[Haskell-cafe] first the platform, the cabal
I just installed the Haskell Platform 2009.2.0.2 on Windows. There is no cabal.exe, only Cabal-1.6.0.3 How to continue: build cabal? Then what to download from where and what to execute? greetings, Peter J. Veger, Best Netherlands ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] TFM09: Call for Participation (FMWeek, Eindhoven, November 2009)
TFM2009 2nd Int. FME Conference on Teaching Formal Methods Friday, November 6th 2009, co-located with FM2009 : 16th Int. Symposium on Formal Methods Eindhoven, the Netherlands, November 2 - November 6, 2009 CALL FOR PARTICIPATION (URL: http://www.di.uminho.pt/tfm09) 1. About the conference --- Ten years after the First World Formal Methods Congress (FM'99) in Toulouse, formal methods communities from all over the world will once again have an opportunity to come together. As part of the First Formal Methods Week event surrounding the FM2009 conference in Eindhoven, Formal Methods Europe will be organizing TFM2009, the Second International Conference on Teaching Formal Methods. The conference will serve as a forum to explore the successes and failures of Formal Methods (FM) education, and to promote cooperative projects to further education and training in FMs. TFM2009 will include a panel discussion on the idea of building a 'Guide to the Formal Methods Body of Knowledge' (FMBoK), inspired by similar efforts for software engineering (SWEBoK) and for project management (PMBoK); such a resource would provide guidance to teachers, managers, and developers on what should be expected from a comprehensive, balanced programme of education in FMs. 2. Invited speaker -- Jeff Kramer(Imperial College London, UK) 3. Accepted papers -- * Teaching Concurrency: Theory in Practice (Luca Aceto, Anna Ingolfsdottir, Kim Guldstrand Larsen, Jiri Srba) * Integrated and Tool-Supported Teaching of Testing, Debugging, and Verification (Wolfgang Ahrendt, Richard Bubel, Reiner Haehnle) * What Top-Level Software Engineers Tackle after Learning Formal Methods - Experiences from the Top SE Project (Fuyuki Ishikawa, Kenji Taguchi, Nobukazu Yoshioka, Shinichi Honiden) * Teaching program specification and verification using JML and ESC/Java2 (Erik Poll) * Chief Chefs of Z to Alloy: Using A Kitchen Example to Teach Alloy with Z (Sureyya Tarkan, Vibha Sazawal) * Teaching Formal Methods based on Rewriting Logic and Maude (Peter Olveczky) * Which Mathematics for the Information Society? (Joao Ferreira, Alexandra Mendes, Roland Backhouse, Luis Barbosa) * How to explain mistakes (Stefan Hallerstede, Michael Leuschel) * On Teaching Formal Methods: Behavior Models and Code Analysis (Jan Kofron, Ondrej Sery, Pavel Parizek) * Teaching Formal Methods for the Unconquered Territory (Nestor Catano, Camilo Rueda) 4. Sponsors -- * Formal Methods Europe Association (FME) * Software Improvement Group (SIG) , Amsterdam, Netherlands 5. Programme Committee -- Izzat Alsmadi(North Dakota State University, USA) Dines Bjorner(IIMM Institute, Denmark) Eerke Boiten(University of Kent, UK) Raymond Boute(Universiteit Gent, Belgium) Andrew Butterfield(Trinity College, Dublin) Jim Davies(University of Oxford, UK) David Duce(Oxford Brookes University, UK) John Fitzgerald(University of Newcastle upon Tyne, UK) Jeremy Gibbons(University of Oxford, UK) Randolph Johnson(National Security Agency, USA) Michael Mac an Airchinnigh(Trinity College, Dublin) Dino Mandrioli(Politecnico di Milano, Italy) Jose Oliveira(Universidade do Minho, Portugal) Kees Pronk(Technische Universiteit Delft, NL) Bernhard Schaetz(Tecnical University of Munique, Germany) Wolfgang Schreiner(Johannes Kepler University Linz, Austria) Simao Melo de Sousa(Universidade da Beira Interior, Portugal) Kenji Taguchi(National Institute of Informatics, Japan) Jeannette Wing(Carnegie-Mellon University, USA) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Is it safe to use unsafePerformIO here?
On Sat, Sep 19, 2009 at 6:53 PM, Ben Franksen ben.frank...@online.de wrote: Cristiano Paris wrote: Daniel Fischer wrote: I would separate the reading of headers and bodies, reopening the files whose body is needed, for some (maybe compelling) reason he wants to do it differently. Yes, that's the way Haskell forces you to do that as it's the only way for you to go safe. I don't think it has anything to do with Haskell. My sentence was to be understood in a positive way. I think this has a lot to do with Haskell, as it forbids you to write certain kinds of programs: this is a distinguished feature of all the static typed languages and more specifically in Haskell, which has a very expressive type system. In particular, you can't have a program that runs IO out-of-order: if you really want to do that, you must use unsafe(Perform|Interleave)IO which is like cheating, in a way. Indeed, the only way to do that not using unsafePerformIO is to have a two stage reading, either making the body an IO action or having an intermediate data structure which represents a file whose body has not been read yet: in general this is safer, unless you know something about your program and can assure the compiler it won't behave badly with respect to side effects. How would you do this in C? You'd pass a flag indicating whether to read the whole file or just the header. You can do the same in Haskell, of course, no lazy IO needed. The body remains undefined if the flag indicates header only. Even better wrap the body in a Maybe. The difference is in the expressivity of the type system. In C I may use a NULL pointer indicating the body has not been read yet, but then the compiler won't enforce good uses of that pointer and can't assure you that in no way a NULL pointer would be ever dereferenced, leaving room for untested, uncaught bugs. In Haskell this is simply not possible. ... I have a hard time believing this is possible, if you demand that the files should not stay opened indefinitely. How is the runtime supposed to know whether to close the file or not? What you /can/ do is use unsafePerformIO to lazily re-open, read the body, and close the file, as soon as the body gets demanded. However, this is ugly and not advised. Here in Cafè once I had a discussion about when is safe and advisable to use unsafePerformIO. I don't think this function is evil per-se and indeed THERE ARE situations where it's more elegant and clear implementing things using unsafePerformIO. I see it as way to tell the compiler don't mind: I know what I'm doing. This is certainly true when using FFI to implement in C pure functions, but it's true in other situations, like mine, in which using unsafeInterleaveIO allows me to write my code cleanly and easily, separating IO from processing, and avoid having to read the files in a two-stage way. Of course, I can be wrong and I can't look forward to hearing from the wise people and argument againts my point. Cheers Ben Thanks. Cristiano ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] first the platform, the cabal
Hello Peter, cabal.exe is locatated in extralibs\bin. On my machine the installer added this directory to the PATH, too. Regards, Martin. Peter J. Veger schrieb: I just installed the Haskell Platform 2009.2.0.2 on Windows. There is no cabal.exe, only Cabal-1.6.0.3 How to continue: build cabal? Then what to download from where and what to execute? greetings, Peter J. Veger, Best Netherlands ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to generate random string?
does this compile at all? i don't think i understand the first line. anyway, a few hints: - if you want to have all numbers between 0..n in your output for some n, just in random order, google for permutation. - perhaps you can generate the output in an ordered fashion first, eg. into an array, and then shuffle the list by plucking elements from it at random into a new list. - do not use unsafePerformIO. it may reduce the entropy (randomness) of the results, but even if it doesn't, the code is prettier without. good luck! if you get stuck again, just post more code. matthias On Fri, Sep 18, 2009 at 10:14:53AM -0700, Snouser wrote: To: haskell-cafe@haskell.org From: Snouser linusolean...@gmail.com Date: Fri, 18 Sep 2009 10:14:53 -0700 (PDT) Subject: Re: [Haskell-cafe] How to generate random string? Snouser wrote: I need to generate a random string from 1 to 30. This is the parts I've done so far. unikString xs | let x = unsafePerformIO (randomRIO (1,30)) elem x xs = x : unikString xs | otherwise = unikString xs How do I proceed? I need the string/list to look like this: [1,9,3,6,2] et.c with only unik numbers. Thanks! I wasnt added to the mailinglist, but now I'm. -- View this message in context: http://www.nabble.com/How-to-generate-random-string--tp25512293p25512298.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ** ACCEPT: CRM114 PASS osb unique microgroom Matcher ** CLASSIFY succeeds; success probability: 1. pR: 6.3668 Best match to file #0 (nonspam.css) prob: 1. pR: 6.3668 Total features in input file: 2688 #0 (nonspam.css): features: 758386, hits: 2881904, prob: 1.00e+00, pR: 6.37 #1 (spam.css): features: 1686754, hits: 3078784, prob: 4.30e-07, pR: -6.37 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Building com-1.2.3
C:\com-1.2.3runhaskell Setup configure Configuring com-1.2.3... Setup: Missing dependencies on foreign libraries: * Missing header file: include/WideStringSrc.h * Missing C libraries: kernel32, user32, ole32, oleaut32, advapi32 This problem can usually be solved by installing the system packages that provide these libraries (you may need the -dev versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. Any hints? (It is conspicuous that the hissing header file is actually present at the exact path indicated... WTH?) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [ANN] histogram-fill, library for creating hitograms
Hello. I'm glad to announce library for filling histograms. Its purpose to provide generic and convenient API and be fast. Features list: * Allows to fill many histograms at once. I used it to fill about hundred. * It provide support for arbitrary binning algorithm. Currently there are integer bins, equal sized floating point bins and generic 2D bins. One however could implement more exotic variants. Bins with variable width for example. * Immutable histograms. It's relatively recent addition so it could have few rough edges. * Histogram serialization to/from human readable text. So data could be used with other tools. -- Khudyakov Alexey ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANN] histogram-fill, library for creating hitograms
alexey.skladnoy: Hello. I'm glad to announce library for filling histograms. Its purpose to provide generic and convenient API and be fast. Features list: * Allows to fill many histograms at once. I used it to fill about hundred. * It provide support for arbitrary binning algorithm. Currently there are integer bins, equal sized floating point bins and generic 2D bins. One however could implement more exotic variants. Bins with variable width for example. * Immutable histograms. It's relatively recent addition so it could have few rough edges. * Histogram serialization to/from human readable text. So data could be used with other tools. Where can we get the code? :) http://hackage.haskell.org/package/histogram-fill-0.1.0 -- Don (who thinks it is interesting that hackage is now implied) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] first the platform, the cabal
veger: I just installed the Haskell Platform 2009.2.0.2 on Windows. There is no cabal.exe, only Cabal-1.6.0.3 How to continue: build cabal? Then what to download from where and what to execute? It does come with the cabal executable. Maybe it isn't in your path? -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Weekly News: Issue 131 - September 19, 2009
Joe Fredette wrote: Haskell Weekly News http://sequence.complete.org/hwn/20090918 Issue 131 - September 18, 2009 Does anybody else get page not found for this URL? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Weekly News: Issue 131 - September 19, 2009
Ahh, I found the issue. I generated this on the 18th, the software makes files of the form yearmonthdate.ext, so when Brent uploaded the hwn for me, the link it generates is to the date it was generated on, not the date it was published on. The appropriate link is http://sequence.complete.org/hwn/20090919 In the future, I'll have to make sure to do the `make` on the date of publication, but ATM I don't have access to the sequence.complete.org to post the hwns myself. So I try to get the issue to Brent a day early. It shouldn't happen again, thanks for catching it. /Joe On Sep 20, 2009, at 3:06 PM, Andrew Coppin wrote: http://sequence.complete.org/hwn/20090918 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANN] histogram-fill, library for creating hitograms
В сообщении от Воскресенье 20 сентября 2009 22:03:42 вы написали: alexey.skladnoy: Hello. ... skipped ... Where can we get the code? :) http://hackage.haskell.org/package/histogram-fill-0.1.0 -- Don (who thinks it is interesting that hackage is now implied) It's so easy something important (-: That's how things become de-facto standard. You wake up one day and find that it's standard. Or someone tell you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] first the platform, the cabal
Martin Huschenbett told me: cabal.exe is locatated in extralibs\bin. On my machine the installer added this directory to the PATH, too. Thanks you both for your answers greetings, Peter J. Veger, Best Netherlands -Original Message- From: Don Stewart [mailto:d...@galois.com] Sent: zondag 20 september 2009 20:43 To: Peter J. Veger Cc: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] first the platform, the cabal veger: I just installed the Haskell Platform 2009.2.0.2 on Windows. There is no cabal.exe, only Cabal-1.6.0.3 How to continue: build cabal? Then what to download from where and what to execute? It does come with the cabal executable. Maybe it isn't in your path? -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GHC will not let me install
I am trying to install Xmonad on my Mac. I download GHC installer for mac the .dmg from Haskell.org and when I install it gets stuck here [img]http://www.jmstephens.99k.org/picture.png[/img] As you can see the install button is grey and will not let me click it.___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC will not let me install
jmstephens: I am trying to install Xmonad on my Mac. I download GHC installer for mac the .dmg from Haskell.org and when I install it gets stuck here [img]http://www.jmstephens.99k.org/picture.png[/img] As you can see the install button is grey and will not let me click it. Are you running Snow Leopard? If so, you need to build GHC manually first. http://www.reddit.com/r/haskell/comments/9krbo/whats_the_status_of_ghc_on_the_64_bit_mac_osx/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal packages - cabbages
Some day, we're going to need a short, catchy name for Cabal packages. Let's call them cabbages. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal packages - cabbages
On Sun, Sep 20, 2009 at 5:11 PM, Jason Dusek jason.du...@gmail.com wrote: Some day, we're going to need a short, catchy name for Cabal packages. Let's call them cabbages. +1 Yes, let's. Jeff Wheeler ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal packages - cabbages
I also agree. Hackage should also be renamed to something appropriate. The Cabbage Patch? On Sep 20, 2009, at 6:12 PM, Jeff Wheeler wrote: On Sun, Sep 20, 2009 at 5:11 PM, Jason Dusek jason.du...@gmail.com wrote: Some day, we're going to need a short, catchy name for Cabal packages. Let's call them cabbages. +1 Yes, let's. Jeff Wheeler ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal packages - cabbages
File extension ideas: .choux -- My favorite. .kohl -- Less characters. .cbz-- More conventional. .cbg.gz, .cbg.bz2 -- Allows one to be specific about -- compression. The last one can be extended to the other ones, at the cost of a few characters. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal packages - cabbages
2009/09/20 Joe Fredette jfred...@gmail.com: I also agree. Hackage should also be renamed to something appropriate. The Cabbage Patch? +1 -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal packages - cabbages
On Sun, Sep 20, 2009 at 5:20 PM, Joe Fredette jfred...@gmail.com wrote: The Cabbage Patch? 'Patch' is pretty well defined, so using it here seems somewhat awkward and confused to me. Plus, I don't think we really want to sound childish, and the first thing I think of is the cabbage patch kid dolls. The original idea, cabbage, doesn't seem silly to me. Jeff Wheeler ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal packages - cabbages
jeff: On Sun, Sep 20, 2009 at 5:20 PM, Joe Fredette jfred...@gmail.com wrote: The Cabbage Patch? 'Patch' is pretty well defined, so using it here seems somewhat awkward and confused to me. Plus, I don't think we really want to sound childish, and the first thing I think of is the cabbage patch kid dolls. The original idea, cabbage, doesn't seem silly to me. Cabbage patches would be tweaks and fixes you upload to Hackage. Hackage is more of a cabbage farm. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Type Families
(I'm using a fixed width font, so if you don't see nice formatting, you need to use a fixed width font. This is literate Haskell, but I copied and pasted the code. YMMV) Hi Everybody! (Hi Dr. Nick) I've been looking for a good way to use some richer notions of polymorphism than Haskell98 allows. First, I tried to define a monad of the things I want to quantify over (so each type of view or type of evaluable thing would be a constructor in a monadic type.) But that didn't seem to offer the kind of extensibility I wanted, since I basically want to join several types together. I tried FunDeps next, and that worked okay, but it was a bit difficult to keep track of what was meant to do what. I guess I could have plowed through the work, but it wasn't any fun. I finally heard about TypeFamilies, and they seem to give me the kind of extensibility I want, while keeping the theoretical foundations relatively clean. But I am not so sure I understand them. Let us consider the code: type AbstractValue = Int class Evaluate asset where data Value asset :: * value :: (Value asset) - AbstractValue That's easy enough. Value asset is an indexed type. That is reflected in the instance declaration: instance Evaluate Abstract where data Value Abstract = AbstractValue Abstract value (AbstractValue int) = int Okay, easy enough. But what happens when we want to add Evaluate instances? data Add a b = Add a b instance ( Evaluate a , Evaluate b ) = Evaluate (Add a b) where data Value (Sum a b) = SumValue (Sum a b) Even this much is straightforward. We require a and b to be Evaluate'able before we can find the sum of a and b as values. Now I want to write my definition for the value function. But... how is that supposed to work? My first guess is value (SumValue (Sum a b)) = (value a) + (value b) But I more-or-less expected that to fail. I realize I need some more typing information. What am I supposed to fill in? My next guess was value (SumValue (Sum a b)) = (value $ Value a) + (value $ Value b) But Value doesn't exist as a type constructor. So now that I am starting to get what's going on, I wonder why I don't get what's going on. Since I need to use a type constructor for the (Value a) and (Value b) things, it kind of defeats the point. (I hesitate to say value, since I have been using value to mean the result/blah of an Evaluate instance) Speaking of which, I am still not sure what the difference between associate data type families and associated type constructor families are. The former use the data keyword in class declarations, and the latter use type keywords. What can I do with one and not the other? I would really appreciate some guidance. Thanks! Alex___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type Families
On Sunday 20 September 2009 9:43:53 pm Alexander Solla wrote: But I more-or-less expected that to fail. I realize I need some more typing information. What am I supposed to fill in? My next guess was value (SumValue (Sum a b)) = (value $ Value a) + (value $ Value b) But Value doesn't exist as a type constructor. So now that I am starting to get what's going on, I wonder why I don't get what's going on. Since I need to use a type constructor for the (Value a) and (Value b) things, it kind of defeats the point. (I hesitate to say value, since I have been using value to mean the result/blah of an Evaluate instance) Well, the obvious answer is that you should instead write data Value (Add a b) = SumValue (Sum (Value a) (Value b)) So that they are already Values, and value can be called on them. I don't really understand what you're using the data families for, though. Value looks like sort of an identity wrapper around its argument. Speaking of which, I am still not sure what the difference between associate data type families and associated type constructor families are. The former use the data keyword in class declarations, and the latter use type keywords. What can I do with one and not the other? Type families (as far as their use in classes goes) are for when the associated type already exists. For instance, in a collection class: class Collection c where type Elem c :: * ... You'll have instances: instance Collection [a] where type Elem [a] = a ... By contrast, data families are for when you want to define new data types indexed by the type. For instance, if you're doing generalized tries: class Key k where data Trie k :: * - * ... Then: instance (Key k) = Key [k] where data Trie [k] a = ListTrie (Maybe a) (Trie k (Trie [k] a)) ... You can, of course, approximate one with the other. If you use a data family, you can use newtypes so there's no additional overhead (but you'll have to sprinkle constructors in your code). And data families can be simulated like (using the Trie example): class Key k where type Trie k :: * - * ... data ListTrie k a = ListTrie (Maybe a) (Trie k (ListTrie k a)) instance Key k = Key [k] where type Trie [k] = ListTrie k ... But in cases where you're writing lots of new data/newtype declarations, just to refer to them with an associated type, you may was well use associated data instead and remove the middle man. Of course, sometimes you may not be clearly in either situation, so it may be a judgment call. Type families are also useful if you want to do computation at the type level. In that sense, type families are like (value-level) functions, and data families are like (value-level) constructors (I think that's accurate). Hope that helped a bit, -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type Families
On Sun, Sep 20, 2009 at 06:43:53PM -0700, Alexander Solla wrote: data Add a b = Add a b instance ( Evaluate a , Evaluate b ) = Evaluate (Add a b) where Okay. data Value (Sum a b) = SumValue (Sum a b) Hmmm, have you tried data Value (Add a b) = AddValue (Value a) (Value b) Now your 'value' function would be value (AddValue va vb) = value va + value vb because you're holding 'Value a' and 'Value b', not 'a' and 'b'. It may help to think as if this class represented a container. For value, do you need the whole container or just one of its elements? I know other will give a better explanation, but maybe this is enough to get you in the right track :). HTH, -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC will not let me install
Don Stewart d...@galois.com writes: jmstephens: I am trying to install Xmonad on my Mac. I download GHC installer for mac the .dmg from Haskell.org and when I install it gets stuck here [img]http://www.jmstephens.99k.org/picture.png[/img] As you can see the install button is grey and will not let me click it. Are you running Snow Leopard? If so, you need to build GHC manually first. http://www.reddit.com/r/haskell/comments/9krbo/whats_the_status_of_ghc_on_the_64_bit_mac_osx/ Also you need to download and install XCode from Apple before the GHC installer will run. G -- Gregory Collins g...@gregorycollins.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
