Re: [Haskell-cafe] Wikipedia article
Simon Marlow marlo...@gmail.com writes: There's no need to do any page moving or anything; the new version can just be pasted in. Ok, done! http://en.wikipedia.org/wiki/Haskell_%28programming_language%29 After conferring briefly with people on IRC (yeah, on a Saturday morning, who am I kidding?), I moved the talk page to an archive, and started a new one. (The archive is linked from the new talk page.) Most of the discussion seemed to be quite outdated, many of the issues had been addressed, and since we got a new structure on the main page, it seemed like a good idea to stow the old stuff and start afresh. But it was a long page, so if you had a cause you feel needs more arguing, please copy back from the old page or, perhaps better, restate your issues on the new one. Okay? -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] What is the rank of a polymorphic type?
Hello. Consider the type: (forall a . a) - String. On one hand, it is rank-2 polymorphic, because it abstracts over a rank-1 polymorphic type. On the other hand, it is monomorphic because it isn't actually quantified itself: in my intuitive view, a parametrically polymorphic type has infinitely many instantiations (for example, Int - Int is an instantiation of forall a . a - a, and String - String also is), and this type doesn't have any instantiations at all. Which is correct? Is there really a contradiction? What is the definition of rank of a polymorphic type? -- Eugene Kirpichov Web IR developer, market.yandex.ru ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia article
2009/12/4 Simon Marlow marlo...@gmail.com: As noted before, the Wikipedia article for Haskell is a disorganised mess. http://en.wikipedia.org/wiki/Haskell_%28programming_language%29 earlier this year, dons suggested reorganising it and posted a template on the Haskell wiki: http://haskell.org/haskellwiki/WikipediaArticleDesign I've made a start on a new version of the page: http://en.wikipedia.org/wiki/User:Simonmar/Haskell_%28programming_language%29 I've kept most of the existing information, but reorganised it more or less according to Don's template, and I filled out the overview section. Also I fixed numerous things, but the page still has a long way to go Does anyone mind if I spam the existing Haskell article with this new one, or do people think we should continue editing the sandbox version until it's in better shape? Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Could someone please do something about the horrible syntax highlighting for strings in the Wikipedia article? Black on dark green, really? -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: From function over expression (+, *) derive function over expression (+)
Radek Micek wrote: Hi, thank you for your reply but your MulExpr does not support expressions like (2*3)+5 Oh! You're right, how silly of me. Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] SYB looping very, very mysteriously
On Fri, Dec 4, 2009 at 8:51 PM, Jeremy Shaw jer...@n-heptane.com wrote:
I have stripped things down to the bare minimum, and test under GHC 6.10,
GHC 6.12, Linux, and Mac OS X. Results are consistent.
In the following code,
1. if you load the code into ghci and evaluate e it will hang, but
(defaultValueD dict) :: Expression returns fine
2. if you change the gunfold instance for Proposition to, error gunfold
it stops hanging -- even though this code is never called.
3. if you change, ( Data ctx [Expression], Sat (ctx Expression) = Data ctx
Expression, to (Data ctx Expression, ) = ... it stops hanging.
If someone could explain why each of these cases perform as they do, that
would be awesome! Right now it is a big mystery to me.. e calls dict .. and
there is only one instance of dict available, which should call error right
away. I can't see how something could get in the way there...
It's less of a mystery if you think about the actual dictionaries ghc
uses to implement typeclasses.
The instance for Data ctx [a] depends on Data ctx a, so by requiring
Data ctx [Expression] in the Data ctx Expression instance you're
indeed making a loop there, though typeclasses do allow this, and the
implementation has to be lazy enough to permit it.
Strange that with a direct Data ctx Expression = Data ctx Expression
loop we don't get the same problem.
The reason the implementation of Proposition's gunfold matters is
probably that k gets passed the dictionary for Data DefaultD
Expression at the site of its call and some optimization is making it
stricter than necessary.
Looks like we need a ghc dev here to fully unravel the mystery, in the
meantime i'll try to reduce the test case even further.
- jeremy
{-# LANGUAGE DeriveDataTypeable, FlexibleContexts, FlexibleInstances,
MultiParamTypeClasses, UndecidableInstances, RankNTypes,
ScopedTypeVariables, KindSignatures, EmptyDataDecls,
NoMonomorphismRestriction #-}
module Main where
import qualified Data.Data as Data
import Data.Typeable
--- syb-with-class
data Constr = Constr deriving (Eq, Show)
data Proxy (a :: * - *)
class Sat a where
dict :: a
class (Typeable a, Sat (ctx a)) = Data ctx a where
gunfold :: Proxy ctx
- (forall b r. Data ctx b = c (b - r) - c r)
- (forall r. r - c r)
- Constr
- c a
instance (Sat (ctx [a]),Data ctx a) = Data ctx [a]
--- Default
class (Data DefaultD a) = Default a where
defaultValue :: a
data DefaultD a = DefaultD { defaultValueD :: a }
instance Default t = Sat (DefaultD t) where
dict = error Sat (DefaultD t) not implemented
instance Default a = Default [a] where
defaultValue = error Default [a] not implemented
--- Trouble
data Proposition = Proposition Expression deriving (Show, Data.Data,
Typeable)
data Expression = Conjunction Expression deriving (Show, Data.Data,
Typeable)
-- instance (Sat (ctx [Expression]), Sat (ctx Expression), Sat (ctx
Proposition)) = Data ctx Proposition where
instance Data DefaultD Proposition where
gunfold _ k z c = k (z Proposition)
-- gunfold _ k z c = error gunfold
instance Default Proposition
-- Change Data ctx [Expression] to Data ctx Expression and main works.
instance ( Data ctx [Expression]
, Sat (ctx Expression)
) = Data ctx Expression
instance Default Expression
e :: Expression
e = defaultValueD (dict :: DefaultD Expression)
main = print e
___
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] What is the rank of a polymorphic type?
Eugene Kirpichov wrote: Hello. Consider the type: (forall a . a) - String. On one hand, it is rank-2 polymorphic, because it abstracts over a rank-1 polymorphic type. On the other hand, it is monomorphic because it isn't actually quantified itself: in my intuitive view, a parametrically polymorphic type has infinitely many instantiations (for example, Int - Int is an instantiation of forall a . a - a, and String - String also is), and this type doesn't have any instantiations at all. Which is correct? Is there really a contradiction? What is the definition of rank of a polymorphic type? There's a nice paper about this: Simon Peyton Jones, Dimitrios Vytiniotis, Stephanie Weirich and Mark Shields Practical type inference for arbitrary-rank types http://research.microsoft.com/en-us/um/people/simonpj/papers/higher-rank/putting.pdf Section 3.1 of that paper defines what rank types have: The rank of a type describes the depth at which universal quantifiers appear contravariantly Looking at the examples that are then given I'd say your example has rank 2 (but I'm no expert). It only mentions the depth of the forall, not whether it has any instantiations. HTH, Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Do you need Windows USB in Haskell?
Hi, I keep this direct binding to libusb-1.0.x: http://hackage.haskell.org/package/bindings-libusb on top of which Bas maintains a nice USB library: http://hackage.haskell.org/package/usb Work has been done to support libusb-1.0.x in Windows. So, as long as my bindings-libusb works properly with that, Bas' as well as any other library based on it will work too. Problem is: I don't have a Windows machine where I could test this. So, if you need USB in windows, please keep in touch. I wouldn't ask you to write any code, but I need to know what builds and what doesn't. Best, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: hakyll-0.1
Hello all, Hakyll is a simple static site generator library, mostly aimed at blogs. It supports markdown, tex and html templates. It is inspired by the ruby Jekyll program. It has a very small codebase because it makes extensive use of the excellent pandoc and Text.Template libraries. More information can be found on: http://hackage.haskell.org/package/hakyll-0.1 http://github.com/jaspervdj/Hakyll Kind regards, Jasper Van der Jeugt ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia article
On Sat, Dec 5, 2009 at 4:53 AM, Deniz Dogan deniz.a.m.do...@gmail.com wrote: 2009/12/4 Simon Marlow marlo...@gmail.com: As noted before, the Wikipedia article for Haskell is a disorganised mess. http://en.wikipedia.org/wiki/Haskell_%28programming_language%29 earlier this year, dons suggested reorganising it and posted a template on the Haskell wiki: http://haskell.org/haskellwiki/WikipediaArticleDesign I've made a start on a new version of the page: http://en.wikipedia.org/wiki/User:Simonmar/Haskell_%28programming_language%29 I've kept most of the existing information, but reorganised it more or less according to Don's template, and I filled out the overview section. Also I fixed numerous things, but the page still has a long way to go Does anyone mind if I spam the existing Haskell article with this new one, or do people think we should continue editing the sandbox version until it's in better shape? Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Could someone please do something about the horrible syntax highlighting for strings in the Wikipedia article? Black on dark green, really? Syntax highlighting on En for Haskell snippets is done, I believe, through GeSHi: http://www.mediawiki.org/wiki/Extension:SyntaxHighlight_GeSHi So complain to them? -- gwern ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the rank of a polymorphic type?
Eugene, Consider the type: (forall a . a) - String. It's of rank 2. What is the definition of rank of a polymorphic type? The minimal rank of a type is given by rank (forall a. t) = 1 `max` rank t rank (t - u) = (if rank t == 0 then 0 else rank t + 1) `max` rank u rank _ = 0 HTH, Stefan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Finding HP
Malcolm Wallace wrote: The suggestion was to have a single Download button, leading to a *page* of suitably described links, allowing the user to choose whether they only wanted the basics (a choice of compiler/interpreter + cabal), or the whole Platform, or something else. It would be the ideal place to explain what cabal is and how to use hackage to get more libraries than are contained in the platform. It would perhaps reduce the clutter on the front page that some people complained of (although I don't personally think it cluttered). It seems I'm contraversial even when I'm trying to be uncontraversial. :-} Anyway, the above suggestion sounds most optimal to me. Haskell tends to suffer from a frustrating degree of information dragmentation (I love whoever came up with that term...), and collecting a bunch of information in one place like this sounds very useful. I guess in a way, the current implementations page could become this page (or this new page makes the existing implementations page obsolete...) I also think it might be worth mentioning HP from the GHC homepage, just in case anybody has that bookmarked directly... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HP + Gtk2hs?
So I decided to try out the Haskell Platform instead of just installing GHC directly. To be honest, I didn't really notice much difference, except for the files being installed in a different place. But then, initially HP ~= GHC; presumably the plan is for it to grow as time goes on. Anyway, I'm sure you can all see where I'm going with this: Latest Gtk2hs binary for Windows doesn't seem to like the latest HP installation. A few things: - It is unclear to be which Gtk2hs binaries require which GHC version. Can we tabulate this information somewhere? - It is also unclear to me which HP versions contain what stuff. The HP page tells you all about the *current* HP version, and contains a link to a raw directory listing for the older versions. (I especially love the way the server truncates the filenames to just before where the version number starts. Very helpful. :-D ) Can we get propper descriptions for _all_ releases of HP? A table summarising the GHC version and major packages/versions in each release would be nice. - Any idea why the HP says beta on it? - Apart from HP providing GHC 6.10.4 while Gtk2hs currently requires 6.10.3, it appears that the Gtk2hs installer package doesn't like GHC being installed in a path with spaces. Apparently Gtk2hs has a bug tracker. (I only just discovered this, so perhaps it needs to be more prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. (I emphasize visible. Maybe they've seen this and they're working on it, but there's no visible indication of activity.) Gtk2hs is currently the *only* GUI binding that actually works on Windows. It's always been slightly frustrating that every time a new version of GHC comes out, us Windows users have to beg for somebody to build a new binary. (Linux users, on the other hand, can just download the sources and compile them with any compiler they like.) Presumably going forward Gtk2hs will synchronise to the (less frequent) HP releases rather than the individual GHC releases, so many this particular frustration will be reduced. (It would be even less frustrating if Gtk2hs was *in* HP, but I gather this won't ever happen.) Of course, being able to actually build C bindings on Windows would be even better, but this is apparently infeasible... :-( That being the case, I'll settle for just a little bit more documentation. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell-Newbie and Char-Function
Hi guys, I only started learning Haskell some days ago. Maybe one of you can give me a hint on how to implement a function that needs a character in the range (a,b,...z) and an integer number k and returns the k-next neighbor of the character? For example, fct a 5 would result in output f. Tobias -- View this message in context: http://old.nabble.com/Haskell-Newbie-and-Char-Function-tp26656676p26656676.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] Low Level Audio - Writing bytes to the sound card?
M Xyz wrote: if you get it to work As a spoiled Java programmer, this new role as pioneer is a bit intimidating, but I will give it a shot. :) I wish there was a multimedia standard library for beginners like me. Writing audio to the speakers shouldn't be such a journey. Unfortunately, I've yet to find a single Haskell package that binds to C which will actually compile on Windows. :-( (It still makes me chuckle that even the COM bindings - which, by definition, can *only* work on Windows - also don't compile. One wonders how the author managed to test it...) Fortunately, for GUI work we have Gtk2hs, which works just fine on Windows. (Although obviously, Windows boxes don't usually have GTK+ installed.) But most of the really interesting stuff on Hackage is just unusable on Windows, sadly. If you ever do manage to get audio working, I'd be interested to know how. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell-Newbie and Char-Function
MeAdAstra wrote: Hi guys, I only started learning Haskell some days ago. Maybe one of you can give me a hint on how to implement a function that needs a character in the range (a,b,...z) and an integer number k and returns the k-next neighbor of the character? For example, fct a 5 would result in output f. You might want to use the functions ord and chr from Data.Char, and the mod function from the Prelude. Regards, Jochem -- Jochem Berndsen | joc...@functor.nl | joc...@牛在田里.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
Careful Gregory, you've hit a hot-button issue: you have dared to refer to exceptions as errors! For the record, I find this pedanticism misplaced, as the line between the two is rather blurry. Nonetheless, for control-monad-failure and attempt, we purposely refer to the whole slew of things not succeeding as failures. Not to be confused with public enemy number 2 of Haskell users: the fail function. /tongue-in-cheek Michael On Fri, Dec 4, 2009 at 5:57 PM, Henning Thielemann lemm...@henning-thielemann.de wrote: Gregory Crosswhite schrieb: When I uploaded my new package, error-message, I also went ahead and created a new category: Error Handling. Error handling is the same as debugging for you? I hope it is not intended for generating further confusion about exception handling and debugging (= help programmers to analyse errors). ___ 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] HP + Gtk2hs?
Hello Andrew, Saturday, December 5, 2009, 6:40:23 PM, you wrote: prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. Developer. many Haskell problems is due to the fact that we have a few volunteers doing things and lot of consumers begging for features :) Gtk2hs is currently the *only* GUI binding that actually works on Windows. i thought that wx and even qt are in rather good shape now -- 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] Re: Binding to C in Windows (was: Low Level Audio - Writing bytes to the sound card?)
Unfortunately, I've yet to find a single Haskell package that binds to C which will actually compile on Windows. :-( Do you know how can we check dependencies to C libraries in Windows? Is pkg-config available? What about packages with no pkg-config configuration? Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Hello Andrew Plenty compile on Windows: Some OpenVG, OpenGL[1] (still? - I'm a bit behind the times) only compile with MinGW. Others are fine with Cygwin provided you have the dev packages installed (readline, pcre-light...). Yet others - no chance... If you can get the raw C library to work in either Cygwin or MinGW, you should have a good chance. The only sound software I've had working on Cygwin has been ChucK though I haven't tried many - ChucK uses RtAudio to talk to the soundcard which probably isn't easy to write a binding for as its C++. I had ChucK working two years ago, maybe things have improved in the Cygwin world regarding sound since then and other systems now work. http://www.music.mcgill.ca/~gary/rtaudio/ Best wishes Stephen [1] OpenGL worked fine when it was bundled with GHC, when it got unbundled things seemed to go amiss, plus it seemed to be the thing to use freeglut - hence the complicated instructions here: http://netsuperbrain.com/blog/posts/freeglut-windows-hopengl-hglut/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
On Sat, Dec 05, 2009 at 05:52:11PM +0200, Michael Snoyman wrote: For the record, I find this pedanticism misplaced, ... I think you'll find that's pedantry. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
On Sat, Dec 5, 2009 at 7:41 PM, Ross Paterson r...@soi.city.ac.uk wrote: On Sat, Dec 05, 2009 at 05:52:11PM +0200, Michael Snoyman wrote: For the record, I find this pedanticism misplaced, ... I think you'll find that's pedantry. Hoped someone would comment exactly that ;). ___ 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
[Haskell-cafe] Avoiding undecidables
Hi all, Well, I've got two problems which both want to be solved with undecidable and overlapping instances. Obviously, I'd like to try and avoid them. For the record, the problems have to do with the control-monad-failure and convertible packages. The code below *should* make clear what I'm trying to accomplish: -- failure should not be limited to just monads, so... class Failure e f where failure :: e - f v class (Functor f, Failure e f) = FunctorFailure e f instance (Functor f, Failure e f) = FunctorFailure e f -- undecidable, overlaps class (Applicative f, Failure e f) = ApplicativeFailure e f instance (Applicative f, Failure e f) = ApplicativeFailure e f -- undecidable, overlaps class (Monad f, Failure e f) = MonadFailure e f instance (Monad f, Failure e f) = MonadFailure e f -- undecidable, overlaps And now the convertible issue. I want two type classes: Convert for anything which *might* be convertible, but might not. For example, sometimes a String can be converted to an Int (like the string 5), but sometimes it will fail (like five). TotalConvert is when something *is* convertible, such as Int to String (simply the show function). Thus the following: class Convert x y where convert :: x - Maybe y class Convert x y = TotalConvert x y where totalConvert :: x - y instance TotalConvert x y = Convert x y where -- Boom! convert = Just . totalConvert Any ideas are most welcome. Both of these seem like cases where the compiler could do some DWIMery, but isn't. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HP + Gtk2hs?
- Apart from HP providing GHC 6.10.4 while Gtk2hs currently requires 6.10.3, it appears that the Gtk2hs installer package doesn't like GHC being installed in a path with spaces. Apparently Gtk2hs has a bug tracker. (I only just discovered this, so perhaps it needs to be more prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. (I emphasize visible. Maybe they've seen this and they're working on it, but there's no visible indication of activity.) Thank you so much for this post. I tried to install Gtk2hs yesterday to play with its Cairo bindings and I hit the Setup found what appears to be a non-working installation of GHC brickwall. I found a closed ticket about this problem: http://hackage.haskell.org/trac/gtk2hs/ticket/1117 I posted this issue on the Gtk2hs-devel mailing list and got a response today: http://sourceforge.net/mailarchive/forum.php?thread_name=EF0EE62B-259C-4F62-9BF2-65FA1F01949E%40di.ens.frforum_name=gtk2hs-devel I don't think I have the will to uninstall the Haskell Platform and everything I've set up just to install in a path with no spaces. :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: readline-statevar-1.0.1.0
Hello I am happy to announce a release of small package called readline-statevar. It's a small wrapping library around readline, which in turn wraps libreadline. The reason I wrote it is because I wasn't happy with the API of readline. It was composed of tons of functions like setX/getX, where there could be just one StateVar instead, yielding OpenGL-kind API. This version aims to match readline-1.0.1.0. (Hence the version number chosen). I wrote it mostly manually, with a little help from my emacs-fu, so there is a chance I missed a thing or two. There is git repo available [1], along with issue tracker [2] and Hackage page [3]. Feel encouraged to: cabal update cabal install readline-statevar And give it a try! Best regards Krzysztof Skrzętnicki [1] http://github.com/Tener/haskell-readline-statevar/ [2] http://github.com/Tener/haskell-readline-statevar/issues [3] http://hackage.haskell.org/package/readline-statevar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HP + Gtk2hs?
M Xyz wrote: - Apart from HP providing GHC 6.10.4 while Gtk2hs currently requires 6.10.3, it appears that the Gtk2hs installer package doesn't like GHC being installed in a path with spaces. Apparently Gtk2hs has a bug tracker. (I only just discovered this, so perhaps it needs to be more prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. (I emphasize visible. Maybe they've seen this and they're working on it, but there's no visible indication of activity.) Thank you so much for this post. I tried to install Gtk2hs yesterday to play with its Cairo bindings and I hit the Setup found what appears to be a non-working installation of GHC brickwall. I found a closed ticket about this problem: http://hackage.haskell.org/trac/gtk2hs/ticket/1117 I posted this issue on the Gtk2hs-devel mailing list and got a response today: http://sourceforge.net/mailarchive/forum.php?thread_name=EF0EE62B-259C-4F62-9BF2-65FA1F01949E%40di.ens.frforum_name=gtk2hs-devel I don't think I have the will to uninstall the Haskell Platform and everything I've set up just to install in a path with no spaces. :) My information is from here: http://hackage.haskell.org/trac/gtk2hs/ticket/1165 In case it makes any difference to you. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HP + Gtk2hs?
Bulat Ziganshin wrote: Hello Andrew, Saturday, December 5, 2009, 6:40:23 PM, you wrote: prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. Developer. many Haskell problems is due to the fact that we have a few volunteers doing things and lot of consumers begging for features :) That *does* in fact seem to be a recurring problem, yes. Now, how to fix this...? Gtk2hs is currently the *only* GUI binding that actually works on Windows. i thought that wx and even qt are in rather good shape now I did try to get wxHaskell going once or twice. And the SDL binding. (I wasn't aware we have Qt now...) I've never got any of them to work yet. :-( Interestingly, while you can't compile bindings to external C libraries, GHC does appear to ship with all the header files for Windows, which is odd. It seems if you try to FFI to a standard Win32 function, it magically knows where the hell the header files are, and it Just Works(tm). Hell, I even followed a C++ guide to Win32 programming and managed to translate an open a blank window program to Haskell, and it worked. Maybe somebody just needs to sit down and write a nice binding for doing native GUI stuff under Win32? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Andrew Coppin wrote: Unfortunately, I've yet to find a single Haskell package that binds to C which will actually compile on Windows. :-( Take a look at logfloat[1], it builds cleanly on Windows XP using GHC 6.10.1 without needing Cygwin nor Mingw/Msys (however GHCi has some DLL errors[2]). Not that that has anything to do with audio ;) [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/logfloat [2] If you know how to resolve these, I'd be much obliged. I don't have a Windows machine to test on but I've been much irked that there's still this outstanding portability bug. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] HP + Gtk2hs?
Hello Andrew, Saturday, December 5, 2009, 10:14:17 PM, you wrote: I did try to get wxHaskell going once or twice. And the SDL binding. (I wasn't aware we have Qt now...) I've never got any of them to work yet. it depends on when you have tried. wx made significant progress in last year or two -- 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] HP + Gtk2hs?
Am Samstag 05 Dezember 2009 20:14:17 schrieb Andrew Coppin: Bulat Ziganshin wrote: Hello Andrew, Saturday, December 5, 2009, 6:40:23 PM, you wrote: prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. Developer. many Haskell problems is due to the fact that we have a few volunteers doing things and lot of consumers begging for features :) That *does* in fact seem to be a recurring problem, yes. Now, how to fix this...? How about: get the sources, try proposed fix, if it works, send Duncan(*) the patch? Even better, become a gtk2hs developer yourself (though that's more work and probably requires some serious knowledge of gtk). (*) for gtk2hs, would be somebody else for other packages of course. Gtk2hs is currently the *only* GUI binding that actually works on Windows. i thought that wx and even qt are in rather good shape now I did try to get wxHaskell going once or twice. And the SDL binding. (I wasn't aware we have Qt now...) I've never got any of them to work yet. :-( Interestingly, while you can't compile bindings to external C libraries, GHC does appear to ship with all the header files for Windows, which is odd. It seems if you try to FFI to a standard Win32 function, it magically knows where the hell the header files are, and it Just Works(tm). Hell, I even followed a C++ guide to Win32 programming and managed to translate an open a blank window program to Haskell, and it worked. Maybe somebody just needs to sit down and write a nice binding for doing native GUI stuff under Win32? Maybe you could try to be that somebody? I'm sure the Windows folks would appreciate it very much. Or, if you think that's beyond your ken, try organising the writing. Perhaps create a windows-haskell mailing list where Windows users can help each other making things work on Windows. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell-Newbie and Char-Function
On Sat, Dec 5, 2009 at 4:48 PM, Jochem Berndsen joc...@functor.nl wrote: MeAdAstra wrote: Hi guys, I only started learning Haskell some days ago. Maybe one of you can give me a hint on how to implement a function that needs a character in the range (a,b,...z) and an integer number k and returns the k-next neighbor of the character? For example, fct a 5 would result in output f. You might want to use the functions ord and chr from Data.Char, and the mod function from the Prelude. Right, and by the way I would suggest you reverse the parameter order of your function so that it takes the shift first, then you can write : shift :: Int - Char - Char shift n c ... rot13 :: String - String rot13 = map (shift 13) -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HP + Gtk2hs?
2009/12/5 Andrew Coppin andrewcop...@btinternet.com: Interestingly, while you can't compile bindings to external C libraries, Ah Mr Coppin, maybe you should change you to I. I had (Haskell bindings) SDL-0.5.3 working August last year - so I think I would be using GHC 6.8.3 at that time, the version of the SDL C library was 1.2.13. SDL has no prepared package in the Cygwin package manager, so you have to download it yourself. I seem to remember it being more tricky to get SDL working under Cygwin as a C library (you need extra DirectX header files at least), than it was to compile the Haskell binding once the C library was working. Instructions for compiling the C library for Cygwin are on the SDL website. I haven't tried it since as I don't need SDL for anything I do, but don't I think it would be any harder (lemmih's binding seems to be pretty stable and at the time I used it, it was impressively tidy). Best wishes again Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HP + Gtk2hs?
Daniel Fischer wrote: Am Samstag 05 Dezember 2009 20:14:17 schrieb Andrew Coppin: Bulat Ziganshin wrote: Developer. many Haskell problems is due to the fact that we have a few volunteers doing things and lot of consumers begging for features :) That *does* in fact seem to be a recurring problem, yes. Now, how to fix this...? How about: get the sources, try proposed fix, if it works, send Duncan(*) the patch? Even better, become a gtk2hs developer yourself (though that's more work and probably requires some serious knowledge of gtk). In order to do this, I'd have to know how to build Gtk2hs from source on Windows. I imagine this is quite nontrivial. Interestingly, while you can't compile bindings to external C libraries, GHC does appear to ship with all the header files for Windows, which is odd. It seems if you try to FFI to a standard Win32 function, it magically knows where the hell the header files are, and it Just Works(tm). Hell, I even followed a C++ guide to Win32 programming and managed to translate an open a blank window program to Haskell, and it worked. Maybe somebody just needs to sit down and write a nice binding for doing native GUI stuff under Win32? Maybe you could try to be that somebody? I'm sure the Windows folks would appreciate it very much The thought has certainly crossed my mind. If I could write such a package, I imagine a lot of people would find it seriously useful. Native Windows GUI programs, without any 3rd party DLLs to distribute with your compiled binary... It'd be great, wouldn't it? Of course, thinking about how great it would be doesn't get the code written. ;-) I'd have to learn how to call Win32 from C first, for a start... o_O The various I/O libraries sometimes return weird results, and I'm told this is because GHC is using the emulated POSIX interfaces rather than native Win32 calls. I did think about turning my attention to fixing that. However, I notice the next version of GHC seems to have a radically reworked set of I/O libraries, so maybe it's already fixed? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Stephen Tetley wrote: Hello Andrew Plenty compile on Windows: Some OpenVG, OpenGL[1] (still? - I'm a bit behind the times) only compile with MinGW. Others are fine with Cygwin provided you have the dev packages installed (readline, pcre-light...). You're talking about MinGW and Cygwin. So... Unix emulators, basically. I don't think it should be necessary to install a Unix emulator just so that I can write Windows programs. Maybe others disagree. If you can get the raw C library to work in either Cygwin or MinGW, you should have a good chance. I'm by no means an expert here, but isn't it usual for C libraries on Windows to be supplied as a compiled DLL and a header file for using it? I don't quite understand why you need a C compiler. [1] OpenGL worked fine when it was bundled with GHC, when it got unbundled things seemed to go amiss. Apparently there is some talk of removing OpenGL from the Haskell Platform. And if this happens, it'll be one more thing I can't use on Windows. :-( Personally, I'd like to see *more* C bindings in HP, so that I can start doing cool stuff on Windows. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Avoiding undecidables
On Dec 5, 2009, at 6:58 PM, Michael Snoyman wrote: Hi all, Well, I've got two problems which both want to be solved with undecidable and overlapping instances. Obviously, I'd like to try and avoid them. For the record, the problems have to do with the control-monad-failure and convertible packages. The code below *should* make clear what I'm trying to accomplish: -- failure should not be limited to just monads, so... class Failure e f where failure :: e - f v class (Functor f, Failure e f) = FunctorFailure e f instance (Functor f, Failure e f) = FunctorFailure e f -- undecidable, overlaps class (Applicative f, Failure e f) = ApplicativeFailure e f instance (Applicative f, Failure e f) = ApplicativeFailure e f -- undecidable, overlaps class (Monad f, Failure e f) = MonadFailure e f instance (Monad f, Failure e f) = MonadFailure e f -- undecidable, overlaps (Functor|Monad|Applicative)Failure are little more than class synonyms, right ? Or equivalently, do you envision the need of writing, say, a MonadFailure instance for a type A which which works differently than the existing Failure instance for A? If the answer is no as I presume, then you don't want overlapping instances. Regarding undecidable instances, I will say that from my point of view they do not constitute a language extension. MPTCs are the language extension here. Since MPTCs can lead to non-terminating type checking, a compiler can either allow any use of them, employ a termination prover to ensure that only well-behaved instances are defined, or impose a set of restrictions that ensure termination. GHC does the latter, rather conservatively in some cases, and undecidable instances is just a compiler flag that puts the burden of termination checking on the user. In this case it is obvious that non-termination is not going to be a problem for the instances defined above. Since you have already decided MPTCs are ok, in my opinion undecidable instances are fine here. But I realize this is not the usual stance, so I might be wrong. And now the convertible issue. I want two type classes: Convert for anything which *might* be convertible, but might not. For example, sometimes a String can be converted to an Int (like the string 5), but sometimes it will fail (like five). TotalConvert is when something *is* convertible, such as Int to String (simply the show function). Thus the following: class Convert x y where convert :: x - Maybe y class Convert x y = TotalConvert x y where totalConvert :: x - y instance TotalConvert x y = Convert x y where -- Boom! convert = Just . totalConvert In this case Convert is not just a class synonym, so you are going to run into trouble with that code. I would do this as follows: class Convert x y = TotalConvert x y where totalConvert :: x - y totalConvert = fromJust . convert For instance, instance Convert Integer Double where convert = Just . fromIntegral instance TotalConvert Double-- that's all Cheers, pepe___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
I'm constantly amused by those who manage to use Windows without installing Cygwin. On 5 Dec 2009, at 23:33, Andrew Coppin wrote: Stephen Tetley wrote: Hello Andrew Plenty compile on Windows: Some OpenVG, OpenGL[1] (still? - I'm a bit behind the times) only compile with MinGW. Others are fine with Cygwin provided you have the dev packages installed (readline, pcre-light...). You're talking about MinGW and Cygwin. So... Unix emulators, basically. I don't think it should be necessary to install a Unix emulator just so that I can write Windows programs. Maybe others disagree. If you can get the raw C library to work in either Cygwin or MinGW, you should have a good chance. I'm by no means an expert here, but isn't it usual for C libraries on Windows to be supplied as a compiled DLL and a header file for using it? I don't quite understand why you need a C compiler. [1] OpenGL worked fine when it was bundled with GHC, when it got unbundled things seemed to go amiss. Apparently there is some talk of removing OpenGL from the Haskell Platform. And if this happens, it'll be one more thing I can't use on Windows. :-( Personally, I'd like to see *more* C bindings in HP, so that I can start doing cool stuff on Windows. ___ 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-Newbie and Char-Function
fct a n = (snd $ break (==a) ['a'..'z']) !! n Hi guys, I only started learning Haskell some days ago. Maybe one of you can give me a hint on how to implement a function that needs a character in the range (a,b,...z) and an integer number k and returns the k-next neighbor of the character? For example, fct a 5 would result in output f. Tobias ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Avoiding undecidables
On Sat, Dec 5, 2009 at 10:33 PM, José Iborra pepeibo...@gmail.com wrote: On Dec 5, 2009, at 6:58 PM, Michael Snoyman wrote: Hi all, Well, I've got two problems which both want to be solved with undecidable and overlapping instances. Obviously, I'd like to try and avoid them. For the record, the problems have to do with the control-monad-failure and convertible packages. The code below *should* make clear what I'm trying to accomplish: -- failure should not be limited to just monads, so... class Failure e f where failure :: e - f v class (Functor f, Failure e f) = FunctorFailure e f instance (Functor f, Failure e f) = FunctorFailure e f -- undecidable, overlaps class (Applicative f, Failure e f) = ApplicativeFailure e f instance (Applicative f, Failure e f) = ApplicativeFailure e f -- undecidable, overlaps class (Monad f, Failure e f) = MonadFailure e f instance (Monad f, Failure e f) = MonadFailure e f -- undecidable, overlaps (Functor|Monad|Applicative)Failure are little more than class synonyms, right ? Or equivalently, do you envision the need of writing, say, a MonadFailure instance for a type A which which works differently than the existing Failure instance for A? If the answer is no as I presume, then you don't want overlapping instances. Regarding undecidable instances, I will say that from my point of view they do not constitute a language extension. MPTCs are the language extension here. Since MPTCs can lead to non-terminating type checking, a compiler can either allow any use of them, employ a termination prover to ensure that only well-behaved instances are defined, or impose a set of restrictions that ensure termination. GHC does the latter, rather conservatively in some cases, and undecidable instances is just a compiler flag that puts the burden of termination checking on the user. In this case it is obvious that non-termination is not going to be a problem for the instances defined above. Since you have already decided MPTCs are ok, in my opinion undecidable instances are fine here. But I realize this is not the usual stance, so I might be wrong. Sounds reasonable to me. I'm waiting for the boogey man to jump out though and explain why undecidables here will get me gored to death by a raptor [1]. And now the convertible issue. I want two type classes: Convert for anything which *might* be convertible, but might not. For example, sometimes a String can be converted to an Int (like the string 5), but sometimes it will fail (like five). TotalConvert is when something *is* convertible, such as Int to String (simply the show function). Thus the following: class Convert x y where convert :: x - Maybe y class Convert x y = TotalConvert x y where totalConvert :: x - y instance TotalConvert x y = Convert x y where -- Boom! convert = Just . totalConvert In this case Convert is not just a class synonym, so you are going to run into trouble with that code. I would do this as follows: class Convert x y = TotalConvert x y where totalConvert :: x - y totalConvert = fromJust . convert For instance, instance Convert Integer Double where convert = Just . fromIntegral instance TotalConvert Double-- that's all Interestng approach. The current approach is *almost* the same, just leaves off the default definition. I'd be wary of putting in a definition like that; although it saves a line of typing, it let's a partial function get in which could cause trouble for unsuspecting users. But it is a possibility. Cheers, pepe [1] http://xkcd.com/292/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Hi Andrew 2009/12/5 Andrew Coppin andrewcop...@btinternet.com: I don't think it should be necessary to install a Unix emulator just so that I can write Windows programs. Maybe others disagree. ... I'm by no means an expert here, but isn't it usual for C libraries on Windows to be supplied as a compiled DLL and a header file for using it? I don't quite understand why you need a C compiler. The thing is, all the bindings on Hackage (or at least something most likely above 95%) are to Unix C libraries so you need a C compiler and a Unix emulator to use them. I do have have some sympathy with your point though - it is possible to get things to compile once you have Cygwin, but deployment on any other machine Windows thereafter is 'challenging' to say the least. Apparently there is some talk of removing OpenGL from the Haskell Platform. And if this happens, it'll be one more thing I can't use on Windows. :-( I didn't realise until I looked today that OpenGL was in the Haskell Platform. If the proposal to remove it is from Sven Panne then fair enough, otherwise it would be a bit disappointing - it always just worked when it was part of GHCs extralibs... Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the rank of a polymorphic type?
2009/12/5 Stefan Holdermans ste...@cs.uu.nl: Eugene, Consider the type: (forall a . a) - String. It's of rank 2. What is the definition of rank of a polymorphic type? The minimal rank of a type is given by rank (forall a. t) = 1 `max` rank t rank (t - u) = (if rank t == 0 then 0 else rank t + 1) `max` rank u rank _ = 0 Thanks! 1) Does there exist an authoritative source saying the same? Not that I'm doubting, just supposing that the source would have other interesting information, too :) 2) Is it true that rank (forall a . a, forall a . a) == 0 ? HTH, Stefan -- Eugene Kirpichov Web IR developer, market.yandex.ru ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Miguel Mitrofanov wrote: I'm constantly amused by those who manage to use Windows without installing Cygwin. I'm constantly puzzled by those who think that Cygwin is a mandatory part of Windows. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HP + Gtk2hs?
Am Samstag 05 Dezember 2009 21:31:39 schrieb Andrew Coppin: Daniel Fischer wrote: Am Samstag 05 Dezember 2009 20:14:17 schrieb Andrew Coppin: Bulat Ziganshin wrote: Developer. many Haskell problems is due to the fact that we have a few volunteers doing things and lot of consumers begging for features :) That *does* in fact seem to be a recurring problem, yes. Now, how to fix this...? How about: get the sources, try proposed fix, if it works, send Duncan(*) the patch? Even better, become a gtk2hs developer yourself (though that's more work and probably requires some serious knowledge of gtk). In order to do this, I'd have to know how to build Gtk2hs from source on Windows. I imagine this is quite nontrivial. I thought in this case, it was a proposed change in the installer, so you'd only have to change that and could leave the gtk2hs binary untouched. Of course that can only work if Windows installers are some sort of script or otherwise customisable. Are they? Interestingly, while you can't compile bindings to external C libraries, GHC does appear to ship with all the header files for Windows, which is odd. It seems if you try to FFI to a standard Win32 function, it magically knows where the hell the header files are, and it Just Works(tm). Hell, I even followed a C++ guide to Win32 programming and managed to translate an open a blank window program to Haskell, and it worked. Maybe somebody just needs to sit down and write a nice binding for doing native GUI stuff under Win32? Maybe you could try to be that somebody? I'm sure the Windows folks would appreciate it very much The thought has certainly crossed my mind. If I could write such a package, I imagine a lot of people would find it seriously useful. Native Windows GUI programs, without any 3rd party DLLs to distribute with your compiled binary... It'd be great, wouldn't it? Of course, thinking about how great it would be doesn't get the code written. ;-) I'd have to learn how to call Win32 from C first, for a start... o_O Yes, of course, ultra posse nemo obligatur. As long as you can't do something, you can only hope somebody else can and does. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Am Samstag 05 Dezember 2009 21:43:13 schrieb Miguel Mitrofanov: I'm constantly amused by those who manage to use Windows without installing Cygwin. I'm constantly amazed by those who manage to use Windows. (In case you want to misunderstand, it's not a Windows bashing, I just never managed to work with it) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: error-message
On Thu, Dec 03, 2009 at 01:50:06PM -0800, Gregory Crosswhite wrote: Or, even more concisely: == sumWithError_3 = liftM2 (+) == Unfortunately though, neither of these definitions have the same semantics as the original @sumWithError@, as using both we get the following error message for @showSumOrErrorOf (-1) (-2)@: == Error computing the square root of -1: Square roots cannot be taken of negative numbers. == That is, we have lost the second of the two error messages. The reason for this is that 'Monad'-style error processing expresses the computation as a sequence, and gives up as soon as it sees any error. In this case of @sumWithError@, however, the evaluation of the second argument can proceed even if there was an error in the first argument. Thus, rather than using a 'Monad' pattern, we use an 'Applicative' pattern: == sumWithError_4 = liftA2 (+) == Now both error messages are displayed. I see no inherent reason that liftM2 (+) cannot collect both error messages. No one says that monad-style error processing *must* stop as soon as it sees an error. And having different semantics for liftA2 and liftM2 (etc.) is strange at best. They ought to be equivalent for any type constructor with both Monad and Applicative instances. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing Parsec 3 -- was: Wiki software?
On Friday December 4, 2009, John MacFarlane wrote: I used criterion to compare pandoc compiled with parsec2 to pandoc compiled with your version of parsec3. (The benchmark is converting testsuite.txt from markdown to HTML.) The difference was minor: parsec2: mean: 67.66576 ms, lb 67.56722 ms, ub 67.88983 ms, ci 0.950 std dev: 722.3878 us, lb 323.0343 us, ub 1.356013 ms, ci 0.950 parsec3: mean: 68.20847 ms, lb 68.16387 ms, ub 68.26284 ms, ci 0.950 std dev: 252.7773 us, lb 204.5512 us, ub 325.2424 us, ci 0.950 So, once you release the new parsec3, I am prepared to remove the parsec 3 restriction from the libraries I maintain: pandoc, highlighting-kate, filestore, gitit, and yst. I don't know what the performance of the current parsec3 is compared to parsec2. It would be helpful if you could run your benchmark for that also and include it. If the only issue is performance, I respectfully request that you remove the parsec 3 requirement even before the new version of parsec3 is released. Thank you. Howard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Avoiding undecidables
Am Samstag 05 Dezember 2009 21:51:26 schrieb Michael Snoyman: On Sat, Dec 5, 2009 at 10:33 PM, José Iborra pepeibo...@gmail.com wrote: Since you have already decided MPTCs are ok, in my opinion undecidable instances are fine here. But I realize this is not the usual stance, so I might be wrong. As far as I understand, all UndecidableInstances does is tell the compiler Maybe instance checking won't terminate, try anyway, so they're dangerous *only during compilation*, once things compile, everything's dandy. Sounds reasonable to me. I'm waiting for the boogey man to jump out though and explain why undecidables here will get me gored to death by a raptor [1]. They won't. They might suck you into a black hole, but raptors are very specialised. instance Convert Integer Double where convert = Just . fromIntegral instance TotalConvert Double-- that's all instance TotalConvert Integer Double Interestng approach. The current approach is *almost* the same, just leaves off the default definition. I'd be wary of putting in a definition like that; although it saves a line of typing, it let's a partial function get in which could cause trouble for unsuspecting users. But it is a possibility. But only if they declare misbehaved instances of TotalConvert. Whenever a reasonable instance TotalConvert x y exists, the Convert instance should satisfy the demands of the default definition. Cheers, pepe [1] http://xkcd.com/292/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the rank of a polymorphic type?
Eugene, 1) Does there exist an authoritative source saying the same? Not that I'm doubting, just supposing that the source would have other interesting information, too :) You may want to have a look at the already mentioned JFP-article by Peyton Jones et al. and perhaps the work of Kfoury and Wells. 2) Is it true that rank (forall a . a, forall a . a) == 0 ? No, for pairs one takes the maximum of the constituent types. So, here you'd get rank 1. Note that this is an impredicative type, which is yet another extension of the standard Hindley-Milner typing discipline. Cheers, Stefan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing Parsec 3 -- was: Wiki software?
+++ Howard B. Golden [Dec 05 09 13:36 ]: On Friday December 4, 2009, John MacFarlane wrote: I used criterion to compare pandoc compiled with parsec2 to pandoc compiled with your version of parsec3. (The benchmark is converting testsuite.txt from markdown to HTML.) The difference was minor: parsec2: mean: 67.66576 ms, lb 67.56722 ms, ub 67.88983 ms, ci 0.950 std dev: 722.3878 us, lb 323.0343 us, ub 1.356013 ms, ci 0.950 parsec3: mean: 68.20847 ms, lb 68.16387 ms, ub 68.26284 ms, ci 0.950 std dev: 252.7773 us, lb 204.5512 us, ub 325.2424 us, ci 0.950 So, once you release the new parsec3, I am prepared to remove the parsec 3 restriction from the libraries I maintain: pandoc, highlighting-kate, filestore, gitit, and yst. I don't know what the performance of the current parsec3 is compared to parsec2. It would be helpful if you could run your benchmark for that also and include it. parsec 2.1.0.1 from HackageDB: mean: 67.71456 ms, lb 67.65181 ms, ub 67.82660 ms, ci 0.950 std dev: 416.1303 us, lb 274.0063 us, ub 761.6995 us, ci 0.950 parsec 3.0.1 from HackageDB: mean: 188.5380 ms, lb 188.3217 ms, ub 188.7615 ms, ci 0.950 std dev: 1.136199 ms, lb 964.3489 us, ub 1.366720 ms, ci 0.950 parsec 3.0.1 from Antoine: mean: 69.29665 ms, lb 69.22450 ms, ub 69.48016 ms, ci 0.950 std dev: 551.3562 us, lb 263.7954 us, ub 1.156183 ms, ci 0.950 If the only issue is performance, I respectfully request that you remove the parsec 3 requirement even before the new version of parsec3 is released. Thank you. Sorry, I don't want to do that. Lots of people have both parsec-2 and parsec-3 installed, and if I remove the restriction, their pandoc (and gitit and...) will be much slower unless they take special steps. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HP + Gtk2hs?
--- On Sat, 12/5/09, Daniel Fischer daniel.is.fisc...@web.de wrote: I thought in this case, it was a proposed change in the installer, so you'd only have to change that and could leave the gtk2hs binary untouched. Of course that can only work if Windows installers are some sort of script or otherwise customisable. Are they? If they used a tool like NSIS then it would be as easy as modifying the script. I emailed a Gtk developer offering to help if that were the case. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Daniel Fischer wrote: I'm constantly amazed by those who manage to use Windows. (In case you want to misunderstand, it's not a Windows bashing, I just never managed to work with it I've not had a lot of luck with Linux. I imagine this is merely due to having a lot more experience with Windows. FWIW, I used to hate Windows too - AmigaOS is far nicer. ;-) But now we're drifting wildly off-topic. For better or worse, Windows is the most popular desktop OS currently. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Compiling the C PortAudio library for either Cygwin or MinGW will be challenging at the moment. The current release doesn't compile as is, and although there should be patch for the configure script as an attachment to this message it seems to have gone amiss: http://music.columbia.edu/pipermail/portaudio/2009-May/009116.html I'd look for a different library to talk to the sound card... Best wishes Stephen 2009/12/4 M Xyz functionallyharmoni...@yahoo.com What is the most minimal (preferably platform independent) library available for writing bytes to the sound card? I see 60 wonderful libraries on Hackage, but I really just need the Haskell equivalent of an audio.write(byte[]) method. What sound api are these 60 libraries using? I think the portaudio library is the only contender but when I try to install it I get: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Try Mac. /commercial On 6 Dec 2009, at 01:00, Andrew Coppin wrote: Daniel Fischer wrote: I'm constantly amazed by those who manage to use Windows. (In case you want to misunderstand, it's not a Windows bashing, I just never managed to work with it I've not had a lot of luck with Linux. I imagine this is merely due to having a lot more experience with Windows. FWIW, I used to hate Windows too - AmigaOS is far nicer. ;-) But now we're drifting wildly off-topic. For better or worse, Windows is the most popular desktop OS currently. ___ 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] Low Level Audio - Writing bytes to the sound card?
Miguel Mitrofanov wrote: Try Mac. /commercial You're not the first to suggest this either. ;-) Maybe once I get hired by some financial modelling consultants and get paid shedloads of money to write Haskell all day, I'll be able to afford a Mac. But until then... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: error-message
Recall that the definition of liftM2 is
==
liftM2 :: (Monad m) = (a1 - a2 - r) - m a1 - m a2 - m r
liftM2 f m1 m2 = do { x1 - m1; x2 - m2; return (f x1 x2) }
==
which, if I understand correctly, desugars to
==
liftM2 f m1 m2 =
m1 =
(
\x1 -
m2 =
(
\x2 -
return (f x1 x2)
)
)
==
The problem comes from the fact that = takes a *function* as its second
argument, and so if the first argument is an error then we can't evaluate the
second argument in order to see if it has an error as well. For example,
consider the following script:
===
import Control.Applicative
import Control.Monad
import Data.ErrorMessage
newtype E a = E (Either String a)
instance Functor E where
fmap _ (E (Left error)) = E (Left error)
fmap f (E (Right argument)) = E (Right (f argument))
instance Applicative E where
pure = E . Right
(*) (E (Left error2)) (E (Left error1)) = E (Left (error1 ++ error2))
(*) (E (Left error)) _ = E (Left error)
(*) _ (E (Left error)) = E (Left error)
(*) (E (Right function)) (E (Right argument)) = E (Right (function
argument))
instance Monad E where
return= E . Right
E (Left l) = _ = E (Left l)
E (Right r) = f = f r
fail msg = E (Left msg)
sum_using_monad :: Either String Int
(E sum_using_monad) = (liftM2 (+)) (E (Left A)) (E (Left B))
sum_using_applicative :: Either String Int
(E sum_using_applicative) = (liftA2 (+)) (E (Left A)) (E (Left B))
main = do
putStrLn . show $ sum_using_monad
putStrLn . show $ sum_using_applicative
===
(Sorry about all of the annoying E's; I needed to do this in order to override
the instance declaration for Either String.)
Run this script and you will see:
Left A
Left BA
Thus, the difference in the semantics is inherent from the way that = and
liftM2 are defined. The only way that I can think to get around this is change
the definition of = so that if the first argument is an error then it calls
the second argument with undefined; if this returns a (Left error) then
combine the two errors, and if it returns anything else or throws an exception
(e.g. Prelude.undefined) then ignore it and just return the first argument.
Cheers,
Greg
On Dec 5, 2009, at 1:28 PM, Brent Yorgey wrote:
On Thu, Dec 03, 2009 at 01:50:06PM -0800, Gregory Crosswhite wrote:
Or, even more concisely:
==
sumWithError_3 = liftM2 (+)
==
Unfortunately though, neither of these definitions have the same semantics
as the original @sumWithError@, as using both we get the following error
message for @showSumOrErrorOf (-1) (-2)@:
==
Error computing the square root of -1:
Square roots cannot be taken of negative numbers.
==
That is, we have lost the second of the two error messages. The reason for
this is that 'Monad'-style error processing expresses the computation as a
sequence, and gives up as soon as it sees any error. In this case of
@sumWithError@, however, the evaluation of the second argument can proceed
even if there was an error in the first argument. Thus, rather than using a
'Monad' pattern, we use an 'Applicative' pattern:
==
sumWithError_4 = liftA2 (+)
==
Now both error messages are displayed.
I see no inherent reason that liftM2 (+) cannot collect both error
messages. No one says that monad-style error processing *must* stop
as soon as it sees an error. And having different semantics for liftA2
and liftM2 (etc.) is strange at best. They ought to be equivalent
for any type constructor with both Monad and Applicative instances.
-Brent
___
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
[Haskell-cafe] binding to C libraries on Windows was Low Level Audio - Writing bytes to the sound card?
I think there are some misapprehensions here:- many haskell packages binding to c libraries will compile with ghc without problems on windows - without cygwin, without mingw/msys system. Some such packages build out of the box on windows, like the zlib package which contains the c source for the c zlib library. GHC is able to compile and build this packages without any other c compiler/libraries/unix emulators etc because ghc itself contains part of the gcc c compiler tool chain and comes with all c standard headers, c++ headers and c/c++ runtime libraries. Other packages such as SDL package are relatively straightforward to build on windows - all that is required is to have an import library corresponding to your dll (or static lib) and the headers. You then update the library path field in the cabal file and include path. There is only one gotch-ya - you need to have a import library for the gcc tool chain (thats what ghc uses) i.e. a .a library and not the native windows .LIB import library. If you don't have .a import library but have the dll then the '.a' import library be built for any dll relativley easily. The correct '.a' import libraries and the libraries themselves for many standard unix/gnu packages can be found under the gnuwin32 project. Many unix libraries provide a windows build based on the mingw port of the gcc tool chain which will contain the correct import library. the bigest problem hamperring cleaner builds of haskell packages on windows is the lack of any standardised scheme for the installation of c-libraries and header files (and of course the availability of a suitable build of the library) Another problem hampering the install of haskell packages on windows is the use of the unix autoconf build system (./configure) , for which there is no substitute on windows other than cygwin and to lesser extent msys/mingw, this problem could be obviated by the provision of a standard win32 conf (forgetting about win64 for the moment) - package writters note! Date: Sat, 5 Dec 2009 20:58:14 + Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card? From: stephen.tet...@gmail.com To: Haskell-Cafe@haskell.org CC: Hi Andrew 2009/12/5 Andrew Coppin andrewcop...@btinternet.com: I don't think it should be necessary to install a Unix emulator just so that I can write Windows programs. Maybe others disagree. ... I'm by no means an expert here, but isn't it usual for C libraries on Windows to be supplied as a compiled DLL and a header file for using it? I don't quite understand why you need a C compiler. The thing is, all the bindings on Hackage (or at least something most likely above 95%) are to Unix C libraries so you need a C compiler and a Unix emulator to use them. I do have have some sympathy with your point though - it is possible to get things to compile once you have Cygwin, but deployment on any other machine Windows thereafter is 'challenging' to say the least. Apparently there is some talk of removing OpenGL from the Haskell Platform. And if this happens, it'll be one more thing I can't use on Windows. :-( I didn't realise until I looked today that OpenGL was in the Haskell Platform. If the proposal to remove it is from Sven Panne then fair enough, otherwise it would be a bit disappointing - it always just worked when it was part of GHCs extralibs... Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe _ If It Exists, You'll Find it on SEEK Australia's #1 job site http://clk.atdmt.com/NMN/go/157639755/direct/01/___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
On Sat, 5 Dec 2009, Michael Snoyman wrote: On Sat, Dec 5, 2009 at 7:41 PM, Ross Paterson r...@soi.city.ac.uk wrote: On Sat, Dec 05, 2009 at 05:52:11PM +0200, Michael Snoyman wrote: For the record, I find this pedanticism misplaced, ... I think you'll find that's pedantry. Hoped someone would comment exactly that ;). :-) Nonetheless: Although there might be cases, where it is not immediately clear what is error and what is exception (not to mention, that different people prefer to use the words for the corresponding concepts in a different way, if they would do so consistently, it would be ok), in most cases it is clear. Have you ever tried to handle an array index out of range situation at run-time? I think, it cannot be sensibly handled by the program automatically. Thus there is no other way than terminating the program. Thus I'd call this situation an error not an exception. Of course, people like to throw in here a web server as counterexample. So to speak: With respect to exceptions web servers are an exception. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
On Sun, Dec 6, 2009 at 12:17 AM, Henning Thielemann lemm...@henning-thielemann.de wrote: On Sat, 5 Dec 2009, Michael Snoyman wrote: On Sat, Dec 5, 2009 at 7:41 PM, Ross Paterson r...@soi.city.ac.uk wrote: On Sat, Dec 05, 2009 at 05:52:11PM +0200, Michael Snoyman wrote: For the record, I find this pedanticism misplaced, ... I think you'll find that's pedantry. Hoped someone would comment exactly that ;). :-) Nonetheless: Although there might be cases, where it is not immediately clear what is error and what is exception (not to mention, that different people prefer to use the words for the corresponding concepts in a different way, if they would do so consistently, it would be ok), in most cases it is clear. Have you ever tried to handle an array index out of range situation at run-time? I think, it cannot be sensibly handled by the program automatically. Thus there is no other way than terminating the program. Thus I'd call this situation an error not an exception. Of course, people like to throw in here a web server as counterexample. So to speak: With respect to exceptions web servers are an exception. I think there are plenty of examples like web servers. A text editor with plugins? I don't want to lose three hours worth of work just because some plugin wasn't written correctly. For many classes of programs, the distinction between error and exception is not only blurred, it's fully irrelevant. Harping on people every time they use error in the wrong sense seems unhelpful. Hope my commenting on this subject doesn't become my own form of *pedantry*. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
On Sun, 6 Dec 2009, Michael Snoyman wrote: I think there are plenty of examples like web servers. A text editor with plugins? I don't want to lose three hours worth of work just because some plugin wasn't written correctly. For many classes of programs, the distinction between error and exception is not only blurred, it's fully irrelevant. Harping on people every time they use error in the wrong sense seems unhelpful. Hope my commenting on this subject doesn't become my own form of *pedantry*. In an earlier thread I have explained that one can consider a software architecture as divided into levels. What is an error in one level (text editor plugin, web server thread, operating system process) is an exception in the next higher level (text editor, web server, shell respectively). This doesn't reduce the importance to distinguish between errors and exceptions within one level. All approaches so far that I have seen in Haskell just mix exceptions and errors in an arbitrary way. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
On Sun, Dec 6, 2009 at 12:55 AM, Henning Thielemann lemm...@henning-thielemann.de wrote: On Sun, 6 Dec 2009, Michael Snoyman wrote: I think there are plenty of examples like web servers. A text editor with plugins? I don't want to lose three hours worth of work just because some plugin wasn't written correctly. For many classes of programs, the distinction between error and exception is not only blurred, it's fully irrelevant. Harping on people every time they use error in the wrong sense seems unhelpful. Hope my commenting on this subject doesn't become my own form of *pedantry*. In an earlier thread I have explained that one can consider a software architecture as divided into levels. What is an error in one level (text editor plugin, web server thread, operating system process) is an exception in the next higher level (text editor, web server, shell respectively). This doesn't reduce the importance to distinguish between errors and exceptions within one level. All approaches so far that I have seen in Haskell just mix exceptions and errors in an arbitrary way. I think we can all appreciate why it would be a bad thing is we treat exceptions as errors. For example, I don't want my program to crash on a file not found. On the other hand, what's so bad about treating errors as exceptions? If instead of the program crashing on an array-out-of-bound or pattern-match it throws an exception which can be caught, so what? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Stephen, I had no problem compiling the portaudio binaries on Windows. It came with a msvc project that worked. The problem I'm getting currently is that when I cabal install portaudio etc etc I get a c2hs.exe does not exist error when c2hs.exe clearly exists and is in my system path. Just like this post from months ago: http://www.mail-archive.com/haskell-...@lurk.org/msg00101.html --- On Sat, 12/5/09, Stephen Tetley stephen.tet...@gmail.com wrote: From: Stephen Tetley stephen.tet...@gmail.com Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card? To: haskell-cafe@haskell.org Date: Saturday, December 5, 2009, 5:00 PM Compiling the C PortAudio library for either Cygwin or MinGW will be challenging at the moment. The current release doesn't compile as is, and although there should be patch for the configure script as an attachment to this message it seems to have gone amiss: http://music.columbia.edu/pipermail/portaudio/2009-May/009116.html I'd look for a different library to talk to the sound card... Best wishes Stephen 2009/12/4 M Xyz functionallyharmoni...@yahoo.com What is the most minimal (preferably platform independent) library available for writing bytes to the sound card? I see 60 wonderful libraries on Hackage, but I really just need the Haskell equivalent of an audio.write(byte[]) method. What sound api are these 60 libraries using? I think the portaudio library is the only contender but when I try to install it I get: ___ 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] New Hackage category: Error Handling
On Dec 5, 2009, at 3:00 PM, Michael Snoyman wrote: I think we can all appreciate why it would be a bad thing is we treat exceptions as errors. For example, I don't want my program to crash on a file not found. On the other hand, what's so bad about treating errors as exceptions? If instead of the program crashing on an array-out-of-bound or pattern-match it throws an exception which can be caught, so what? As I understand it, an error is a problem which aborts a computation and an exception is a problem that simply needs to be dealt with before the computation can continue. You are correct that there should be as few irrecoverable errors as possible in an application. In particular, if we think of an application as being a whole bunch of sub-computation tied together into a larger computation, then in a sense what we want is for no the failure of no sub-computation to cause the whole application-wide computation to fail. This, however, does not mean that there will be no circumstances under which any sub-computation fails, such as in the case of discovering in the middle of leading a file that it is irrecoverably corrupt. When these circumstances occur, one has an error and not an exception because there is no way to finish loading the file. However, at a higher lever, the sub-computation of loading the file was not necessary for the application to keep running, and so an error in the sub-computation becomes merely an exception when propagated up to the application level. Cheers, Greg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Am Sonntag 06 Dezember 2009 00:10:05 schrieb M Xyz: Stephen, I had no problem compiling the portaudio binaries on Windows. It came with a msvc project that worked. The problem I'm getting currently is that when I cabal install portaudio etc etc I get a c2hs.exe does not exist error when c2hs.exe clearly exists and is in my system path. Just like this post from months ago: http://www.mail-archive.com/haskell-...@lurk.org/msg00101.html Try cabal install --with-c2hs=C:\path\to\c2hs.exe portaudio maybe that'll work. If not, run cabal --verbose=3 install portaudio, perhaps that gives more information about what went wrong. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
--- On Sat, 12/5/09, Daniel Fischer daniel.is.fisc...@web.de wrote: Try cabal install --with-c2hs=C:\path\to\c2hs.exe portaudio maybe that'll work. If not, run cabal --verbose=3 install portaudio, perhaps that gives more information about what went wrong. Daniel, Thank you for your thoughtful reply. I didn't know about those flags. The log is fairly long, and as I'm new to Haskell and Cabal it is mostly meaningless to me. I see very many incidences of searching for ___ in path. Cannot find ___ on the path so maybe this is all as simple as me not setting my environment correctly. Log: cabal install portaudio --verbose=3 --with-c2hs=C:\Program Files\Haskell\bin\c2hs.exe --extra-include-dirs=C:\A\install\programming\portaudio\portaudio\include --extra-lib-dirs=C:\A\install\programming\portaudio\portaudio\build\msvc\Win32\Release log.txt searching for ghc in path. found ghc at C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc.exe (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc.exe,[--numeric-version]) C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc.exe is version 6.10.4 looking for package tool: ghc-pkg near compiler in C:\Program Files\Haskell Platform\2009.2.0.2\bin found package tool in C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc-pkg.exe (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc-pkg.exe,[--version]) C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc-pkg.exe is version 6.10.4 (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc.exe,[--supported-languages]) Reading installed packages... (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc-pkg.exe,[dump,--global]) Reading available packages... Resolving dependencies... selecting portaudio-0.0.1 (hackage) and discarding mtl-1.0 selecting mtl-1.1.0.2 (installed or hackage) and discarding mtl-1.1.0.0 and 1.1.0.1 selecting haskell98-1.0.1.0 (installed or hackage) and discarding haskell98-1.0 selecting random-1.0.0.1 (installed or hackage) and discarding random-1.0.0.0 selecting process-1.0.1.1 (installed or hackage) and discarding filepath-1.0 and process-1.0.0.0 selecting directory-1.0.0.3 (installed or hackage) and discarding directory-1.0.0.0 selecting old-time-1.0.0.2 (installed or hackage) and discarding old-time-1.0.0.0 selecting old-locale-1.0.0.1 (installed or hackage) and discarding old-locale-1.0.0.0 selecting filepath-1.1.0.2 (installed or hackage) and discarding filepath-1.1.0.0 and 1.1.0.1 selecting Win32-2.2.0.0 (installed or hackage) and discarding Win32-2.1 and 2.1.0.0 selecting bytestring-0.9.1.4 (installed or hackage) and discarding bytestring-0.9, 0.9.0.1, 0.9.0.2, 0.9.0.3, 0.9.0.4, 0.9.1.0, 0.9.1.1, 0.9.1.2, 0.9.1.3 and 0.9.1.5 selecting ghc-prim-0.1.0.0 (installed) selecting rts-1.0 (installed) selecting array-0.2.0.0 (installed or hackage) and discarding array-0.1.0.0 selecting base-3.0.3.1 (installed) and 4.1.0.0 (installed) and discarding syb-0.1.0.0 and 0.1.0.1 selecting integer-0.1.0.1 (installed) selecting syb-0.1.0.1 (installed) In order, the following would be installed: portaudio-0.0.1 (new package) portaudio-0.0.1 has already been downloaded. Extracting C:\Documents and Settings\M\Application Data\cabal\packages\hackage.haskell.org\portaudio\0.0.1\portaudio-0.0.1.tar.gz to C:\DOCUME~1\M\LOCALS~1\Temp\portaudio-0.0.13824... Using internal setup method with build-type Simple and args: [configure,--verbose=3,--ghc,--global,--extra-include-dirs=C:\\A\\install\\programming\\portaudio\\portaudio\\include,--extra-lib-dirs=C:\\A\\install\\programming\\portaudio\\portaudio\\build\\msvc\\Win32\\Release,--constraint=base ==3.0.3.1,--constraint=haskell98 ==1.0.1.0,--constraint=mtl ==1.1.0.2,--with-c2hs=C:\\Program Files\\Haskell\\bin\\c2hs.exe] Configuring portaudio-0.0.1... Creating dist (and its parents) searching for ghc in path. found ghc at C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc.exe (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc.exe,[--numeric-version]) C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc.exe is version 6.10.4 looking for package tool: ghc-pkg near compiler in C:\Program Files\Haskell Platform\2009.2.0.2\bin found package tool in C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc-pkg.exe (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc-pkg.exe,[--version]) C:\Program Files\Haskell Platform\2009.2.0.2\bin\ghc-pkg.exe is version 6.10.4 (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc.exe,[--supported-languages]) Reading installed packages... (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\bin\\ghc-pkg.exe,[dump,--global]) Dependency base 3 ==3.0.3.1: using base-3.0.3.1 Dependency haskell98 -any ==1.0.1.0: using haskell98-1.0.1.0 Dependency mtl =1.1.0.0 ==1.1.0.2: using mtl-1.1.0.2 searching for alex in path. found alex at C:\Program Files\Haskell Platform\2009.2.0.2\extralibs\bin\alex.exe (C:\\Program Files\\Haskell Platform\\2009.2.0.2\\extralibs\\bin\\alex.exe,[--version]) C:\Program
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Am Sonntag 06 Dezember 2009 00:47:38 schrieb M Xyz: Daniel, Thank you for your thoughtful reply. I didn't know about those flags. The log is fairly long, and as I'm new to Haskell and Cabal it is mostly meaningless to me. I see very many incidences of searching for ___ in path. Cannot find ___ on the path so maybe this is all as simple as me not setting my environment correctly. If you have cpphs, hugs, jhc, greencard etc., it is probably something about your environment. If you don't have them, it's clear that they aren't found. On the other hand, that doesn't explain Using c2hs version 0.16.0 given by user at: C:\Program Files\Haskell\bin\c2hs.exe -- so it finds c2hs, and can apparently run c2hs --version (C:\\Program Files\\Haskell\\bin\\c2hs.exe,[--include=dist\\build,--cppopts=- D__GLASGOW_HASKELL__=610,--cppopts=-IC: \\A\\install\\programming\\portaudio\\portaudio\\include,--output-dir=dist\\build,-- output=Sound\\PortAudio\\Base.hs,.\\Sound\\PortAudio\\Base.chs]) c2hs.exe: does not exist C:\Program Files\Haskell\bin\c2hs.exe returned ExitFailure 1 -- bang To ascertain whether c2hs works at all, can you try to run it manually? (cd to an appropriate directory, cabal unpack portaudio cd portaudio (or whatever, so that Base.chs is found via .\Sound\PortAudio\Base.chs md dist\build c2hs.exe --include=dist\build --cppopts=-D__GLASGOW_HASKELL__=610 --cppopts=-IC: \A\install\programming\portaudio\portaudio\include --output-dir=dist\build -- output=Sound\PortAudio\Base.hs .\Sound\PortAudio\Base.chs ) If that works, the problem is somewhere in cabal, otherwise in c2hs, either way, we'll know more. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz: I just had another idea. da...@linux-mkk1:~ c2hs -o memyself.hs memyself.chs c2hs: does not exist it's not that c2hs isn't found or something, c2hs doesn't find Base.chs! Try installing from the unpacked sources (cd portaudio; cabal install) or the old- fashioned way: cd portaudio-0.0.1 ghc --make Setup ./Setup configure --help (choose your options, prefix, profiling, ...) ./Setup configure $OPTIONS ./Setup build if all's well, ./Setup haddock ./Setup install (dies for me with dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei oder Verzeichnisnicht gefunden c2hs: Error during preprocessing custom header file cabal: Error: some packages failed to install: portaudio-0.0.1 failed during the building phase. The exception was: exit: ExitFailure 1 because I don't have portaudio installed) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Hackage category: Error Handling
On Sat, 5 Dec 2009, Henning Thielemann wrote: On Sun, 6 Dec 2009, Michael Snoyman wrote: I think there are plenty of examples like web servers. A text editor with plugins? I don't want to lose three hours worth of work just because some plugin wasn't written correctly. For many classes of programs, the distinction between error and exception is not only blurred, it's fully irrelevant. Harping on people every time they use error in the wrong sense seems unhelpful. Hope my commenting on this subject doesn't become my own form of *pedantry*. In an earlier thread I have explained that one can consider a software architecture as divided into levels. What is an error in one level (text editor plugin, web server thread, operating system process) is an exception in the next higher level (text editor, web server, shell respectively). This doesn't reduce the importance to distinguish between errors and exceptions within one level. All approaches so far that I have seen in Haskell just mix exceptions and errors in an arbitrary way. I have just written more details on this topic: http://www.haskell.org/haskellwiki/Error_vs._Exception ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
--- On Sat, 12/5/09, Daniel Fischer daniel.is.fisc...@web.de wrote: cd portaudio-0.0.1 ghc --make Setup ../Setup configure --help (choose your options, prefix, profiling, ...) ../Setup configure $OPTIONS ../Setup build Everything went well until Setup build which yielded our friend c2hs.exe does not exist. C:\A\install\programming\portaudio\haskell\portaudio-0.0.1ghc --make Setup [1 of 1] Compiling Main ( Setup.hs, Setup.o ) Linking Setup.exe ... C:\A\install\programming\portaudio\haskell\portaudio-0.0.1Setup configure --hel p Usage: Setup configure [FLAGS] Flags for configure: ...(edited out) C:\A\install\programming\portaudio\haskell\portaudio-0.0.1Setup configure --ext ra-include-dirs=C:\A\install\programming\portaudio\portaudio\include --extra-l ib-dirs=C:\A\install\programming\portaudio\portaudio\build\msvc\Win32\Release Configuring portaudio-0.0.1... C:\A\install\programming\portaudio\haskell\portaudio-0.0.1Setup build Preprocessing library portaudio-0.0.1... c2hs.exe: does not exist ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card?
I am going to give this a try. Thanks. Where can I get the pexports and dlltool utilities? Google yields: http://www.emmestech.com/software/pexports-0.43/download_pexports.html http://sourceware.org/binutils/ Are those correct? --- On Sat, 12/5/09, john lask jvl...@hotmail.com wrote: From: john lask jvl...@hotmail.com Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card? To: daniel.is.fisc...@web.de, functionallyharmoni...@yahoo.com Cc: haskell-cafe@haskell.org Date: Saturday, December 5, 2009, 9:03 PM I don't know whether this will help you but I just downloaded an built the haskell portaudio package ... (I had a windows msvc build of portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19 make an import lib for ghc from dll: pexports libpa19.dll libpa19.def dlltool --input-def libpa19.def --output-lib libpa19.a edit the .cabal file or use command line flags extra-Libraries: pa19 extra-lib-dirs: c:\portaudio19\lib include-dirs: c:\portaudio19\include runghc setup configure make sure you have cpp i.e. the c-preprocessor on your exe path, otherwise you will get 'cpp' is not recognized as an internal or external command, operable program or batch file. c2hs.exe: Error during preprocessing custom header file runghc setup build builds ok ...?? From: daniel.is.fisc...@web.de To: functionallyharmoni...@yahoo.com Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card? Date: Sun, 6 Dec 2009 02:34:17 +0100 CC: haskell-cafe@haskell.org Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz: I just had another idea. da...@linux-mkk1:~ c2hs -o memyself.hs memyself.chs c2hs: does not exist it's not that c2hs isn't found or something, c2hs doesn't find Base.chs! Try installing from the unpacked sources (cd portaudio; cabal install) or the old- fashioned way: cd portaudio-0.0.1 ghc --make Setup ./Setup configure --help (choose your options, prefix, profiling, ...) ./Setup configure $OPTIONS ./Setup build if all's well, ./Setup haddock ./Setup install (dies for me with dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei oder Verzeichnisnicht gefunden c2hs: Error during preprocessing custom header file cabal: Error: some packages failed to install: portaudio-0.0.1 failed during the building phase. The exception was: exit: ExitFailure 1 because I don't have portaudio installed) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Australia's #1 job site If It Exists, You'll Find it on SEEK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] PortAudio library successfully built on Windows
John Lask, The steps you enumerated below successfully built portaudio for me! Thank you! I wonder though, you said to rename the dll to libpa19.dll from portaudio_x86.dll and to change the .cabal entry from extra-Libraries: portaudio to extra-Libraries: pa19. Since my .dll name and .cabal file entry were mismatched, was that what could have been wrong all along? Was the creation of a .a file necessary? I would delete the .a file and retry with libportaudio.dll but I won't push my luck. Now if I could just get Gtk2hs working now, I could be happy *and* productive. :) --- On Sat, 12/5/09, john lask jvl...@hotmail.com wrote: From: john lask jvl...@hotmail.com Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card? To: daniel.is.fisc...@web.de, functionallyharmoni...@yahoo.com Cc: haskell-cafe@haskell.org Date: Saturday, December 5, 2009, 9:03 PM I don't know whether this will help you but I just downloaded an built the haskell portaudio package ... (I had a windows msvc build of portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19 make an import lib for ghc from dll: pexports libpa19.dll libpa19.def dlltool --input-def libpa19.def --output-lib libpa19.a edit the .cabal file or use command line flags extra-Libraries: pa19 extra-lib-dirs: c:\portaudio19\lib include-dirs: c:\portaudio19\include runghc setup configure make sure you have cpp i.e. the c-preprocessor on your exe path, otherwise you will get 'cpp' is not recognized as an internal or external command, operable program or batch file. c2hs.exe: Error during preprocessing custom header file runghc setup build builds ok ...?? From: daniel.is.fisc...@web.de To: functionallyharmoni...@yahoo.com Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound card? Date: Sun, 6 Dec 2009 02:34:17 +0100 CC: haskell-cafe@haskell.org Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz: I just had another idea. da...@linux-mkk1:~ c2hs -o memyself.hs memyself.chs c2hs: does not exist it's not that c2hs isn't found or something, c2hs doesn't find Base.chs! Try installing from the unpacked sources (cd portaudio; cabal install) or the old- fashioned way: cd portaudio-0.0.1 ghc --make Setup ./Setup configure --help (choose your options, prefix, profiling, ...) ./Setup configure $OPTIONS ./Setup build if all's well, ./Setup haddock ./Setup install (dies for me with dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei oder Verzeichnisnicht gefunden c2hs: Error during preprocessing custom header file cabal: Error: some packages failed to install: portaudio-0.0.1 failed during the building phase. The exception was: exit: ExitFailure 1 because I don't have portaudio installed) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Australia's #1 job site If It Exists, You'll Find it on SEEK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] When are undecidables ok?
I know this is basically a rewording of a previous e-mail, but I realized this is the question I *really* wanted to ask. We have this language extension UndecidableInstances (not to mention OverlappingInstances), which seem to divide the Haskell camp into two factions: * Hey, GHC said to turn on this flag. Ok! * Undecidables are the devil! I get the feeling the truth lies in the middle. As I understand it (please correct me if I am wrong), the problem with undecidables is that they can create non-terminating instances. However, for certain cases the programmer should be able to prove to him/herself that the instances will terminate. My question is: how can you make such a proof? I've had to cases in particular that made me want undecidables. Both of them, IMO, could be solved by creating new extensions to GHC which would not require undecidables. Nonetheless, for now we only have undecidables at our disposal. The examples are: * Context synonyms (eg, MonadFailure = Monad + Failure). * Subclass function defaulting For an example of the second, a nifty definition of Monad would be: class Applicative m = Monad m where = ... return ... pure = return (*) = ap fmap = liftM Of course, neither of these is possible in Haskell, so we can use undecidables. How can a programmer prove that a set of instances is, in fact, safe? And if they make a mistake and right a bad set of undecidable/overlapping instances, what's the worst case scenario? Is it a compile-time or run-time error*? Michael * Yes, I mean error. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] When are undecidables ok?
On Sat, Dec 5, 2009 at 10:04 PM, Michael Snoyman mich...@snoyman.com wrote: I know this is basically a rewording of a previous e-mail, but I realized this is the question I *really* wanted to ask. We have this language extension UndecidableInstances (not to mention OverlappingInstances), which seem to divide the Haskell camp into two factions: * Hey, GHC said to turn on this flag. Ok! * Undecidables are the devil! I get the feeling the truth lies in the middle. As I understand it (please correct me if I am wrong), the problem with undecidables is that they can create non-terminating instances. However, for certain cases the programmer should be able to prove to him/herself that the instances will terminate. My question is: how can you make such a proof? Well, the reasoning for the devil camp (which I admit to being firmly in[1]) is that such proofs must rely on the algorithm the compiler uses to resolve instances. You might be able to prove it, but the proof is necessarily only valid for (possibly current versions of) GHC. The typeclass resolution algorithm is not in the report, and there are several conceivable ways of of going about it. So it is fine to use them if you are okay with making your code unportable and future-brittle. I am typically against the mere existence of code that that is future-brittle, because it encourages compiler authors not to innovate (and by that token, unportable too, because it discourages compiler competition). Luke [1] http://lukepalmer.wordpress.com/2008/04/08/stop-using-undecidable-instances/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] When are undecidables ok?
On Sun, Dec 6, 2009 at 7:36 AM, Luke Palmer lrpal...@gmail.com wrote: On Sat, Dec 5, 2009 at 10:04 PM, Michael Snoyman mich...@snoyman.com wrote: I know this is basically a rewording of a previous e-mail, but I realized this is the question I *really* wanted to ask. We have this language extension UndecidableInstances (not to mention OverlappingInstances), which seem to divide the Haskell camp into two factions: * Hey, GHC said to turn on this flag. Ok! * Undecidables are the devil! I get the feeling the truth lies in the middle. As I understand it (please correct me if I am wrong), the problem with undecidables is that they can create non-terminating instances. However, for certain cases the programmer should be able to prove to him/herself that the instances will terminate. My question is: how can you make such a proof? Well, the reasoning for the devil camp (which I admit to being firmly in[1]) is that such proofs must rely on the algorithm the compiler uses to resolve instances. You might be able to prove it, but the proof is necessarily only valid for (possibly current versions of) GHC. The typeclass resolution algorithm is not in the report, and there are several conceivable ways of of going about it. So it is fine to use them if you are okay with making your code unportable and future-brittle. I am typically against the mere existence of code that that is future-brittle, because it encourages compiler authors not to innovate (and by that token, unportable too, because it discourages compiler competition). Luke [1] http://lukepalmer.wordpress.com/2008/04/08/stop-using-undecidable-instances/ So in that case, perhaps the compiler authors can give us some ideas as to when it's safe to use undecidables? Seems like we should go straight to the horse's mouth. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: error-message
In particular, the motivation for this package was that I have written a build system, and I wanted to collect as many errors in the build as possible and show them all to the user at once. YMMV, but at least for me a deluge of errors is less helpful than a short list I can fix quickly, then try again. Often by fixing one error from the list a sizeable portion of the rest just vanish (I forget the English term for that kind of error). (In before you can use sth like quickfix to go through the first few errors and compile again whenever you feel like it.) -- Ariel J. Birnbaum ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the rank of a polymorphic type?
2009/12/6 Stefan Holdermans ste...@cs.uu.nl: Eugene, 1) Does there exist an authoritative source saying the same? Not that I'm doubting, just supposing that the source would have other interesting information, too :) You may want to have a look at the already mentioned JFP-article by Peyton Jones et al. and perhaps the work of Kfoury and Wells. 2) Is it true that rank (forall a . a, forall a . a) == 0 ? No, for pairs one takes the maximum of the constituent types. So, here you'd get rank 1. Note that this is an impredicative type, which is yet another extension of the standard Hindley-Milner typing discipline. OK, thanks. However, isn't the type (forall a . a) - String impredicative because it instantiates a type variable of the type constructor (-) p q with p = forall a . a? Cheers, Stefan -- 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] Re: universal binary version of Haskell Platform?
On Thu, 03 Dec 2009 10:52:35 +, Duncan Coutts duncan.cou...@googlemail.com wrote: [...] There no binary platform installer for OSX PPC. You'll have to grab ghc-6.10.4 for PPC from the ghc download page and then install the platform from the generic source tarball. Ah, that's too bad. That means that I won't be able to invoke GHC outside of the Terminal application by default, and that even if I create a Darwin shell script and alias to invoke it from Aqua, the icon for that shell script will only be generic by default. I'd rather click on an application icon in the Dock. If you'd like to help us next time to make a platform binary for PPC then that'd be great. I don't think we have the setup to make universal binaries but it should be possible to make a PPC build if we have a volunteer. Sure, barring job-related time constraints, I'd be happy to volunteer. My Mac just went out of service because of a hardware problem with the memory, so I'm order new replacement RAM this weekend. As soon as that arrives and I install it, the problem should be resolved. What should I do? -- Benjamin L. Russell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the rank of a polymorphic type?
On Sunday 06 December 2009 1:42:34 am Eugene Kirpichov wrote: OK, thanks. However, isn't the type (forall a . a) - String impredicative because it instantiates a type variable of the type constructor (-) p q with p = forall a . a? There's probably no clear cut answer to this independent of how you think of (-). For instance, if we explain the Haskell type system by way of a pure type system, (-) is a special case of a pi type, which looks like: pi x : k. t where any xs in t are bound by the pi. We then have: p - q = pi _ : p. q forall a : k. b = pi a : k. b pi types are given types by sets of rules, which look like triples. If (s,t,u) is a rule, then: G |- k : sG, a : k |- b : t --- G |- (pi a : k. b) : u is the corresponding typing rule. Type systems like Haskell's are commonly thought of in terms of the lambda cube, which has constant sorts * and [], with * : []. The rule (*,*,*) gives you ordinary functions. (*,[],[]) gives you dependent types, so that's out. ([],*,*) is an impredicative rule for polymorphism. This says that, for instance: forall a. a - a = (pi a : *. pi _ : a. a) : * because (pi _ : a. a) : * if a : *, by the (*,*,*) rule, and then we apply the impredicative rule for the universal quantification. One could also use the predicative rule ([],*,[]), which would result in forall a. a - a having type []. However, Haskell also has arbitrarily higher-order types. This is given by the rule ([],[],[]), which allows expressions like: (* - *) - * = pi _ : (pi _ : *. *). * This type system is called F_omega, while just the ([],*,?) rule is known as F_2. However, the F_omega rule also allows for arbitrary rank polymorphism even with the predicative universal quantifier rule above (predicative F_2 allows a little, but it's very limited*). For instance, the higher rank type: forall a. (forall b. b) - a checks thusly: (forall b. b) : [] via ([],*,[]) ((forall b. b) - a) : [] via ([],*,[]) (forall a. (forall b. b) - a) : [] via ([],[],[]) Data types, by contrast, have kinds like * - *, so using say, Maybe (forall a. a - a) genuinely relies on the impredicative rule. GHC's type system isn't exactly set up in this way, but (-) is similarly special in that it somehow isn't quite just another type constructor with kind * - * - * (or even whatever special kinds GHC uses to support unboxed values and such). Hope that wasn't too confusing. :) -- Dan * Predicative F_2 will essentially allow one universal quantifier somewhere in the type. This can be: forall a. a - a or it can be: (((forall a. a) - T) - U) - V for T, U and V of kind * (the only kind in F_2), which is a rank-4 type. It doesn't allow: forall a b. a - b even, because the inner (forall b. a - b) : [], so adding the forall a requires the F_omega rule. Predicative F_2 and F_w also blow up with quantification on the right of an arrow, because it looks like the rule for dependent types: T - (forall a. a) T : *, (forall a. a) : [] so the rule (*,[],[]) would be invoked. GHC doesn't have this sort of hierarchy, and so doesn't have these sorts of weird cases, despite being predicative of a sort. Instead it distinguishes somehow between monotypes ([Float], String - Int, a - b) and polytypes (forall a. a, ...), although it doesn't really display the difference. Quantifiers are only supposed to range over kinds that classify monotypes (or monotype constructors), which keeps the predicativity (although, even this gets fudged some: If I have forall a. a - a, I can instantiate a to the polytype forall a. a - a with rank-n polymorphism, because it only seems to worry about the validity of the resulting type, and (-) is special; by contrast, the same cannot be said for forall a. Maybe a, because Maybe genuinely only accepts monotypes without -XImpredicativeTypes). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
