is protectin itself against undesired mutations. This is something vital for life. Cancer is one consequence. but another consequences are more deadly: If a mother spend nine months to produce an unfit child this is a dead end for the mother´s genome line. For this reason, undesired mutations, specially in reproductive cells are either repaired or discarded. This selection is more strong in females than in males (for investment reasons) . The rate of mutations in living beings is equal to the theorical optimum for procariots and eucariouts. This is another examople of how finely tuned the DNA has evolved for evolution. The molecular bonds are strong enough just to permit the right rate of mutation . But the DNA i´m sure, has much more secrets to learn and discover. So in conclusion there are much details to learn and to implement to have sucessful general genetic algorithms for genetic programming. But the research promises a lot of fun.

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Operator #
by c8h10n4o2 09 Dec '10

09 Dec '10

What does # mean in this code ? (from Data.List) findIndices p ls = loop 0# ls where loop _ [] = [] loop n (x:xs) | p x = I# n : loop (n +# 1#) xs | otherwise = loop (n +# 1#) xs -- View this message in context: http://haskell.1045720.n5.nabble.com/Operator-tp3299360p3299360.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: [Haskell-cafe] A home-brew iteration-alike library: some extension quiestions
by Permjacov Evgeniy 09 Dec '10

09 Dec '10

-------- Original Message -------- Subject: Re: [Haskell-cafe] A home-brew iteration-alike library: some extension quiestions Date: Thu, 09 Dec 2010 23:07:49 +0300 From: Permjacov Evgeniy <permeakra(a)gmail.com> To: Antoine Latter <aslatter(a)gmail.com> On 12/09/2010 10:54 PM, Antoine Latter wrote: > I only have some surface level questions/comments - > > What existing packages is this similar to? How is it different from > any previous work in the area? > Main idea was taken from Iteratees invented by Oleg Kiselev (there are two packages on hackage implementing this ideas: data-iteraties and enumerator packages) The difference is, that I wished haskell-2010 compilant package for left-foldable streams, including support for easy builing, transcoding, merging and folding of streams relying on do-notation (see Data.Iteration.Unicode.* for examples of transcoding streams: it is quite clean and easily understandable) and ability to specify easily monadic actions in stream processors. > Also, likes looks like you don't need the 'Monad m' constraint on your > various Monad and Functor instances in Data.Iteration.Types, which I > think is one of the nicest properties of the continuation-based > approach to something like this. Errgh. That may be true, but I did not consider non-monadic context at all, so I enforced this constrain mindlessly > It's a mater of taste which way to go, but I prefer importing modules > qualified rather than have type-suffixes on functions - so I would > rather use 'I.next' and 'A.next' instead of 'nextI' and 'nextA'. But > reasonable people can disagree on this. > > Take care, > Antoine Thanks! > On Thu, Dec 9, 2010 at 1:42 PM, Permjacov Evgeniy <permeakra(a)gmail.com> wrote: >> Hi. I Wrote a simple iteration library. It was not intensively tested, >> so it MAY contatin bugs, but it is very unlikely. The library is >> currently on github: https://github.com/permeakra/iteration >> >> I'm not ready to upload it to hackage, as some testing and extension is >> really needed. However, I'd like to know about possible flaws. >> >> Current goal is addition of byte-stream (de)compression and IO functions >> extenstion. After this package will be cabalized and uploaded to >> hackage. So, while design is not frozen yet, I'm interested in criticism -)/ >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >>

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Re: [Haskell-cafe] ANN: hledger 0.13
by Simon Michael 09 Dec '10

09 Dec '10

On Dec 9, 2010, at 7:34 AM, Peter Simons wrote: > I can tell it's doing more harm than good. The situation right now is > that it's impossible to install hledger on ArchLinux -- not because Why ? I haven't yet heard why depending on the higher process version is a problem.

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: genprog-0.1
by Alberto G. Corona 09 Dec '10

09 Dec '10

> > Hi! >> >> On Thu, Dec 9, 2010 at 1:48 PM, Alberto G. Corona <agocorona(a)gmail.com> >> wrote: >> > assign rates of mutation for each statement, >> >> This could be assigned by evolution itself. If "if" will have high >> probability of mutation then resulting programs will not survive. So >> those probabilities can be assigned by evolution itself and be also >> something which is passed on with generations (with again possibility >> of mutations of those probabilities itself). >> > > As any part in a genetic algoritm, it is a trading of flexibility for huge > gains of speed. take into accout that some of these tricks neded a > subtantial fraction of the age of the universe to evolve using massively > paralell hardware (ecosystems). > > > >> What would be interesting is to have an evolution algorithm which >> would allow such protections to evolve during its run. So some kind of >> protection which would lower the rate of mutation for some code part. >> >> > Species of programs means that the seed of the genetic algoritm must not >> be >> > turing comoplete I guess. It must be specific for each problem. >> >> I do not see this as necessity. Just that those specimens which would >> use this power too much would probably not survive. (If they would >> remove protection for some sentences they have build before.) >> > > The mutation weigths are something conventional for coventional languages. Another option is to design an automodifying evolving language from scratch. That "software DNA" I guess, should follow closely the techniques of the real DNA. Your idea fits more here In the conventional approach, the turing incomplete templates can have pre-assigned mutation weights for each statement. These mutation rates can evolve too. However, nothing prevents from having an additional level for selecting the appropriate template for each problem. > >> >> Mitar >> > > Alberto

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Re: [Haskell-cafe] ANN: hledger 0.13
by Simon Michael 09 Dec '10

09 Dec '10

On Dec 9, 2010, at 3:35 AM, Peter Simons wrote: > you said that a dependency of one of those packages would require > process >= 1.0.1.4. Now, what I don't understand is why you added > that restriction to hledger then? Picture this common scenario, which I saw during installability testing - you install hledger to try it out. Cabal builds it with process 1.0.1.3. You get enthusiastic and later try to cabal install hledger-X, but this fails ("can not install hledger-X because hledger requires process-1.0.1.3"). (In other, similar-seeming cases I have seen cabal rebuild the installed depender; I don't understand all of cabal's behaviour.) I presume the user could work around this by - ghc-pkg unregister hledger; cabal install hledger-X - installing hledger the first time with --constraint process-1.0.1.4 but I figured a low-impact to make things "just work" was to bump hledger's process dependency. Is it making sense ? I welcome further insights or better solutions.

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ICFP 2011: Call for papers
by Wouter Swierstra 09 Dec '10

09 Dec '10

===================================================================== Call for Papers ICFP 2011: International Conference on Functional Programming Tokyo, Japan, Monday 19 -- Wednesday 21 September 2011 http://www.icfpconference.org/icfp2011 ===================================================================== Important Dates ~~~~~~~~~~~~~~~ Titles, abstracts & keywords due: Thursday 17 March 2011 at 14:00 UTC Submissions due: Thursday 24 March 2011 at 14:00 UTC Author response: Tuesday & Wednesday 17-18 May Notification: Monday 30 May 2011 Final copy due: Friday 01 July 2011 Conference: Monday-Wednesday 19-21 September 2011 Scope ~~~~~ ICFP 2011 seeks original papers on the art and science of functional programming. Submissions are invited on all topics from principles to practice, from foundations to features, and from abstraction to application. The scope includes all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages with objects, concurrency, or parallelism. Particular topics of interest include * Language Design: type systems; concurrency and distribution; modules; components and composition; metaprogramming; relations to imperative, object-oriented, or logic programming; interoperability * Implementation: abstract machines; virtual machines; interpretation; compilation; compile-time and run-time optimization; memory management; multi-threading; exploiting parallel hardware; interfaces to foreign functions, services, components, or low-level machine resources * Software-Development Techniques: algorithms and data structures; design patterns; specification; verification; validation; proof assistants; debugging; testing; tracing; profiling * Foundations: formal semantics; lambda calculus; rewriting; type theory; mathematical logic; monads; continuations; delimited continuations; global, delimited, or local effects * Transformation and Analysis: abstract interpretation; partial evaluation; program transformation; program calculation; program proofs; normalization by evaluation * Applications and Domain-Specific Languages: symbolic computing; formal-methods tools; artificial intelligence; systems programming; distributed-systems and web programming; hardware design; databases; XML processing; scientific and numerical computing; graphical user interfaces; multimedia programming; scripting; system administration; security; education * Functional Pearls: elegant, instructive, and fun essays on functional programming * Experience Reports: short papers that provide evidence that functional programming really works or describe obstacles that have kept it from working in a particular application Abbreviated instructions for authors ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * By 17 March 2011, 14:00 UTC, submit a title, an abstract of at most 300 words, and keywords. * By 24 March 2011, 14:00 UTC, submit a full paper of at most 12 pages (6 pages for a Functional Pearl and for an Experience Report), including bibliography and figures. The deadlines will be strictly enforced and papers exceeding the page limits will be summarily rejected. * Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. * Each submission must adhere to SIGPLAN's republication policy, as explained on the web at http://www.acm.org/sigplan/republicationpolicy.htm In addition, authors of resubmitted (but previously rejected) papers have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the program chair will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no rewiewer will read the annotated copies of the previous reviews. Overall, a submission will be evaluated according to its relevance, correctness, significance, originality, and clarity. It should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. The technical content should be accessible to a broad audience. Functional Pearls and Experience Reports are separate categories of papers that need not report original research results and must be marked as such at the time of submission. Detailed guidelines on both categories are on the conference web site. Proceedings will be published by ACM Press. Authors of accepted submissions are expected to transfer the copyright to the ACM. Presentations will be videotaped and released online if the presenter consents by signing an additional permission form at the time of the presentation. Formatting: Submissions must be in PDF format printable in black and white on US Letter sized paper and interpretable by Ghostscript. If this requirement is a hardship, make contact with the program chair at least one week before the deadline. Papers must adhere to the standard ACM conference format: two columns, nine-point font on a ten-point baseline, with columns 20pc (3.33in) wide and 54pc (9in) tall, with a column gutter of 2pc (0.33in). A suitable document template for LaTeX is available from SIGPLAN at http://www.acm.org/sigs/sigplan/authorInformation.htm Submission: Submissions will be accepted electronically at a URL to be named later. Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Author response: Authors will have a 48-hour period, starting at 14:00 UTC on Tuesday 17 May 2010, to read reviews and respond to them. Special Journal Issue: There will be a special issue of the Journal of Functional Programming with papers from ICFP 2011. The program committee will invite the authors of select accepted papers to submit a journal version to this issue. Conference Chairs: Manuel M T Chakravarty, University of New South Wales, Australia Zhenjiang Hu, National Institute of Informatics (NII), Japan Program Chair: Olivier Danvy, Aarhus University, Denmark Program Committee: Kenichi Asai, Ochanomizu University, Japan Josh Berdine, Microsoft Research, UK Adam Chlipala, Harvard University, USA William Cook, University of Texas at Austin, USA Maribel Fernandez, King's College London, UK Ronald Garcia, Carnegie Mellon University, USA Neal Glew, Intel Labs, USA Jacques Garrigue, Nagoya University, Japan Suresh Jagannathan, Purdue University, USA Sam Lindley, University of Edinburgh, UK Frank Pfenning, Carnegie Mellon University, USA Paola Quaglia, University of Trento, Italy Alexis Saurin, University of Paris VII, France Mike Spivey, Oxford University, UK Kristian Stoevring, University of Copenhagen, Denmark Doaitse Swierstra, Utrecht University, The Netherlands David Van Horn, Northeastern University, USA Rene Vestergaard, JAIST, Japan Edwin Westbrook, Rice University, USA

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Haskell Weekly News: Issue 161 - December 08, 2010
by Daniel Santa Cruz 09 Dec '10

09 Dec '10

Welcome to issue 161 of the HWN, a newsletter covering developments in the [1]Haskell community in the week of November 28 - December 04. Jan Snajder [2]announced the release of genprog, a genetic programming library. Ian Lynagh informed us that the haskell.org server migration is now complete. There might still be some issues lying around, if you happen to spot one, please let the admins know. The biggest announcement this week came from Galois, Inc. on the [3]immediate release of the Haskell Lightweight Virtual Machine. "The HaLVM is a port of the GHC runtime system to the Xen hypervisor, allowing programmers to create Haskell programs that run directly on Xen's "bare metal."" Isabelle Perseil informed us that there is an [4]extension to the submission deadline for papers for International Conference on the Engineering of Complex Computer Systems (ICECCS) until December 15th. Gregory D. Weber [5]informed us of an update to his Sifflet tool, and sifflet-lib. "Sifflet is a visual, functional programming language and support system for students learning about recursion." This week we had 48 new StackOverflow questions, and 33 new Reddit stories. Hackage saw 108 uploads/updates from 59 distinct contributors. Most active uploaders to hackage were Michael Snoyman (16 uploads) and Andy Stewart (13 uploads). Big note of thanks to Janis Voigtländer and to Benjamin L. Russell for sending in bits for this newsletter. So, what went on this week? Top Reddit Stories * Galois releases the Haskell Lightweight Virtual Machine (HaLVM) Domain: galois.com, Score: 105, Comments: 26 On Reddit: http://www.reddit.com/r/haskell/comments/ee4ve/galois_releases_the_haskell_… Original: http://www.galois.com/blog/2010/11/30/galois-releases-the-haskell-lightweig… * Steve Yegge: Haskell Researchers Announce Discovery of Industry Programmer Who Gives a @#!& Domain: steve-yegge.blogspot.com, Score: 54, Comments: 42 On Reddit: http://www.reddit.com/r/haskell/comments/eeqw9/steve_yegge_haskell_research… Original: http://steve-yegge.blogspot.com/2010/12/haskell-researchers-announce-discov… * Fun with monad comprehensions Domain: blog.n-sch.de, Score: 35, Comments: 9 On Reddit: http://www.reddit.com/r/haskell/comments/ecu0w/fun_with_monad_comprehension… Original: http://blog.n-sch.de/2010/11/27/fun-with-monad-comprehensions/ * The Arrow Calculus Domain: wadler.blogspot.com, Score: 34, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/ee0ux/the_arrow_calculus/ Original: http://wadler.blogspot.com/2010/11/arrow-calculus.html * My strings can beat up your string Domain: finger-tree.blogspot.com, Score: 32, Comments: 13 On Reddit: http://www.reddit.com/r/haskell/comments/eecw2/my_strings_can_beat_up_your_… Original: http://finger-tree.blogspot.com/2010/11/my-strings-can-beat-up-your-strings… * Haskell Package Layout: a proposal Domain: mtnviewmark.wordpress.com, Score: 27, Comments: 8 On Reddit: http://www.reddit.com/r/haskell/comments/efhde/haskell_package_layout_a_pro… Original: http://mtnviewmark.wordpress.com/2010/12/02/haskell-package-layout/ * Real World Haskell ebook today: 60% off. Use code DDF2H Domain: oreil.ly, Score: 25, Comments: 16 On Reddit: http://www.reddit.com/r/haskell/comments/edexw/real_world_haskell_ebook_tod… Original: http://oreil.ly/free2choose * Comprehensive Monad Notation Domain: zenzike.com, Score: 23, Comments: On Reddit: http://www.reddit.com/r/haskell/comments/ef5rf/comprehensive_monad_notation/ Original: http://zenzike.com/posts/2010-12-02-comprehensive-monad-notation/ * Google AI Challenge: Languages Used by the Best Programmers Domain: r-bloggers.com, Score: 23, Comments: 13 On Reddit: http://www.reddit.com/r/haskell/comments/efrfv/google_ai_challenge_language… Original: http://www.r-bloggers.com/google-ai-challenge-languages-used-by-the-best-pr… * A small matter of illegal characters Domain: serpentine.com, Score: 22, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/edkhz/a_small_matter_of_illegal_ch… Original: http://www.serpentine.com/blog/2010/11/29/a-small-matter-of-illegal-charact… Top StackOverflow Questions * Whats really more performant? Haskell or OCaml votes: 12, answers: 4 Read on SO: http://stackoverflow.com/questions/4308137/whats-really-more-performant-has… * Problems on migrating from functional to OO votes: 10, answers: 5 Read on SO: http://stackoverflow.com/questions/4348788/problems-on-migrating-from-funct… * Getting a list of all possible data type values in Haskell votes: 8, answers: 3 Read on SO: http://stackoverflow.com/questions/4299319/getting-a-list-of-all-possible-d… * Haskell: Want a better way of doing: value == x || value == y || … votes: 6, answers: 1 Read on SO: http://stackoverflow.com/questions/4294652/haskell-want-a-better-way-of-doi… * Is/Should wrapping functions into a monad transformer be considered bad practice? votes: 6, answers: 3 Read on SO: http://stackoverflow.com/questions/4317101/is-should-wrapping-functions-int… * Trick for “reusing” arguments in Haskell? votes: 5, answers: 2 Read on SO: http://stackoverflow.com/questions/4333864/trick-for-reusing-arguments-in-h… * How to write common “if” branching in Haskell votes: 4, answers: 5 Read on SO: http://stackoverflow.com/questions/4296887/how-to-write-common-if-branching… * Comparing functions in Haskell votes: 4, answers: 4 Read on SO: http://stackoverflow.com/questions/4328620/comparing-functions-in-haskell * Encapsulating a list of functions in haskell in a single one votes: 4, answers: 2 Read on SO: http://stackoverflow.com/questions/4343951/encapsulating-a-list-of-function… * Can I have a value constructor named “/”"? votes: 4, answers: 3 Read on SO: http://stackoverflow.com/questions/4348605/can-i-have-a-value-constructor-n… Quotes from the Week * camccann: A humor monad? So basically that's a model where jokes about something are equivalent to jokes about jokes about something. In other words, meta-humor in-jokes. * djahandarie: I'm like a massively parallel but slow clocked processor * wlangstroth: It's disgusting hom much talent there is at galois About the Haskell Weekly News New editions are posted to [6]the Haskell mailing list as well as to [7]the Haskell Sequence and [8]Planet Haskell. [9]RSS is also available, and headlines appear on [10]haskell.org. To help create new editions of this newsletter, please send stories to dstcruz * at * gmail * dot * com. The code used to produce this version of the newsletter is not yet publicly available, as it is a complete hack designed to get things started again. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/18322 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18328 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18339 5. http://article.gmane.org/gmane.comp.lang.haskell.general/18344 6. http://www.haskell.org/mailman/listinfo/haskell 7. http://sequence.complete.org/ 8. http://planet.haskell.org/ 9. http://sequence.complete.org/node/feed 10. http://haskell.org/

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ANNOUNCE: packdeps 0.0.0
by Michael Snoyman 08 Dec '10

08 Dec '10

Hi all, I'm happy to announce the first release of packdeps[1]. This is a library and executable containing the same functionality as the original packdeps website[2], namely letting you know when your version bounds exclude the use of the newest version of a library available. While the website is very useful for keeping you up-to-date on your already released packages, it does not help you during the development phase, or for packages not released on Hackage. The executable (packdeps) should be a good fit here. Its usage is very simple: simply pass it a list of cabal files, and it will check each one of them against your 00-index.tar file. (In other words, make sure to run a cabal update before relying on its results too much.) The library, frankly, is a mess: the naming is bad, the performance tradeoffs were chosen for a long-running web application instead of a short-lived console app, and it eats a baby panda each time you run it. I'm more than happy to accept patches on this. Nonetheless, I'm not aware of any bugs in the code, and I think it will be generally useful in its current state. Cheers, Michael [1] http://hackage.haskell.org/package/packdeps [2] http://packdeps.haskellers.com/

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hackage dependencies for cabal setup scripts
by Sönke Hahn 08 Dec '10

08 Dec '10

Hi! If you write a cabal setup script with user hooks, is there a way to tell cabal-install that the setup script itself depends on some package from hackage? (The dependency would be cabal-macosx in my case.) Thanks, Sönke

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Re: [Haskell-cafe] ANN: hledger 0.13
by Simon Michael 08 Dec '10

08 Dec '10

On Dec 8, 2010, at 5:58 AM, Peter Simons wrote: > do you by any chance remember which dependency that was? I wonder, > because I had no trouble compiling hledger 0.13's dependencies on a > standard GHC 6.12.3 system -- only hledger itself fails the "cabal > configure" stage --, so it seems to me like all dependencies work > fine with process 1.0.1.3. Is there something I miss? Hi Peter.. I haven't been able to track it down yet. If I wasn't clear before, hledger-lib and hledger-lib build fine with process-1.0.1.3, but my recollection was that one of hledger-{chart,vty,web} did not. However I might have been outwitted by cabal again. If it turns out we actually can cabal install all five packages with process-1.0.1.3, I'll make a bugfix release.

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LLVM, type-level?
by Lally Singh 08 Dec '10

08 Dec '10

Hey all, I'm generating a structure definition from input, and would like to generate some LLVM code that can use it. I see an 'alloca' function in LLVM.Core that may do the trick, but takes a static type (Ptr a), which I wouldn't have. Is there a dynamic variant? I'm currently generating a TypeDesc Struct type. Also, is everything under LLVM.Core.* private (not LLVM.Core, but LLVM.Core.Util,etc)? I saw from some blog posts that Core.Util has a function for (I think) getting the a function's parameters, but I can't seem to find a way to access it. Is there another way to get the arguments to a function? Thanks for your help, -Lally

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: genprog-0.1
by Alberto G. Corona 08 Dec '10

08 Dec '10

Off topic I was deeply involved in genetic programming in the past (in fact I discovered Haskell on looking for a functional language for genetic programing with better syntax than LISP). But I soon realized that GP was not the holy grial after all. The problem with evolving arbitrary programming code is the fitness landscape<http://www.google.com/search?hl=en&q=fitness+landscape>. Any evolutionary process needs a way to produce small changes that produces small increases or decreases of fitness (parsimony). This is why it is relatively easy to evolve a continuous function towards a desired value. A smal change in a parameter has a small effect in the resulting fitness, so the algoritm can step up trough the smooth fitness landscape upto a local maximum. But programs are non lineal. If I change the expression in a conditional, the flow of the program becomes radically different, so the fitness landscape, instead of a smoth continuous surface is a fractal where there are no way to climb up the mount improbable (Dawkins dixit). http://www.google.com/search?hl=en&q=mount+improbable+dawkins The only way to overcome this is to indentify the smooth parts of the fitness landscape and restrict the exploration to them trough some techniques such is the use of rules, division of the problem in subproblems and ...well any trick programmers use in their ordinary work to restrict and direct the program mutations. It is theoretically possilble to define metalevels of genetic algoritms where rules and strategies are selected by extracting sucessful patterns after evolving a big number of sucessful programs, These metaleves can discover from simple rules such are "if a push is inserted, a pop must be inserted somewhere else (push-pop gene mutation rule), upto the re-discovery of complex rules above mentioned. These rules later would be used to restrict the mutations of the lower levels. Finally the rules could become so accurate that no mutation at the lower level is necessary because the evolved higuer level rules give the solution at the first try. So the genetic algoritms have the potential to design arbitrary complex programs right from scratch, but it may require a few billion years of computing. Anyway this stuff is really interesting and I suspect that the combination of rules and metalevels has some future, at least for helping programmers with intelligent IDEs. 2010/12/8 Kenneth Hoste <kenneth.hoste(a)ugent.be> > Hi Jan, > > Hi Jan, > > On 11/29/2010 12:55 PM, Jan Snajder wrote: > > Dear Haskellers, > > > > I am pleased to announce the release of genprog-0.1, a genetic > > programming library. > > > > (snip) > > Very interesting, and nice job on the code (elegant, well-structured, > well-documented, ...)! > > Genetic programming recently got my attention because one of the bots in > the Google AI contest was built using this technique (see > http://ai-contest.com/forums/viewtopic.php?f=17&t=1136) and it > performed really well (way better than my hand-crafted bot). > > I have a bit of experience with genetic algorithms, on a practical and > pragmatic level. The field of genetic programming is something I hope to > look at and play with in the upcoming months (just for fun). > > I was kind of planning to implement my own genetic programming library > in Haskell as I became familiar with the field, but after diving into > your code it quickly became clear to me you've done a way better job > than I would have. > > I really like the example you provided for evolving an expression that > computes a specified integer value. I plan to start playing with that > and improve the example (faster convergence to a perfect solution, and > also tweaking the current GP config to obtain smaller solutions). > > > A couple of questions (some fairly unrelated to Haskell): > > How hard would it be to extend the current version to support the > evolution of actual Haskell programs? As far as I can tell, the current > version has support for (simple?) self-defined expressions, but this > seems like a long way from supporting Haskell programs with > multi-argument functions that operate on lists, etc., even if you just > limit it to non-monadic Haskell98 code. > > Have you considered playing with dynamic values for the various > parameters that steer the evolution, i.e. population size, > crossover/mutation probabilities, etc.? > One thing I've always wanted to try (but never really got to it) is e.g. > increasing the mutation probability as the evolution seems to be getting > stuck in a (local?) optimum. Also, shrinking the population size if > enough progress is being made could be interesting, to speed up the > evolutionary process. Are you aware of studies that do such a thing? > > Are you planning to actively maintain and extend this library? Are you > using it for research purposes, or did you hack this together just for > fun (if so, nice job!). What do you plan to use it for? > > > Anyway, great job, I hope I'll find the time to play around with this. > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

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Location of .cabal folder
by Michael Snoyman 08 Dec '10

08 Dec '10

Hi all, I'm trying to figure out how to determine the location of the .cabal folder. I'm trying to release the code powering the package dependency site[1] as a standalone library/application, but currently I've simply hardcoded the path to my 00-index.tar file. Thanks, Michael [1] http://packdeps.haskellers.com/

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Question: mime-mail and base64 encoding
by Michael Snoyman 08 Dec '10

08 Dec '10

Hi all, I've gotten a request for the mime-mail package that I'd like some input on. Right now, there's the ability to fully specify whether or not to base64-encode each part in a message, but the included simpleMail function defaults to non-encoded parts for both its HTML and plain text alternatives. This has apparently caused some issues where long HTML strings have been word-wrapped at bad locations, causing breakage in the meaning of the markup. The request is to make both the HTML and plain text parts use base64 encoding by default. This *seems* to me to make a lot of sense, since it will ensure that your message arrives exactly as you intended it, and will ensure that any non-ASCII code points don't get killed somewhere along the way. On the other hand, I'm not sure what client support is like for base-64 encoding. Don't we need to leave *some* form of non-encoded data for less sophisticated email clients? Thanks, Michael

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Fwd: second call for papers: LDTA 2011 / ETAPS
by Paul Brauner 08 Dec '10

08 Dec '10

---------- Forwarded message ---------- From: Emilie Balland <emilie.balland(a)inria.fr> Date: Tue, Dec 7, 2010 at 10:35 PM Subject: second call for papers: LDTA 2011 / ETAPS To: "Paul.Brauner" <Paul.Brauner(a)loria.fr> LDTA 2011 Call for Papers and Tool Challenge Submissions 11th International Workshop on Language Descriptions, Tools, and Applications www.ldta.info Saarbrucken, Germany March 26 & 27, 2011 an ETAPS workshop LDTA is an application and tool-oriented workshop focused on grammarware - software based on grammars in some form. Grammarware applications are typically language processing applications and traditional examples include parsers, program analyzers, optimizers and translators. A primary focus of LDTA is grammarware that is generated from high-level grammar-centric specifications and thus submissions on parser generation, attribute grammar systems, term/graph rewriting systems, and other grammar-related meta-programming tools, techniques, and formalisms are encouraged. LDTA is also a forum in which theory is put to the test, in many cases on real-world software engineering challenges. Thus, LDTA also solicits papers on the application of grammarware to areas including, but not limited to, the following: - program analysis, transformation, generation, and verification, - implementation of Domain-Specific Languages, - reverse engineering and re-engineering, - refactoring and other source-to-source transformations, - language definition and language prototyping, and - debugging, profiling, IDE support, and testing. This year LDTA will also be putting theory, as well as techniques and tools, to the test in a new way - in the LDTA Tool Challenge. Tool developers are invited to participate in the Challenge by developing solutions to a range of language processing tasks over a simple but evolving set of imperative programming languages. Tool challenge participants will present highlights of their solution during a special session of the workshop and contribute to a joint paper on the Tool Challenge and proposed solutions to be co-authored by all participants after the workshop. Note that LDTA is a well-established workshop similar to other conferences on (programming) language engineering topics such as SLE and GPCE, but is solely focused on grammarware. Paper Submission ---------------- LDTA solicits papers in the following categories. - research papers: original research results within the scope of LDTA with a clear motivation, description, analysis, and evaluation. - short research papers: new innovative ideas that have not been completely fleshed out. As a workshop, LDTA strongly encourages these types of submissions. - experience report papers: description of the use of a grammarware tool or technique to solve a non-trivial applied problem with an emphasis on the advantages and disadvantages of the chosen approach to the problem. - tool demo papers: discussion of a tool or technique that explains the contributions of the tool and what specifically will be demonstrated. These papers should describe tools and applications that do not fit neatly into the specific problems in the Tool Challenge. Each submission must clearly state in which of these categories it falls and not be published or submitted elsewhere. Papers are to use the standard LaTeX article style and the authblk style for affiliations; a sample of which is provided at www.ldta.info. Research and experience papers are limited to 15 pages, tool demonstration papers are limited to 10 pages, and short papers are limited to 6 pages. The final version of the accepted papers will, pending approval, be published in the ACM Digital Library and will also be made available during the workshop. Please submit your abstract and paper using EasyChair at http://www.easychair.org/conferences/?conf=ldta2011. The authors of each submission are required to give a presentation at LDTA 2011 and tool demonstration paper presentations are intended to include a significant live, interactive demonstration. The authors of the best papers will be invited to write a journal version of their paper which will be separately reviewed and, assuming acceptance, be published in journal form. As in past years this will be done in a special issue of the journal Science of Computer Programming (Elsevier Science). Invited Speaker --------------- Rinus Plasmeijer, Radboud University Nijmegen, The Netherlands Important Dates --------------- Abstract submission: Dec. 15, 2010 Full paper submission: Dec. 22, 2010 Author notification: Feb. 01, 2011 Camera-ready papers due: TBD LDTA Workshop: March 26-27, 2011 LDTA Tool Challenge ------------------- The aim of the LDTA Tool Challenge is to foster a better understanding, among tool developers and tool users, of relative strengths and weaknesses of different language processing tool techniques as well as different implementations and realizations of those techniques. Tool developers are invited to participate in the Tool Challenge and demonstrate their solution to the problems during a special session of LDTA 2011. The problems in the LDTA Tool Challenge Problem Set can be viewed as points in a two dimensional space: one dimension specifying language processing tasks and the second dimension specifying the set of languages to which these tasks are to be applied. Along the task dimension are several traditional language processing tasks such as parsing, pretty printing, semantic analysis, optimization, and code generation. The language dimension is comprised of a simple, but evolving, suite of imperative programming languages. These two dimensions form a problem space in which various techniques and implementations will find problems in which they excel and others in which they find some challenges; no single technique or tool is expected to be optimal for all problems. Thus, this is a challenge and not a competition; no winner is declared. The full description of the problem set can be found in the LDTA Tool Challenge Problem Set document on the LDTA web page at ( http://www.ldta.info ). The Tool Challenge is open to developers of all kinds of grammarware tools and techniques. To participate, tool developers must submit the following by March 5, 2011. Names of participants and the name of their tool or technique. Presentation title and abstract. The short abstract should specify on what aspects of the problem set the tool was applied, where it excelled and where no solution was offered and/or the solution was considered less than optimal. We expect these to be only a few paragraphs in length. This information is used for scheduling purposes only and is not used for evaluation; as all tool developers interested in participating are welcome and will be given an opportunity to present their solution at the workshop. Submission of this information indicates a commitment to attend LDTA and to participate in the workshop. This information will be listed in the program. Authors of submissions that appear to be outside of the scope of LDTA will be contacted to discuss the relevance of their work to the workshop. Of course tool developers who question whether their work falls with the scope of LDTA are encouraged to contact the PC chairs early on for clarification. After the workshop a joint paper will be written by participants and submitted to a journal, most likely Science of Computer Programming. It is separate from the proceedings of the workshop and any special journal issue for the workshop. Program Committee ----------------- Emilie Balland, INRIA, France Anya Helene Bagge, University of Bergen, Norway, Paulo Borba, Federal University of Pernambuco, Brazil John Boyland, University of Wisconsin, USA Claus Brabrand, IT University of Copenhagen, Denmark, (co-chair), brabrand(a)itu.dk Jim Cordy, Queen's University, Canada Kyung-Goo Doh, Hanyang University, Ansan, South Korea Giorgios Robert Economopoulos, University of Southampton, UK Laurie Hendren, McGill University, Canada Nigel Horspool, University of Victoria, Canada Roberto Ierusalimschy, Pontifícia Universidade Católica do Rio de Janeiro, Brazil Johan Jeuring, Utrecht University, The Netherlands Shane Markstrum, Bucknell University, USA Sukyoung Ryu, Korea Advanced Institute of Science and Technology, Korea Joao Saraiva, Universidade do Minho, Portugal Sylvain Schmitz, Ecole Normale Superieure de Cachan, France Sibylle Schupp, Hamburg University of Technology, Germany Eli Tilevich, Virginia Tech, USA Eric Van Wyk, University of Minnesota, USA (co-chair), evw(a)cs.umn.edu Eelco Visser, Delft University of Technology, The Netherlands Organizing Committee -------------------- Emilie Balland, INRIA, France Giorgios Robert Economopoulos, University of Southampton, UK

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An Haskell implementation of a sweep line algorithm for the detection of segments intersection
by vince vegga 07 Dec '10

07 Dec '10

Hi, Here is my Haskell implementation of the Shamos and Hoey algorithm for detecting segments intersection in the plane: http://neonstorm242.blogspot.com/2010/12/sweep-line-algorithm-for-detection… I'm new to Haskell, so any useful comments will be appreciated. - Eran

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ANN: hledger 0.13
by Simon Michael 07 Dec '10

07 Dec '10

I've released hledger 0.13, with readline editing and tab completion from Judah Jacobson, more ledger compatibility, a more robust and installable web interface, bugfixes, and a much-deliberated package split. Docs and mac and 64-bit linux binaries are at http://hledger.org , and of course you can cabal update and cabal install hledger, cabal install hledger-web and so on. I didn't manage to build new windows or linux 32-bit binaries today, but they'll appear when I do. Let it be noted that maintaining a non-trivial cross-platform haskell app is currently quite hard. Release notes: * move web, vty, chart commands into separate hledger-web, hledger- vty, hledger-chart packages. This both simplifies (no more build flags) and complicates (more room for dependency hassles), but I hope overall it will be easier and more scalable. * all packages but chart are now marked "beta", ie "not finished but suitable for everyday use" * parsing: ledger compatibility: support D default commodity directive * parsing: ledger compatibility: ignore metadata tags on transactions and postings * parsing: ledger compatibility: ignore cleared flags at the start of postings * parsing: ledger compatibility: ignore C commodity conversion directives * parsing: price precisions no longer affect commodities' display precisions * add: readline-style editing * add: tab-completion for account names * add: add the default commodity, if any, to commodity-less amounts (#26) * add: misc. commodity/precision/defaults-related bugfixes * chart: give a meaningful error message for empty journals * chart: update for current Chart lib (0.14) * web: support files now live in ./.hledger/web/ and will be auto- created at startup * web: page layout is more robust with wide content * web: allow editing of included files * web: handle multiple filter patterns correctly * web: allow single- or double-quoted filter patterns containing spaces * web: update for current yesod lib (0.6.*) * transaction balancing is now based on display precision (#23) * briefer, more informative usage error messages Stats: 91 days and 117 commits since last release, now at 5997 lines of code with 151 tests. hledger is at a point where real-world user and developer input is needed to focus it; participants welcome. Best, -Simon

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Help defining a Typeable polymorphic-state monad transformer
by Brandon Simmons 07 Dec '10

07 Dec '10

Hi all, I gave myself until this evening to figure this out on my own, and time is up! Hopefully this makes for a good discussion, though the idea could be dumb. What I'm trying to do is define a state monad in which the passed state can change type during the computation. The only constraint is that the state types must always be of the Typeable class (see: http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Typea… ). The idea is that the new monad would be something like 'StateT s Maybe a', but where the 's' type is not fixed (indeed is hidden in an existential type) and where any programmer errors in the chaining of the polymorphic state will be caught in the Maybe type (or really the 'fail' implementation of any monad). Here is how I imagine a computation might look: computation :: TypeableState Maybe String computation = do (c:cs) <- getTS putTS (length cs) return ("c" ++ " was the first letter of the string passed as initial state.") So TypeableState is very similar to StateT, except that the state type is not present as a type argument. In the example above 'Maybe' is the monad that catches Typeable errors, and String is the return type of the computation. getTS and putTS would be get and put functions that constrain their arguments to the Typeable class. Here is what I have so far (at least this is my most recent uncommented attempt): > {-# LANGUAGE ExistentialQuantification #-} > module Main > where > > import Control.Monad.State > import Data.Typeable > > -- we might have restricted our 'm' to MonadPlus and used the explicit > -- 'mzero', but decided instead to use Monad, with 'fail'. This is > -- more appropriate since we won't be using 'mplus'. See 'liftMaybe'. > data TypeableState m a = forall s0 sN. (Typeable s0, Typeable sN)=> > TypeableState (s0 -> m (a,sN)) > > -- this is probably one of the more non-sensical attempts I've made at > -- this... but I'm not sure: > runTypeableState :: (Monad m, Typeable s0, Typeable sN)=> TypeableState m a -> s0 -> m (a,sN) > runTypeableState (TypeableState st) s0 = (liftMaybe $ cast s0) >>= st > > -- copied from Control.Monad.StateT > instance (Monad m) => Monad (TypeableState m) where > return a = TypeableState $ \s -> return (a, s) > m >>= k = TypeableState $ \s -> do > ~(a, s') <- runTypeableState m s > runTypeableState (k a) s' > fail str = TypeableState $ \_ -> fail str > > -- I imagine using this with 'cast' to thread the type in our monad > -- transformer > liftMaybe :: (Monad m)=> Maybe a -> m a > liftMaybe = maybe (fail "Monadic failure") return So is this even feasible? Or do I not grok what we can and can't do with the Typeable class? Any thoughts on this are appreciated. Sincerely, Brandon Simmons http://coder.bsimmons.name

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Ed Lambda: Functional programming meetup in Edinburgh
by Ollie Saunders 07 Dec '10

07 Dec '10

It's that time again... When: Monday the 13th of December at 7:00pm Where: 12a The Outhouse, Broughton Street Lane, Edinburgh This month Chris Yocum will be talking about some functional fundamentals with his talk: The Loopless Loop: Perl and Ocaml as functional programming languages Phil Scott may also be talking, we're not sure yet. Also I'm not sure if I'm going to be able to make it but I've made provisions if I can't so the show will definitely be going on. As always there will be plenty of beer and friendly banter. I think everyone who comes enjoys themselves and learns something. If you missed out on last month then you can see my talk on Vimeo: <http://vimeo.com/17343181> (2nd part isn't there yet but is uploading right now).

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Categorical description of systems with dependent types
by Petr Pudlak 07 Dec '10

07 Dec '10

Hi, recently, I was studying how cartesian closed categories can be used to describe typed functional languages. Types are objects and morphisms are functions from one type to another. Since I'm also interested in systems with dependent types, I wonder if there is a categorical description of such systems. The problem (as I see it) is that the codomain of a function depends on a value passed to the function. I'd happy if someone could give me some pointers to some papers or other literature. Thanks, Petr

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need help with syntax...
by Daryoush Mehrtash 07 Dec '10

07 Dec '10

I am having hard time understanding the following code. The code is from Applicative Parser library: http://hackage.haskell.org/packages/archive/uu-parsinglib/2.5.5.2/doc/html/… instance (Show a, loc `IsLocationUpdatedBy` a) => Provides (Str a loc) (a -> Bool, String, a) a where splitState (p, msg, a) k (Str tts msgs pos del_ok) = let ins exp = (5, k a (Str tts (msgs ++ [Inserted (show a) pos exp]) pos False)) del exp = (5, splitState (p,msg, a) k (Str (tail tts) (msgs ++ [Deleted (show(head tts)) pos exp]) (advance pos (head tts)) True )) in case tts of (t:ts) -> if p t then show_symbol ("Accepting symbol: " ++ show t ++ " at position: " ++ show pos ++"\n") (Step 1 (k t (Str ts msgs (advance pos t) True))) else Fail [msg] (*ins:* if *del_ok* then *[del*] else []) [] -> Fail [msg] [*ins*] Specifically I am having hard time understanding how the "ins exp" and "del exp" in the "let" is related to "ins:" "del_ok", [del], [ins]. I don't understand how given the "let" expression the following expressions are expanded Fail [msg] (*ins:* if *del_ok* then *[del*] else []) and Fail [msg] [*ins*] Appreciate any help. Thanks Daryoush

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Bifold: a simultaneous foldr and foldl
by Noah Easterly 07 Dec '10

07 Dec '10

Somebody suggested I post this here if I wanted feedback. So I was thinking about the ReverseState monad I saw mentioned on r/haskell a couple days ago, and playing around with the concept of information flowing two directions when I came up with this function: bifold :: (l -> a -> r -> (r,l)) -> (l,r) -> [a] -> (r,l) bifold _ (l,r) [] = (r,l) bifold f (l,r) (a:as) = (ra,las) where (ras,las) = bifold f (la,r) as (ra,la) = f l a ras (I'm sure someone else has come up with this before, so I'll just say I discovered it, not invented it). Basically, it's a simultaneous left and right fold, passing one value from the start of the list toward the end, and one from the end toward the start. It lets you do some interesting stuff, like filter based on positionor other left-dependent information: evenIndexed :: [a] -> [a] evenIndexed = fst . bifold alternate (0,[]) where alternate 0 x xs = (x:xs, 1) alternate 1 _ xs = (xs, 0) maximums :: (Ord a) => [a] -> [a] maximums [] = [] maximums (a:as) = a : (fst $ bifold (\m a l -> if a > m then (a:l,a) else (l,m)) (a,[]) as) As long as you don't examine the left-to-right value, it can still work on infinite lists: ghci> take 20 $ evenIndexed [0..] [0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38] Also, it can be used for corecursive data (or, at least, doubly-linked lists): data DList a = Start { first :: DList a } | Entry { value :: a, next :: DList a, prev :: DList a } | End { last :: DList a } deriving (Eq) ofList :: [a] -> (DList a, DList a) ofList as = (start,end) where start = Start first end = End last (first,last) = bifold mkEntry (start,end) as mkEntry p v n = let e = Entry v n p in (e,e) It's just been running around my head all night, so I thought I'd share.

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Trying out GHC 7
by Andrew Coppin 06 Dec '10

06 Dec '10

OK, so the other day I decided to take GHC 7.0.1 for a spin. Suffice it to say, it definitely compiles stuff. So far, I've only tried running it in a Windows XP virtual machine with a single core, so I haven't been able to test what multicore performance is like. One thing that did interest me is the conflicting information about whether or not dynamic linking is supported on Windows. Half the User Guide claims that this /is/ supported, and the other half still contains statements that it is /not/ supported. So I thought I'd just go physically try it and see if it works. Well... it compiles stuff. Hello World goes from being 518KB to being a piffling 13KB. Which is nice. I almost didn't bother actually trying to /run/ the resulting binary... But when I did, I discovered that it immediately crashes, whining that it can't find the DLL it wants. So, out of the box, the Windows setup is broken. (Obviously the Windows section of the User Guide makes no mention of how DLLs are located; it only explains the situation for Linux and Mac OS. I especially liked the bit where it says that there are "three modes", and then proceeds to list only two...) In the interests of science, I wanted to see if I could make it run by just putting the necessary DLLs into the same folder as the binary. But first I had to /find/ them. I had expected to find a folder somewhere with all the DLLs in it... but no, the installer appears to have sprinkled them around the filesystem more or less at random. Some of them are in folders named for the package, some of them just sit in the root folder. After about 20 minutes of searching, I found the RTS DLL. Running the program, it now instantly crashes because of a /different/ DLL. This one didn't take quite so long to find (now that I know roughly where to look). I fixed that, and now the binary crashes with yet another missing DLL. And so on and so forth. In the end, Hello World required 5 DLLs. Better still, together these totalled 8MB of data. (!) So the distribution package is now about 16x bigger than with static linking. Oh joy. Clearly if you just want to distribute one executable binary, you're going to use static linking. (E.g., darcs.exe will hopefully remain statically linked.) But I suppose if I had a whole heap of Haskell programs then the extra complexity of delivering half a dozen DLLs might may off in terms of space reductions. And of course, on /my/ development box, I don't need a zillion redundant copies of the RTS code, etc. (Or at least, I won't if I can figure out how to make the programs able to actually /find/ the necessary DLLs...) Actually, of all the DLLs, only "base" is actually large - it's approximately 6MB on its own. GHC-Prim is 0.5MB, and the others are all relatively tiny. It feels slightly irritating that I need to inclide the FFI DLL when I'm not doing and FFI - but of course, the entire Haskell I/O subsystem /is/ doing FFI. Similarly, I'm not using arbitrary-precision integers, but various I/O operations return file sizes as Integer, so GMP must also be included. Neither of these things are actually especially large. It's rather confusing that the User Guide is out of date in so many places. (And not just regarding dynamic linking on Windows. For example, one section claims that "+RTS -f" will tell you what options are supported, but that actually yields "unknown RTS opion: -f". It seems that "-?" is the correct option name.) If I can get a suitable Linux VM going, I might have a go at contributing some updates. Just for completeness, I tried asking for dynamic linking with an older version of GHC (6.10, IIRC) - one that supports it on Linux but not Windows. I was expecting to get either "dynamic linking is not supported on this platform", or at worst "unknown option -dynamic". In fact, what I got was "gcc: cannot find file Main.dyn_hi". Oh, that's graceful failure then. >_< I did also briefly see if the LLVM backend would work under Windows. I wasn't entirely sure if LLVM comes with the installer binary or you need to get it seperately. (You might say "obviously it's seperate", but the installer already contains the entire GCC system, for example.) Attempting to use this resulted in a summary error message ("cannot run: opt") which doesn't make it especially clear that the problem is that LLVM isn't installed. Perhaps there's no better way of detecting this condition, I don't know, but something more illuminating would be nice. I briefly had a look at how to install LLVM, but it appears that you have to build it from source. This is not my idea of a fun time, so given the minimal speed difference, I just won't bother. I haven't had time to play with any of the other new good stuff in GHC 7. (The multicore performance, the new GC stuff, etc.)

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ANNOUNCE: Haddock 2.9.0
by David Waern 06 Dec '10

06 Dec '10

-------------------------------------------- -- Haddock 2.9.0 -------------------------------------------- A new version of Haddock, the Haskell documentation tool, is out! This version is compatible with .haddock files produced by the version of Haddock that comes with GHC 7.0.1. -------------------------------------------- -- Changes in version 2.9.0 -------------------------------------------- Changes in version 2.9.0 * Drop support for ghc < 7 * New flag --qual for qualification of names * Print doc coverage information to stdout when generating docs * Include an 'All' option in the A-Z subdivided index * Make TOC group header identifiers validate * Minor changes to the API -------------------------------------------- -- Links -------------------------------------------- Homepage: http://www.haskell.org/haddock Hackage page: http://hackage.haskell.org/package/haddock-2.9.0 Bugtracker and wiki: http://trac.haskell.org/haddock Mailing list: haddock(a)projects.haskell.org Code repository: http://code.haskell.org/haddock -------------------------------------------- -- Contributors -------------------------------------------- The following people contributed patches to this release: Tobias Brandt Mark Lentczner Ian Lynagh Simon Marlow Simon Michael Ryan Newton David Waern -------------------------------------------- -- Get Involved -------------------------------------------- We would be very happy to get more contributors. To get involved, start by grabbing the code: http://code.haskell.org/haddock Then take a look at the bug and feature tracker for things to work on: http://trac.haskell.org/haddock

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include modules in DLL? "undefined reference"
by Gerold Meisinger 06 Dec '10

06 Dec '10

Hello! I'm trying to compile a Windows DLL and need to include an additional module (specifically FRP.Yampa). I was successful with a Hello World type of DLL but when I use Yampa I get: $ ghc -shared -o hs.dll DLLTest.o DLLTest_stub.o StartEnd.o Creating library file: hs.dll.a DLLTest.o:fake:(.text+0x46): undefined reference to `Yampazm0zi9zi2zi3_FRPziYamp a_integral_closure' DLLTest.o:fake:(.text+0x4d): undefined reference to `Yampazm0zi9zi2zi3_FRPziYamp aziVectorSpace_zdfVectorSpaceDoubleDouble_closure' DLLTest.o:fake:(.text+0x194): undefined reference to `Yampazm0zi9zi2zi3_FRPziYam pa_embed_closure' DLLTest.o:fake:(.text+0x381): undefined reference to `__stginit_Yampazm0zi9zi2zi 3_FRPziYampa_' DLLTest.o:fake:(.data+0x0): undefined reference to `Yampazm0zi9zi2zi3_FRPziYampa _integral_closure' DLLTest.o:fake:(.data+0x4): undefined reference to `Yampazm0zi9zi2zi3_FRPziYampa ziVectorSpace_zdfVectorSpaceDoubleDouble_closure' DLLTest.o:fake:(.data+0x38): undefined reference to `Yampazm0zi9zi2zi3_FRPziYamp a_embed_closure' collect2: ld returned 1 exit status How can I define the references of Yampa in the DLL? I also tried to reinstall Yampa shared with: $ cabal install --reinstall --enable-shared yampa Could not find module `Data.IORef': Perhaps you haven't installed the "dyn" libraries for package `base-3.0.3. 2'? Use -v to see a list of the files searched for. $ cabal install --reinstall --enable-shared base # :) Resolving dependencies... cabal: internal error: impossible ---- (StartEnd is taken from: http://www.haskell.org/ghc//docs/latest/html/users_guide/win32-dlls.html ) DLLTest.hs: {-# LANGUAGE ForeignFunctionInterface, Arrows #-} module DLLTest embeddedSF :: Double -> Double -> Double -> IO Double embeddedSF v0 v1 v2 = return . last $ embed integral (v0, [(1.0, Just v1), (1.0, Just v2)]) foreign export ccall embeddedSF :: Double -> Double -> Double -> IO Double

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Storables and Ptrs
by Tyler Pirtle 06 Dec '10

06 Dec '10

Hi cafe, I'm just getting into Foreign.Storable and friends and I'm confused about the class storable. For GHC, there are instances of storable for all kinds of basic types (bool, int, etc) - but I can't find the actual declaration of those instances. I'm confused that it seems that all Storable instances operate on a Ptr, yet none of these types allow access to an underlying Ptr. I noticed that it's possible via Foreign.Marshal.Utils to call 'new' and get a datatype wrapped by a Ptr, but this isn't memory managed - I'd have to explicitly free it? Is that my only choice? Is there a way that given just simply an Int I could obtain a Ptr from it, and then invoke the storable functions on it? Or for that matter, if I go and create some new data type, is there some generic underlying thing (ghc-only or otherwise) that would let me have a Ptr of it? Thanks, Tyler

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Question about TagSoup
by David Virebayre 06 Dec '10

06 Dec '10

Hello café, I have seen tutorials about extracting information from a tag soup, but I have a different use case: I want to read a xml file, find a tag, change its content, and write the xml file back. This is an example of the files <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <idPkg:Story xmlns:idPkg=" http://ns.adobe.com/AdobeInDesign/idml/1.0/packaging" DOMVersion="7.0"> <Story Self="ub9fad" AppliedTOCStyle="n" TrackChanges="false" StoryTitle="$ID/" AppliedNamedGrid="n"> <StoryPreference OpticalMarginAlignment="false" OpticalMarginSize="12" FrameType="TextFrameType" StoryOrientation="Horizontal" StoryDirection="LeftToRightDirection"/> <InCopyExportOption IncludeGraphicProxies="true" IncludeAllResources="false"/> <ParagraphStyleRange AppliedParagraphStyle="ParagraphStyle/prix"> <CharacterStyleRange AppliedCharacterStyle="CharacterStyle/$ID/[No character style]"> <Content>zzznba5</Content> </CharacterStyleRange> </ParagraphStyleRange> </Story> </idPkg:Story> Assuming I want to change the content of the "Content" tag, this is what I came up with (simplified), I'm using direct recursion. Is there a better way ? ts = do soup <- parseTags `fmap` readFile "idml/h00/Stories/Story_ub9fad.xml" writeFile "test" $ renderTagsOptions renderOptions{optMinimize = const True} $ modif soup modif [] = [] modif (x@(TagOpen "Content" []):TagText _m : xs) = x : TagText "modified" : modif xs modif (x:xs) = x : modif xs David.

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Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
by Jacek Generowicz 06 Dec '10

06 Dec '10

In short: I can't cabal install xmonad-contrib. Longer version: It a appears that a program which does not exist on my computer seems to insist on a package version which does not exist in my universe, I'm starting to wonder whether I have lost my marbles. Could some kind soul please point me in some sensible direction? cabal install xmonad-contrib Resolving dependencies... Configuring X11-xft-0.3... cabal: pkg-config version >=0.9.0 is required but it could not be found. cabal: Error: some packages failed to install: X11-xft-0.3 failed during the configure step. The exception was: ExitFailure 1 xmonad-contrib-0.9.1 depends on X11-xft-0.3 which failed to install. cabal install x11-xft Resolving dependencies... Configuring X11-xft-0.3... cabal: pkg-config version >=0.9.0 is required but it could not be found. cabal: Error: some packages failed to install: X11-xft-0.3 failed during the configure step. The exception was: ExitFailure 1 X11-xft version 0.9.0 doesn't even exist, as far a I can tell: 0.3 seems to be the highest. So what is making cabal believe that such a version is needed? Is it pkg-config? I'm not at all familiar with pkg-config, and, as far as I can tell it's not even installed on the Mac on which I am trying to do this. Curiously, its man page *does* work (it's in /usr/X11/man, for some reason). Does Cabal have some sort of embedded pkg-config?

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LLVM, getElementPtr?
by Lally Singh 06 Dec '10

06 Dec '10

Hey all, I'm trying to get started generating LLVM code, but I'm getting a rather cryptic error. I wanted to create a function that takes a string and generates a function calling to "puts" with that string as an argument: buildReaderFun :: String -> CodeGenModule (Function (IO ())) buildReaderFun nm = do puts <- newNamedFunction ExternalLinkage "puts" :: TFunction (Ptr Word8 -> IO Word32) greetz <- createStringNul nm func <- createFunction ExternalLinkage $ do tmp <- getElementPtr0 greetz (0 :: Word32, ()) call puts tmp -- Throw away return value. ret () return func (based off of some code at this blog post: http://augustss.blogspot.com/2009/01/llvm-llvm-low-level-virtual-machine-is… ) But, I get this error: /research/phd/libmet/Listener.hs:16:11: Ambiguous type variable `n' in the constraint: `Data.TypeLevel.Num.Sets.NatI n' arising from a use of `getElementPtr0' at /research/phd/libmet/Listener.hs:16:11-49 Probable fix: add a type signature that fixes these type variable(s) My attempts at figuring out what type-level has to do with this, and how to satisfy it have so far proven unsuccessful. Can anyone shed a little light on what's going on? Or pointers to some documentation on any of this? Cheers, -Lally

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