[Haskell-cafe] Re: Forall and type synonyms in GHC 7.0
On Mon, Nov 1, 2010 at 4:30 AM, Mario Blažević mblaze...@stilo.com wrote:
Before uploading a new version of my project on Hackage, I decided to
future-proof it against GHC 7.0. I ran into several compile errors caused by
the changes in let generalization, but these were easy to fix by adding
extra type annotations. But then I ran into another problem that I can't fix
so easily. Here is its trimmed-down reproduction:
{-# LANGUAGE RankNTypes #-}
module Test where
data Component c = Component {with :: c}
pair1 :: (Bool - c1 - c2 - c3) - Component c1 - Component c2 -
Component c3
pair1 combinator (Component c1) (Component c2) = Component (combinator
True c1 c2)
type PairBinder m = forall x y r. (x - y - m r) - m x - m y - m r
pair2 :: Monad m = (PairBinder m - c1 - c2 - c3) - Component c1 -
Component c2 - Component c3
pair2 combinator = pair1 (combinator . chooseBinder)
chooseBinder :: Monad m = Bool - PairBinder m
chooseBinder right = if right then rightBinder else leftBinder
leftBinder :: Monad m = PairBinder m
leftBinder f mx my = do {x - mx; y - my; f x y}
rightBinder :: Monad m = PairBinder m
rightBinder f mx my = do {y - my; x - mx; f x y}
The general idea here, if you're intrigued, is that pair1 belongs to a
generic module that packages things it knows nothing about into Components.
The remaining definitions belong to a client of the generic module, and
pair2 is a specialization of pair1 to components that have something to do
with monads.
Now this little test compiles fine with GHC 6.12.1, but GHC
7.0.0.20101029 reports the following error in the pair2 definition:
TestForall.lhs:13:42:
Couldn't match expected type `forall x y r.
(x - y - m r) - m x - m y - m r'
with actual type `(x - y - m1 r) - m1 x - m1 y - m1 r'
Expected type: Bool - PairBinder m
Actual type: Bool - (x - y - m1 r) - m1 x - m1 y - m1 r
In the second argument of `(.)', namely `chooseBinder'
In the first argument of `pair1', namely
`(combinator . chooseBinder)'
I've tried adding extra type annotations without making any progress. At
this point I'm beginning to suspect I ran into a bug in GHC 7.0, but I can't
find it in GHC Trac; the only ticket that looks similar is #4347, but that
one works for me. Is this a bug? If not, how do I make my code compile?
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I had the exact same problem in my regional-pointers package in the
withArray function:
withArray ∷ (Storable α, MonadCatchIO pr)
⇒ [α]
→ (∀ s. RegionalPtr α (RegionT s pr) → RegionT s pr β)
→ pr β
I had to replace the original:
withArray vals = withArrayLen vals ∘ const
with:
withArray vals f = withArrayLen vals $ \_ → f
where:
withArrayLen ∷ (Storable α, MonadCatchIO pr)
⇒ [α]
→ (∀ s. Int → RegionalPtr α (RegionT s pr) → RegionT s pr β)
→ pr β
So unfortunately you gave to inline the function composition:
pair2 combinator = pair1 $ \b - combinator (chooseBinder b)
Note that in the other thread I'm describing a similar problem in my
usb-safe package. Where in essence the problem is that the following
won't type check:
foo :: (forall s. ST s a) - a
foo st = ($) runST st
but the following will:
foo :: (forall s. ST s a) - a
foo st = runST st
and surprisingly the following will also type check:
foo :: (forall s. ST s a) - a
foo st = runST $ st
Regards,
Bas
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Re: [Haskell-cafe] Reference for technique wanted
On 31 October 2010 23:05, Gregory Collins g...@gregorycollins.net wrote: They're called difference lists: Andy Gill and Graham Hutton's first worker wrapper paper calls then Hughes lists. This seems more apt to me than difference lists as difference lists (in the Haskell formulation at least*) don't seem to have any connection to a notion difference. Best wishes Stephen * It seems from other commentators on the thread that Haskell Hughes lists are actually different from Prolog difference lists anyway. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: network-2.2.3, merger with network-bytestring
Chris What you are observing is the effects of the delay on the operation of the TCP stacks and the way your 'sleep' works. You are introducing delay (the sleep time is a 'minimum' and then at least one o/s jiffy) - that represents one limit. The other limit is delay/bandwidth product of the connection hiding of this effect is dependent on the window size negotiated. How accurate do you need this control of throughput? To get really accurate rates we had to write our own specialist rate regulated thread library which accounts for any scheduling delay and can even spin if you want low delay variance in the packet dispatch times. Neil On 31 Oct 2010, at 17:56, Christopher Done wrote: On 31 October 2010 16:14, Johan Tibell johan.tib...@gmail.com wrote: This version marks the end of the network-bytestring package, which has now been merged into the network package. This means that efficient and correct networking using ByteStrings is available as part of the standard network package. As part of the merger, two new modules have been added: Network.Socket.ByteString and Network.Socket.ByteString.lAzy Huzzah! I updated my little throttler program to use ByteString.[1] One thing I'm curious about, that maybe you probably know off the top of your head, is that when I'm limiting the speed, I was merely recv'ing and send'ing at 1024 bytes a pop[2], however, when I did this at, say, ~500KB/s, Firefox is really slow at receiving it, whereas when I set it 4096 it's much faster/more accurate to the speed I intend. Chrome doesn't seem to care. I think the difference is that Firefox is single threaded (select/poll-based?) and has to switch between various jobs while receiving every tiny block that I'm sending. Chrome probably has the receiver in a separate process. So it seems like, short of balancing the package size (at powers of 2) and the delay to get some ideal throughput, it's easiest and probably realistically equivalent to set it to 4096 and just rely on an accurate delay? What do you think? Just curious. This is something I think I'll look into in the future, I really don't have a good feel for typical network latency and throughput. It's not a big deal right now as 56k slow is all I need to test my web app. [1]: http://github.com/chrisdone/throttle/commit/97e03bfc64adc074c9d1f19c2605cb496576c593 [2]: http://github.com/chrisdone/throttle/commit/30dc1d970a7c0d43c1b6dc33da9deecf30808114 ___ 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] Re: Parsing workflow
Malcolm Wallace wrote: Nils Schweinsberg wrote: Vo Minh Thu wrote: So you have to either factorize you parsers or use the 'try'. This is exactly what gives me headaches. It's hard to tell where you need try/lookAhead and where you don't need them. And I don't really feel comfortable wrapping everything into try blocks... Have you considered using a different set of parser combinators, a set that is actually composable, and does not require the mysterious try? I would recommend polyparse (because I wrote it), but uuparse would also be a fine choice. I second that, the semantics of Parsec are quite tricky. It's worth learning them properly if you insist on using Parsec. If you don't want to do that, it's easier to use a different library. The two defining properties of Parsec's alternative | combinator are: 1) If a parser p consumes a character, then it will take precedence over its alternatives p | q = p . 2) Parsers that are in sequence with an alternative don't have any influence on which alternative is chosen. (p | q) = k = p = k if p succeeds q = k if p does not succeed but p = k might not succeed even if p does succeed and q = k would succeed. I found the following rule of thumbs helpful: * Try to use alternatives p | q only when p and q recognize different first characters. * Don't do recursion yourself, use premade combinators like many1 etc. instead. * lookAhead is very useful for avoiding capturing input in the second argument of manyTill Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Reference for technique wanted
To simplify, the difference in persistence between the two representations is enough to consider them very different as it makes a dramatic difference in interface. Interesting discussion. I still think it is the same idea, namely to represent not-yet-known list tails by variables, embedded into two different kinds of languages. \rest-start++rest [start|rest]\rest-- '\' is an infix constructor The differences arise from the different handling of variables and scoping in those languages: - functional languages: explicit, local scopes, variables are bound by injecting values from outside the scope (applying the binding construct to values); scoped expressions can be copied, allowing multiple instantiations of variables - logic languages: implicit, global scopes, variables are bound by finding possible values inside the scope (unifying bound variables); outside of non-determinism/ sets-of-solutions handling, only non-scoped terms can be copied, allowing single instantiation only If current functional language implementations had not abandoned support for reducing under binders, one could float out the binder for a difference list, and get limitations closer to those of logic languages (though binding to values would then become much more unwieldy). If logic languages allowed local binders in terms, one could copy difference lists more easily (though substitution and unification would then involve binders). So, yes, the realization of the idea is different, as are the language frameworks, and the junk in the representations, but the idea is the same. Btw, functional language implementations not reducing under binders also implies that functional difference list operations are not shared to the same extent as logic difference list operations are - copying a closure copies un-evaluated expressions, to be re-evaluated every time the closure is opened with different variable bindings, so the functional representation is not as efficient as the logical one, in most implementations. I can't confirm the reference, but several authors point to this for an early description [CT77] Clark, K.L.; Tärnlund, S,Å: A First Order Theory of Data and Programs. In: Inf. Proc. (B. Gilchrist, ed.), North Holland, pp. 939-944, 1977. To close the circle: I understand that difference lists in Prolog might have been a declarative translation of in-place updating in Lisp lists:-) Claus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] commutativity
On 31/10/2010 16:55, Brent Yorgey wrote: Note that the first parameter to commutative shadows the previous definition of com, I don't know if that's what you intended. Does the following avoid the shadowing? infixl 5 `op` op :: Int - Int - Int x `op` y = (x + y) commutative op1 = \a b - (a `op` b) == (b `op` a) This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] commutativity
Yes, that would prevent the shadowing. But now you are ignoring the argument op1. Choosing a name that is more different from 'op' might be helpful. You can even invent your own operator as an argument to your commutative function: commutative (⊕) = \a b - (a ⊕ b) == (b ⊕ a) On Mon, Nov 1, 2010 at 11:15 AM, Patrick Browne patrick.bro...@dit.ie wrote: Does the following avoid the shadowing? infixl 5 `op` op :: Int - Int - Int x `op` y = (x + y) commutative op1 = \a b - (a `op` b) == (b `op` a) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Regex lib doesn't load
Hi Haskellers. I'm trying to read a text file using GHCi on Haskell Platform 2010.2.0.0. The import line in my program is import Text.Regex. When I run :main it says unknown symbol `_regerror' and unable to load package `regex-posix-0.94.2'. Any clues on how fix this problem? Please let me know if there's a better place to ask about it. --Dan Bensen___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Am I using type families well?
Hi,
There's nothing wrong with your type families. The problem is that the compiler
doesn't know that the m and rsc of eval are the same as m and rsc of runLoader.
(Also you had a small bug in the type of eval)
You need the ScopedTypeVariables extension, with a forall on runLoader to tell
GHC that they should be scoped:
runLoader :: forall m rsc a. (Monad m, Resource rsc) = CfgOf (IdOf rsc) -
RscLoader rsc m a - m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc) =
M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL (IdOf rsc)) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
Load id - do let loc = retrieveLoc cfg id
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
greetings,
Sjoerd
On Nov 1, 2010, at 1:53 AM, Yves Parès wrote:
Hello,
I'm trying to make a simple monad (built on operational's ProgramT) for
resource loading.
I have classes featuring type families :
{-# LANGUAGE TypeFamilies, FlexibleContexts, GADTs #-}
-- | A ResourceId is something that identifies a resource.
-- It should be unique for one resource, and should be used to find the
location (the path) of the resource,
-- possibly by using a configuration datatype
class (Ord id) = ResourceId id where
type LocOf id
type CfgOf id
retrieveLoc :: CfgOf id - id - LocOf id
-- | Class describing a resource of type @rsc@
class (ResourceId (IdOf rsc)) = Resource rsc where
type IdOf rsc
load :: LocOf (IdOf rsc) - IO (Maybe rsc)
-- ^ Called when a resource needs to be loaded
unload :: rsc - IO ()
-- ^ Idem for unloading
-- | Then, the operations that the loader can perform
data EDSL id a where
Load :: id - EDSL id ()
IsLoaded :: id - EDSL id Bool
Unload :: id - EDSL id ()
-- | The loader monad itself
type RscLoader rsc m a = ProgramT (EDSL (IdOf rsc)) m a
-- | And finally, how to run a loader
runLoader :: (Monad m, Resource rsc) = CfgOf (IdOf rsc) - RscLoader rsc m a
- m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc) =
M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL rsc) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
Load id - do let loc = retrieveLoc cfg id
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
Well, there is no way I can get it type-check. I think I must be misusing the
type families (I tried with multi-param typeclasses and functional
dependencies, but it ends up to be the same kind of nightmare...).
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--
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sjo...@w3future.com
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Re: [Haskell-cafe] Regex lib doesn't load
On 1 November 2010 23:36, Dan Bensen danben...@att.net wrote: Hi Haskellers. I'm trying to read a text file using GHCi on Haskell Platform 2010.2.0.0. The import line in my program is import Text.Regex. When I run :main it says unknown symbol `_regerror' and unable to load package `regex-posix-0.94.2'. Any clues on how fix this problem? Please let me know if there's a better place to ask about it. I'm going to randomly guess that you're using Windows, and that these previous reports of similar behaviour have the same problem as you do: http://www.mail-archive.com/haskell-cafe@haskell.org/msg51707.html http://www.mail-archive.com/haskell-platf...@projects.haskell.org/msg01153.html -- 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] Red links in the new haskell theme
On 2010-10-30 08:11 -0700, Mark Lentczner wrote: 1) HTML supports the concept of alternate style sheets. If present, then the idea was that browsers would give the user the choice, somewhere, to choose among them. While Firefox does this (View Page Style), The implementation in Firefox is such that the style sheet resets to the default if you reload the page or follow any link. This makes the feature completely useless in practice. -- Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Regex lib doesn't load
See this conclusion of this thread - installing the latest version from Hackage seems to be the solution: http://www.haskell.org/pipermail/haskell-cafe/2010-August/082141.html Note that although regex-posix is a binding to a C library, because the library and headers are delivered with the Platform you should be able to upgrade without needing MinGW (MinGW is otherwise usually needed for C library bindings on Windows). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Finding the contents of haskell platform?
I know there's a .cabal file for the latest version of HP somewhere, but I can't coerce Google into finding me a link that actually works. Furthermore, the following page: http://hackage.haskell.org/platform/contents.html does list all the contents, but to my big surprise it doesn't link to the specific versions of the packages for HP, instead it links to the latest version found on Hackage. Would someone with the power to make changes on the HP pages *please* make it as easy as possible to find the *exact* specification of what HP contains? Please, pretty please with sugar on top. No, a changelog entry (http://hackage.haskell.org/platform/changelog.html) is not very helpful (why the HP front page links to it I can't understand). Going via the Haskell wiki (http://www.haskell.org/haskellwiki/Haskell_Platform#What.27s_in_the_platform) to find a link to the .cabal (http://code.haskell.org/haskell-platform/haskell-platform.cabal) is not that user friendly. It's even worse that the latter link doesn't seem to work at all at the moment. (The short irritated tone in this email accurately shows my desperation with the situation: I thought I would be able to find this information with only 5 minutes to spare before my next meeting.) /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Finding the contents of haskell platform?
magnus: I know there's a .cabal file for the latest version of HP somewhere, but I can't coerce Google into finding me a link that actually works. Furthermore, the following page: http://hackage.haskell.org/platform/contents.html does list all the contents, but to my big surprise it doesn't link to the specific versions of the packages for HP, instead it links to the latest version found on Hackage. Would someone with the power to make changes on the HP pages *please* make it as easy as possible to find the *exact* specification of what HP contains? Please, pretty please with sugar on top. No, a changelog entry (http://hackage.haskell.org/platform/changelog.html) is not very helpful (why the HP front page links to it I can't understand). Going via the Haskell wiki (http://www.haskell.org/haskellwiki/Haskell_Platform#What.27s_in_the_platform) to find a link to the .cabal (http://code.haskell.org/haskell-platform/haskell-platform.cabal) is not that user friendly. It's even worse that the latter link doesn't seem to work at all at the moment. (The short irritated tone in this email accurately shows my desperation with the situation: I thought I would be able to find this information with only 5 minutes to spare before my next meeting.) Currently, the versions are specified in the .cabal file. A script is used to generate the changelog page (diffcabal, iirc). I'll generate a spec page from the .cabal file this week sometime. -- Don P.S. better sent to the haskell-platform@ list ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Forall and type synonyms in GHC 7.0
I had the exact same problem in my regional-pointers package in the withArray function: withArray ∷ (Storable α, MonadCatchIO pr) ⇒ [α] → (∀ s. RegionalPtr α (RegionT s pr) → RegionT s pr β) → pr β I had to replace the original: withArray vals = withArrayLen vals ∘ const with: withArray vals f = withArrayLen vals $ \_ → f where: withArrayLen ∷ (Storable α, MonadCatchIO pr) ⇒ [α] → (∀ s. Int → RegionalPtr α (RegionT s pr) → RegionT s pr β) → pr β So unfortunately you gave to inline the function composition: pair2 combinator = pair1 $ \b - combinator (chooseBinder b) This worked for me, thank you! I was worried I'd have to make a sweeping change to the module interfaces. I find this solution rather surprising, but as long as it's localized I don't mind. Note that in the other thread I'm describing a similar problem in my usb-safe package. Where in essence the problem is that the following won't type check: foo :: (forall s. ST s a) - a foo st = ($) runST st but the following will: foo :: (forall s. ST s a) - a foo st = runST st and surprisingly the following will also type check: foo :: (forall s. ST s a) - a foo st = runST $ st Yes, I hadn't seen that thread until this morning. The same issue with impredicative types appears to cause my problem and both problems you've encountered. I wonder what percentage of Hackage libraries will be affected by the change. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Edit Hackage
Stack Overflow and Reddit are at least improvements over the traditional web forums, starting to acquire some of the features Usenet had twenty years ago. Much like Planet-style meta-blogs and RSS syndication makes it liveable to follow blogs. Very much this. I mourn Usenet's potential as much as anyone, but life goes on. Agreed, in principle. However, the quality of discussions on Reddit makes me want to run away more often than not - it is already worse than Usenet was in its last throws (yes, I know it is living an afterlive;-). One thing we learned from Usenet is that trying to add to a thread gone bad is very unlikely to make it any better, and too many Reddit threads go bad so quickly that I've never felt like even trying to improve the signal/noise ratio. Just my own impression, of course (and perhaps the Haskell Reddit doesn't suffer quite as much). Also, while both Reddit and Stack Overflow can be read without Javascript, both require Javascript for posting (can't even log in to Reddit without, and have to edit half-blind in Stack Overflow without). Community-edited sites like these are the last ones on which I'd want to be forced to enable Javascript. Moving from a few Haskell mailing lists to many lists, to added IRC channels, to added blogs and RSS-feeds and aggregators, and added sites like Reddit and Stack Overflow does give more options, but makes it rather harder to follow everthing (in the beginning, feeds and aggregators give you the feeling that you're more up to date than ever, but at some point your feed handler overflows your number of hours per day:-). Which means that it is also getting more and more difficult to reach people as easily as before (do you ask on haskell-cafe, haskell-beginners, reddit, or SO? do you announce on haskell, haskell-cafe, or reddit? do you survey on haskell, haskell-cafe, google, or reddit? do you answer queries on the wiki, on -cafe, on -beginners, on reddit, on SO, or where? and so on..). Some people try to crosspost items to their favourite sites, in the hope of finding them again, in a single place. So many social sites now compete with each other that blog entries come with one-click-forward-this-there buttons. So, I agree with Don that you're missing things if you only follow the -cafe, and I agree with others that the -cafe is the most important forum for me. Overall, I'm not too happy with the way things are diverging, though.. Apart from the Usenet-mailing list move, it also reminds me of the command line-GUI movement - some people are quite happy with tools that at least remind them of command line control (such as most mail readers or programmer's editors), while others want web and guis that do not remind them of something they've never seen or put to good use (the command line prompt). Or perhaps, it is just a tick easier to get started on web forums - you can read without subscribing, you can subscribe without committing yourself (throwaway accounts on reddit, for instance) or installing tools (if I recall correctly, my last Windows notebook no longer came with pre-installed email client..). As you say, most email archives leave something to be desired. As far as I know, the best way to find anything in old -cafe threads is to do a google search with site:http://www.haskell.org/pipermail/haskell-cafe/;, and there's no good way to get an overview. Especially as topic drift leads to subject lines being uninformative (I mean, Edit Hackage? What?). I have the feeling that the existence of 4-5 archives for some Haskell lists means that the Google ranking will be spread among them, giving each a weaker ranking than one would hope for (it certainly didn't help that some time ago, haskell.org had robots banned from its mailing list archives for a while). Btw, does anyone know why searching with list:haskell-cafe does not help much, even though every single posting to this list has a List-Archive: heading pointing to the pipermail archive? Claus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Finding the contents of haskell platform?
On Mon, Nov 1, 2010 at 14:47, Don Stewart d...@galois.com wrote: magnus: I know there's a .cabal file for the latest version of HP somewhere, but I can't coerce Google into finding me a link that actually works. Furthermore, the following page: http://hackage.haskell.org/platform/contents.html does list all the contents, but to my big surprise it doesn't link to the specific versions of the packages for HP, instead it links to the latest version found on Hackage. Would someone with the power to make changes on the HP pages *please* make it as easy as possible to find the *exact* specification of what HP contains? Please, pretty please with sugar on top. No, a changelog entry (http://hackage.haskell.org/platform/changelog.html) is not very helpful (why the HP front page links to it I can't understand). Going via the Haskell wiki (http://www.haskell.org/haskellwiki/Haskell_Platform#What.27s_in_the_platform) to find a link to the .cabal (http://code.haskell.org/haskell-platform/haskell-platform.cabal) is not that user friendly. It's even worse that the latter link doesn't seem to work at all at the moment. (The short irritated tone in this email accurately shows my desperation with the situation: I thought I would be able to find this information with only 5 minutes to spare before my next meeting.) Currently, the versions are specified in the .cabal file. A script is used to generate the changelog page (diffcabal, iirc). I'll generate a spec page from the .cabal file this week sometime. Ah, excellent. Sorry for the rather rant-y email before. I've now been to the meeting and managed to calm down a bit :-) P.S. better sent to the haskell-platform@ list Yes, of course. I'm now trying to fix that by cross-posting, let's hope I won't get too many angry emails about that ;-) /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [ANNAUNCE] ghcjs-0.1.0 Haskell to Javascript compiler
On 29-10-10 22:20, Aaron Gray wrote: On 27 October 2010 13:30, Martijn Schrage mart...@oblomov.com mailto:mart...@oblomov.com wrote: On 21-10-10 01:01, Victor Nazarov wrote: This example creates a text field that turns red if it contains any non-digit characters. It is on-line at http://tryout.oblomov.com/ghcjs/ghcjs.html (Note: I only tested it on Firefox on a Mac) All used files are in a zip file at http://tryout.oblomov.com/ghcjs/ghcjs.zip (validate is in Test.hs, the JS monad in JS.hs, and the JavaScript for execHaskell in util.js) What browser are you using, IE8, IE9, FF and Chrome on Windows throw up errors, both locally and to your above code. That's weird, since http://tryout.oblomov.com/ghcjs/ghcjs.html works fine for me with Firefox both on Mac and Windows (XP 7). There is only a small bug that causes a key event to get lost when the Haskell JavaScript modules are loaded. What error messages do you get from Firefox? -- Martijn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] template haskell for typeclass synonyms
Hello. I'd like to have a template haskell function that take some constraints and a class name and write an empty class from those and relative empty instance to simulate typeclass synonyms. As I've never written TH and couldn't find a easily adaptable code around, I ask here for the code, or some hints on how to arrive there. Thanks paolino ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] commutativity
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 10/30/10 06:55 , Patrick Browne wrote: -- Question 1 -- commutative com 1 3 -- This also gives true. Is it because of commutative equation or because of the plus operation? Haskell doesn't know about commutativity; you got true because (+) happens to be commutative. There was a discussion about this recently on the list. - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkzO8MMACgkQIn7hlCsL25XC2ACgulNd5A+Gf33lplW3HOmhPLlZ u3EAoMsrbEkMQuU1yR/VaG5XqvNdhS5+ =jMQe -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] install GHC 7.0.1 RC on OS X?
I'd like to install the GHC 7.0.1 RC on my mac (Snow Leopard, x86_64), but I don't want it to run over my current GHC 6.12.2 install. If I use the .pkg installer, it doesn't allow me to select the destination, and I worry that it will overwrite my 6.12.2 install. If I try to build from source, that requires me to use my current GHC, which (as I understand) would build for 32 bit. What other options do I have, or am I misunderstanding something? -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] template haskell for typeclass synonyms
On 1 November 2010 17:53, Paolino paolo.verone...@gmail.com wrote: I'd like to have a template haskell function that take some constraints and a class name and write an empty class from those and relative empty instance to simulate typeclass synonyms. As I've never written TH and couldn't find a easily adaptable code around, I ask here for the code, or some hints on how to arrive there. I took Justin Bailey's haskelldb-th library as a TH example to work from and rewrote one TH function to try my hand at it, it's quite easy to follow with a simple example: http://hpaste.org/paste/41035/demo Maybe this is enough example to get you going. The rest you can find syntax parts from the TH Haddock documentation. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: network-2.2.3, merger with network-bytestring
On 1 November 2010 09:55, Neil Davies semanticphilosop...@gmail.com wrote: How accurate do you need this control of throughput? To get really accurate rates we had to write our own specialist rate regulated thread library which accounts for any scheduling delay and can even spin if you want low delay variance in the packet dispatch times. I don't need particular accuracy, about as slow as dial-up and about as slow as broadband are good enough for my purposes (merely testing a GMail-like AJAXy web app) and I've got that. But I was curious about how one might get accurate rates if you needed. What project did you need such accuracy for? I imagine a real-time system. What did you write the thread library in? C? Links? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] template haskell for typeclass synonyms
On Mon, Nov 1, 2010 at 6:09 PM, Christopher Done chrisd...@googlemail.com wrote: On 1 November 2010 17:53, Paolino paolo.verone...@gmail.com wrote: I'd like to have a template haskell function that take some constraints and a class name and write an empty class from those and relative empty instance to simulate typeclass synonyms. As I've never written TH and couldn't find a easily adaptable code around, I ask here for the code, or some hints on how to arrive there. I took Justin Bailey's haskelldb-th library as a TH example to work from and rewrote one TH function to try my hand at it, it's quite easy to follow with a simple example: http://hpaste.org/paste/41035/demo Maybe this is enough example to get you going. The rest you can find syntax parts from the TH Haddock documentation. A useful FYI: the API docs are (almost) completely devoid of comments, but if you click to see the source, it does have some additional information in comments there, just not Haddock-formatted. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Work is punishment for failing to procrastinate effectively. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] template haskell for typeclass synonyms
Thanks. I annotated the function http://hpaste.org/paste/41035/test_simpleclasssynonym It seems to produce the right code. How should I use the Parents synonym in my functions? This is a noob question I suppose. paolino 2010/11/1 Gábor Lehel illiss...@gmail.com On Mon, Nov 1, 2010 at 6:09 PM, Christopher Done chrisd...@googlemail.com wrote: On 1 November 2010 17:53, Paolino paolo.verone...@gmail.com wrote: I'd like to have a template haskell function that take some constraints and a class name and write an empty class from those and relative empty instance to simulate typeclass synonyms. As I've never written TH and couldn't find a easily adaptable code around, I ask here for the code, or some hints on how to arrive there. I took Justin Bailey's haskelldb-th library as a TH example to work from and rewrote one TH function to try my hand at it, it's quite easy to follow with a simple example: http://hpaste.org/paste/41035/demo Maybe this is enough example to get you going. The rest you can find syntax parts from the TH Haddock documentation. A useful FYI: the API docs are (almost) completely devoid of comments, but if you click to see the source, it does have some additional information in comments there, just not Haddock-formatted. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Work is punishment for failing to procrastinate effectively. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Generating random tuples
I'm toying with generating random objects (for example tuples) and started wondering what pearls of wisdom Cafe might have on the matter. Two obvious points (relating to my toy code, shown below) are 1) The meaning of the limits required by randomR is not obvious for types such as tuples (you could come up with some definition, but it wouldn't be unique: how would you allow for different ones?[*]; you might decide that having such limits is nonsensical and not want to provide a randomR: would you then leave it undefinded?). [*] I guess this is related to issues such as Num being both a sum and and product monoid. 2) I'm sure there are at least half a dozen prettier definitions of random. But I suspect that the juicy bits will be in offerings about issues that I haven't even dreamed about. Presumably QuickCheck's test-data generation mechanism would be interesting to look at in this context. Is there a gentle explanation of how it works somewhere? Here's my initial effort: import Control.Monad import System.Random main :: IO (Int, Int) main = randomIO instance (Random a, Random b) = Random (a, b) where randomR = undefined random g0 = let (i1,g1) = random g0 (i2,g2) = random g1 in ((i1,i2), g1) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] install GHC 7.0.1 RC on OS X?
On Mon, Nov 1, 2010 at 12:07 PM, Edward Amsden eca7...@cs.rit.edu wrote: I'd like to install the GHC 7.0.1 RC on my mac (Snow Leopard, x86_64), but I don't want it to run over my current GHC 6.12.2 install. If I use the .pkg installer, it doesn't allow me to select the destination, and I worry that it will overwrite my 6.12.2 install. If I try to build from source, that requires me to use my current GHC, which (as I understand) would build for 32 bit. What other options do I have, or am I misunderstanding something? Does GHC 7 support 64 bit? For some reason I had thought it was still 32 bit. Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Generating random tuples
On Monday 01 November 2010 19:18:33, Jacek Generowicz wrote: I'm toying with generating random objects (for example tuples) and started wondering what pearls of wisdom Cafe might have on the matter. Two obvious points (relating to my toy code, shown below) are 1) The meaning of the limits required by randomR is not obvious for types such as tuples But there's a pretty natural one, much like the Ix instance for tuples: randomR ((x1,y1),(x2,y2)) g0 = ((x,y),g2) where (x,g1) = randomR (x1,x2) g0 (y,g2) = randomR (y1,y2) g1 Of course, if there is an Ord instance, it would be tempting to use the limits as bounds for that, i.e. randomR (p1,p2) g should produce a pair p with p1 = p = p2, but that's not particularly nice to implement (in particular, if you don't want skewed sample distributions). (you could come up with some definition, but it wouldn't be unique: how would you allow for different ones?[*]; newtype you might decide that having such limits is nonsensical and not want to provide a randomR: would you then leave it undefinded?). Yes. [*] I guess this is related to issues such as Num being both a sum and and product monoid. 2) I'm sure there are at least half a dozen prettier definitions of random. But I suspect that the juicy bits will be in offerings about issues that I haven't even dreamed about. Presumably QuickCheck's test-data generation mechanism would be interesting to look at in this context. Is there a gentle explanation of how it works somewhere? Here's my initial effort: import Control.Monad import System.Random main :: IO (Int, Int) main = randomIO instance (Random a, Random b) = Random (a, b) where randomR = undefined random g0 = let (i1,g1) = random g0 (i2,g2) = random g1 in ((i1,i2), g1) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskellers browse users form
I'm using Safari on Snow Leopard. On the Browse Users page on Haskellers, there are little buttons that look like number spinners on the two numerical fields, like Using Haskell since... When I press one of those, the number -1.7976931348623157e+308 appears in the field. That must be Lennart. Thanks, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Generating random tuples
On 2010-11-01 19:18 +0100, Jacek Generowicz wrote:
I'm toying with generating random objects (for example tuples) and
started wondering what pearls of wisdom Cafe might have on the matter.
Two obvious points (relating to my toy code, shown below) are
1) The meaning of the limits required by randomR is not obvious for
types such as tuples (you could come up with some definition, but it
wouldn't be unique: how would you allow for different ones?[*]; you
might decide that having such limits is nonsensical and not want to
provide a randomR: would you then leave it undefinded?).
Indeed, the Random class has a fairly narrow everything fits on the
real line view of the world: not only is the talk about closed
intervals ambiguous in general, but so is the talk about uniform
distributions on those intervals. That being said, there is an Ord
instance for tuples (a lexicographic ordering) and for this case I think
it would make the most sense to use that: select an element from the set
{ x : lo = x = hi }
--
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
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Re: [Haskell-cafe] Generating random tuples
On Monday 01 November 2010 19:55:22, Nick Bowler wrote:
On 2010-11-01 19:18 +0100, Jacek Generowicz wrote:
I'm toying with generating random objects (for example tuples) and
started wondering what pearls of wisdom Cafe might have on the matter.
Two obvious points (relating to my toy code, shown below) are
1) The meaning of the limits required by randomR is not obvious for
types such as tuples (you could come up with some definition, but it
wouldn't be unique: how would you allow for different ones?[*]; you
might decide that having such limits is nonsensical and not want to
provide a randomR: would you then leave it undefinded?).
Indeed, the Random class has a fairly narrow everything fits on the
real line view of the world: not only is the talk about closed
intervals ambiguous in general, but so is the talk about uniform
distributions on those intervals. That being said, there is an Ord
instance for tuples (a lexicographic ordering) and for this case I think
it would make the most sense to use that: select an element from the set
{ x : lo = x = hi }
Really bad for
lo, hi :: (Int,Integer)
lo = (0,0)
hi = (3,4)
the product (partial) order seems much better to me.
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Re: [Haskell-cafe] Generating random tuples
On 2010-11-01 20:09 +0100, Daniel Fischer wrote:
On Monday 01 November 2010 19:55:22, Nick Bowler wrote:
That being said, there is an Ord instance for tuples (a
lexicographic ordering) and for this case I think it would make the
most sense to use that: select an element from the set
{ x : lo = x = hi }
Really bad for
lo, hi :: (Int,Integer)
lo = (0,0)
hi = (3,4)
Good point, that's not so hot.
the product (partial) order seems much better to me.
Indeed it does.
--
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
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Re: [Haskell-cafe] Am I using type families well?
Yes, I did make a small mistake in the type of eval.
In fact, through the compiler messages, I guessed that it was a problem of
matching between the 'rsc' type variable of runLoader and the 'rsc' of eval.
I thought that this kind of matching was automatic in Haskell, well I was
wrong... Thanks !
2010/11/1 Sjoerd Visscher sjo...@w3future.com
Hi,
There's nothing wrong with your type families. The problem is that the
compiler doesn't know that the m and rsc of eval are the same as m and rsc
of runLoader. (Also you had a small bug in the type of eval)
You need the ScopedTypeVariables extension, with a forall on runLoader to
tell GHC that they should be scoped:
runLoader :: forall m rsc a. (Monad m, Resource rsc) = CfgOf (IdOf rsc) -
RscLoader rsc m a - m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc) =
M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL (IdOf rsc)) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
Load id - do let loc = retrieveLoc cfg id
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
greetings,
Sjoerd
On Nov 1, 2010, at 1:53 AM, Yves Parès wrote:
Hello,
I'm trying to make a simple monad (built on operational's ProgramT) for
resource loading.
I have classes featuring type families :
{-# LANGUAGE TypeFamilies, FlexibleContexts, GADTs #-}
-- | A ResourceId is something that identifies a resource.
-- It should be unique for one resource, and should be used to find the
location (the path) of the resource,
-- possibly by using a configuration datatype
class (Ord id) = ResourceId id where
type LocOf id
type CfgOf id
retrieveLoc :: CfgOf id - id - LocOf id
-- | Class describing a resource of type @rsc@
class (ResourceId (IdOf rsc)) = Resource rsc where
type IdOf rsc
load :: LocOf (IdOf rsc) - IO (Maybe rsc)
-- ^ Called when a resource needs to be loaded
unload :: rsc - IO ()
-- ^ Idem for unloading
-- | Then, the operations that the loader can perform
data EDSL id a where
Load :: id - EDSL id ()
IsLoaded :: id - EDSL id Bool
Unload :: id - EDSL id ()
-- | The loader monad itself
type RscLoader rsc m a = ProgramT (EDSL (IdOf rsc)) m a
-- | And finally, how to run a loader
runLoader :: (Monad m, Resource rsc) = CfgOf (IdOf rsc) - RscLoader rsc
m a - m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc) =
M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL rsc) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
Load id - do let loc = retrieveLoc cfg id
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
Well, there is no way I can get it type-check. I think I must be misusing
the type families (I tried with multi-param typeclasses and functional
dependencies, but it ends up to be the same kind of nightmare...).
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Re: [Haskell-cafe] Am I using type families well?
Hi Yves,
On 11/01/2010 09:44 PM, Yves Parès wrote:
Yes, I did make a small mistake in the type of eval.
In fact, through the compiler messages, I guessed that it was a problem of
matching between the 'rsc' type variable of runLoader and the 'rsc' of eval.
I thought that this kind of matching was automatic in Haskell, well I was
wrong... Thanks !
Just out of curiosity: Does it work if you omit eval's type signature?
-- Steffen
2010/11/1 Sjoerd Visscher sjo...@w3future.com mailto:sjo...@w3future.com
Hi,
There's nothing wrong with your type families. The problem is that the
compiler doesn't know that the m and rsc of eval are the same as m and rsc
of runLoader. (Also you had a small bug in the type of eval)
You need the ScopedTypeVariables extension, with a forall on runLoader to
tell GHC that they should be scoped:
runLoader :: forall m rsc a. (Monad m, Resource rsc) = CfgOf (IdOf rsc)
- RscLoader rsc m a - m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc) =
M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL (IdOf rsc)) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
Load id - do let loc = retrieveLoc cfg id
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
greetings,
Sjoerd
On Nov 1, 2010, at 1:53 AM, Yves Parès wrote:
Hello,
I'm trying to make a simple monad (built on operational's ProgramT) for
resource loading.
I have classes featuring type families :
{-# LANGUAGE TypeFamilies, FlexibleContexts, GADTs #-}
-- | A ResourceId is something that identifies a resource.
-- It should be unique for one resource, and should be used to find the
location (the path) of the resource,
-- possibly by using a configuration datatype
class (Ord id) = ResourceId id where
type LocOf id
type CfgOf id
retrieveLoc :: CfgOf id - id - LocOf id
-- | Class describing a resource of type @rsc@
class (ResourceId (IdOf rsc)) = Resource rsc where
type IdOf rsc
load :: LocOf (IdOf rsc) - IO (Maybe rsc)
-- ^ Called when a resource needs to be loaded
unload :: rsc - IO ()
-- ^ Idem for unloading
-- | Then, the operations that the loader can perform
data EDSL id a where
Load :: id - EDSL id ()
IsLoaded :: id - EDSL id Bool
Unload :: id - EDSL id ()
-- | The loader monad itself
type RscLoader rsc m a = ProgramT (EDSL (IdOf rsc)) m a
-- | And finally, how to run a loader
runLoader :: (Monad m, Resource rsc) = CfgOf (IdOf rsc) - RscLoader
rsc m a - m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc) =
M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL rsc) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
Load id - do let loc = retrieveLoc cfg id
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
Well, there is no way I can get it type-check. I think I must be
misusing the type families (I tried with multi-param typeclasses and
functional dependencies, but it ends up to be the same kind of
nightmare...).
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Re: [Haskell-cafe] Am I using type families well?
Just out of curiosity: Does it work if you omit eval's type signature?
In fact you can't omit it since EDSL is a GADT.
I don't know why there is this restriction, but it is written in
operational's documentation:
http://hackage.haskell.org/packages/archive/operational/0.2.0.1/doc/html/Control-Monad-Operational.html
(At the very bottom of the page)
But there still must be something I don't get :
I tried to merge the two classes ResourceId and Resource in only one
Resource class, which leads to a few changes in runLoader :
{-# LANGUAGE TypeFamilies, FlexibleContexts, GADTs, ScopedTypeVariables #-}
import qualified Data.Map as M
import Control.Monad.Operational
-- | A ResourceId is something that identifies a resource.
-- It should be unique for one resource, and should be used to find the
location (the path) of the resource,
-- possibly by using a configuration datatype
--class (Ord id) = ResourceId id where
-- | Class describing a resource of type @rsc@
class (Ord (IdOf rsc)) = Resource rsc where
type IdOf rsc
type LocOf rsc
type CfgOf rsc
retrieveLoc :: CfgOf rsc - IdOf rsc - LocOf rsc
load :: LocOf rsc - IO (Maybe rsc)
-- ^ Called when a resource needs to be loaded
unload :: rsc - IO ()
-- ^ Idem for unloading
-- | Then, the operations that the loader can perform
data EDSL id a where
Load :: id - EDSL id ()
IsLoaded :: id - EDSL id Bool
Unload :: id - EDSL id ()
-- | The loader monad itself
type RscLoader rsc m a = ProgramT (EDSL (IdOf rsc)) m a
-- | And finally, how to run a loader
runLoader :: forall m rsc a. (Monad m, Resource rsc)
= CfgOf rsc - RscLoader rsc m a - m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc)
= M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL (IdOf rsc)) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
* Load id - do let loc = retrieveLoc cfg id*
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
This leads to new errors with 'IdOf rsc' and 'CfgOf rsc' :
GameBasics/Resources.hs:46:42:
Couldn't match expected type `CfgOf rsc'
against inferred type `CfgOf rsc1'
NB: `CfgOf' is a type function, and may not be injective
In the first argument of `retrieveLoc', namely `cfg'
In the expression: retrieveLoc cfg id
In the definition of `loc': loc = retrieveLoc cfg id
GameBasics/Resources.hs:46:46:
Couldn't match expected type `IdOf rsc'
against inferred type `IdOf rsc1'
NB: `IdOf' is a type function, and may not be injective
In the second argument of `retrieveLoc', namely `id'
In the expression: retrieveLoc cfg id
In the definition of `loc': loc = retrieveLoc cfg id
Seems like the compiler still has a 'rsc1' type despite the scoped type
variable 'rsc'.
2010/11/1 Yves Parès limestr...@gmail.com
Yes, I did make a small mistake in the type of eval.
In fact, through the compiler messages, I guessed that it was a problem of
matching between the 'rsc' type variable of runLoader and the 'rsc' of eval.
I thought that this kind of matching was automatic in Haskell, well I was
wrong... Thanks !
2010/11/1 Sjoerd Visscher sjo...@w3future.com
Hi,
There's nothing wrong with your type families. The problem is that the
compiler doesn't know that the m and rsc of eval are the same as m and rsc
of runLoader. (Also you had a small bug in the type of eval)
You need the ScopedTypeVariables extension, with a forall on runLoader to
tell GHC that they should be scoped:
runLoader :: forall m rsc a. (Monad m, Resource rsc) = CfgOf (IdOf rsc)
- RscLoader rsc m a - m a
runLoader cfg loader = viewT loader = eval M.empty
where
eval :: (Monad m, Resource rsc) =
M.Map (IdOf rsc) rsc
- ProgramViewT (EDSL (IdOf rsc)) m a
- m a
eval _(Return x) = return x
eval rscs (instr := k) = case instr of
Load id - do let loc = retrieveLoc cfg id
-- open and load from loc will go here
viewT (k ()) = eval rscs
-- -- -- Other cases yet to come...
greetings,
Sjoerd
On Nov 1, 2010, at 1:53 AM, Yves Parès wrote:
Hello,
I'm trying to make a simple monad (built on operational's ProgramT) for
resource loading.
I have classes featuring type families :
{-# LANGUAGE TypeFamilies, FlexibleContexts, GADTs #-}
-- | A ResourceId is something that identifies a resource.
-- It should be unique for one resource, and should be used to find the
location (the path) of the resource,
-- possibly by using a configuration datatype
class (Ord id) = ResourceId id where
type LocOf id
type CfgOf id
retrieveLoc :: CfgOf id - id - LocOf id
-- | Class describing a resource of type @rsc@
class (ResourceId (IdOf rsc)) = Resource rsc where
type IdOf
Re: [Haskell-cafe] template haskell for typeclass synonyms
I think I've got something nice in the end. http://hpaste.org/41042/classsynonymhs example: class (ParteDi (Servizio a) s ,Read a ,Eq a , Show a , Integer `ParteDi` s ) = SClass s a $(classSynonym ''SClass) ghci :i SClass command is printing some strange type variables but it compiles paolino 2010/11/1 Gábor Lehel illiss...@gmail.com On Mon, Nov 1, 2010 at 6:09 PM, Christopher Done chrisd...@googlemail.com wrote: On 1 November 2010 17:53, Paolino paolo.verone...@gmail.com wrote: I'd like to have a template haskell function that take some constraints and a class name and write an empty class from those and relative empty instance to simulate typeclass synonyms. As I've never written TH and couldn't find a easily adaptable code around, I ask here for the code, or some hints on how to arrive there. I took Justin Bailey's haskelldb-th library as a TH example to work from and rewrote one TH function to try my hand at it, it's quite easy to follow with a simple example: http://hpaste.org/paste/41035/demo Maybe this is enough example to get you going. The rest you can find syntax parts from the TH Haddock documentation. A useful FYI: the API docs are (almost) completely devoid of comments, but if you click to see the source, it does have some additional information in comments there, just not Haddock-formatted. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Work is punishment for failing to procrastinate effectively. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsing workflow
On 31/10/2010 04:15 PM, Nils Schweinsberg wrote: This is exactly what gives me headaches. It's hard to tell where you need try/lookAhead and where you don't need them. And I don't really feel comfortable wrapping everything into try blocks... I vaguely recall somebody mentioning a parser library on Hackage where try is the default behaviour and you turn it off explicitly, rather than turning it on explicitly. Apparently this is much more intuitive. But unfortunately I can't remember what the hell the library was... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Mysterious fact
The other day, I accidentally came up with this:
|{-# LANGUAGE RankNTypes #-}
type Either x y= forall r. (x - r) - (y - r) - r
left :: x - Either x y
left x f g= f x
right :: y - Either x y
right y f g= g y
|
This is one example; it seems that just about any algebraic type can be
encoded this way. I presume that somebody else has thought of this
before. Does it have a name?
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Re: [Haskell-cafe] Mysterious fact
Looks a lot like Church encoding to me:
http://en.wikipedia.org/wiki/Church_encoding
It was first discovered by the guy who invented lambda calculus :p
- jeremy
On Nov 1, 2010, at 5:28 PM, Andrew Coppin wrote:
The other day, I accidentally came up with this:
{-# LANGUAGE RankNTypes #-}
type Either x y = forall r. (x - r) - (y - r) - r
left :: x - Either x y
left x f g = f x
right :: y - Either x y
right y f g = g y
This is one example; it seems that just about any algebraic type can
be encoded this way. I presume that somebody else has thought of
this before. Does it have a name?
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Re: [Haskell-cafe] Mysterious fact
On Mon, 1 Nov 2010, Andrew Coppin wrote:
The other day, I accidentally came up with this:
{-# LANGUAGE RankNTypes #-}
type Either x y = forall r. (x - r) - (y - r) - r
left :: x - Either x y
left x f g = f x
right :: y - Either x y
right y f g = g y
This is one example; it seems that just about any algebraic type can be encoded
this
way. I presume that somebody else has thought of this before. Does it have a
name?
http://www.haskell.org/haskellwiki/Functions_not_data_structures
The article could be more informative. This was asked several times in
Haskell-Cafe, thus it should certainly be Category:FAQ - but with what
title?
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Re: [Haskell-cafe] Parsing workflow
On 1 November 2010 22:18, Andrew Coppin andrewcop...@btinternet.com wrote: I vaguely recall somebody mentioning a parser library on Hackage where try is the default behaviour and you turn it off explicitly, rather than turning it on explicitly. Apparently this is much more intuitive. But unfortunately I can't remember what the hell the library was... polyparse, is it? from http://code.haskell.org/~malcolm/polyparse/docs/index.html#what If you have only ever used the parsec combinators before, then you might be pleasantly surprised by polyparse: all of the same functionality is available, but it removes the confusion that all too commonly arises from a failure to use parsec's try combinator correctly. Ambiguous grammars often fail to be compositional in parsec, and it can be a black art guessing where to introduce a try to fix it. In contrast, polyparsers are by default fully compositional. It is possible to improve their efficiency (and the accuracy of error messages) by inserting commits (which are the dual of try), but it is not necessary for writing a correct parser, and furthermore, it is usually obvious where it can be beneficial to add a commit. Ozgur ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Mysterious fact
On Monday 01 November 2010 6:40:30 pm Jeremy Shaw wrote: Looks a lot like Church encoding to me: http://en.wikipedia.org/wiki/Church_encoding It was first discovered by the guy who invented lambda calculus :p Also, if you're interested in this, you can read Proofs and Types by Girard (not an easy read). In it, (I think) he notes, and probably proves, that you can encode any inductive type in System F (which is relatively close to Haskell with rank-n types) by this method (that is, it has the right types; of course it works in the untyped lambda calculus, too, but not in, say, the simply typed lambda calculus). You can also encode coinductive types: nu F = exists s. s * (s - F s) exists s. T[s] = forall r. (forall s. T[s] - r) - r -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] template haskell for typeclass synonyms
2010/11/1 Paolino paolo.verone...@gmail.com: I think I've got something nice in the end. http://hpaste.org/41042/classsynonymhs example: class ( ParteDi (Servizio a) s , Read a , Eq a , Show a , Integer `ParteDi` s ) ⇒ SClass s a $(classSynonym ''SClass) ghci :i SClass command is printing some strange type variables but it compiles Template Haskell might be overkill for this. In the past, I've done: class (Eq b, Show b, MyClass b, MyOtherClass b) = MySynonym b instance (Eq b, Show b, MyClass b, MyOtherClass b) = MySynonym b I think this requires a couple of GHC extensions, but TemplateHaskell is an extension as well. Maybe there are pitfalls with this approach. Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] windows network programming
I took a quick look on hackage for an interface to windows networking function calls, and didn't find anything that worked. I may have overlooked something. What's the state of windows network programming? Any recommendations for a good package? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] windows network programming
Have you tried the 'network' package on Hackage? I had thought it was cross-platform. I do not do much development on Windows. On Nov 1, 2010 6:45 PM, Michael Litchard mich...@schmong.org wrote: I took a quick look on hackage for an interface to windows networking function calls, and didn't find anything that worked. I may have overlooked something. What's the state of windows network programming? Any recommendations for a good package? ___ 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] windows network programming
On Mon, Nov 1, 2010 at 7:04 PM, Antoine Latter aslat...@gmail.com wrote: Have you tried the 'network' package on Hackage? I had thought it was cross-platform. I do not do much development on Windows. On Nov 1, 2010 6:45 PM, Michael Litchard mich...@schmong.org wrote: I took a quick look on hackage for an interface to windows networking function calls, and didn't find anything that worked. I may have overlooked something. What's the state of windows network programming? Any recommendations for a good package? Yes, I think it is cross-platform and it ships with Haskell Platform (so you don't have to compile by yourself). http://hackage.haskell.org/platform/contents.html Michael, also note that the newest version on Hackage merges network and network-bytestring. http://hackage.haskell.org/package/network Paulo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is Curry alive?
Hey everyone, This is a little off-topic, but I just ran into a problem which might benefit from being attacked by a logic language, so I've been looking for a good one to try out --- and hopefully one that has a very efficient implementation since I want to iterate through billions and possibly trillions of nondeterministically generated solutions. I was thinking about using Curry, but it looks to me like the language is dead and hasn't seen much activity for a few years. Does anyone know about whether there is still much going on over there? Or, alternatively, do you have any suggestions regarding other logic language/implementations I should check out? I've also been looking at Prolog but I am having trouble seeing whether I can process N non-deterministic solutions in O(1) space (rather than first generating a O(N) size list), and I checked out Mercury but the documentation for it is a bit sparse. Thanks! Greg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Am I using type families well?
This one is easy: -- | Class describing a resource of type @rsc@ class (Ord (IdOf rsc)) = Resource rsc where type IdOf rsc type LocOf rsc type CfgOf rsc retrieveLoc :: CfgOf rsc - IdOf rsc - LocOf rsc load :: LocOf rsc - IO (Maybe rsc) -- ^ Called when a resource needs to be loaded unload :: rsc - IO () -- ^ Idem for unloading Consider this: instance Resource () where type IdOf () = Int type LocOf () = String type CfgOf () = () retrieveLoc () n = Unit_ ++ show n load = undefined unload = undefined instance Resource Int where type IdOf () = Int type LocOf () = String type CfgOf () = () retrieveLoc () n = Int_ ++ show n load = undefined unload = undefined foo = retrieveLoc :: () - Int - String -- which retrieveLoc is called here? The problem, in case you haven't surmised it, is that retrieveLoc is ambiguous; you can never call it! There's no way to know which instance you might be referring to. You can work around it by making one of the type families into a data family (which is injective; you know that if CfgOf x = CfgOf y, then x = y). Or you can add a proxy parameter to retrieveLoc: data Proxy a = Proxy retrieveLoc :: Proxy rsc - CfgOf rsc - IdOf rsc - LocOf rsc now: foo = retrieveLoc (Proxy :: Proxy ()) and ghc can correctly infer foo's type as foo :: () - Int - String and foo will call the retrieveLoc from the () instance. -- ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is Curry alive?
On 2/11/2010, at 1:27 PM, Gregory Crosswhite wrote: Hey everyone, This is a little off-topic, but I just ran into a problem which might benefit from being attacked by a logic language, Why not describe the problem? so I've been looking for a good one to try out --- and hopefully one that has a very efficient implementation since I want to iterate through billions and possibly trillions of nondeterministically generated solutions. I think about the practical success of Model Checking, and wonder whether it might be better NOT to iterate through so many. I've also been looking at Prolog but I am having trouble seeing whether I can process N non-deterministic solutions in O(1) space (rather than first generating a O(N) size list), The point of backtracking search is that you need only space for the current candidate solution, not for all solutions visited so far. So much so that the Iterative Deepening family of search algorithms cheerfully *revisit* graph nodes in order to save time over all. and I checked out Mercury but the documentation for it is a bit sparse. Packl The Mercury documentation I downloaded in March comes to 773 pages. faq.pdf 6 pages library.pdf 470 pages reference_manual.pdf150 pages transition_guide.pdf 10 pages (Mercury for Prolog programmers) user_guide.pdf 137 pages Packing the tutorial into a single HTML file gives another 19 pages. Ralph Beckett's tutorial adds another 53 pages of PDF. So that's 845 pages all up. sparse? a bit sparse?___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is let special?
Hi all, is there something special about let? I don't mean only its use in haskell, but in the general context of programming languages. I've been given a few hints over time when I asked question concerning DSLs but regretfully didn't follow them up. Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is let special?
2010/11/2 Günther Schmidt gue.schm...@web.de: Hi all, is there something special about let? I don't mean only its use in haskell, but in the general context of programming languages. It means whatever the language specification/definition/implementation says it means. It's usually used for some kind of name binding however (there might be some language theory definition of let, but I wouldn't know). -- 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] Is Curry alive?
On 11/01/2010 06:19 PM, Richard O'Keefe wrote: On 2/11/2010, at 1:27 PM, Gregory Crosswhite wrote: Hey everyone, This is a little off-topic, but I just ran into a problem which might benefit from being attacked by a logic language, Why not describe the problem? My goal is to exhaustively search through a space in order to categorize all of the elements in that space. This space is combinatorial, so I am looking for a good domain specific language for letting me break up the space into a bunch of generators which can be combined combinatorically to generate the list of elements in the space. What makes the generators non-trivial is that I am choosing them carefully in order to eliminate many symmetries of the problem that effectively result in equivalent/redundant elements of the search space, and a consequence of this is that some generators depend on the results of other generators. The combinatorics of the problem are such that there are about a billion elements in the space if I try tackling a small version of my problem, and a trillion if I try tackling a slightly larger version of my problem. (More background: The elements in this space are choices of quantum measurement operators which are used to implement a quantum error-correcting code, and I am interested in knowing if the code is good or not. My goal is to systematically search through all codes with a small (= 5-6) number of qubits in order to be able to classify all of the possible of error-correcting codes one can implement using that many qubits.) It is worth mentioning that the function I am applying to these elements to compute the desired properties is very fast. I have had benchmarks showing the ability for this function to scan through up to ~ 500,000 elements a second (It helps that it is written in C++ :-) ). Actually, the more that I think about my problem the more that I'm thinking I should just stick with the List monad. This gives me a way to create generators that can rely on the results of other generators and put them all together using the List monad, taking advantage of Haskell's laziness to iterate in O(1) space. Which does raise the question: when is it better to use a logic programming language instead of the list monad? so I've been looking for a good one to try out --- and hopefully one that has a very efficient implementation since I want to iterate through billions and possibly trillions of nondeterministically generated solutions. I think about the practical success of Model Checking, and wonder whether it might be better NOT to iterate through so many. What exactly do you mean by Model Checking? Anyway, there might be more clever ways to eliminate possibilities from my space (other than the ones I have already) but the advantage of having a computer search all of it is that it can scan through all of the millions and even billions of possibilities in a stupid brute-force fashion in less time than it takes for me to come up with a clever way to analyze the space using theoretical analysis. :-) I've also been looking at Prolog but I am having trouble seeing whether I can process N non-deterministic solutions in O(1) space (rather than first generating a O(N) size list), The point of backtracking search is that you need only space for the current candidate solution, not for all solutions visited so far. So much so that the Iterative Deepening family of search algorithms cheerfully *revisit* graph nodes in order to save time over all. Yes, exactly, but my point is that in Prolog I am having trouble figuring out if there is a way to iterate over all of the solutions generated non-deterministically in O(1) space because all of the library functions which run an accumulator over a generated set of results seem to operate by first generating the full list and then accumulating over it which takes O(n) space, which is wasteful since as you point out it should only take O(1) space to do this. However, it is also possible that I misunderstand the semantics of how Prolog works and so things which look like O(n) to me are actually O(1) --- similar to laziness in Haskell. and I checked out Mercury but the documentation for it is a bit sparse. Packl The Mercury documentation I downloaded in March comes to 773 pages. faq.pdf 6 pages library.pdf 470 pages reference_manual.pdf150 pages transition_guide.pdf 10 pages (Mercury for Prolog programmers) user_guide.pdf 137 pages Packing the tutorial into a single HTML file gives another 19 pages. Ralph Beckett's tutorial adds another 53 pages of PDF. So that's 845 pages all up. sparse? a bit sparse? Yes, because although there is a tutorial with the trivial stuff, and a references for people who already know what they are doing, there is not much intermediate-level documentation for someone who understands the basic ideas behind the language
Re: [Haskell-cafe] Reference for technique wanted
On 1/11/2010, at 10:37 PM, Claus Reinke wrote: Interesting discussion. I still think it is the same idea, namely to represent not-yet-known list tails by variables, embedded into two different kinds of languages. \rest-start++rest [start|rest]\rest-- '\' is an infix constructor Savvy Prolog programmers wouldn't *DREAM* of using an infix constructor here. The art of doing list differences well in Prolog is to think of a list difference as a RELATIONSHIP between TWO terms, not as a single data structure. (The same is true for the queue example I mentioned. Keeping the length, the front, and the back as separate arguments gives usefully better performance.) The differences arise from the different handling of variables and scoping in those languages: - functional languages: explicit, local scopes, variables are bound by injecting values from outside the scope (applying the binding construct to values); scoped expressions can be copied, allowing multiple instantiations of variables - logic languages: implicit, global scopes, variables are bound by finding possible values inside the scope Eh? The scope of *identifiers* is strictly LOCAL in Prolog. Logic *variables* don't *have* scope. So, yes, the realization of the idea is different, as are the language frameworks, and the junk in the representations, but the idea is the same. In an extremely vague and not obviously useful sense. This is rather like saying that association lists and hash tables are both implementations of the finite map idea, so we might as well call them by the same name. The algorithmic and observability properties of the two approaches are very different. Since there already is a DList implementation for Haskell, I decided to write one for SML. It was very frustrating, because while everything is possible, almost nothing is easy. Many of the functions degenerated into fun foo x ... = fromList (List.foo (toList x) ...) and this included head and tail. Afterwards, looking at Data.DList to find out what clever trick I had missed, I was glumly pleased to find out there wasn't one: head and tail are O(size of list) in Data.DList too. The bottom line for anything that's supposed to make concatenation fast is that it ought to be able to make singleton and ++ fast. So I tried a test case. datatype tree = LEAF of int | FORK of (tree * tree); For SML/NJ I used a full binary tree of depth 22; for MLton I used a full binary tree of depth 25. SML/NJ MLton 0.899 0.244boring old plain list 5.481 1.244build a raum using raums 8.186 1.380build a raum then convert it to a list 12.581 4.449build a dlist using dlists 16.209 5.096build a dlist then convert it to a list Times were measured on an Intel Core 2 Duo Mac running Mac OS X 10.6.4, SSML/NJ v110.70 [built: Wed Jun 17 16:24:00 2009] MLton MLTONVERSION (built Mon Jun 15 11:10:01 CDT 2009 on fenrir.uchicago.edu) Building a list using dlists is 16 (SML/NJ) or 20 (MLton) times slower than using a plain list. Caveat: because raums handle reverse in O(1) time as well as concatenation, for a fair comparison I made dlists do the same, so type 'x dlist = bool - 'x list - 'x list fun fromList xs flag tail = if flag then xs @ tail else List.revAppend(xs, tail) fun list_flatten t = let fun flat (LEAF x) ys = x :: ys | flat (FORK(a,b)) ys = flat a (flat b ys) in flat t [] end fun raum_flat (LEAF x)= Raum.singleton x | raum_flat (FORK(a,b)) = Raum.cat (raum_flat a) (raum_flat b) fun raum_flatten t = Raum.toList (raum_flat t) fun dlist_flat (LEAF x)= DList.singleton x | dlist_flat (FORK(a,b)) = DList.cat (dlist_flat a) (dlist_flat b) fun dlist_flatten t = DList.toList (dlist_flat t) To close the circle: I understand that difference lists in Prolog might have been a declarative translation of in-place updating in Lisp lists:-) It seems unlikely. Prolog was born as a grammar formalism (metamorphosis grammars) and the idea of a non-terminal as a relation between a (starting point, end point) pair owes nothing to Lisp. I mean, do you call parser combinators in Haskell a declarative translation of in-place updating in Lisp lists? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is let special?
As syntax, let goes back at least to ISWIM. As for there being something special, Milner's algorithm for type checking/inference in SML had to treat let specially. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Haskellers browse users form
Alright, I've brushed up on my HTML5 form fields a bit and added appropriate min, max and step attributes for those fields, as well as the Haskeller since field in the profile. Let me know if you still have any problems with it. Thanks, Michael On Mon, Nov 1, 2010 at 8:47 PM, Yitzchak Gale g...@sefer.org wrote: I'm using Safari on Snow Leopard. On the Browse Users page on Haskellers, there are little buttons that look like number spinners on the two numerical fields, like Using Haskell since... When I press one of those, the number -1.7976931348623157e+308 appears in the field. That must be Lennart. Thanks, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
