Re: [Haskell-cafe] Regression test utility suggestions?
On 22 October 2010 08:38, Peter Schmitz ps.hask...@gmail.com wrote: I am seeking suggestions for a regression test utility or framework to use while developing in Haskell (in a MS Windows environment). [snip] For this kind of task I use shelltestrunner http://hackage.haskell.org/package/shelltestrunner It can do recursive search through directories to find test cases, which I find particularly handy. Cheers, Bernie. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: suspected problem with network.curl version 1.3.5
Perhaps you can use Network.Browser (from HTTP) http://hackage.haskell.org/package/HTTP-4000.0.9 It handles cookies under the hood (you don't see it, but it works) because it keeps a browser session state. J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Bug in HTTP (bad internal error handling)
Bit Connor wrote: On Sat, Oct 16, 2010 at 10:29 AM, Claus Reinke claus.rei...@talk21.com wrote: After it catches this error, the function returns (line 376): return (fail (show e)) The fail is running in the Either monad (The Result type = Either). This calls the default Monad implementation of fail, which is just a call to plain old error. This basically causes the entire program to crash. Actually, it appears that simpleHTTP isn't actually supposed to throw an IOException, and it is instead supposed to return a ConnError result. So the real fix is to fix the code to make this happen. But Sounds like a victim of http://hackage.haskell.org/trac/ghc/ticket/4159 For mtl clients, 'fail' for 'Either' used to call 'Left'. That was changed, though the ticket does not indicate the library versions affected. This looks like the problem. Any idea how to get the HTTP package fixed? I could try making a patch myself, but I would prefer hearing from the HTTP maintainer first, who doesn't seem to be around. I've tried contacting him a few times about getting the base dependencies in HTTP bumped and an upload made, without success. This is a widely used package that's in the platform and that won't work with GHC 7.0 with the current dependencies, so it really needs to get fixed soon. libraries@, what's the right way to proceed? Can I make a Debian-style non-maintainer upload with minimal changes to fix urgent issues like these? Cheers, Ganesh === Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html === ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Weekly News: Issue 155 - October 20, 2010
On 10/21/10 5:38 AM, Ketil Malde wrote: I'm always getting two copies of everything in haskell@, since everything is cross-posted to -cafe. Are there actually people subscribed to -cafe, but *not* to hask...@? And if so, why? I am. In part because I don't want to get two copies of everything, but in part because I'm lazy. So adding another list to my reading queue, especially one that's specified as sort of being a subset of the content here, seems like it'd be too much. Usually communities in this situation will have the subset list set up to automatically forward everything to the main list as well, in order to alleviate these sorts of things. Did I mention the lazy? :) -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskellers design
On 10/21/10 2:32 PM, Christopher Done wrote: [1] http://imgur.com/lnkE7.png [2] http://previasports.com/haskellers_website/ I like the colour theme of the former and the layout of the latter. The colour theme of the first is more professional, I think. I vote that styles should be consistent. +1. I'd vote for the second layout (though the map looks glitched up) but changing the red/dayglow/teal/orange scheme to match the first color scheme better. The orange and teal of #2 are fairly close to the orange and navy of #1, so it shouldn't alter things too badly. Though because of the dark background, we may want #2' to have slightly lighter colors than #1. It's the dayglow and red which strike me as out of place. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Haskell Weekly News: Issue 155 - October 20, 2010
On 10/22/2010 09:37 AM, wren ng thornton wrote: On 10/21/10 5:38 AM, Ketil Malde wrote: I'm always getting two copies of everything in haskell@, since everything is cross-posted to -cafe. Are there actually people subscribed to -cafe, but *not* to hask...@? And if so, why? I am. In part because I don't want to get two copies of everything, but in part because I'm lazy. This is my case too. As for as the amount of messages, who cares. Get it through NNTP. You will download only the headers. Bodies will be downloaded only for messages you read. You can check only the threads you consider interesting. There is not much new threads. Mark newsgroup read is a quick operation. I do not think HWN should not be posted to haskell-cafe. If you decide so I do not really care but post a message to haskell-cafe list that you are switching HWN to haskell list only (so I can subscribe there too). Peter. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Convert Either to Tree - Occurs check
Tks for the answer, the data structure of Either is: data Either a b = Left a | Right b deriving (Eq, Ord, Read, Show) one example of what i want convert is: Left(Right(Left(Left( No dia 22 de Outubro de 2010 04:58, Dan Piponi dpip...@gmail.com escreveu: André Batista Martins asked: i want convert Either to a tree. Example: Either ( Either 1 2 ) ( Either 3 4) Branch ( Branch (Leafl 1) (Leafr2) ) ( Branch (Leafl 3) (Leafr4)) ) Before writing the function to convert your data structure, why not try writing down the precise type signature you expect it to have. In fact, before that, try writing down the precise type signature of the thing you call an Either. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNOUNCE] text 0.10.0.0 - fast Unicode text handling
On 22 October 2010 16:38, Bryan O'Sullivan b...@serpentine.com wrote: [Blog copy of the announcement here.] I just pushed it to bitbucket and github, and you can install it from the text site on Hackage in the usual way: cabal update cabal install text What's in this release? New functions for reading integers and floating point numbers, an oft-requested feature. They're fast, too: they range from parity with their bytestring counterparts, to up to 4 times faster. You can expect to parse 3 to 4 million Int values per second out of a text file, or up 2 million Double values per second. They're also easy to use, give error messages, and come in strict and lazy variants. UTF-8 decoding and encoding are now very fast. They're up to 9x faster than they were, and close to the performance of pure C UTF-8 decoding and encoding. The Eq and Ord instances are also now very fast, up to 5x faster than before. They're now faster than the bytestring instances. Several other common functions received drive-by performance improvements too. Better protection against rare crashes on really huge volumes of data. Is there a best practices guide on how to deal with Text values? For example, I assume that it's better to try and use Text throughout rather than continually packing String values (in my case, I'm looking at using Text for I/O in graphviz; should I then start using Text rather than String for all the parameters?). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNOUNCE] text 0.10.0.0 - fast Unicode text handling
On Fri, Oct 22, 2010 at 10:30 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: For example, I assume that it's better to try and use Text throughout rather than continually packing String values (in my case, I'm looking at using Text for I/O in graphviz; should I then start using Text rather than String for all the parameters?). Yes. Just like with ByteString, frequent packs or unpacks kills performance. The only thing I pack is compile time constants (and, at least for ByteStrings, that's cheap). Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell Weekly News: Issue 155 - October 20, 2010
Peter Hercek pher...@gmail.com writes: I am. In part because I don't want to get two copies of everything, but in part because I'm lazy. This is my case too. As for as the amount of messages, who cares. Right. So the question is, what is (or should be) the contents of the messages that are posted only to haskell@, but *not* crossposted to café? Because I think this set of messages is (or should be) empty, which suggests that we 1) remove the people subscribed to haskell-cafe@ from haskell@ 2) automatically post all messages to haskell@ to -cafe as well 3) post announcements to haskell@ without any crossposting. This way, most people will subscribe to -cafe and get a single copy of each message, not miss out on any important stuff, and as an added benefit discussion will mostly go to that list. People who only want low-bandwith subscription to announcements, HWN, and the like, may subscribe to haskell@ only. -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
Re: [Haskell-cafe] Bug in HTTP (bad internal error handling)
On Fri, Oct 22, 2010 at 9:35 AM, Sittampalam, Ganesh ganesh.sittampa...@credit-suisse.com wrote: Bit Connor wrote: On Sat, Oct 16, 2010 at 10:29 AM, Claus Reinke claus.rei...@talk21.com wrote: After it catches this error, the function returns (line 376): return (fail (show e)) The fail is running in the Either monad (The Result type = Either). This calls the default Monad implementation of fail, which is just a call to plain old error. This basically causes the entire program to crash. Actually, it appears that simpleHTTP isn't actually supposed to throw an IOException, and it is instead supposed to return a ConnError result. So the real fix is to fix the code to make this happen. But Sounds like a victim of http://hackage.haskell.org/trac/ghc/ticket/4159 For mtl clients, 'fail' for 'Either' used to call 'Left'. That was changed, though the ticket does not indicate the library versions affected. This looks like the problem. Any idea how to get the HTTP package fixed? I could try making a patch myself, but I would prefer hearing from the HTTP maintainer first, who doesn't seem to be around. I've tried contacting him a few times about getting the base dependencies in HTTP bumped and an upload made, without success. This is a widely used package that's in the platform and that won't work with GHC 7.0 with the current dependencies, so it really needs to get fixed soon. libraries@, what's the right way to proceed? Can I make a Debian-style non-maintainer upload with minimal changes to fix urgent issues like these? I'd be much obliged if you could, and I do apologise for leaving all of this just hanging. No time available for Haskell projects these days unfortunately, Opera engine development taking up most of my waking hours. Getting someone to take over HTTP would be best, or maybe rewrite it altogether..it is not the prettiest thing around :) --sigbjorn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Eta-expansion and existentials (or: types destroy my laziness)
On 19 October 2010 19:01, Dan Doel dan.d...@gmail.com wrote: However, this argument is a bit circular, since that eliminator could be defined to behave similarly to an irrefutable match. Right. Or, put another way, eta expansion of a dictionary-holding existential would result in a value holding a bottom dictionary, whereas that's otherwise impossible, I think. I think evaluating dictionaries strictly is more of a want to have rather than actually implemented. In particular, GHC supports building value-recursive dictionaries - and making dictionary arguments strict indiscriminately would make this feature rather useless. I think this means that even with constrained existential things would be OK. What is definitely not OK is lazy pattern matching on GADTs which have *type equality* constraints on their existentials - because the type equalities are erased at compile time, lazy pattern matching on a GADT would leave no opportunity for us to observe that the proof of the type equality was bogus (a bottom) - so allowing this would let our programs segfault. For example, this program would erroneously typecheck: data Eq a b where Eq :: EQ a a f :: Eq Int Bool - Bool f (~Eq) = ((1 :: Int) + 1) :: Bool main = print $ f undefined I'm sticking with my unsafeCoerce based solution for now. It's ugly, but it's nicely *localised* ugliness :-) Cheers, Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Convert Either to Tree - Occurs check
On 22/10/10 09:23, André Batista Martins wrote: Tks for the answer, the data structure of Either is: data Either a b = Left a | Right bderiving (Eq, Ord, Read, Show) one example of what i want convert is: Left(Right(Left(Left( Hi, The problem here is that the type of Left () is: Either () a The type of Left (Left ()) is: Either (Either () a) b The type of Right (Left (Left ())) is: Either c (Either (Either () a) b) and finally, the type of Left (Right (Left (Left ( is: Either (Either c (Either (Either () a) b)) d That is, each level in the tree must have a different type. For this reason, you can't sensibly use Either for tree types of varying depth (a type-class would help, but I doubt it's what you want). A sensible type for a tree is the one you gave in your original post, TreeE. So why do you want to encode the tree with Either (not really possible) and then convert to your TreeE type? Why not just start out with the values in your tree type? Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Scrap your rolls/unrolls
Hi Cafe,
In generic programming, e.g. as in Data Types a la Carte and Compos,
you often wish to work with data types in their fix-point of a functor
form. For example:
data ListF a rec = Nil | Cons a rec
newtype List a = Roll { unroll :: ListF a (List a) }
In some presentations, this is done by factoring the fix point like so:
newtype FixF f = Roll { unroll :: f (FixF f) }
type List a = FixF (ListF a)
This is all well and good, but it means when working with data types
defined in this manner you have to write Roll and unroll everywhere.
This is tedious :-(
Something I have long wished for is equirecursion, which would let you
write this instead:
type List a = ListF a (List a)
Note that we now have a type instead of a newtype, so we won't need to
write any injection/extraction operators. However, currently GHC
rightly rejects this with a complaint about a cycle in type synonym
declarations.
However, you can use type families to hide the cycle from GHC:
type List a = ListF a (Force (ListThunk a))
data ListThunk a
type family Force a
type instance Force (ListThunk a) = List a
Unfortunately, this requires UndecidableInstances (the type instance
RHS is not smaller than the instance head). And indeed when we turn
that extension on, GHC goes into a loop, so this may not seem very
useful.
However, we can make this slight modification to the data type to make
things work again:
data ListF a rec = Nil | Cons a (Force rec)
type List a = ListF a (ListThunk a)
Note that the application of Force has moved into the *use site* of
rec rather than the *application site*. This now requires no
extensions other than TypeFamilies, and the client code of the library
is beautiful (i.e. has no rolls/unrolls):
example, ones :: List Int
example = Cons 1 (Cons 2 Nil)
ones = Cons 1 ones
We can factor this trick into a fix point combinator that does not
require roll/unroll:
type Fix f = f (FixThunk f)
type List a = Fix (ListF a)
data FixThunk f
type family Force a
type instance Force (FixThunk f) = Fix f
The annoying part of this exercise is the the presence of a Force in
the functor definition (e.g ListF) means that you can't make them into
actual Functor instances! The fmap definition gives you a function of
type (a - b) and you need one of type (Force a - Force b). However,
you can make them into a category-extras:Control.Functor.QFunctor
instance
(http://hackage.haskell.org/packages/archive/category-extras/0.53.5/doc/html/Control-Functor.html)
by choosing the s Category to be:
newtype ForceCat a b = ForceCat { unForceCat :: Force a - Force b }
instance Category ForceCat where
id = ForceCat id
ForceCat f . ForceCat g = ForceCat (f . g)
Rather than the usual Hask Category which is used in the standard
Functor. This is somewhat unsatisfying, but I'm not sure there is a
better way.
I haven't seen this trick to emulate equirecursion before. Has it
showed up anywhere else?
Cheers,
Max
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Re: [Haskell-cafe] Bug in HTTP (bad internal error handling)
On Fri, Oct 22, 2010 at 11:36 AM, Sigbjorn Finne sigbjorn.fi...@gmail.com wrote: On Fri, Oct 22, 2010 at 9:35 AM, Sittampalam, Ganesh ganesh.sittampa...@credit-suisse.com wrote: Bit Connor wrote: On Sat, Oct 16, 2010 at 10:29 AM, Claus Reinke claus.rei...@talk21.com wrote: After it catches this error, the function returns (line 376): return (fail (show e)) The fail is running in the Either monad (The Result type = Either). This calls the default Monad implementation of fail, which is just a call to plain old error. This basically causes the entire program to crash. Actually, it appears that simpleHTTP isn't actually supposed to throw an IOException, and it is instead supposed to return a ConnError result. So the real fix is to fix the code to make this happen. But Sounds like a victim of http://hackage.haskell.org/trac/ghc/ticket/4159 For mtl clients, 'fail' for 'Either' used to call 'Left'. That was changed, though the ticket does not indicate the library versions affected. This looks like the problem. Any idea how to get the HTTP package fixed? I could try making a patch myself, but I would prefer hearing from the HTTP maintainer first, who doesn't seem to be around. I've tried contacting him a few times about getting the base dependencies in HTTP bumped and an upload made, without success. This is a widely used package that's in the platform and that won't work with GHC 7.0 with the current dependencies, so it really needs to get fixed soon. libraries@, what's the right way to proceed? Can I make a Debian-style non-maintainer upload with minimal changes to fix urgent issues like these? I'd be much obliged if you could, and I do apologise for leaving all of this just hanging. No time available for Haskell projects these days unfortunately, Opera engine development taking up most of my waking hours. Getting someone to take over HTTP would be best, or maybe rewrite it altogether..it is not the prettiest thing around :) I know it may not be appropriate as-is due to its dependency list, but http-enumerator[1] may be something to consider. It's still young, but I think the API is pretty clean, and I've heard from users that it performs favorably versus HTTP. Michael [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/http-enumerator ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Eta-expansion and existentials (or: types destroy my laziness)
On Friday 22 October 2010 5:48:28 am Max Bolingbroke wrote:
I think evaluating dictionaries strictly is more of a want to have
rather than actually implemented. In particular, GHC supports
building value-recursive dictionaries - and making dictionary
arguments strict indiscriminately would make this feature rather
useless.
It now occurs to me that I might be thinking of your paper on strict core.
When does this come up? I only have one example that seems likely:
data Mu f = In { out :: f (Mu f) }
instance Show (f (Mu f)) = Show (Mu f) where
show = show . out
Is that an example of a value recursive dictionary? I also considered:
data AnyShow = forall a. Show a = AS a
instance Show AnyShow where
show (AS x) = AS ( ++ show x ++ )
inf = AS inf
but I don't think the dictionary is actually recursive there. Translating to
explicit dictionary passing seems to confirm the latter impression. The former
is more iffy.
The most obvious way to build a value recursive dictionary would be an
existential like:
inf' = case inf' of AS x - AS (x, x)
but this is prevented from happening by the lack of irrefutable match.
What is definitely not OK is lazy pattern matching on GADTs which have
*type equality* constraints on their existentials.
This is certainly the more compelling deal breaker.
-- Dan
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Re: [Haskell-cafe] Convert Either to Tree - Occurs check
Tks for the answser, I need to continue a work that has already been developed. In this work i have Eithers and i want convert to another datatype with more information, because I want to generate Eithers, which will contain the information from the first but with positions exchanged. No dia 22 de Outubro de 2010 11:30, Neil Brown nc...@kent.ac.uk escreveu: On 22/10/10 09:23, André Batista Martins wrote: Tks for the answer, the data structure of Either is: data Either a b = Left a | Right b deriving (Eq, Ord, Read, Show) one example of what i want convert is: Left(Right(Left(Left( Hi, The problem here is that the type of Left () is: Either () a The type of Left (Left ()) is: Either (Either () a) b The type of Right (Left (Left ())) is: Either c (Either (Either () a) b) and finally, the type of Left (Right (Left (Left ( is: Either (Either c (Either (Either () a) b)) d That is, each level in the tree must have a different type. For this reason, you can't sensibly use Either for tree types of varying depth (a type-class would help, but I doubt it's what you want). A sensible type for a tree is the one you gave in your original post, TreeE. So why do you want to encode the tree with Either (not really possible) and then convert to your TreeE type? Why not just start out with the values in your tree type? Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Scrap your rolls/unrolls
On Friday 22 October 2010 6:37:49 am Max Bolingbroke wrote: This is all well and good, but it means when working with data types defined in this manner you have to write Roll and unroll everywhere. This is tedious :-( Your discovery is interesting (and I haven't seen it before). Another solution, though, is SHE. With it, you can write: data ListF a r = NilF | ConsF a r newtype List a = Roll (ListF a (List a)) pattern Nil = Roll NilF pattern Cons x xs = Roll (ConsF x xs) And not worry about Rolls anymore. -- Dan http://personal.cis.strath.ac.uk/~conor/pub/she/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Eta-expansion and existentials (or: types destroy my laziness)
On 22 October 2010 12:03, Dan Doel dan.d...@gmail.com wrote:
data Mu f = In { out :: f (Mu f) }
instance Show (f (Mu f)) = Show (Mu f) where
show = show . out
Is that an example of a value recursive dictionary?
Assuming the Show (f (Mu f)) instance uses the (Mu f) one, AFAIK this
should indeed build a loopy dictionary.
I think this extension was motivated by Scrap your Boilerplate with
Class - see section 5 of
http://research.microsoft.com/en-us/um/people/simonpj/papers/hmap/gmap3.pdf.
Cheers,
Max
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[Haskell-cafe] Re: Scrap your rolls/unrolls
Forgot to reply to list On 22 October 2010 12:14, Dan Doel dan.d...@gmail.com wrote: Another solution, though, is SHE. With it, you can write: data ListF a r = NilF | ConsF a r newtype List a = Roll (ListF a (List a)) pattern Nil = Roll NilF pattern Cons x xs = Roll (ConsF x xs) And not worry about Rolls anymore. Ah yes, pattern synonyms. This solution is somewhat unsatisfying because you will also need some smart constructors: nil = Roll NilF cons x xs = Roll (ConsF x xs) Now the names of the smart constructors for building the data type are not the same as the things you pattern match on, which is a slightly annoying asymmetry. It's certainly less complicated than the TypeFamilies based solution though! Cheers, Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] vector-space and standard API for vectors
Hello everyone! It's well known that Num Co type classes are not adequate for vectors (I don't mean arrays). I have an idea how to address this problem. Conal Elliott wrote very nice set of type classes for vectors. (Definition below). I used them for some time and quite pleased. Code is concise and readable. class AdditiveGroup v where zeroV :: v (^+^) :: v - v - v negateV :: v - v class AdditiveGroup v = VectorSpace v where type Scalar v :: * (*^) :: Scalar v - v - v class VectorSpace v = InnerSpace v where (.) :: v - v - Scalar v There are few problems though. Fisrt one is inlining. Functions are not inlined so if client code uses uses stream fusion it breaks. Second is dependecies. Vector-space doesn't have big chain of dependencies. People may be reluctant to use vector-spaces just for API for small packages. My proposal is to split type classes above into separate package which provide only type classes, doesn't have any dependencies. Second point is to lean more on performance side in performance vs elegance. Add INLINE pragmas everywhere (unfortunate feature of stream fusion), move ^-^ to AdditiveGroup with default implementation. I'd like to know opinion of haskellers on this and specifically opinion of Conal Eliott as author and maintainer (I CC'ed him) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] tried to use the example given in the source of network.browser
This is what is in HTTPbis/Network/Browser.hs do rsp - Network.Browser.browse $ do setAllowRedirects True -- handle HTTP redirects request $ getRequest http://google.com/; fmap (take 100) (getResponseBody rsp) And how I changed it slightly to test it out import Network.HTTP import Network.Browser main = do rsp - Network.Browser.browse $ do setAllowRedirects True -- handle HTTP redirects request $ getRequest http://google.com/; fmap (take 100) (getResponseBody rsp) but I got this errortest.lhs:10:39: Couldn't match expected type `Network.Stream.Result (Response [a])' against inferred type `(Network.URI.URI, Response String)' In the first argument of `getResponseBody', namely `rsp' In the second argument of `fmap', namely `(getResponseBody rsp)' In the expression: fmap (take 100) (getResponseBody rsp) how did I get this error? I'm perplexed as this came right from the source. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ICFP 2011: Call for Workshop Proposals
CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS ICFP 2011 16th ACM SIGPLAN International Conference on Functional Programming September 19 - 21, 2011 Tokyo, Japan http://www.icfpconference.org/icfp2011 The 16th ACM SIGPLAN International Conference on Functional Programming will be held in Tokyo, Japan on September 19-21, 2011. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for workshops (and other co-located events, such as tutorials) to be affiliated with ICFP 2011 and sponsored by SIGPLAN. These events should be more informal and focused than ICFP itself, include sessions that enable interaction among the attendees, and be fairly low-cost. The preference is for one-day events, but other schedules can also be considered. NEW THIS YEAR: The workshops are scheduled to occur on September 18 (the day before ICFP) and September 22-24 (the three days after ICFP). -- Submission details Deadline for submission: November 19, 2010 Notification of acceptance: December 17, 2010 Prospective organizers of workshops or other co-located events are invited to submit a completed workshop proposal form in plain text format to the ICFP 2011 workshop co-chairs (Gabriele Keller and Derek Dreyer), via email to icfp11-workshops at mpi-sws.org by November 19, 2010. (For proposals of co-located events other than workshops, please fill in the workshop proposal form and just leave blank any sections that do not apply.) Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by December 17, 2010, and if successful, depending on the event, they will be asked to produce a final report after the event has taken place that is suitable for publication in SIGPLAN Notices. The proposal form is available at: http://www.icfpconference.org/icfp2011/icfp11-workshops-form.txt Further information about SIGPLAN sponsorship is available at: http://acm.org/sigplan/sigplan_workshop_proposal.htm -- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2010 organizing committee, together with the members of the SIGPLAN executive committee. Workshop Co-Chair: Gabriele Keller (University of New South Wales) Workshop Co-Chair: Derek Dreyer (MPI-SWS) General Co-Chair: Manuel Chakravarty (University of New South Wales) General Co-Chair: Zhenjiang Hu (National Institute of Informatics) Program Chair: Olivier Danvy (Aarhus University) -- Further information Any queries should be addressed to the workshop co-chairs (Gabriele Keller and Derek Dreyer), via email to icfp11-workshops at mpi-sws.org. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Haskell theme
I agree with Mark that we shouldn't try to over-constrain things. However, basic startup-resources are perfectly fine. It gives a good default for people who don't really like (web-)design, and can serve as a baseline for others. I.e., encourage consistency but don't enforce it. On 12 October 2010 22:17, Christopher Done chrisd...@googlemail.com wrote: http://img840.imageshack.us/img840/3577/ideasv.png I mostly like it, with the following remarks: - Only blue for a colour scheme is too cold. This is why I used this orange-red for the new wiki. There are other ways to do this, of course. I'd just like to encourage people to not only use blueish tones. - The wiki edit links in your sketch are very dark. I prefer the light grey as used in the new wiki, because it doesn't stand out that much. To download the Inkscape SVG grab it here: http://chrisdone.com/designs/haskell-theme-1.svg I don't know what I was thinking here but it seemed like fun: http://img412.imageshack.us/img412/1827/rect5935.png With a bit of tuning, this can look nice. I get bored really quickly, I was alright for 15 minutes and then I lost the will to point and click. Anyway, I was thinking rather than trying to come up with a brilliant all-encompassing design, we could agree on conventions: * colours * headings * spacing * links * the particular incarnation of the logo etc. I'm pretty happy to go with the colour theme of http://new-www.haskell.org/haskellwiki/Haskell Haskellers.com also makes me think we need an umbrella theme that encompasses all Haskell sites. Maybe we should do a theme poll like the logo poll. I don't know. Regardless, I think we do need to decide on something and stick with it. Should this discussion be taken to the web devel mailing list? Is that appropriate? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Push the envelope. Watch it bend. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] tried to use the example given in the source of network.browser
Hi, On 22/10/10 14:58, Michael Litchard wrote: main = do rsp- Network.Browser.browse $ do setAllowRedirects True -- handle HTTP redirects request $ getRequest http://google.com/; fmap (take 100) (getResponseBody rsp) but I got this errortest.lhs:10:39: Couldn't match expected type `Network.Stream.Result (Response [a])' against inferred type `(Network.URI.URI, Response String)' In the first argument of `getResponseBody', namely `rsp' In the second argument of `fmap', namely `(getResponseBody rsp)' In the expression: fmap (take 100) (getResponseBody rsp) how did I get this error? I'm perplexed as this came right from the source. To be specific, it came from the documentation of the library... which turns out not to match the source. It seems you instead want: main = do (_, rsp) - Network.Browser.browse $ do setAllowRedirects True -- handle HTTP redirects request $ getRequest http://google.com/; print (take 100 $ rspBody rsp) I've changed the last bit to print the first 100 lines of the result rather than return them, as I imagine that is what you want if you're using it as a main function. Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] JavaScript in a browser as a Windows GUI?
On 21/10/2010 07:00 PM, Jeremy Shaw wrote: But, you are correct that happstack does not currently have support for running CGI executables. I imagine that you could write a CGI handler (with out modifying the core code) in a few hours (maybe less). Mostly just a matter of turning the values in the Request type into a environment variables, and calling the executable? And writing a HTTP server is mostly a matter of parsing the request headers and constructing some response headers. However, this turns out to be significantly less easy to do properly than you'd first imagine. ;-) That said, I am not sure why you want CGI. Because my hired web server runs Apache? Sure, if I'm only doing stuff on the local machine, I can use any kind of server/application linkage I like, because I can use any server I want. But if I ever decide to actually put this stuff on the web, for real, it'll have to be plain CGI. (Or maybe FastCGI is supported, I'm not actually sure...) That being the case, I might as well develop it as CGI to start with. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] JavaScript in a browser as a Windows GUI?
On Fri, Oct 22, 2010 at 12:05 PM, Andrew Coppin andrewcop...@btinternet.com wrote: On 21/10/2010 07:00 PM, Jeremy Shaw wrote: But, you are correct that happstack does not currently have support for running CGI executables. I imagine that you could write a CGI handler (with out modifying the core code) in a few hours (maybe less). Mostly just a matter of turning the values in the Request type into a environment variables, and calling the executable? And writing a HTTP server is mostly a matter of parsing the request headers and constructing some response headers. However, this turns out to be significantly less easy to do properly than you'd first imagine. ;-) True. Though I am basing my assumption on the fact that we have code which goes the opposite way (allows happstack to run as a CGI process), and those bindings are pretty short (less than 100 lines) and simple looking. That said, I am not sure why you want CGI. Because my hired web server runs Apache? Sure, if I'm only doing stuff on the local machine, I can use any kind of server/application linkage I like, because I can use any server I want. But if I ever decide to actually put this stuff on the web, for real, it'll have to be plain CGI. (Or maybe FastCGI is supported, I'm not actually sure...) That being the case, I might as well develop it as CGI to start with. happstack-server has FastCGI support. Plain-old CGI support is no great challenge either. Your web application is basically just a , ServerPart Response, value. Typically you would run that using simpleHTTP simpleHTTP :: (ToMessage a) = Conf - ServerPart a - IO () but you can just as easily run it as CGI using: serverPartToCGI :: ToMessage a = ServerPart a - CGI CGIResult (from the happstack-fastcgi package). - jeremy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Redy to release gtk2hs-0.12.0!
Dear gtk2hs user: We have ready to release next version : gtk2hs-0.12.0 Please pull gtk2hs darcs to test, if no bug report, we will release. You can use below commands (Debian) to install gtk2hs darcs: darcs get --lazy http://code.haskell.org/gtk2hs/ cd ./gtk2hs sudo chmod +x ./bootstrap.sh ./bootstrap.sh Then recompile your gtk2hs program to test. Of course, any successful feedback are welcome! Thanks, -- Gtk2hs Team ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HSCurses - Hello World? (can't find much documentation)
Hi everyone, Haven't posted here since I was a kid, when this language first warped my poor imperative brain. My main work environment is a three-split terminal session using `Yakuake' as a dropdown-terminal (one for vim, one for interactive interpreter, one for MySQL). I don't mind using the MySQL cli *that* much, but I find typing my queries all the time much takes up precious time when I'm developing things, and it annoys me. Since there is currently no TUI for mysql administration (besides links/phpadmin? o.0). I decided to make one, choosing Haskell because, well, it's awesome. I've made curses apps before, but never in Haskell (only wx, cgi, cli, etc). Couldn't find anything besides an api reference; Which was impossible to find before typing haddock specifically, even after an exhausting search on google, krugle, archives, etc... It's livable (I've learned more complex things with less). But since I've never seen how the HSCurses functions really integrate together, or any tutorials/examples (besides hsFishEx), I fear toying with it is going to be annoying until I figure it out on my own, especially since I'm already doing a project for someone... So, I was wondering if anyone would be kind enough to point me to (or write me) a basic example of how HSCurses works, maybe w/ some very simple example of interactivity (e.g. getch processing, screen refresh, ..) support. Also, maybe warn me of some of the common pitfalls and differences in hscurses vs ncurses in other languages. Having found the haddock, and having done curses apps in other languages, that should be enough for me to get a handle on it. I'm just dreading the read the haddock, assume it works this way, find out you do it this way, repeat loop of learning w/o a starting point. Any help would be greatly appreciated, and will save me some (anticipated) hassle. TYIA, -Pete ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Scrap your rolls/unrolls
On Friday 22 October 2010 7:24:37 am Max Bolingbroke wrote: Ah yes, pattern synonyms. This solution is somewhat unsatisfying because you will also need some smart constructors: nil = Roll NilF cons x xs = Roll (ConsF x xs) Now the names of the smart constructors for building the data type are not the same as the things you pattern match on, which is a slightly annoying asymmetry. It's certainly less complicated than the TypeFamilies based solution though! SHE's pattern synonyms also work as expressions, so there's no asymmetry. They work just like constructors as far as I can tell (with what little I've played with them); you can even partially apply them (in expressions). It doesn't do infix synonyms currently, though. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HSCurses - Hello World? (can't find much documentation)
On Fri, Oct 22, 2010 at 11:18 PM, Anonymous Void byteasphy...@gmail.com wrote: But since I've never seen how the HSCurses functions really integrate together, or any tutorials/examples (besides hsFishEx), I fear toying with it is going to be annoying until I figure it out on my own, especially since I'm already doing a project for someone... So, I was wondering if anyone would be kind enough to point me to (or write me) a basic example of how HSCurses works, maybe w/ some very simple example of interactivity (e.g. getch processing, screen refresh, ..) support. Also, maybe warn me of some of the common pitfalls and differences in hscurses vs ncurses in other languages. UI.HSCurses.Curses follows ncurses quite closely so you can get pretty far reading the NCurses Programming HOWTO: http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/ .Don't forget to have the ncurses man pages handy - usually you'll just need to lowercase the name of a HSCurses function to get the name of the same function in ncurses. If you're going to be using colours or styles (bold, underline, etc), do take a look at CursesHelper too - its API documentation is somewhat better than Curses's. You could also try looking at the ContactManager program in hscurses's example directory. Just to get you started, though, here's a trivial HSCurses program to exhibit simple interaction (a walking '@'): module Main where import UI.HSCurses.Curses -- | Useful for transforming a Char to a ChType. Not sure if this is safe outside of the 7-bit ASCII range. castEnum = toEnum . fromEnum -- note that curses positions are (y, x) coordinates, with (0, 0) being the upmost leftmost position moveAbout pY pX = do erase -- clear curses's virtual screen but don't force a redraw mvAddCh pY pX (castEnum '@') -- place a character in curses's virtual screen refresh -- copy the virtual screen to the terminal c - getCh case c of KeyUp - moveAbout (pY - 1) pX KeyDown - moveAbout (pY + 1) pX KeyLeft - moveAbout pY (pX - 1) KeyRight - moveAbout pY (pX + 1) _ - return () main = do initCurses keypad stdScr True -- make the cursor keys usable echo False -- disable terminal echo cursSet CursorInvisible (sizeY, sizeX) - scrSize moveAbout (sizeY `div` 2) (sizeX `div` 2) endWin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
profiling and strictness (was: Re: [Haskell-cafe] An interesting paper from Google)
Any time you see something inexplicable like lots of time being attributed to something simple like get, it means that something isn't strict enough and get is having to force a bunch of lazy evaluations to do its job. Since you're using State.Strict but lift-ing to get there, I'd first look at the strictness of the monad you're lift-ing from. (I'm assuming State.Strict does what the label says, but it's possible that it's not strict in the way you need; strictness is kinda tricky.) Ahh, thanks, this makes sense to me. The monads involved are an ErrorT and one other strict StateT. When the monads say they are strict, they seem to mean that = will force the evaluation of the monadic mechanics of the first argument when the second is demanded. By monadic mechanics I mean the work done by = itself, so for StateT it binds the result of the first argument with either 'let' or '~(a, s') -' instead of 'case' or '(a, s') -'. So in my understanding, a lazy State will build thunks on every = and they won't ever be forced until you pull the final value and pass it to a strict function in IO like print or an FFI call, and then they are forced recursively, at which point there is a stack overflow unless it's a short sequence. Talking about strictness seems complicated to me because it's not really about what is actually forced, it's about who is forced by who (i.e., when 'a' is forced then 'b' will be) and whether it's forced in sequence or nested. So a strict State is also not forced until the strict IO function, but it turns into a sequential series of thunks rather than a nested one. If this is accurate, why would anyone want to use the lazy State? Anyway, State doesn't provide the really critical bit of strictness, which is in the actual state being modified. So 'State.modify' will inevitably lead to stack overflow if you don't intersperse 'get's in there. What is needed is both $! on State.put (or define your own strict modify that puts $! on put), and strictness annotation of the fields of the record that is being modified (provided it's a record and not a scalar type). In any case, ErrorT has a strict = by necessity, both States have a strict =, and all modifys and puts (I think) are strict, as are all the record fields. In any case, a simple 'get' should only have to force the state to whnf, so it shouldn't matter if the fields are huge thunks or not, so really all that should matter is if the state is already in whnf or is a huge nest of thunks. Which a strict = should prevent, right? This is right next to a 'lookup' function which is called twice as many times and should be doing more work since it actually looks in a Map, but is credited with less cpu and alloc. A lift . get should turn into -- ErrorT a - do a - StateT (\s - return (s, s)) -- 'get' of the outer StateT return (a, s) -- = belongs to inner StateT return (Right a) Anyway, it's sort of a mishmash of semi inlined functions since this is especially nested and hard to understand with transformers, but it looks like a lot of applications of (\a - (a, s)) type functions, so (,) constructors and a 'Right' constructor, inside of 'case's to make sure this are evaluations and not allocations (and I remember from the STG paper that a constructor inside a case need not even be constructed). So I don't totally understand where the forcing is happening to make credit the 'get' with so much work. BTW, I have a theory about what the '0' might mean... perhaps if a function is inlined away, it still appears in the profile list, but with 0 entries. Moral of the story: time is accounted to the function that forces evaluation of lazy thunks, not to the thunks themselves or the function that created the lazy thunks. (I think the latter is impossible without passing around a lot of expensive baggage, and in any case doesn't tell you anything useful; unexpected functions taking a lot of time, on the other hand, tells you right away that there's excessive laziness in the invocation somewhere and gives you a starting point to track it down.) Indeed, this is a good point that I hadn't realized in quite that way before, but tracking it down is still the tricky part. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Scrap your rolls/unrolls
On 22 October 2010 22:06, Dan Doel dan.d...@gmail.com wrote: SHE's pattern synonyms also work as expressions, so there's no asymmetry. They work just like constructors as far as I can tell (with what little I've played with them); you can even partially apply them (in expressions). I didn't realise that - pretty cool! Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] concurrency vs. I/O in GHC
Hello John, Monday, October 18, 2010, 8:15:42 PM, you wrote: If anyone is listening, I would very much like for there to be a mechanism by which external functions can be called unsafe-ly, but without blocking all other Haskell threads. I have code that does this: +RTS -N2 -- 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] readProcess exception
Hello Leskó, Friday, October 22, 2010, 1:50:54 AM, you wrote: I run into a problem with readProcessWithExitCode (from System.Process module). Basically what i want is to start an exe file, giving it some input on stdin and receiving the results on stdout. But id the stdin and look for other functions in the library. one that you need should read and write data simultaneously, for example by using separate thread -- 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] vector-space and standard API for vectors
On 10/22/10 8:46 AM, Alexey Khudyakov wrote: Hello everyone! It's well known that Num Co type classes are not adequate for vectors (I don't mean arrays). I have an idea how to address this problem. Conal Elliott wrote very nice set of type classes for vectors. (Definition below). I used them for some time and quite pleased. Code is concise and readable. class AdditiveGroup v where zeroV :: v (^+^) :: v - v - v negateV :: v - v [...] I'd like to know opinion of haskellers on this and specifically opinion of Conal Eliott as author and maintainer (I CC'ed him) Just my standard complaint: lack of support for semirings, modules, and other simple/general structures. How come everyone's in such a hurry to run off towards Euclidean spaces et al.? I'd rather see, class Additive v where -- or AdditiveMonoid, if preferred zeroV :: v (^+^) :: v - v - v class Additive v = AdditiveGroup v where negateV :: v - v type family Scalar :: * - * class Additive v = LeftModule v where (*^) :: Scalar v - v - v class Additive v = RightModule v where (^*) :: v - Scalar v - v ... Though I don't know how much that'd affect the niceness properties you mentioned. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskellers design
Hi guys, It's me again, I made a new proposal for the website with the standard colors. I've put my pretentions of content being grouped by color, and just used what I thought looked better for each part of the site. Here's the link: http://previasports.com/haskellers_website_standard/ Let me know what you think cheers! nubis :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Error Calling Lua Function
Hi all, I'm having some issues calling Lua functions from Haskell. I have the following in Haskell2Lua.lua: function hello () return hello world end And my Haskell file Haskell2Lua.hs looks like this: import qualified Scripting.Lua as Lua main = do l - Lua.newstate Lua.openlibs l succ - Lua.loadfile l /Haskell2Lua.lua print succ Lua.callproc l hello Lua.close l When I compile and run this file I get: 0 Haskell2Lua: user error (attempt to call a nil value) I have tried some variations on calling the function including: Lua.callproc l hello Lua.callfunc l hello Lua.callfunc l hello I know the Lua bridge is working because the following works: Lua.callproc l print Hello from Lua Any help is appreciated! -deech ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Haskell theme Haskellers design
You might have seen the post I did yesterday about the Haskell project I'm currently working on. In it I posted an screen shot or a web page, which you can find here: http://mtnviewmark.files.wordpress.com/2010/10/source-editing.png I think that page illustrates what I was thinking in terms of themes: It actually has yet a different color scheme, though it shares some colors with the basic pallet. What further ties it together, and what I'd like to propose Haskell sites use, is that top bar. It is the same as the top bar used in the Haddock Ocean theme. For sites, I suggest the top bar appear as it does in that image: The Haskell logotype on the left (linked to haskell.org), and some or all of the community links on the right. (Though I think the lambdas should be smaller versions of the logo.) Specific site branding and navigation goes under. Another way to use the bar would be like Haddock does: The left side contains the name of a major collection of pages. The links on the right are constant links to major sections. - Mark P.S.: The CSS for the top bar in that image can be found here: http://github.com/mtnviewmark/barley/blob/master/seed/static/scaffold.css Look for selectors with topbar in them. The CSS for the same bar in Haddock can be found here: http://code.haskell.org/haddock/html/Ocean.std-theme/ocean.css Look for selectors with package-header in them.___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Haskell theme Haskellers design
On Sat, Oct 23, 2010 at 1:27 AM, Mark Lentczner ma...@glyphic.com wrote: You might have seen the post I did yesterday about the Haskell project I'm currently working on. In it I posted an screen shot or a web page, which you can find here: http://mtnviewmark.files.wordpress.com/2010/10/source-editing.png That's cool! I'm working on a proposal for the haskellers website and that top bar is exactly what it's missing from it. cheers nubis :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
