Re: [Haskell-cafe] Thread scheduling
On Fri, Jun 11, 2010 at 3:34 PM, Luke Palmer lrpal...@gmail.com wrote: Say, using System.Time.getClockTime. Luke On Thu, Jun 10, 2010 at 11:31 PM, Luke Palmer lrpal...@gmail.com wrote: On Thu, Jun 10, 2010 at 11:50 AM, Andrew Coppin andrewcop...@btinternet.com wrote: Control.Concurrent provides the threadDelay function, which allows you to make the current thread sleep until T=now+X. However, I can't find any way of making the current thread sleep until T=X. In other words, I want to specify an absolute wakeup time, not a relative one. Modulo a small epsilon between the two actions, can't you just get the current time and subtract it from the target time? threadDelay is allowed to delay for too long anyway, so doing it this way does not lose you any correctness. Luke This is a slightly different issue, but isn't there a potential problem with threadDelay? I noticed that internally threadDelay uses gettimeofday() as the absolute time source (on linux at least). Isn't there potential problem with this since wall-clock time isn't guaranteed to be monotonic increasing? On linux, I'd have thought the right thing to do would be to use clock_gettime(CLOCK_MONOTONIC) although that is probably not very portable. -- David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] CGI differences FastCGI
Hi. This is probably I must be blind department I have a very basic strip down echo cgi that runs with apache2. When I try to modfi it to be a FastCGI instead and run it with spawn-fcgi with nginx It don't behave as expected. I suppose that the line that don't get any data is mn - getInputFPS file when running under FastGCI. So is the code wrong? or have I missed something with the setup? I can run the example of fastcgi provided in http://mult.ifario.us/p/wiring-haskell-into-a-fastcgi-web-server with no problem. Description:Ubuntu 10.04 LTS 2.6.32-22-generic-pae #36-Ubuntu SMP The Glorious Glasgow Haskell Compilation System, version 6.12.1 + import Control.Concurrent import Network.CGI -- import Network.FastCGI import Text.Html import qualified Data.ByteString.Lazy as BS import qualified Data.ByteString.Lazy.Char8 as BS8 import Control.Monad (liftM) import Data.Maybe (fromJust) import Char import Data.List import System.Time import qualified Data.ByteString.Char8 as C import Text.JSON.Generic import Text.JSON insertthis fb = do let f = BS8.unpack fb return (f) fileForm = form ! [method post, enctype multipart/form-data] [textfield file, submit Upload] saveFile cont = do r-liftIO $ insertthis cont return $ paragraph (Inserted ++ (show r)) page t b = header thetitle t +++ body b test :: CGI CGIResult test = do setHeader Content-Type text/html; charset=utf-8 mn - getInputFPS file h - maybe (return fileForm) saveFile mn output $ renderHtml $ page Upload h main = runCGI $ handleErrors test --main= runFastCGI $ handleErrors test + ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Help with Bird problem 3.3.3
Günther Schmidt wrote: I'm just re-reading the book again, this time doing the exercises though :) Is there a site with solutions for the exercises? Unless you count the haskell-cafe and beginners mailing lists as sites, I don't know any sites which have the solutions. ;) Problem 3.3.3: Construct a program for division from the specification (m * n) / n = m and prove that it's correct. Sketch of a solution: To define a / n , the usual approach of subtracting n from the first argument until something less than n remains will work. Correctness can then be proven by induction on m . Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How to Show an Operation?
On Friday 11 June 2010 07:47:03, Martin Drautzburg wrote: On Friday, 11. June 2010 00:12:03 Daniel Fischer wrote: Thanks Daniel. Upgrade. We're at 6.12 now! Did that. Everything is available now. I am still having trouble with the test function. First it seems I need braces, so I can mix == and *. test :: Num a = (a - a) - (a - a) - (a - a) - [String] test f g h = do [f', g', h'] - permutations [Named f f, Named g g, Named h h] guard $ namedPure 42 == (f' * g' * h' * namedPure 42) return $ show f' ++ . ++ show g' ++ . ++ show h' But this leads to Occurs check: cannot construct the infinite type: a = (a - a) - a1 - t When generalising the type(s) for `test' Ah, yes, (*) is left associative (infixl 4, hence you also need the parentheses since (==) is infix 4; same fixity and different associativities don't mix), here it must be associated to the right, namedPure 42 == (f' * (g' * (h' * namedPure 42))) :( If you'd want to use it a lot, define a right associative alias with higher fixity: infixr 5 * (*) = (*) This error message is still the maximum penalty for me (along with Corba marshall exception in J2EE and Missing right parenthesis in Oracle SQL) Then generally speaking, I have the feeling that this code does not allow namifying existing code either. In this respect it does not seem to do better than the apply method pattern discussed earlier in this thread. You'd have to rewrite; either way. The problem it solves is very simple and therefore using (*) and namedPure isn't much of a drawback. But if I had tons of code to namify I would still have to do significant changes to it, right? Yes. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How to Show an Operation?
On Thu, Jun 10, 2010 at 2:10 PM, Maciej Piechotka uzytkown...@gmail.com wrote: data Named a = Named String a instance Functor Named where f `fmap` (Named s v) = Named s (f v) instance Applicative Named where pure x = Named x (Named s f) * (Named t v) = Named (s ++ ( ++ t ++ )) (f v) This is not technically a legal applicative instance, because it is not associative. This can be seen when you try to clean up the usage as we have been discussing: g . f = liftA2 (.) g f f = Named f (+1) g = Named g (*2) h = Named h (^3) ghci f * (g * (h * namedPure 42)) f(g(h(42))) ghci (f . g . h) * namedPure 42 f(g)(h)(42) The Applicative laws are supposed to guarantee that this refactor is legal. Of course, the latter answer is nonsense. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] threadDelay correctness
* David Powell da...@drp.id.au [2010-06-11 16:09:55+1000] This is a slightly different issue, but isn't there a potential problem with threadDelay? I noticed that internally threadDelay uses gettimeofday() as the absolute time source (on linux at least). Isn't there potential problem with this since wall-clock time isn't guaranteed to be monotonic increasing? On linux, I'd have thought the right thing to do would be to use clock_gettime(CLOCK_MONOTONIC) although that is probably not very portable. Good point -- I remember xmobar hanging after adjusting clock. Seems like this is the cause. -- 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] Using the ContT monads for early exits of IO ?
* Günther Schmidt gue.schm...@web.de [2010-06-11 01:22:27+0200] there is nothing wrong with ifs as such except the won't actually exit a long piece of code, the computation will continue, just in a useless way. Can you clarify? -- 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] Re: How to Show an Operation?
On Friday 11 June 2010 11:50:55, Luke Palmer wrote: On Thu, Jun 10, 2010 at 2:10 PM, Maciej Piechotka uzytkown...@gmail.com wrote: data Named a = Named String a instance Functor Named where f `fmap` (Named s v) = Named s (f v) instance Applicative Named where pure x = Named x (Named s f) * (Named t v) = Named (s ++ ( ++ t ++ )) (f v) This is not technically a legal applicative instance, because it is not associative. Good spot. I think (Named s f) * (Named t v) = Named (s ++ $ ++ t) (f v) fixes it. This can be seen when you try to clean up the usage as we have been discussing: g . f = liftA2 (.) g f f = Named f (+1) g = Named g (*2) h = Named h (^3) ghci f * (g * (h * namedPure 42)) f(g(h(42))) ghci (f . g . h) * namedPure 42 f(g)(h)(42) The Applicative laws are supposed to guarantee that this refactor is legal. Of course, the latter answer is nonsense. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: package naming policy
On Tue, 8 Jun 2010, Don Stewart wrote: Great points: I've added them to this wiki page of for and against points: http://haskell.org/haskellwiki/Libraries/WhenToRewriteOrRename Please add points as you see fit, and maybe we can come up with a mitigation/change plan. Closely related is the question of module names. 'transformers'+'monads-fd' are somehow an successor of 'mtl' and chose distinct package names, but there were module name clashes. They mostly hurted GHCi users, but this led to a lot of confusion, too. So the question is, if FGL gets a new name, should it also use different module names? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: package naming policy
Henning Thielemann lemm...@henning-thielemann.de writes: Closely related is the question of module names. 'transformers'+'monads-fd' are somehow an successor of 'mtl' and chose distinct package names, but there were module name clashes. They mostly hurted GHCi users, but this led to a lot of confusion, too. So the question is, if FGL gets a new name, should it also use different module names? This has been brought up already. My intention is, before we release it publically/visibly, we get in contact with all package maintainers of hackage packages that use FGL and help them migrate to the new version so we can do a mass migrate/upgrade so that there would be no reason for users to have the old version of FGL installed (unless there's a system package vs cabal-install package clash, but there's not much we can do about that). The unfortunate aspect of this IMHO is that the FGL package name doesn't match the module names; if it was the consensus of the community that we change the package name of FGL one option I was thinking of was something along the lines of inductive-graphs, but the obvious choice of module names for that would be Data.Graph.Inductive, which FGL has already taken. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to Show an Operation?
On Mon, Jun 7, 2010 at 9:49 PM, Claus Reinke claus.rei...@talk21.com wrote: As others have pointed out, you can't go from operation to representation, but you can pair operations and expressions with their representations. This idea is also implemented in my little 'repr' package: http://hackage.haskell.org/package/repr Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: GATD and pattern matching
On Fri, Jun 11, 2010 at 12:46 AM, Felipe Lessa felipe.le...@gmail.com wrote: eqTypeable :: (Typeable a, Eq a, Typeable b, Eq b) = a - b - Bool eqTypeable x y = case cast y of Just y' - x == y' Nothing - False ...or indeed: eqTypeable x y = cast x == Just y ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using the ContT monads for early exits of IO ?
On 11 June 2010 10:12, Roman Cheplyaka r...@ro-che.info wrote: * Günther Schmidt gue.schm...@web.de [2010-06-11 01:22:27+0200] there is nothing wrong with ifs as such except the won't actually exit a long piece of code, the computation will continue, just in a useless way. Can you clarify? I think Günther assumed that I was suggesting: do if x then return () else bar continueComputation The problem is that if 'x' is true, continueComputation should never happen. So you can solve it like this, which is what I was actually suggesting: do if x then return () else do bar; continueComputation But then you have this problem, which Günther addressed: 2010/6/11 Günther Schmidt gue.schm...@web.de: Primarily for every if I need two forks, so at every if the branches double. Which can be a big problem if you have a sequence of heterogenous actions that must be executed in order and are dependant and nested. Continutations solve this, as do ErrorT and MaybeT which are both restricted subsets for returning values. I'd use MaybeT if a value needed to be returned, or nothing. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Using the ContT monads for early exits of IO ?
Hello Christopher, Friday, June 11, 2010, 4:06:05 PM, you wrote: do if x then return () else do bar; continueComputation i format it this way: if x then return () else do bar continueComputation -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: [Haskell-cafe] Using the ContT monads for early exits of IO ?
On 11 June 2010 14:27, Bulat Ziganshin bulat.zigans...@gmail.com wrote: i format it this way: if x then return () else do bar continueComputation That's a nice way of formatting! God bless optional formatting! I like this problem-specific indentation. Another is: if xthen foo else if y then bar else if z then mu else zot Kind of similar to a COND statement from Lisp. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[4]: [Haskell-cafe] Using the ContT monads for early exits of IO ?
Hello Christopher, Friday, June 11, 2010, 4:35:00 PM, you wrote: if xthen foo else if y then bar else if z then mu else zot case () of _ | x - foo | y - bar | otherwise - zor it's usually considered as haskell way of doing this -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: GATD and pattern matching
I don't know whether its a good name or not (the ===), but I have the following in a generic utilities file I have, and I use it every now and then. (===) :: (Typeable a, Typeable b, Eq b) = a - b - Bool (===) x y = cast x == Just y (Notice you don't need Eq a in the context) On 11 June 2010 12:51, Ben Millwood hask...@benmachine.co.uk wrote: On Fri, Jun 11, 2010 at 12:46 AM, Felipe Lessa felipe.le...@gmail.com wrote: eqTypeable :: (Typeable a, Eq a, Typeable b, Eq b) = a - b - Bool eqTypeable x y = case cast y of Just y' - x == y' Nothing - False ...or indeed: eqTypeable x y = cast x == Just y ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] Woes on MacOS 10.6 - linking issues
(moving to the cafe) There is an incompatibility between the version of iconv in Mac Os and the one included in MacPorts. As the RTS of the build of ghc in the Haskell Platform is linked against Mac Os iconv, you cannot use it with the build of gtk2hs from MacPorts. This is a known issue already commented elsewhere, in case you haven't found it already: http://www.mail-archive.com/haskell-cafe@haskell.org/msg69139.html http://stackoverflow.com/questions/2726248/ghc-6-12-and-macports Cheers, On Fri, Jun 11, 2010 at 4:53 AM, Brett Giles brett.gi...@ucalgary.ca wrote: Hi Folks I seem to have Gtk2HS 0.11 installed, but not quite working. Interestingly, I can run a demo, such as the hello/World.hs example, directly in ghci. However, when I try to do a ghc --make on any code containing gtk2hs I get a link error like this: Undefined symbols: _iconv_close, referenced from: _hs_iconv_close in libHSbase-4.2.0.0.a(iconv.o) (maybe you meant: _hs_iconv_close) _iconv, referenced from: _hs_iconv in libHSbase-4.2.0.0.a(iconv.o) (maybe you meant: _hs_iconv_open, _hs_iconv , _hs_iconv_close ) _iconv_open, referenced from: _hs_iconv_open in libHSbase-4.2.0.0.a(iconv.o) (maybe you meant: _hs_iconv_open) ld: symbol(s) not found I do have libiconv installed as a universal library via macports. gtk, glade etc., are also universal installed via macports. I downloaded the OSX Haskell Platform package and am running ghc 6.12.1 Other programs seem to be having some issues as well though, For instance, a command line program seems to compile fine, but when it runs I get the message: $ emlqpl (--- My successfully compiled program - batch only, no gtk items) dyld: Library not loaded: /opt/local/lib/libgtk-quartz-2.0.0.dylib Referenced from: /usr/local/bin/emlqpl Reason: image not found Trace/BPT trap Does anyone have any suggestions? Brett Giles Grad Student, Formal Methods, Category Theory, University of Calgary brett.gi...@ucalgary.ca ___ Haskell mailing list hask...@haskell.org http://www.haskell.org/mailman/listinfo/haskell -- -- José Iborrahttp://www.dsic.upv.es/~jiborra -- UPV Valencia Telf. (+34) 96 387 00 00 (ext) 83529 -- Camino de Vera s/n. 46022 Valencia (Spain) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[4]: [Haskell-cafe] Using the ContT monads for early exits of IO ?
On 11 June 2010 14:40, Bulat Ziganshin bulat.zigans...@gmail.com wrote: if x then foo else if y then bar else if z then mu else zot case () of _ | x - foo | y - bar | otherwise - zor it's usually considered as haskell way of doing this The example is merely to demonstrate how optional layout can encode useful patterns, not to claim there aren't other ways to do it in Haskell. For what it's worth, this solution is pretty hackish and so not really Haskelly. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Encoding the encoding type of a string into its type
There are a lot of issues with string encoding type mismatches. Especially automatic conversions. This mailing list gets enough posts about encoding confusions. Would it make sense to make the string depend on its encoding type? E.g. a String UTF16 cannot be used with putStrLn :: String UTF8, it has to be used with putStrLn :: String UTF16. Provided the fundamental functions that read and write strings are type safe, there'll be no mix-ups? I'll think about this more later. Just putting the question out there so that I remember when I get home. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Encoding the encoding type of a string into its type
On Fri, Jun 11, 2010 at 04:17:25PM +0200, Christopher Done wrote: There are a lot of issues with string encoding type mismatches. Especially automatic conversions. This mailing list gets enough posts about encoding confusions. Would it make sense to make the string depend on its encoding type? I think our String type doesn't have semantic problems, a string really is a list of Unicode codepoints. However this representation has serious performance drawbacks. Now we have Data.Text, which should have better performance and maintain nice semantics. However it uses a single internal encoding for various reasons. So, if your input and your output are on the same coding X, where X isn't UTF-16 (IIRC), then you will have to do two reencodes, perhaps unnecessarily. So maybe annotating the encoding *could* be useful on some applications. But I can't imagine how hairy the implementation of such a generalised Data.Text would be, nor the performance impact if the dictionary isn't inlined/specialized for the case in hand. E.g. a String UTF16 cannot be used with putStrLn :: String UTF8, it has to be used with putStrLn :: String UTF16. Provided the fundamental functions that read and write strings are type safe, there'll be no mix-ups? Note that right now you don't need this extra burden to get the safety you want. Just use Data.Text everywhere. The problem isn't Data.Text but the Prelude IO functions using String where there should be [Word8]. Cheers, -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANNOUNCE: Sifflet visual programming language, release 0.1.7
On Fri, 11 Jun 2010, Ben Millwood wrote: On Fri, Jun 11, 2010 at 2:52 PM, Henning Thielemann lemm...@henning-thielemann.de wrote: I'm uncertain whether fgl conforms to the package versioning policy, but if it does, then changes in its Cabal file should not bother sifflet. Thus upper bound fgl 5.4.3 should be restrictive enough. The PVP says that one of the first two numbers are required to change if an API change is likely to break code using it, so 5.5 would probably suffice. A bump to fgl-5.4.3 might include API *extensions* that may break sifflet, if it imports entire FGL modules in an unqualified way. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Code review of text-xml-generic
Hi, I've been working on a (de)serialization package from/to XML (using SYB) and wondering if anyone feels like giving me a quick code review before I upload it to hackagedb. The source code can be found at http://github.com/finnsson/Text.XML.Generic It is *heavily* inspired by Text.JSON.Generic. The three files DataEx.hs (slightly modified version of Olegs code), ExGeneric.hs and ExTestGeneric.hs are not part of the package yet since I haven't got the deserialization to work for existentials yet (but I haven't given up!). I plan to upload the package to hackagedb by the end of this weekend so any comments before (and after) are more than welcome. -- Oscar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Using the ContT monads for early exits of IO ?
On Thu, 2010-06-10 at 21:21 +0100, Ben Millwood wrote: On Thu, Jun 10, 2010 at 8:57 PM, Maciej Piechotka uzytkown...@gmail.com wrote: Error monad seems not to be a semantic solution as we exit on success not failure. Which is really why the Either monad should not necessarily have Error associations :) If you forget about the fail method, the Monad (Either e) instance doesn't need the e to be an error type. Alternatively, if even Error is more information than you need, you could use MaybeT: http://hackage.haskell.org/package/MaybeT which allows you to just stop. Given you're using it with IO it'd be easy to write a result to an IORef before terminating the computation, so it's of equivalent power, if slightly less convenient. Over MaybeT I would prefer to simply iterate over list using helper recursive function. Either monad (without Error part) seems to be good solution - and it do not contain too much information. But the function with ContT IO seemed... nice. Also as it deals with network I/O speed does not seems to be a great issue. Regards signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with threading?
--- On Thu, 6/10/10, Louis Wasserman wasserman.lo...@gmail.com wrote: Date: Thursday, June 10, 2010, 1:32 AM Yeah, Control.Parallel would be nice to have. Heck, ideally I could get the whole Haskell Platform, which would be a reasonable comparison to the huge Java and C++ libraries accessible to those languages. And having the whole Haskell Platform still isn't enough to compile those regex-dna programs. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: GATD and pattern matching
Thanks all, it works fine (see below). I lamentably try to make the same for show: showTypeable :: (Typeable a) = a - String showTypeable x = case cast x of Just x' - show x' Nothing - Because it really upsets me to add this show constraints to the Equ constructor ;) what if i want to make an Obs instance with non showable elements, with no intention to show it of course? Corentin instance Typeable1 Obs where typeOf1 _ = mkTyConApp (mkTyCon Obs) [] (===) :: (Typeable a, Typeable b, Eq b) = a - b - Bool (===) x y = cast x == Just y data Obs a where Player :: Obs Player Official :: Obs Bool Equ :: (Eq a, Show a, Typeable a) = Obs a - Obs a - Obs Bool Plus :: (Num a) = Obs a - Obs a - Obs a Time :: (Num a) = Obs a - Obs a - Obs a Minus:: (Num a) = Obs a - Obs a - Obs a And :: Obs Bool - Obs Bool - Obs Bool Or :: Obs Bool - Obs Bool - Obs Bool Not :: Obs Bool - Obs Bool Konst:: (Show a, Eq a) = a - Obs a instance Show t = Show (Obs t) where show Player = Player show Official= Official show (Equ a b) = (show a) ++ Eq ++ (show b) show (Plus a b) = (show a) ++ Plus ++ (show b) show (Minus a b) = (show a) ++ Minus ++ (show b) show (Time a b) = (show a) ++ Time ++ (show b) show (Konst a) = (Konst ++ (show a) ++ ) show (And a b) = (show a) ++ And ++ (show b) show (Or a b)= (show a) ++ Or ++ (show b) show (Not a) = (Not ++ (show a) ++ ) instance Eq t = Eq (Obs t) where Player == Player = True Official == Official = True Equ a b == Equ c d = (a,b) === (c,d) Plus a b == Plus c d = (a == c) (b == d) Minus a b == Minus c d = (a == c) (b == d) Time a b == Time c d = (a == c) (b == d) And a b == And c d = (a == c) (b == d) Or a b == Or c d = (a == c) (b == d) Not a == Not b = (a == b) Konst a == Konst b = a == b _ == _ = False ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: GATD and pattern matching
On Sat, Jun 12, 2010 at 12:13:14AM +0200, Dupont Corentin wrote: Thanks all, it works fine (see below). I lamentably try to make the same for show: showTypeable :: (Typeable a) = a - String showTypeable x = case cast x of Just x' - show x' Nothing - Because it really upsets me to add this show constraints to the Equ constructor ;) what if i want to make an Obs instance with non showable elements, with no intention to show it of course? Ad hoc solution: class MaybeShow a where maybeShow :: a - Maybe String instance Show a = MaybeShow a where maybeShow = Just . show instance MaybeShow a where maybeShow = Nothing data MyData where Something :: MaybeShow a = a - MyData instance MaybeShow MyData where maybeShow (Something x) = fmap (\s - Something ( ++ s ++ )) (maybeShow x) Hahahaha :). Try to guess without using GHC/GHCi: 1) Which extensions are required to make the code compile. 2) After compiled, if it works as intended or not. Cheers, -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GATD and pattern matching
On Friday, June 11, 2010, Felipe Lessa felipe.le...@gmail.com wrote: On Sat, Jun 12, 2010 at 12:13:14AM +0200, Dupont Corentin wrote: Thanks all, it works fine (see below). I lamentably try to make the same for show: showTypeable :: (Typeable a) = a - String showTypeable x = case cast x of Just x' - show x' Nothing - Because it really upsets me to add this show constraints to the Equ constructor ;) what if i want to make an Obs instance with non showable elements, with no intention to show it of course? Ad hoc solution: class MaybeShow a where maybeShow :: a - Maybe String instance Show a = MaybeShow a where maybeShow = Just . show instance MaybeShow a where maybeShow = Nothing data MyData where Something :: MaybeShow a = a - MyData instance MaybeShow MyData where maybeShow (Something x) = fmap (\s - Something ( ++ s ++ )) (maybeShow x) Hahahaha :). Try to guess without using GHC/GHCi: 1) Which extensions are required to make the code compile. OverlappingInstances (of course), and IncoherrentInstances, since neither instance is more specific than the other. 2) After compiled, if it works as intended or not. It's hard for me to concieve of a situation where something requiring IncoherrentInstances is work as intended, but maybe that's a failure of imagtination. -Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GATD and pattern matching
On Fri, Jun 11, 2010 at 08:12:43PM -0500, Antoine Latter wrote: 1) Which extensions are required to make the code compile. OverlappingInstances (of course), and IncoherrentInstances, since neither instance is more specific than the other. Well, I guess it can't be compiled at all :( $ ghci -XGADTs -XOverlappingInstances -XIncoherentInstances -XFlexibleInstances -XUndecidableInstances GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude :l T [1 of 1] Compiling Main ( T.lhs, interpreted ) T.lhs:4:12: Duplicate instance declarations: instance [incoherent] (Show a) = MaybeShow a -- Defined at T.lhs:4:12-32 instance [incoherent] MaybeShow a -- Defined at T.lhs:7:12-22 2) After compiled, if it works as intended or not. It's hard for me to concieve of a situation where something requiring IncoherrentInstances is work as intended, but maybe that's a failure of imagtination. Perhaps we should omit the Nothing instance: class MaybeShow a where maybeShow :: a - Maybe String instance Show a = MaybeShow a where maybeShow = Just . show Instances for any non-Show-able data types should be manually written, such as: instance MaybeShow (a - b) where maybeShow = const Nothing I think this solution still requires OverlappingInstances and UndecidableInstances. Finally we could omit the Show a = MaybeShow a definition as well and just manually write everything: class MaybeShow a where may_I_show_you :: a - Maybe String yes_please :: Show a = a - Maybe String yes_please = Just . show no_thanks :: a - Maybe String no_thanks = const Nothing instance MaybeShow () where may_I_show_you = yes_please instance MaybeShow Char where may_I_show_you = yes_please instance MaybeShow Int where may_I_show_you = yes_please instance MaybeShow (a - b) where may_I_show_you = no_thanks instance MaybeShow (IO a) where may_I_show_you = no_thanks ... -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with threading?
--- On Wed, 6/9/10, Don Stewart d...@galois.com wrote: -snip- Now how do we get those regex-dna and binary-trees programs to compile? http://shootout.alioth.debian.org/u32/measurements.php?lang=ghc binary-trees: Could not find module `Control.Parallel.Strategies': -- cabal install parallel regex-dna: cannot satisfy -package regex-posix -- cabal install regex-posix parallel, regex-posix, regex-pcre are now installed and the current compile errors are caused by the programs not the absence of required libraries - http://shootout.alioth.debian.org/u64q/program.php?test=binarytreeslang=ghcid=2#log http://shootout.alioth.debian.org/u64q/program.php?test=binarytreeslang=ghcid=3#log http://shootout.alioth.debian.org/u64q/program.php?test=regexdnalang=ghcid=4#log http://shootout.alioth.debian.org/u64q/program.php?test=regexdnalang=ghcid=1#log ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with threading?
igouy2: parallel, regex-posix, regex-pcre are now installed and the current compile errors are caused by the programs not the absence of required libraries - http://shootout.alioth.debian.org/u64q/program.php?test=binarytreeslang=ghcid=2#log http://shootout.alioth.debian.org/u64q/program.php?test=binarytreeslang=ghcid=3#log http://shootout.alioth.debian.org/u64q/program.php?test=regexdnalang=ghcid=4#log http://shootout.alioth.debian.org/u64q/program.php?test=regexdnalang=ghcid=1#log Great work! For those keen to help out the Haskell programs, both compile failures in regexdna and binarytrees are related to the change in how parallel strategies work, as described here. http://hackage.haskell.org/packages/archive/parallel/2.2.0.1/doc/html/Control-Parallel-Strategies.html -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
