Re: [Haskell-cafe] Unicode workaround for getDirectoryContents under Windows?
Hello Shu-yu, Sunday, June 14, 2009, 7:41:46 AM, you wrote: It seems like getDirectoryContents applies codepage conversion based it's not a bug, but old-fashioned architecture of entire file apis you may find my Win32Files.hs module useful - it adopts UTF-16 versions of file operations http://downloads.sourceforge.net/freearc/FreeArc-0.51-sources.tar.bz2 -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] I need a hint in list processing
Hi all If I have a number of list example list1 = [2,3] list2 = [1,2] list3 = [2,3,4] list4 = [1,2,3] I want to create a list from the list above with n elements, non-repeating and each elements index represents 1 of the elements from the corresponding list so for the above input I would get. a = [3,2,4,1] ofcourse there may be several set that will satisfy the problem, so a list of list that satisfies would be good. How do I do this in haskell? or is there a code snippet that seems to work similarly? thanks fernan -- http://www.fernski.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I need a hint in list processing
Fernan Bolando wrote: Hi all If I have a number of list example list1 = [2,3] list2 = [1,2] list3 = [2,3,4] list4 = [1,2,3] I want to create a list from the list above with n elements, non-repeating and each elements index represents 1 of the elements from the corresponding list so for the above input I would get. a = [3,2,4,1] ofcourse there may be several set that will satisfy the problem, so a list of list that satisfies would be good. How do I do this in haskell? or is there a code snippet that seems to work similarly? Well you could simply concatenate all the lists using the (++) operator and then use Data.List.nub: http://haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v:nub to remove duplicates. Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] install problems ...
On Thu, 2009-06-11 at 23:50 -0500, Vasili I. Galchin wrote: Hello, As I have said before I a, cabalizing Swish (a semantic web toolkit). I have it built and have run most of the original author's tests by and they pass. There are numerous warnings which seem to be either lack of a function type signature or unreferenced symbols ... I will go through one-by-one and clean these up. However, now I am getting the following install-time errors any advice on how to track down will be greatly apprecriated the following is the result of cabal build -v: Preprocessing executables for swish-0.2.1... Building swish-0.2.1... /usr/bin/ar: creating dist/build/libHSswish-0.2.1.a Warning: output was redirected with -o, but no output will be generated because there is no Main module. This warning is very suspicious. Perhaps you can post your .cabal file. I suspect that it's using an inappropriate ghc flag. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I need a hint in list processing
On Sun, Jun 14, 2009 at 4:13 PM, Erik de Castro Lopomle...@mega-nerd.com wrote: Fernan Bolando wrote: Hi all If I have a number of list example list1 = [2,3] list2 = [1,2] list3 = [2,3,4] list4 = [1,2,3] I want to create a list from the list above with n elements, non-repeating and each elements index represents 1 of the elements from the corresponding list so for the above input I would get. a = [3,2,4,1] ofcourse there may be several set that will satisfy the problem, so a list of list that satisfies would be good. How do I do this in haskell? or is there a code snippet that seems to work similarly? Well you could simply concatenate all the lists using the (++) operator and then use Data.List.nub: http://haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v:nub to remove duplicates. Using Data.List.nub Data.List nub [2,3,1,2,2,3,4,1,2,3] [2,3,1,4] that is not exactly what I want. list1 only has 2,3 has elements and list2 only has elements 1,2...this means the first element should only be 2 or 3 and the second element should only have 1 or 2...etc fernan -- http://www.fernski.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I need a hint in list processing
ghci map reverse $ foldM (\answer list - [x:answer | x - list, not $ x `elem` answer]) [] [[2,3], [1,2], [2,3,4], [1,2,3]] [[2,1,4,3],[3,1,4,2],[3,2,4,1]] On 14 Jun 2009, at 12:06, Fernan Bolando wrote: Hi all If I have a number of list example list1 = [2,3] list2 = [1,2] list3 = [2,3,4] list4 = [1,2,3] I want to create a list from the list above with n elements, non-repeating and each elements index represents 1 of the elements from the corresponding list so for the above input I would get. a = [3,2,4,1] ofcourse there may be several set that will satisfy the problem, so a list of list that satisfies would be good. How do I do this in haskell? or is there a code snippet that seems to work similarly? thanks fernan -- http://www.fernski.com ___ 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] install problems ...
Hi Duncan, Actually it was do to a typo on an Executable I specified N3Parser where I meant N3ParserTest = DUH . I am totally ashamed . Vasili On Sun, Jun 14, 2009 at 3:31 AM, Duncan Coutts duncan.cou...@worc.ox.ac.ukwrote: On Thu, 2009-06-11 at 23:50 -0500, Vasili I. Galchin wrote: Hello, As I have said before I a, cabalizing Swish (a semantic web toolkit). I have it built and have run most of the original author's tests by and they pass. There are numerous warnings which seem to be either lack of a function type signature or unreferenced symbols ... I will go through one-by-one and clean these up. However, now I am getting the following install-time errors any advice on how to track down will be greatly apprecriated the following is the result of cabal build -v: Preprocessing executables for swish-0.2.1... Building swish-0.2.1... /usr/bin/ar: creating dist/build/libHSswish-0.2.1.a Warning: output was redirected with -o, but no output will be generated because there is no Main module. This warning is very suspicious. Perhaps you can post your .cabal file. I suspect that it's using an inappropriate ghc flag. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] install problems ...
BTW is TimeDate a Hugism? Vasili On Sun, Jun 14, 2009 at 3:58 AM, Vasili I. Galchin vigalc...@gmail.comwrote: Hi Duncan, Actually it was do to a typo on an Executable I specified N3Parser where I meant N3ParserTest = DUH . I am totally ashamed . Vasili On Sun, Jun 14, 2009 at 3:31 AM, Duncan Coutts duncan.cou...@worc.ox.ac.uk wrote: On Thu, 2009-06-11 at 23:50 -0500, Vasili I. Galchin wrote: Hello, As I have said before I a, cabalizing Swish (a semantic web toolkit). I have it built and have run most of the original author's tests by and they pass. There are numerous warnings which seem to be either lack of a function type signature or unreferenced symbols ... I will go through one-by-one and clean these up. However, now I am getting the following install-time errors any advice on how to track down will be greatly apprecriated the following is the result of cabal build -v: Preprocessing executables for swish-0.2.1... Building swish-0.2.1... /usr/bin/ar: creating dist/build/libHSswish-0.2.1.a Warning: output was redirected with -o, but no output will be generated because there is no Main module. This warning is very suspicious. Perhaps you can post your .cabal file. I suspect that it's using an inappropriate ghc flag. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [cabal] How to deal with build-depency that not under cabal's control?
Hi, I use gtk2hs in linux. Well, I have no idea how to install gtk2hs by cabal, but my program needs it, and I want my program cabalized. So how to do this? Thanks. -- 竹密岂妨流水过 山高哪阻野云飞 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Logo fun
Graphics are fun. Here's my version. http://s201.photobucket.com/albums/aa280/Zakardis/?action=viewcurrent=lambda_haskell_platform.png ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to know the build dependencies?
2009/6/14 Gwern Branwen gwe...@gmail.com: -BEGIN PGP SIGNED MESSAGE- Hash: SHA512 On Sat, Jun 13, 2009 at 10:22 PM, Magicloud Magiclouds wrote: Hi, I am learning to use cabal for my code. Just when I start, I met a question, is there an easy way to find out what packages my code depends? Thanks. Not really. The easiest way is to just build your code and add every package Cabal complains about being hid into your build-depends. (Usually this won't take more than a minute or 3 if you're toggling between a terminal and an editor.) - -- gwern Someone really ought to write a tool for this... -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Running Hoogle as a cgi script.
Hi all, I'd like to run my own version of Hoogle: http://hackage.haskell.org/package/hoogle as a CGI script much like this: http://www.haskell.org/hoogle/ but there doesn't seem to be any documentation on how to do this. Clues anyone? Cheers, Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to know the build dependencies?
I am learning to use cabal for my code. Just when I start, I met a question, is there an easy way to find out what packages my code depends? If you've managed to get your code to compile, ghc --show-iface Main.hi is perhaps the easiest way (ghc --make and ghci will also report package dependencies as they encounter them). If you're looking for the package for a particular module, ghc-pkg can help ghc-pkg find-module Control.Concurrent c:/ghc/ghc-6.10.3\package.conf: base-3.0.3.1, base-4.1.0.0 ghc-pkg find-module Data.Map c:/ghc/ghc-6.10.3\package.conf: containers-0.2.0.1 If you're looking for a minimal set of imports before hunting for packages, ghc's -ddump-minimal-imports will create a file Main.imports with that information. You could then run ghc-pkg find-module over that list. These are not the only options. Perhaps the available tools need to be advertized more?-) Claus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [cabal] How to deal with build-depency that not under cabal's control?
* Magicloud Magiclouds magicloud.magiclo...@gmail.com [2009-06-14 17:30:33+0800] Hi, I use gtk2hs in linux. Well, I have no idea how to install gtk2hs by cabal, but my program needs it, and I want my program cabalized. So how to do this? Thanks. gtk2hs consists of several cabal packages, e.g. gtk, glib and so on. (See `ghc-pkg list`) Specify those of them you need as dependencies in cabal file. -- Roman I. Cheplyaka :: http://ro-che.info/ Don't let school get in the way of your education. - Mark Twain ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] curious about sum
* Deniz Dogan deniz.a.m.do...@gmail.com [2009-06-13 16:17:57+0200] I remember needing a non-strict sum at least once, but I do not remember the exact application. We may agree that lazy sum is sometimes (rarely) needed, but then it can be always written as fold. However, in most cases user wants strict sum. So it's not really an excuse. -- Roman I. Cheplyaka :: http://ro-che.info/ Don't let school get in the way of your education. - Mark Twain ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [cabal] How to deal with build-depency that not under cabal's control?
* Magicloud Magiclouds magicloud.magiclo...@gmail.com [2009-06-14 18:48:26+0800] My gtk2hs is install manually, `configure make make install`. So It's okay. when I add gtk to build-dependency, it tells me Setup.hs: At least the following dependencies are missing: gtk -any Installation of gtk2hs registers these packages for you. Again, check `ghc-pkg list gtk`. If you installed gtk2hs, it must be there. If you, say, upgraded your ghc after you installed gtk2hs, you have to reinstall gtk2hs. How to register my manual-installed gtk2hs to cabal? On Sun, Jun 14, 2009 at 6:25 PM, Roman Cheplyakar...@ro-che.info wrote: * Magicloud Magiclouds magicloud.magiclo...@gmail.com [2009-06-14 17:30:33+0800] Hi, I use gtk2hs in linux. Well, I have no idea how to install gtk2hs by cabal, but my program needs it, and I want my program cabalized. So how to do this? Thanks. gtk2hs consists of several cabal packages, e.g. gtk, glib and so on. (See `ghc-pkg list`) Specify those of them you need as dependencies in cabal file. -- Roman I. Cheplyaka :: http://ro-che.info/ Don't let school get in the way of your education. - Mark Twain ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- 竹密岂妨流水过 山高哪阻野云飞 -- Roman I. Cheplyaka :: http://ro-che.info/ Don't let school get in the way of your education. - Mark Twain ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to know the build dependencies?
If your module compiles, you can get the info by passing '-ddump-types': TYPE SIGNATURES numbersTests :: Test testAverage :: Test testBindInt :: Test TYPE CONSTRUCTORS Dependent modules: [(MoresmauJP.Util.Numbers, False)] Dependent packages: [HUnit-1.2.0.3, base, ghc-prim, integer] It is, however, available only after your code has successfully compiled. Best regards Krzysztof Skrzętnicki On Sun, Jun 14, 2009 at 04:22, Magicloud Magicloudsmagicloud.magiclo...@gmail.com wrote: Hi, I am learning to use cabal for my code. Just when I start, I met a question, is there an easy way to find out what packages my code depends? Thanks. ___ 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 know the build dependencies?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA512 On Sun, Jun 14, 2009 at 6:05 AM, Deniz Dogan wrote: Someone really ought to write a tool for this... Well, it's an issue of time. Just building and adding the deps is fast and straightforward. A tool I'd need to know about, have installed, and remember to use in the middle of a Cabalizing session. The people who most need such a tool are those who are least likely to use it. And given the overhead, it's unclear that it would actually save time. Sometimes, somethings aren't worth automating. Now, if someone were to create such a tool and integrate it into 'mkcabal', then it might make sense. You could create the basic .cabal with the build-depends filled in. But as a separate tool it's too small a task to handle. Even memorizing the -show-iface or - -ddump-types options may not be worthwhile - how often does one create Cabal packages from scratch? - -- gwern -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.9 (GNU/Linux) iEYEAREKAAYFAko1BWEACgkQvpDo5Pfl1oKvigCeO7ABRVr/9+kT62dIFpo0k5+f y/AAnR6wLaDpX5/lZPqQzB/Wb4kuj8i9 =L2iA -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to know the build dependencies?
2009/6/14 Gwern Branwen gwe...@gmail.com: -BEGIN PGP SIGNED MESSAGE- Hash: SHA512 On Sun, Jun 14, 2009 at 6:05 AM, Deniz Dogan wrote: Someone really ought to write a tool for this... Well, it's an issue of time. Just building and adding the deps is fast and straightforward. A tool I'd need to know about, have installed, and remember to use in the middle of a Cabalizing session. The people who most need such a tool are those who are least likely to use it. And given the overhead, it's unclear that it would actually save time. Sometimes, somethings aren't worth automating. Now, if someone were to create such a tool and integrate it into 'mkcabal', then it might make sense. You could create the basic .cabal with the build-depends filled in. But as a separate tool it's too small a task to handle. Even memorizing the -show-iface or - -ddump-types options may not be worthwhile - how often does one create Cabal packages from scratch? I'm sorry, I was not aware of those flags when I wrote my message. You're right. -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell - string to list isusses, and more
Hello everyone! Im a Haskell newbie, and Ive have few unanswered questions. For someone more experienced (at least I think so) its a very simple task, but I just cant get a grip on it and its pretty frustrating. It wouldn't be that bad if I haven't browse thru bunch of pages and tutorials and still nothing... The problem is: take a string, and if every words starts with uppercase letter then print yes, else no. Forum Text Bold - yes Frog image File - no Ive had my share of approaches to this, but I just cant make it work. Standard one seemed the most simple: search :: String - String search [] = [] and then use words (splits string on space) to split the string so I could get a list and go through it recursively. But how to apply words to entered string in this form? To find the first letter I came up with: first = take 1 (head x). And compare it with elem or ASCII values to determine if its upper case. Any help, advice or suggestion is appreciated. Thanks in advance! -- View this message in context: http://www.nabble.com/Haskell---string-to-list-isusses%2C-and-more-tp24022673p24022673.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
Re: [Haskell-cafe] Haskell - string to list isusses, and more
2009/6/14 Gjuro Chensen daim...@gmail.com: Hello everyone! Im a Haskell newbie, and Ive have few unanswered questions. For someone more experienced (at least I think so) its a very simple task, but I just cant get a grip on it and its pretty frustrating. It wouldn't be that bad if I haven't browse thru bunch of pages and tutorials and still nothing... The problem is: take a string, and if every words starts with uppercase letter then print yes, else no. Forum Text Bold - yes Frog image File - no Ive had my share of approaches to this, but I just cant make it work. Standard one seemed the most simple: search :: String - String search [] = [] and then use words (splits string on space) to split the string so I could get a list and go through it recursively. But how to apply words to entered string in this form? To find the first letter I came up with: first = take 1 (head x). And compare it with elem or ASCII values to determine if its upper case. Any help, advice or suggestion is appreciated. Thanks in advance! -- View this message in context: http://www.nabble.com/Haskell---string-to-list-isusses%2C-and-more-tp24022673p24022673.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 As you say, there are a number of possible approaches to take here. I'd say take a look at functions all [1] and isUpper [2], those should be all you need. * all takes a predicate (a function) and a list of elements. It returns True if that predicate holds for all of the elements in the list, otherwise False. * isUpper takes a Char and returns True if that character is an uppercase letter, otherwise False. [1] http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html [2] http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Char.html -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Gjuro Chensen wrote: Hello everyone! Im a Haskell newbie, and Ive have few unanswered questions. For someone more experienced (at least I think so) its a very simple task, but I just cant get a grip on it and its pretty frustrating. It wouldn't be that bad if I haven't browse thru bunch of pages and tutorials and still nothing... The problem is: take a string, and if every words starts with uppercase letter then print yes, else no. Forum Text Bold - yes Frog image File - no Ive had my share of approaches to this, but I just cant make it work. Standard one seemed the most simple: search :: String - String search [] = [] and then use words (splits string on space) to split the string so I could get a list and go through it recursively. But how to apply words to entered string in this form? To find the first letter I came up with: first = take 1 (head x). And compare it with elem or ASCII values to determine if its upper case. The idea of using `words' is very good. If we want to use a bottom-up approach, we should have a function that determines if a word starts with an upper-case letter, i.e. a function of type startsWithUppercase :: String - Bool startsWithUppercase = ... (Hint: look at 'isUpper' from Data.Char) Now we need a way to see if for each word, some predicate is satisfied. There is a standard function for this, all. You can also do this by using map and and. The resulting function can be very concise if you get the hang of it :) Regards, -- Jochem Berndsen | joc...@functor.nl GPG: 0xE6FABFAB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
2009/6/14 Deniz Dogan deniz.a.m.do...@gmail.com: I'd say take a look at functions all [1] and isUpper [2], those should be all you need. Sorry, words is also needed for the idea I was thinking of. -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Am Sonntag 14 Juni 2009 17:19:22 schrieb Gjuro Chensen: Hello everyone! Im a Haskell newbie, and Ive have few unanswered questions. For someone more experienced (at least I think so) its a very simple task, but I just cant get a grip on it and its pretty frustrating. It wouldn't be that bad if I haven't browse thru bunch of pages and tutorials and still nothing... The problem is: take a string, and if every words starts with uppercase letter then print yes, else no. Forum Text Bold - yes Frog image File - no Ive had my share of approaches to this, but I just cant make it work. Standard one seemed the most simple: search :: String - String search [] = [] and then use words (splits string on space) to split the string so I could That's good. So you have everyWordStartsWithAnUppercaseLetter string = doSomething (words string) doSomething :: [String] - Bool checks wordStartsWithAnUppercaseLetter :: String - Bool for each word in the list and returns True if all words satisfy the condition, False if not. There's a handy function in the prelude for that: Prelude :t all all :: (a - Bool) - [a] - Bool get a list and go through it recursively. But how to apply words to entered string in this form? To find the first letter I came up with: first = take 1 (head x). And No, I don't think that's what you want: Prelude :t (take 1 . head) (take 1 . head) :: [[a]] - [a] Since String is a synonym for [Char], head gets the first letter of a word. compare it with elem or ASCII values to determine if its upper case. What about unicode strings? Prelude :t Data.Char.isUpper Data.Char.isUpper :: Char - Bool is what you want. Any help, advice or suggestion is appreciated. Thanks in advance! How to assemble that is left to you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Here's what I came up with. I especially like the 2nd version, even though it's longer, as it seems very declarative. caps1 s = all (\x - isUpper (head x)) (words s) caps2 s = all startsWithUpper (words s) where startsWithUpper w = isUpper (head w) I'm also fairly new to Haskell, so I would appreciate feedback from the more experienced. Thanks. On Jun 14, 2009, at 11:19 AM, Gjuro Chensen wrote: Hello everyone! Im a Haskell newbie, and Ive have few unanswered questions. For someone more experienced (at least I think so) its a very simple task, but I just cant get a grip on it and its pretty frustrating. It wouldn't be that bad if I haven't browse thru bunch of pages and tutorials and still nothing... The problem is: take a string, and if every words starts with uppercase letter then print yes, else no. Forum Text Bold - yes Frog image File - no Ive had my share of approaches to this, but I just cant make it work. Standard one seemed the most simple: search :: String - String search [] = [] and then use words (splits string on space) to split the string so I could get a list and go through it recursively. But how to apply words to entered string in this form? To find the first letter I came up with: first = take 1 (head x). And compare it with elem or ASCII values to determine if its upper case. Any help, advice or suggestion is appreciated. Thanks in advance! -- View this message in context: http://www.nabble.com/Haskell---string-to-list-isusses%2C-and-more-tp24022673p24022673.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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Toby Miller wrote: Here's what I came up with. I especially like the 2nd version, even though it's longer, as it seems very declarative. caps1 s = all (\x - isUpper (head x)) (words s) caps2 s = all startsWithUpper (words s) where startsWithUpper w = isUpper (head w) I'm also fairly new to Haskell, so I would appreciate feedback from the more experienced. This seems fine, but you need to check that words never returns a list containing the empty string (otherwise `head' will fail). I prefer in this case a point free style though, but some might disagree. Cheers, -- Jochem Berndsen | joc...@functor.nl GPG: 0xE6FABFAB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
2009/6/14 Toby Miller t...@miller.ms: Here's what I came up with. I especially like the 2nd version, even though it's longer, as it seems very declarative. caps1 s = all (\x - isUpper (head x)) (words s) caps2 s = all startsWithUpper (words s) where startsWithUpper w = isUpper (head w) I'm also fairly new to Haskell, so I would appreciate feedback from the more experienced. Thanks. Not that I'm very experienced myself, but I came up with the first idea as well: caps1 = all (isUpper . head) . words -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Toby Miller wrote: Here's what I came up with. I especially like the 2nd version, even though it's longer, as it seems very declarative. caps1 s = all (\x - isUpper (head x)) (words s) caps2 s = all startsWithUpper (words s) where startsWithUpper w = isUpper (head w) I'm also fairly new to Haskell, so I would appreciate feedback from the more experienced. Thanks. caps = all (isUpper . head) . words But then, I'm strange like that... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
2009/6/14 Jochem Berndsen joc...@functor.nl: Toby Miller wrote: caps1 s = all (\x - isUpper (head x)) (words s) This seems fine, but you need to check that words never returns a list containing the empty string (otherwise `head' will fail). Is there any such case? I was thinking about that as well, but couldn't think of any case where head would be called on an empty list. -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Deniz Dogan wrote: 2009/6/14 Jochem Berndsen joc...@functor.nl: Toby Miller wrote: caps1 s = all (\x - isUpper (head x)) (words s) This seems fine, but you need to check that words never returns a list containing the empty string (otherwise `head' will fail). Is there any such case? I was thinking about that as well, but couldn't think of any case where head would be called on an empty list. Not that I know of; but I tested this in order to make sure that I didn't overlook something obvious. (At least, it's a potential issue that we need to check, since `head' is partial.) Regards, -- Jochem Berndsen | joc...@functor.nl GPG: 0xE6FABFAB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to know the build dependencies?
On Jun 14, 2009, at 6:05 AM, Deniz Dogan wrote: 2009/6/14 Gwern Branwen gwe...@gmail.com: -BEGIN PGP SIGNED MESSAGE- Hash: SHA512 On Sat, Jun 13, 2009 at 10:22 PM, Magicloud Magiclouds wrote: Hi, I am learning to use cabal for my code. Just when I start, I met a question, is there an easy way to find out what packages my code depends? Thanks. Not really. The easiest way is to just build your code and add every package Cabal complains about being hid into your build-depends. (Usually this won't take more than a minute or 3 if you're toggling between a terminal and an editor.) - -- gwern Someone really ought to write a tool for this... Visualising the Haskell Universe « Control.Monad.Writer___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Gjuro Chensen wrote: /cut I dont know everyone will see this, but I would like thank everyone who found time to help, and not spam too much doing it:D. Well, I did it! Its not great (especially comparing to those one line solutions, wow!), but it works. module Main where startsWithUpper :: String - Bool startsWithUpper []= False startsWithUpper string = if myIsUpper(head(string)) then True else False myIsUpper :: Char - Bool myIsUpper x = if x='A' x = 'Z' then True else False checkAll string = check (words string) check :: [String] - Bool check []=False check x = if all startsWithUpper x then True else False Since importing modules isnt allowed, I made my own isUpper. And thats it, for few days of Haskell, Im happy. Once again, many many thanks to everyone! -- View this message in context: http://www.nabble.com/Haskell---string-to-list-isusses%2C-and-more-tp24022673p24023759.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
Re: [Haskell-cafe] Haskell - string to list isusses, and more
Gjuro Chensen wrote: startsWithUpper :: String - Bool startsWithUpper []= False startsWithUpper string = if myIsUpper(head(string)) then True else False It is very good that you caught the issue of taking the head of an empty list :) I saw here and also below, that you did things like if P then True else False You can shorten this to 'P'. Also, normally Haskellers like to pattern match, changing the second clause of your function into startsWithUpper (x:xs) = myIsUpper x check :: [String] - Bool check []=False Why is this False and not True? Certainly in the empty string all words start with an uppercase letter, don't they? (If it's True, you can even remove this clause, and let the other one take care of the rest.) Regards, -- Jochem Berndsen | joc...@functor.nl GPG: 0xE6FABFAB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] slow code
Haskell Gurus, I have tried to use profiling to tell me what's going on here, but it hasn't helped much, probably because I'm not interpreting the results correctly. Empirically I have determined that the show's are pretty slow, so an alternative to them would be helpful. I replaced the show's with , and compiled with -O2 and not much improvement. I need to write _a lot_ of code in this style. A few words about how best to do this would be helpful. Laziness, infinite lists, uvector ?? Help... Thanks, Brian import Complex import System.IO genData :: Double - Int - (Double - Complex Double) - ([Double], [Complex Double]) genData tstop n f = let deltat = tstop / (fromIntegral n) t = [ fromIntegral(i) * deltat | i - [0..n-1]] in (t, map f t) main = do let (t, y) = genData 100.0E-6 (2 ^ 15) (\x - x :+ 0.0) h - openFile data.txt WriteMode mapM_ (\(x, y) - do hPutStr h (show t) hPutStr h hPutStrLn h (show (realPart y))) (zip t y) hClose h ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Fwd: [Haskell-cafe] curious about sum
Once more I forgot to send my messages to the haskell cafe list. All the rest of the list which I´m suscribed to, send the mail replies to the list automatically, but this doesn´t. Please, can this be changed?. -- Forwarded message -- From: Alberto G. Corona agocor...@gmail.com Date: 2009/6/13 Subject: Re: [Haskell-cafe] curious about sum To: Deniz Dogan deniz.a.m.do...@gmail.com first, I was completely wrong. It is foldl what is neccesary. sum is defined in terms of foldl: sum= foldl (+) 0 but Prelude foldl (+) 0 [1..100] *** Exception: stack overflow that is not because + is non strict, but because foldl is: foldl f z0 xs0 = lgo z0 xs0 where lgo z [] = z lgo z (x:xs) = lgo (f z x) xs this version of foldl IS strict: foldlStrict f z0 xs0 = lgo z0 xs0 where lgo z [] = z lgo z (x:xs) =let t= f z x in t `seq` lgo t xs main= print $ foldlStrict (+) 0 [1..100] 5050 so the garbage collector do the job in freeing the consumed part of the list. 2009/6/13 Alberto G. Corona agocor...@gmail.com Prelude let strictplus x y= let z=x +y in z `seq` z; sum1= foldr strictplus 0 in sum1[0..100] *** Exception: stack overflow I suppose that strictplus is strict, so the garbage collector would free the consumed part of the list. Then, why the stack overflow? 2009/6/13 Deniz Dogan deniz.a.m.do...@gmail.com 2009/6/13 Jochem Berndsen joc...@functor.nl: Keith Sheppard wrote: Is there any reason that sum isn't strict? I can't think of any case where that is a good thing. Prelude sum [0 .. 100] *** Exception: stack overflow It is useful if the (+) is nonstrict; although I cannot think of any useful mathematical structure where (+) would be nonstrict. I remember needing a non-strict sum at least once, but I do not remember the exact application. But imagine having a (very) long list of numbers and you want to do A if the sum exceeds a small number, otherwise B. if sum [0..10] 10 then A else B However, this idea didn't work, because of strictness. -- Deniz Dogan ___ 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] curious about sum
On 14 Jun 2009, at 12:47, Roman Cheplyaka wrote: * Deniz Dogan deniz.a.m.do...@gmail.com [2009-06-13 16:17:57+0200] I remember needing a non-strict sum at least once, but I do not remember the exact application. We may agree that lazy sum is sometimes (rarely) needed, but then it can be always written as fold. However, in most cases user wants strict sum. So it's not really an excuse. How's this for an excuse - Haskell is a lazy language. It also happens to have support for strictifying things when necessary. The Haskell API is designed to be lazy, like the rest of the language, similarly though, where commonly used, strict versions are provided, like for example foldl'. A much better idea than making sum strict, would simply be to add a sum'. Bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Fwd: [Haskell-cafe] curious about sum
Alberto G. Corona wrote: Once more I forgot to send my messages to the haskell cafe list. All the rest of the list which I´m suscribed to, send the mail replies to the list automatically, but this doesn´t. Please, can this be changed?. This comes up every so often, but I would be against this. Your e-mail client should support mailing lists. this version of foldl IS strict: foldlStrict f z0 xs0 = lgo z0 xs0 where lgo z [] = z lgo z (x:xs) =let t= f z x in t `seq` lgo t xs main= print $ foldlStrict (+) 0 [1..100] 5050 so the garbage collector do the job in freeing the consumed part of the list This is correct; the function you defined is equivalent to foldl' in Data.List, if I'm not mistaken. Regards, -- Jochem Berndsen | joc...@functor.nl GPG: 0xE6FABFAB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] curious about sum
A much better idea than making sum strict, would simply be to add a
sum'.
Even better to abstract over strictness, to keep a lid on code duplication?
{-# LANGUAGE TypeOperators #-}
sum = foldlS ($) (+) 0
sum' = foldlS ($!) (+) 0
-- identity on constructors of t (from a), modulo strictness in a
type a :-? t = (a - t) - (a - t)
foldlS :: (b :-? ([a] - b)) - (a - b - b) - (b - [a] - b)
foldlS ($) op n []= n
foldlS ($) op n (h:t) = (foldlS ($) op $ (op h n)) t
Strictness is encoded as a constructor transformer - ($) keeps the
constructor in question unchanged, ($!) makes it strict. Also works
with container types (Maps strict or not strict in their elements can
share the same strictness-abstracted code, for instance). Though
sometimes there is more than one strictness choice to make in the
same piece of code..
Claus
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[Haskell-cafe] traversal transformations
Hi,
While playing with Church Encodings of data structures, I realized
there are generalisations in the same way Data.Foldable and
Data.Traversable are generalisations of lists.
The normal Church Encoding of lists is like this:
newtype List a = L { unL :: forall b. (a - b - b) - b - b }
It represents a list by a right fold:
foldr f z l = unL l f z
List can be constructed with cons and nil:
nil = L $ \f - id
cons a l = L $ \f - f a . unL l f
Oleg has written about this: http://okmij.org/ftp/Haskell/zip-folds.lhs
Now function of type (b - b) are endomorphisms which have a
Data.Monoid instance, so the type can be generalized:
newtype FM a = FM { unFM :: forall b. Monoid b = (a - b) - b }
fmnil = FM $ \f - mempty
fmcons a l = FM $ \f - f a `mappend` unFM l f
Now lists are represented by (almost) their foldMap function:
instance Foldable FM where
foldMap = flip unFM
But notice that there is now nothing list specific in the FM type,
nothing prevents us to add other constructor functions.
fmsnoc l a = FM $ \f - unFM l f `mappend` f a
fmlist = fmcons 2 $ fmcons 3 $ fmnil `fmsnoc` 4 `fmsnoc` 5
*Main getProduct $ foldMap Product fmlist
120
Now that we have a container type represented by foldMap, there's
nothing stopping us to do a container type represented by traverse
from Data.Traversable:
{-# LANGUAGE RankNTypes #-}
import Data.Monoid
import Data.Foldable
import Data.Traversable
import Control.Monad
import Control.Applicative
newtype Container a = C { travC :: forall f b . Applicative f = (a -
f b) - f (Container b) }
czero :: Container a
cpure :: a - Container a
ccons :: a - Container a - Container a
csnoc :: Container a - a - Container a
cpair :: Container a - Container a - Container a
cnode :: Container a - a - Container a - Container a
ctree :: a - Container (Container a) - Container a
cflat :: Container (Container a) - Container a
czero = C $ \f - pure czero
cpure x = C $ \f - cpure $ f x
ccons x l = C $ \f - ccons $ f x * travC l f
csnoc l x = C $ \f - csnoc $ travC l f * f x
cpair l r = C $ \f - cpair $ travC l f * travC r f
cnode l x r = C $ \f - cnode $ travC l f * f x * travC r f
ctree x l = C $ \f - ctree $ f x * travC l (traverse f)
cflat l = C $ \f - cflat $ travC l (traverse f)
instance Functor Container where
fmap g c = C $ \f - travC c (f . g)
instance Foldable Container where
foldMap = foldMapDefault
instance Traversable Container where
traverse = flip travC
instance Monad Container where
return = cpure
m = f = cflat $ fmap f m
instance Monoid (Container a) where
mempty = czero
mappend = cpair
Note that there are all kinds of constructors, and they can all be
combined. Writing their definitions is similar to how you would write
Traversable instances.
So I'm not sure what we have here, as I just ran into it, I wasn't
looking for a solution to a problem. It is also all quite abstract,
and I'm not sure I understand what is going on everywhere. Is this
useful? Has this been done before? Are there better implementations of
foldMap and (=) for Container?
Finally, a little example. A Show instance (for debugging purposes)
which shows the nesting structure.
newtype ShowContainer a = ShowContainer { doShowContainer :: String }
instance Functor ShowContainer where
fmap _ (ShowContainer x) = ShowContainer $ ( ++ x ++ )
instance Applicative ShowContainer where
pure _ = ShowContainer ()
ShowContainer l * ShowContainer r = ShowContainer $ init l ++ ,
++ r ++ )
instance Show a = Show (Container a) where
show = doShowContainer . traverse (ShowContainer . show)
greetings,
--
Sjoerd Visscher
sjo...@w3future.com
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Re: [Haskell-cafe] Wiki user accounts
On Fri, Jun 12, 2009 at 12:46 PM, Gwern Branwengwe...@gmail.com wrote: ... If I might suggest some users we might give the bit to: myself, dons, Magnus Therning, Neil Mitchell, and byorgey. All have been editing the wiki for some time, some have administrator experience on Wikipedia, and all have commit bits for various Haskell repos (and so presumably can be trusted). (Of course, this list isn't intended to be exhaustive; they're just who comes to mind looking over Recent Changes.) I've spoken with John Peterson (the other admin/bureaucrat besides Ashley), and he has no problem with giving these people the bit. If there aren't any objections by next Saturday/Sunday, I will email him and ask him to do so. -- gwern ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Wiki user accounts
Gwern Branwen wrote: This runs on MediaWiki, right? How about adding a CAPTCHA for account registrations? http://www.mediawiki.org/wiki/Extension:ConfirmEdit See http://haskell.org/haskellwiki/Special:Version ConfirmEdit would require an upgrade. This is the ideal solution. But it requires an update of the machine from an old Red Hat distro (RHEL AS release 3 update 9) to something a bit more modern, like Debian 5.0 or Ubuntu Server 9.04. -- Ashley Yakeley ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Wiki user accounts
Gwern Branwen wrote: Presumably Ashley is busy. Yes. Average request rate is about one each day; I tend to do them in a lump about once a week. One solution would be to have Ashley re-enable user registrations. This has been suggested before, but no one knows how bad the spam would be. Basically, someone was creating thousands of accounts automatically. It seems likely this will happen again. Another solution would be to sysop a few users to admin/bureaucrat, so that even if a few are inactive or away, the rest can handle requests. What would the process be? -- Ashley Yakeley ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Runtime strictness analysis for polymorphic HOFs?
2009/6/15 Paul Chiusano paul.chius...@gmail.com: Hello, I was recently trying to figure out if there was a way, at runtime, to do better strictness analysis for polymorphic HOFs, for which the strictness of some arguments might depend on the strictness of the strictness of function types that are passed as arguments [1]. As an example, consider foldl. The 'seed' parameter of foldl can be made strict as long as the binary function used for the fold is strict in its arguments. Unfortunately, because strictness analysis is done statically, Haskell can't assume anything about the strictness of the binary function - assuming we only compile one instance of foldl, it must be the most conservative version possible, and that means making the seed parameter lazy. :-( I started thinking about ways you could to a check at runtime for this sort of thing, something to the effect of asking foldl, before heap-allocating a thunk for the seed parameter, whether that parameter could be made strict. foldl could then inspect other arguments that have been supplied, and based on these arguments, evaluate or go ahead with creating a thunk the seed parameter. It's a runtime cost, sure, but would it be more than the cost of having to do an additional heap allocation? In any case a small runtime cost might be worth it if the analysis becomes more uniform. So, my question is: does doing this sort of runtime analysis seem like a horrible idea? Is it even possible? Has anyone tried this in the past? (So far I haven't found anything, but would love references if people have them.) Note that I'm not suggesting Haskell should do anything like this. I'm playing around with the ideas because I'm interesting in creating a lazy language and I was hoping to have strictness analysis be very predictable and uniform, something the programmer can count on and use to simply reason about space usage ... which might be hopelessly unrealistic goal! I guess the more general question is - is perfect strictness analysis (however that is defined) possible, if we're willing to incur some runtime cost? What would that look like? The idea looks cool, but perfect strictness analysis is not possible, t.i. the problem of determining whether f _|_ = _|_ is undecidable, since it is a non-trivial property of f (there exist f's for which it is true, and ones for which it is false) and non-trivial properties are undecidable, thanks to Rice theorem. Best, Paul [1]: More background on my thinking here - a bit half-baked, so bear with me! http://pchiusano.blogspot.com/2009/06/perfect-strictness-analysis-part-1.html http://pchiusano.blogspot.com/2009/06/perfect-strictness-analysis-part-2.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Eugene Kirpichov Web IR developer, market.yandex.ru ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Performance of functional priority queues
There's a current thread in the Erlang mailing list about priority queues. I'm aware of, for example, the Brodal/Okasaki paper and the David King paper. I'm also aware of James Cook's priority queue package in Hackage, have my own copy of Okasaki's book, and have just spent an hour searching the web. One of the correspondents in that thread claims that it is provably impossible to have an efficient priority queue implementation without mutability. I think he's cuckoo. But I'd like to have some numbers to back me up. Can anyone point me to some actual benchmark results comparing priority queue performance *with* mutation and priority queue performance *without* mutation, in the same functional or mostly-functional language? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I need a hint in list processing
On 14 Jun 2009, at 8:06 pm, Fernan Bolando wrote: Hi all If I have a number of list example list1 = [2,3] list2 = [1,2] list3 = [2,3,4] list4 = [1,2,3] I want to create a list from the list above with n elements, non-repeating and each elements index represents 1 of the elements from the corresponding list so for the above input I would get. a = [3,2,4,1] I have been staring at this off and on all day, and I haven't the faintest idea what you want. What is n. What is it that doesn't repeat? How does the index of an element represent 1 element? Which list corresponds to what? I'm beginning to suspect that what you want is a choice function: f [s1,...,sn] = [x1,...,xn] when each xi is an element of the corresponding si and no two xs are the same. Instead of finding one answer, let's find them all. all_choices :: Eq a = [[a]] - [[a]] all_choices [] = [[]] all_choices (set:sets) = [x:xs | xs - all_choices sets, x - set, not(x `elem` xs)] The test case all_choices [[2,3], [1,2], [2,3,4], [1,2,3]] has the answer [[3,2,4,1], [3,1,4,2], [2,1,4,3]] and you probably want to use it something like case all_choices sets of [] - there are no such choices (first_choice:_) - first_choice is one such choice For inputs like [[1,2],[2,1],[1]] there is of course no such choice function. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I need a hint in list processing
nub . concat ? Richard O'Keefe wrote: On 14 Jun 2009, at 8:06 pm, Fernan Bolando wrote: Hi all If I have a number of list example list1 = [2,3] list2 = [1,2] list3 = [2,3,4] list4 = [1,2,3] I want to create a list from the list above with n elements, non-repeating and each elements index represents 1 of the elements from the corresponding list so for the above input I would get. a = [3,2,4,1] I have been staring at this off and on all day, and I haven't the faintest idea what you want. What is n. What is it that doesn't repeat? How does the index of an element represent 1 element? Which list corresponds to what? I'm beginning to suspect that what you want is a choice function: f [s1,...,sn] = [x1,...,xn] when each xi is an element of the corresponding si and no two xs are the same. Instead of finding one answer, let's find them all. all_choices :: Eq a = [[a]] - [[a]] all_choices [] = [[]] all_choices (set:sets) = [x:xs | xs - all_choices sets, x - set, not(x `elem` xs)] The test case all_choices [[2,3], [1,2], [2,3,4], [1,2,3]] has the answer [[3,2,4,1], [3,1,4,2], [2,1,4,3]] and you probably want to use it something like case all_choices sets of [] - there are no such choices (first_choice:_) - first_choice is one such choice For inputs like [[1,2],[2,1],[1]] there is of course no such choice function. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Tony Morris http://tmorris.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I need a hint in list processing
Just guessing. How do you know it's an accident? Richard O'Keefe wrote: On 15 Jun 2009, at 4:26 pm, Tony Morris wrote: Prelude Data.List nub . concat $ [[2, 3], [1, 2], [2, 3, 4], [1, 2, 3]] [2,3,1,4] In this particular case. But that's a lucky accident.\ -- Tony Morris http://tmorris.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Runtime strictness analysis for polymorphic HOFs?
On Sun, Jun 14, 2009 at 8:18 PM, Eugene Kirpichov ekirpic...@gmail.comwrote: The idea looks cool, but perfect strictness analysis is not possible, t.i. the problem of determining whether f _|_ = _|_ is undecidable, since it is a non-trivial property of f (there exist f's for which it is true, and ones for which it is false) and non-trivial properties are undecidable, thanks to Rice theorem. Unless you remove _|_ from the language. If you have a total functional programming language[1] it becomes a trivial property, right? I guess this would also extend to some dependently typed languages too. [1] http://lambda-the-ultimate.org/node/2003 Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] a now abandoned experimental extension to Haskell?
Hello, In some code that I am cabalizing I ran into: type DataLiteral = ref RDFgraph defs type URIReference = ref RDFgraph defs type NonNegativeInteger = ??? What is this? Kind regards, Vasili ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
