Re: [Haskell-cafe] DpH/repa cache locality
Hi, 2010/7/13 Gregory Crosswhite gcr...@phys.washington.edu: Just out of curiosity, what work is being done in the data parallel haskell / repa projects regarding cache locality? Hi, I'm not knowledgeable at all about this, but for a technical introduction to DPH, I found the following excellent. Locality is a recurring theme in the talk, IIRC. (Sorry for the double reply) http://www.youtube.com/watch?v=NWSZ4c9yqW8 Dominique ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Please report any bug of gtk2hs-0.11.0!
Hi all, We plan to release bug fix version : gtk2hs-0.11.1 Please report any bug of gtk2hs-0.11.0, we will fix it before release gtk2hs-0.11.1 We plan to add many new APIs in gtk2hs-0.12.0, so gtk2hs-0.11.1 will be the last stable version with current APIs. Thanks for your help! -- Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] ANNOUNCE: Haskell 2010 Report (final)
On 12/07/2010 18:29, Felipe Lessa wrote:
On Mon, Jul 12, 2010 at 9:50 AM, Simon Marlowmarlo...@gmail.com wrote:
And hopefully things will improve over time, as fewer packages will need to
depend on base. We could also start pulling out APIs that are currently in
base into separate packages, without actually pulling out the code - e.g.
concurrency, and that would be a good way to migrate people away from
depending on base, but without breaking everything.
Is the plan to stop using base and start using 'haskell2010', even if
you use extensions that aren't Haskell 2010?
You can make an independent choice about whether to use the Haskell 2010
language, and/or the Haskell 2010 libraries.
If you need to use modules from base that are not part of Haskell 2010,
then you will not be able to use the haskell2010 package, but you will
still be able to use {-# LANGUAGE Haskell2010 #-}.
Cheers,
Simon
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] lists of arbitrary depth
hello, iam really new to haskell, i want to define a function which takes as a parameter a list which can contain other lists, eg. [1,[2,3],[4,[5,6]]] how would i define a function that can iterate through the items so (in this example) iter1 = 1 iter2 = [2,3] iter3 = [4,[5,6]] ? ( can i do that without using the Tree data type? ) THANKS! -- View this message in context: http://old.nabble.com/lists-of-arbitrary-depth-tp29139641p29139641.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lists of arbitrary depth
On 13 July 2010 10:58, vadali shlomivak...@gmail.com wrote: hello, iam really new to haskell, i want to define a function which takes as a parameter a list which can contain other lists, eg. [1,[2,3],[4,[5,6]]] how would i define a function that can iterate through the items so (in this example) iter1 = 1 iter2 = [2,3] iter3 = [4,[5,6]] ? ( can i do that without using the Tree data type? ) Maybe this should be moved to Haskell-Beginnners. It's impossible to have a function that works on a list of arbitrary nesting. But you could use a tree data type, yeah. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lists of arbitrary depth
Hi Vadali, On Tue, Jul 13, 2010 at 10:58 AM, vadali shlomivak...@gmail.com wrote: hello, iam really new to haskell, i want to define a function which takes as a parameter a list which can contain other lists, eg. [1,[2,3],[4,[5,6]]] how would i define a function that can iterate through the items so (in this example) iter1 = 1 iter2 = [2,3] iter3 = [4,[5,6]] ? ( can i do that without using the Tree data type? No, a list contains a homogeneous sequence of values (i.e. a sequence of values of the same type). If you explain what you're trying to achieve we might be able to offer you better help. Cheers, Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lists of arbitrary depth
vadali shlomivak...@gmail.com writes: hello, iam really new to haskell, i want to define a function which takes as a parameter a list which can contain other lists, eg. [1,[2,3],[4,[5,6]]] how would i define a function that can iterate through the items so (in this example) iter1 = 1 iter2 = [2,3] iter3 = [4,[5,6]] ? ( can i do that without using the Tree data type? ) Well, that's what a tree is, so why not use a tree? Your only other option is to define your own tree-like structure: data MyTree a = Value a | SubTree [MyTree a] THANKS! YOUR WELCOME! :p -- 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] lists of arbitrary depth
Thank you all for replying! I am really beginning my baby steps in this fascinating language, and was just wondering if it was possible to naturally scan lists with arbitrary lists (aka trees :) ). I guess this forum specifically is too advancaed for me (yet!), so my next questions will be posted on the beginners forum. Thanks, Vadali On Tue, Jul 13, 2010 at 11:07 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: vadali shlomivak...@gmail.com writes: hello, iam really new to haskell, i want to define a function which takes as a parameter a list which can contain other lists, eg. [1,[2,3],[4,[5,6]]] how would i define a function that can iterate through the items so (in this example) iter1 = 1 iter2 = [2,3] iter3 = [4,[5,6]] ? ( can i do that without using the Tree data type? ) Well, that's what a tree is, so why not use a tree? Your only other option is to define your own tree-like structure: data MyTree a = Value a | SubTree [MyTree a] THANKS! YOUR WELCOME! :p -- 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] lists of arbitrary depth
2010/7/13 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com: vadali shlomivak...@gmail.com writes: hello, iam really new to haskell, i want to define a function which takes as a parameter a list which can contain other lists, eg. [1,[2,3],[4,[5,6]]] how would i define a function that can iterate through the items so (in this example) iter1 = 1 iter2 = [2,3] iter3 = [4,[5,6]] ? ( can i do that without using the Tree data type? ) Well, that's what a tree is, so why not use a tree? Your only other option is to define your own tree-like structure: data MyTree a = Value a | SubTree [MyTree a] Defining your own tree structure is better in this case as Data.Tree store elements in each node, not just in the leaves. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lists of arbitrary depth
On 13 Jul 2010, at 10:11, Shlomi Vaknin wrote: Thank you all for replying! I am really beginning my baby steps in this fascinating language, and was just wondering if it was possible to naturally scan lists with arbitrary lists (aka trees :) ). Trees aren't lists, Trees are trees... Here's how you create one* data Tree a = Leaf | Branch a [Tree a] This roughly says, a tree can be made up of two possible things... First, it could be a leaf, and secondly, it could be a branch with an element at it, and a list of subtrees. Some example trees using this data type: 1) Leaf 2) Branch 5 [] 3) Branch 5 [Leaf] 4) Branch 5 [Branch 10 [], Branch 20 [], Leaf, Branch 50 [Branch 10 [], Leaf]] When you have really strong typing, you also have very well specified types. You don't just use a list as if it were a tree, you declare what a tree is. Bob * In this case an arbitrarily branching tree, we could ofc declare different forms of tree here.___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANNOUNCE: Haskell 2010 Report (final)
On 12/07/2010 22:12, John Meacham wrote: On Mon, Jul 12, 2010 at 01:50:01PM +0100, Simon Marlow wrote: Right. I like the idea of packages being able to declare re-exported modules, indeed I considered doing this in GHC (when we needed base3) but decided not to mainly because we would still need PackageImports, and once you have PackageImports you can implement re-exports using that, albeit with more boilerplate. The advantage of direct re-exports, as you say, is that it avoids a conflict when the module is imported. However, since some of the modules would conflict anyway, there didn't seem to be much advantage in avoiding the conflict in some cases but not others. Well, a main useful case is that I can do -phaskell98 and -phaskell2010 at the same time. So I can make the default jhc behavior be the union of the two languages easily. That works in GHC too: the modules of those two packages don't overlap. That is partly because we never moved Prelude from base to haskell98. But suppose the Haskell 2010 Prelude had some differences from the Haskell 98 Prelude - then a direct re-export wouldn't work, and you'd be stuck with conflicts again. So my main point is that while direct re-exports avoid conflicts sometimes, they're not a general solution, and eventually you run into the same problems again. There are differences between several Haskell 2010 modules and the equivalent base modules, so you won't be able to use re-exports for those. There is also some philosophy behind it. I don't like coupling things that don't need to be coupled, such as the interface a library exports and the place that interface is implemented. I agree with the philosophy, but I don't understand how package re-exports are part of its implementation - the Haskell module system already lets you re-export entities and therefore decouple the implementation from the API. I think the ability for a package to define an 'interface' built up from other re-exported modules will be very useful going forward, I am not sure how hard something like that would be to implement in ghc, but it may be worth it in the future. Isn't that what PackageImports lets you do? Hmm.. maybe. Jhc doesn't have PackageImports, the idea being that you re-export modules rather than importing them from a specific package and exporting their interface. So, it sort of shifts the effort from the interface makers to the implementors, as in, the Haskell 98 Prelude will actually have to be in a module called Compat.Haskell98.Prelude and just re-exported by the 'haskell98' and 'haskell2010' modules. I don't think the difference is as fundamental as you make out. In Haskell you can already write module A ( module B ) where import B which is the essence of re-exporting a module, and preserves the interface/implementation separation. Now suppose A and B are the same module name, from different packages. To implement this re-export you can either (1) Use a package re-export (in JHC) (2) Somehow avoid A and B being the same, e.g. by having an intermediate like Compat.Haskell98.Prelude (3) Use PackageImports (in GHC) the advantage of (1) is that you can have both packages in scope without a conflict, whereas in (2/3) the two modules can export different interfaces, while still separating the implementation from the interface. I think of PackageImports as just an optimisation that lets you avoid the intermediate module in (2). So again, my point is that in the general case the APIs diverge, so you don't get to do (1), or you only get to do it for some modules, which could be confusing for users. In one sense 'Compat.Haskell98' sort of acts as a package import, but it isn't actually tied to a package, it just refers to the Compat.Haskell98.Prelude in scope. I also have a large aversion to allowing package names to infect source files carte blanche. It blurs the line between the language itself and the environment the language runs in. It may be neccesarry at some point, but I'll put it off until a case comes up that makes it abundantly clear that it is needed. I agree with your aversion to putting package names in the source code, which is why we don't advertise PackageImports as an extension that we expect end users to use, and we don't let you use version numbers. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lists of arbitrary depth
Thank you Bob, your example clarified how actually using such data type would appear in haskell. I naively thought it would be as simple as defining a regular list, but i see it is slightly more strict than that. I appreciate your help! Vadali On Tue, Jul 13, 2010 at 11:18 AM, Thomas Davie tom.da...@gmail.com wrote: On 13 Jul 2010, at 10:11, Shlomi Vaknin wrote: Thank you all for replying! I am really beginning my baby steps in this fascinating language, and was just wondering if it was possible to naturally scan lists with arbitrary lists (aka trees :) ). Trees aren't lists, Trees are trees... Here's how you create one* data Tree a = Leaf | Branch a [Tree a] This roughly says, a tree can be made up of two possible things... First, it could be a leaf, and secondly, it could be a branch with an element at it, and a list of subtrees. Some example trees using this data type: 1) Leaf 2) Branch 5 [] 3) Branch 5 [Leaf] 4) Branch 5 [Branch 10 [], Branch 20 [], Leaf, Branch 50 [Branch 10 [], Leaf]] When you have really strong typing, you also have very well specified types. You don't just use a list as if it were a tree, you declare what a tree is. Bob * In this case an arbitrarily branching tree, we could ofc declare different forms of tree here. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Please report any bug of gtk2hs-0.11.0!
Andy Stewart schrieb: Hi all, We plan to release bug fix version : gtk2hs-0.11.1 Please report any bug of gtk2hs-0.11.0, we will fix it before release gtk2hs-0.11.1 I'm looking forward for this bug-fix release (since gtk2hs-0.11.0 did not work for me). Because I've almost missed this message I reply to gtk2hs-us...@lists.sourceforge.net, too. Christian We plan to add many new APIs in gtk2hs-0.12.0, so gtk2hs-0.11.1 will be the last stable version with current APIs. Thanks for your help! -- Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Finding zipper for custom tree
2010/7/2 Heinrich Apfelmus apfel...@quantentunnel.de:
Sergey Mironov wrote:
Hello list!
I am trying to understand zipper concept using papers like [1] and [2].
Though main idea looks clear, I still have a problem in applying it for
custom data types.
Please help me with deriving Zipper-type from
data DTree a = P | D [(a, DTree)]
Looking in [1] ('Zippers via Differentiation' chapter) I tried to do
the following:
1. Find a DTreeF type which is a pattern functor ([2], chapter 2.1) of my
DTree
2. Write DTreeF in 'algebraic' form (using '+' and '*')
3. Find DTreeF' - derivative of DTreeF
4. Define my zipper type using list of DTreeF'
These are the right steps.
Step 1 likely ends with
data DTreeF a x = P | D [(a,x)]
[2] says that using this pattern functor one could build a fixed-point
version of DTree:
data Fix f = In {out :: (f (Fix f))}
data DTreeFP = Fix DTreeF
but seems that I have nothing to do with it right now.
The fixed point is just another way to write DTree .
DTreeFP a = DTree a
Step 2 is my main question:
In [1] authors did it for binary tree:
data Tree a = Leaf a | Bin (Tree a) (Tree a)
data TreeF a x = Leaf a | Bin x x
and thus
TreeF = a + x * x
TreeF' = x + x
My DTree has inner list of tuples. How should I rewrite it in terms of
'+' and '*' ?
Ah, you can't write it in terms of only '+' and '*' because you also have
the list type in there:
DTreeF = 1 + List (a * x)
^^ List involves a fixed point
So, to find the derivate, you have to calculate the derivative of List
first:
List' x = List x * List x
and then you can use the chain rule to find DTreeF .
Regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Sorry for late answer. Luke, Heinrich - thank you very much for explanations.
I feel that I need more reading to get familiar with differentiation
of functors and chain rule. Could you suggest some books or papers?
--
Thanks,
Sergey
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Functional dependencies and Peano numbers
On Sun, Jul 11, 2010 at 12:43:47AM +0200, Jose A. Ortega Ruiz wrote: On Sat, Jul 10 2010, wren ng thornton wrote: [...] Yes, you can add multiple dependencies. The syntax is to use , after the first |. While having eight parameters is surely a desperate need for refactoring, there are times when you'd want multiple dependencies. For example, you can say class F a b | a - b, b - a where... to express a bijective function on types (that is, for every pair of A and B, if you know one of them then you know what the other must be uniquely). I know i should read the relevant articles, but how would one express such a bijection using type families? You would just create two type families, one for each direction of the mapping: type family F1 a :: * type instance F1 Int = Bool type instance F1 ... type family F2 a :: * type instance F2 Bool = Int type instance F2 ... Of course, this is not quite the same thing, since with the MPTC version we are guaranteed to get a bijection, but there is nothing forcing F1 and F2 to have anything to do with one another (for example I could have written type instance F2 Char = Int). But I don't know whether this would make a difference in practice. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambda calculus and equational logic
On Wed, Jul 07, 2010 at 09:56:08AM +0100, Patrick Browne wrote: Hi, In Haskell what roles are played by 1)lambda calculus and 2) equational logic? Are these roles related? Hopefully this question can be answered at a level suitable for this forum. Since no one else has responded I'll take a quick stab at answering, and others can fill in more information as appropriate, or ask further questions. 1) In general, the lambda calculus is seen as foundational conceptual basis for functional programming: Haskell has anonymous lambda expressions, higher-order functions, and currying, all of which come directly from the lambda calculus. More specifically, GHC's core language is based on a variant of System F omega, which is a fancy version of the simply-typed lambda calculus with polymorphism and type constructors. If you were to print out the core language code generated by GHC for some Haskell program, you would essentially see a bunch of lambda calculus expressions. 2) Haskell is able to embrace equational logic because of its insistence on purity: in a Haskell program (leaving aside for the moment things like seq and unsafePerformIO) you can always replace equals by equals (where equality is the normal beta-equality for System F omega, plus definitional equality introduced by Haskell declarations) without changing the semantics of your program. So the story of an equational logic for System F omega and the story of evaluating Haskell programs are to a large extent the same story. Coming up with equational logics corresponding to most imperative languages (or even a non-pure functional language like OCaml) is massively complicated by the need to keep track of an implicit state of the world due to the presence of side effects. I am not sure what to say about their relationship. Perhaps my above answers have already shed some light on that. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ByteString, zipWith', and rewrite rules
Thomas M. DuBuisson wrote: Comments on the zipWith' function inside of Data.ByteString say: -- Rewrite rules -- are used to automatically covert zipWith into zipWith' when a pack is -- performed on the result of zipWith. This is only true internally to Data.ByteString because the zipWith' function could be inlined away by GHC once that module is compiled, right? If I want pack (zipWith xor bs1 bs2) to be efficient then I'll have to either get zipWith' exported or write my own lower level zipWith'? As far as I know GHC prefers RULES to INLINE, but it's fragile. You may check with -ddump-simpl-stat. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Marshalling
Hello I'm wondering if anyone ever benchmarked marshalling in Haskell/GHC. No matter how much I optimize my Haskell code my program still seems to run slow, which leads me to beleive that Marshalling is painfully slow. Does anyone know a way I can test this and fix it? Regards, Phyx ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Marshalling
On Tue, Jul 13, 2010 at 13:29, Phyx loneti...@gmail.com wrote: Hello I'm wondering if anyone ever benchmarked marshalling in Haskell/GHC. No matter how much I optimize my Haskell code my program still seems to run slow, which leads me to beleive that Marshalling is painfully slow. Does anyone know a way I can test this and fix it? What kind of marshalling are you referring to? /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] lambda calculus and equational logic
On 13/07/2010, at 20:47 , Brent Yorgey wrote: On Wed, Jul 07, 2010 at 09:56:08AM +0100, Patrick Browne wrote: Hi, In Haskell what roles are played by 1)lambda calculus and 2) equational logic? Are these roles related? Hopefully this question can be answered at a level suitable for this forum. Since no one else has responded I'll take a quick stab at answering, and others can fill in more information as appropriate, or ask further questions. 2) Haskell is able to embrace equational logic because of its insistence on purity: in a Haskell program (leaving aside for the moment things like seq and unsafePerformIO) you can always replace equals by equals (where equality is the normal beta-equality for System F omega, plus definitional equality introduced by Haskell declarations) without changing the semantics of your program. So the story of an equational logic for System F omega and the story of evaluating Haskell programs are to a large extent the same story. Replacing equals by equals usually doesn't change anything. What kind of equality do you use for getChar :: IO Char ? Coming up with equational logics corresponding to most imperative languages (or even a non-pure functional language like OCaml) is massively complicated by the need to keep track of an implicit state of the world due to the presence of side effects. By massively complicated you mean harder than the simplest case. Haskell's do-notation makes the state of the world implicit, and performing the desugaring makes it explicit again -- but then that state isn't really the state of the word... Sorry or my heckling. You gave a fine answer, to the standard question. However, I propose mandating that all such questions asked on the haskell-beginners list are answered with Haskell's purity solves everything -- but on haskell-cafe they should get Haskell's purity solves everything, but read Sabry's paper on What is a Purely Functional Language, because it's really more subtle than that. Cheers, Ben. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambda calculus and equational logic
Ben, comments from the peanut gallery: On 13/07/2010, at 11:51 PM, Ben Lippmeier wrote: What kind of equality do you use for getChar :: IO Char ? Surely this is easy: getChar denotes a particular IO action, which is always the same thing (i.e. self-identical and distinct from all other IO actions). By massively complicated you mean harder than the simplest case. Haskell's do-notation makes the state of the world implicit, and performing the desugaring makes it explicit again -- but then that state isn't really the state of the word... ... which tells you that the passing-the-world semantics is not a faithful model of I/O. In the archives of this list there are many comments on exactly this topic. A couple of quick pointers: - Wouter Swierstra wrote a paper on this. http://www.cse.chalmers.se/~wouter/repos/IOSpec/index.html - Resumptions are a better model: http://www.haskell.org/pipermail/haskell-cafe/2003-August/004892.html Intuitively the state monad used by GHC works because it only needs to track dependencies between I/O actions - there is no need for the compiler to impose a total order on everything going on in the world (taken to be all of the context that could influence the execution of the program). For interesting programs it cannot, anyway. cheers peter -- http://peteg.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] New FGL naming survey
Whether or not the new FGL that Thomas Bereknyei and I are working on should keep the name was a semi-hot issue when we first mentioned the fact that we were working on a new version about a month ago. As such, I've created a survey here to try and find out what the Haskell community overall thinks we should call it: https://spreadsheets.google.com/viewform?formkey=dGpzMmFnUWY3Uktodk5wdHlLQk5kT1E6MA More info can be found on the actual survey page. -- 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] Re: The site has been exploited (again)
begin Gwern Branwen quotation: Ashley has made me admin; I've spent the last 1.5 hours deleting all the vandalism and indef blocking the accounts. I have Recent Changes in my RSS reader, so hopefully in the future there will be no greater than 24 hours delay before vandalism is dealt with. A MW upgrade will also help (eg. currently checkuser* seems to be unavailable). * http://www.mediawiki.org/wiki/Extension:CheckUser Excellent! Putting aside what I said earlier about protection, which doesn't really work well with a single active admin, it may still be worth putting some protection in place to avoid a non-bot account maliciously sticking something like the goatse.cx pic on the home page of Haskell.org. The options I know of for doing this are the Patrolled Edits feature and the FlaggedRevs extension. Unfortunately, I don't think either of these can be applied only to a limited set of pages because of the MediaWiki team's asinine insistence that they'll never support per-page authorization mechanism properly. -md ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Marshalling
Marshalling large amount of data from and to C http://phyx.pastebin.com/WXGBr1bX shows the code I use to do this (it's autogenerated, so just looking at 1 block should be enough) The tool is mine, so i can change the code it generates, but i would need to know how to do it better first. On Tue, Jul 13, 2010 at 3:30 PM, Magnus Therning mag...@therning.orgwrote: On Tue, Jul 13, 2010 at 13:29, Phyx loneti...@gmail.com wrote: Hello I'm wondering if anyone ever benchmarked marshalling in Haskell/GHC. No matter how much I optimize my Haskell code my program still seems to run slow, which leads me to beleive that Marshalling is painfully slow. Does anyone know a way I can test this and fix it? What kind of marshalling are you referring to? /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] Re: [Haskell] ANNOUNCE: jhc 0.7.4
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 7/12/10 22:29 , Richard O'Keefe wrote: On Jul 11, 2010, at 9:38 AM, wren ng thornton wrote: Generally OSX takes UTF16 to be the standard encoding (I don't recall if it's LE or BE), though UTF8 is supported almost everywhere. I haven't checked to see whether that would affect this particular task though. Mac OS X 10.5 came with a lot of locales, including a lot of UTF-8 ones. Indeed, the default was a UTF-8 one. But it didn't come with *any* UTF-16 locales. (As tested by 'locale -a'.) wren is half right: at the level of Unixy APIs (and this includes anything that goes on in a Terminal window and anything that you will be doing from Haskell) you use UTF8, but OSX APIs --- that is, Carbon and Cocoa --- use UTF16. So for the purposes of ghc/jhc OSX is UTF8, but if someone wrote a fully native Cocoa-based runtime it would use UTF16. (Compare Win32 APIs to mingw APIs; very similar situation.) - -- 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/ iEYEARECAAYFAkw8kXcACgkQIn7hlCsL25XMBwCghhWYpvyhhpG5L3tnOZQcJPIQ h8oAnA5c5kCbrjtD5bMe/yAyw/BDUTAl =p0QN -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Marshalling
That code is effectively copying the data (thats what those peeks / pokes do), so it stands to reason it would be slow by most performance standards. The reason ByteStrings are fast when used both by C and Haskell is there is a zero-copy `useAsCString`. Cheers, Thomas On Tue, Jul 13, 2010 at 7:49 AM, Phyx loneti...@gmail.com wrote: Marshalling large amount of data from and to C http://phyx.pastebin.com/WXGBr1bX shows the code I use to do this (it's autogenerated, so just looking at 1 block should be enough) The tool is mine, so i can change the code it generates, but i would need to know how to do it better first. On Tue, Jul 13, 2010 at 3:30 PM, Magnus Therning mag...@therning.org wrote: On Tue, Jul 13, 2010 at 13:29, Phyx loneti...@gmail.com wrote: Hello I'm wondering if anyone ever benchmarked marshalling in Haskell/GHC. No matter how much I optimize my Haskell code my program still seems to run slow, which leads me to beleive that Marshalling is painfully slow. Does anyone know a way I can test this and fix it? What kind of marshalling are you referring to? /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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Marshalling
I understand that part, but the strings are generated from SDocs, and So unless internally SDoc doesn't use String then I'm afraid there's nothing I can do about that :/ Or rather, Is there a way to efficiently make CWStrings from SDocs? Regards, Phyx On Tue, Jul 13, 2010 at 6:56 PM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: That code is effectively copying the data (thats what those peeks / pokes do), so it stands to reason it would be slow by most performance standards. The reason ByteStrings are fast when used both by C and Haskell is there is a zero-copy `useAsCString`. Cheers, Thomas On Tue, Jul 13, 2010 at 7:49 AM, Phyx loneti...@gmail.com wrote: Marshalling large amount of data from and to C http://phyx.pastebin.com/WXGBr1bX shows the code I use to do this (it's autogenerated, so just looking at 1 block should be enough) The tool is mine, so i can change the code it generates, but i would need to know how to do it better first. On Tue, Jul 13, 2010 at 3:30 PM, Magnus Therning mag...@therning.org wrote: On Tue, Jul 13, 2010 at 13:29, Phyx loneti...@gmail.com wrote: Hello I'm wondering if anyone ever benchmarked marshalling in Haskell/GHC. No matter how much I optimize my Haskell code my program still seems to run slow, which leads me to beleive that Marshalling is painfully slow. Does anyone know a way I can test this and fix it? What kind of marshalling are you referring to? /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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Comments on Haskell 2010 Report
On 16:21 Fri 09 Jul , John Meacham wrote: I would think it is a typo in the report. Every language out there seems to think 0**0 is 1 and 0**y | y /= 0 is 0. I am not sure whether it is mandated by the IEEE standard but a quick review doesn't say they should be undefined (and the report mentions all the operations with undefined results) IEEE 754 has three different power operations. They are recommended operations, which means that supporting them is optional. pown only allows integral exponents, and the standard says the following: pown (x, 0) is 1 for any x (even a zero, quiet NaN, or infinity) pow handles integral exponents as a special case, and is similar: pow (x, ±0) is 1 for any x (even a zero, quiet NaN, or infinity) powr is defined as exp(y*log(x)). powr (±0, ±0) signals the invalid operation exception [NB: this means that the operation returns a quiet NaN]. In C, the pow function corresponds to the pow operation here, assuming the implementation conforms to annex F of the standard (an optional feature). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The site has been exploited (again)
gwern0: Ashley has made me admin; I've spent the last 1.5 hours deleting all the vandalism and indef blocking the accounts. I have Recent Changes in my RSS reader, so hopefully in the future there will be no greater than 24 hours delay before vandalism is dealt with. A MW upgrade will also help (eg. currently checkuser* seems to be unavailable). * http://www.mediawiki.org/wiki/Extension:CheckUser Thank you so much, Gwern! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] AngloHaskell 2010
Are you interested in AngloHaskell 2010? AngloHaskell is a gathering of all people Haskell-related from beginners to seasoned hackers. Previously it has been held in Cambridge (three times) and London (once). Last year I volunteered to organise it but I want know when you can attend. Traditionally it is the first Friday and Saturday in August, which this year is the 6th and 7th August. But we may only have enough time to organise one day so the question for you is: Q) Which day is better for you? Friday, Saturday or either? I am looking for venues in London but if you can suggest or offer a venue then let me know. As well as attendees we are looking for talks on all and any Haskell related subjects. There is a section on the wiki page http://www.haskell.org/haskellwiki/AngloHaskell/2010 for talks. Please go ahead and add your talk to it. Let me know by email, the wiki or the #anglohaskell IRC channel. I planning to have the venue confirmed this week and then a full announcement will be made. Thanks, Derek. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] library for objective-j?
Hi all, is there a haskell library for generating Objective-J? Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambda calculus and equational logic
In Haskell what roles are played by 1)lambda calculus and 2) equational logic? Are these roles related? Hi, Thanks for your clear and helpful responses. I am aware that this question can lead to into very deep water. I am comparing Haskell with languages based on equational logic (EL) (e.g. Maude/CafeOBJ, lets call them ELLs). I need to identify the fundamental distinction between the semantics of ELLs and Haskell. The focus of my original question was just the purely functional, side effect free, part of Haskell. Semantics can be understood under three headings: *Denotational Semantics; is a model theoretical approach which describes a program in terms of precise mathematical objects (e.g. sets and functions) which provide meaning to a program text. *Operational semantics: provides a technique for computing a result, ELs use term rewriting systems for their operational semantics. *Proof theoretic semantic: syntactically derivable proofs, can use the rules of a logic The relationship between the denotational and the proof theoretic semantic is important for soundness and completeness. Which was sort of behind my original question. Would it be fair to say 1)Lambda calculus provides the operational semantics for Haskell 2)Maybe equational logic provides the denotational semantics. 3)I am not sure of proof theoretic semantic for Haskell. The Curry-Howard correspondence is a proof theoretic view but only at type level. Obviously, the last three points are represent my efforts to address this question. Hopefully the café can comment on the accuracy of these points. Thanks, Pat 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] library for objective-j?
2010/7/13 Günther Schmidt gue.schm...@web.de Hi all, is there a haskell library for generating Objective-J? http://www.google.co.uk/search?hl=enas_sitesearch=hackage.haskell.org/packageas_q=object-j Hackage upload or it didn't happen! Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] library for objective-j?
Jason dearest, http://hoc.sourceforge.net/ did happen but isn't on hackage, WASH did happen but isn't on hackage ... and I presume quite a few other goodies didn't make it to hackage either. So I was hoping I'd finally be admitted to the inner haskellers circle where the dark arts are practized and the secrets are revealed that mere newbies don't even know about. :) Günther Am 13.07.10 22:28, schrieb Jason Dagit: 2010/7/13 Günther Schmidtgue.schm...@web.de Hi all, is there a haskell library for generating Objective-J? http://www.google.co.uk/search?hl=enas_sitesearch=hackage.haskell.org/packageas_q=object-j Hackage upload or it didn't happen! Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Newbie] What to improve in my code
First of all: I'm not sure if this question is allowed here. If not, I apologize I'm trying to solve the following problem: For each word in a text find the number of occurences for each unique word in the text. i've come up with the following steps to solve this: * remove all punctuation except for whitespace and make the text lowercase * find all unique words in the text * for each unique word, count the number of occurences. This has resulted in the following code: removePunctuation :: [Char] - [Char] removePunctuation str = filter (\c - elem c (['a'..'z'] ++ ['A'..'Z'] ++ ['\t', ' ', '\n'])) str process :: [Char] - [String] process str = words (map toLower (removePunctuation str)) unique :: (Eq a) = [a] - [a] unique [] = [] unique (x:xs) = [x] ++ unique (filter (\s - x /= s) xs) occurenceCount :: (Eq a) = a - [a] - Int occurenceCount _ [] = 0 occurenceCount x (y:ys) | x == y = 1 + occurenceCount x ys | otherwise = occurenceCount x ys occurenceCount' :: [String] - [String] - [(String, Int)] occurenceCount' [] _ = [(, 0)] occurenceCount' (u:us) xs = [(u, occurenceCount u xs)] ++ occurenceCount' us xs Please remember i've only been playing with Haskell for three afternoons now and i'm happy that the above code is working correctly. However i've got three questions: 1) occurenceCount' [] _ = [(, 0)] is plain ugly and also adds a useless tuple to the end result. Is there a better way to solve this? 2) I'm forcing elements into a singleton list on two occasions, both in my unique function and in my occurenceCount' function. Once again this seems ugly and I'm wondering if there is a better solution. 3) The whole process as i'm doing it now feels pretty imperatively (been working for years as a Java / PHP programmer). I've got this feeling that the occurenceCount' function could be implemented using a mapping function. What ways are there to make this more functional? -- View this message in context: http://old.nabble.com/-Newbie--What-to-improve-in-my-code-tp29156025p29156025.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] library for objective-j?
2010/7/13 Günther Schmidt gue.schm...@web.de Jason dearest, http://hoc.sourceforge.net/ did happen but isn't on hackage, http://code.google.com/p/hoc/issues/detail?id=26#c0 WASH did happen but isn't on hackage ... http://hackage.haskell.org/package/WashNGo http://hackage.haskell.org/package/WashNGo Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Collecting MonadError errors generically
Hello, This is my first post to the Haskell Café, and I'm hoping the issue I'm tackling here isn't one that's been thoroughly explored elsewhere. If that's the case, I'll apologize in advance for my insufficient google chops. Otherwise, here goes... I do a lot of work within the error monad. Having read Eric Kidd's blog on error reporting in Haskell (http://www.randomhacks.net/articles/2007/03/10/haskell-8-ways-to-report-errors), I'm always a bit paranoid about dealing with errors in the most generic, flexible way possible. As a result, a lot of the functions I use that could result in errors have signatures along these lines: couldThrowError :: (Error e, MonadError e m) = t1 - t2 - m t3 The way I figure it, this means that I can use these functions within any particular MonadError, which keeps me happy if I decide to change implementations at any particular point during development. Usually, I use these couldThrowError functions in a standard do block. Something along the lines of: couldThrowError :: (Error e, MonadError e m) = t1 - t2 - m t3 couldThrowError = do x - processWithPossibleError t1 y - processWithPossibleError t2 ... return (z :: t3) Things stay generic at this level. I can still choose any MonadError implementation I want, and if any of the computations in the do block throws an Error, the whole function short-circuits. Often enough, however, I don't want this kind of short-circuiting behavior. What I want, instead, is to run a whole bunch of computations that may throw errors. If there are any errors, I want to collect them all into one big master error. If not, I want a list of results. Here's an example of usage: couldThrowError :: (Error e, MonadError e m) = t1 - m t2 getParams :: (Error e, MonadError e m) = [t1] -- m [t2] getParams = groupErrors . map couldThrowError I found it pretty easy to implement groupErrors for Either String: groupErrors :: (Error e, MonadError e m) = [Either String a] - m [a] groupErrors eithers = case partitionEithers eithers of ([], xs) - return xs (es, _) - strError $ unlines es The problem, though, is that running this function now causes type inference to provide Either String as my MonadError implementation. If any of the potential error sources are dealing with a different concrete implementation, I'm stuck! It would be nice if I could stay generic. I made an effort at this that you can see below, but it strikes me as very awkward. collectErrors :: (Monoid e, Error e, MonadError e m) = m a - m [a] - m [a] collectErrors m1 m2 = do m1r - (m1 `catchError` (\e1 - (m2 `catchError` (\e2 - throwError $ mappend e1 e2)) throwError e1)) m2r - m2 return $ m1r : m2r groupErrors' :: (Monoid e, Error e, MonadError e m) = [m a] - m [a] groupErrors' = foldr collectErrors (return []) As you can see, I now require an error type that implements monoid. An example I've tested is: newtype ErrorString = ES String deriving (Read, Show, Eq, Ord, Error) instance Monoid ErrorString where mempty = ES mappend (ES s1) (ES s2) = ES $ s1 `mappend` \n `mappend` s2 This seems to work, but something strikes me as being very hackish here. Maybe it's just that collectErrors looks very ugly, and in Haskell my intuition tells me that what looks ugly on the surface is often ugly down below. I suspect that I might really not be approaching this problem the right way, but after a lot of time spent wrestling with it, I'm eager to read your suggestions. Is there a better way to do groupErrors, or should I be looking at an entirely different philosophy? Thanks, Grynszpan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] What to improve in my code
On Tuesday 13 July 2010 23:49:45, Frank1981 wrote: First of all: I'm not sure if this question is allowed here. If not, I apologize I'm trying to solve the following problem: For each word in a text find the number of occurences for each unique word in the text. i've come up with the following steps to solve this: * remove all punctuation except for whitespace and make the text lowercase * find all unique words in the text * for each unique word, count the number of occurences. This has resulted in the following code: removePunctuation :: [Char] - [Char] removePunctuation str = filter (\c - elem c (['a'..'z'] ++ ['A'..'Z'] ++ ['\t', ' ', '\n'])) str Depending on your criteria, maybe import Data.Char removePunctuation = filter (\c - isAlpha c || isSpace c) is better process :: [Char] - [String] process str = words (map toLower (removePunctuation str)) Or perhaps process = map (fiter isLower) . words . map toLower unique :: (Eq a) = [a] - [a] unique [] = [] unique (x:xs) = [x] ++ unique (filter (\s - x /= s) xs) import Data.List unique = nub but it's not particularly efficient. If you don't need to keep the order of first occurrence and have an Ord instance, you could take unique' = map head . group . sort or import qualified Data.Set as Set unique'' = Set.toList . Set.fromList occurenceCount :: (Eq a) = a - [a] - Int occurenceCount _ [] = 0 occurenceCount x (y:ys) | x == y = 1 + occurenceCount x ys | otherwise = occurenceCount x ys occurrenceCount a xs = length (filter (== a) xs) or occurrenceCount a = length . filter (== a) occurenceCount' :: [String] - [String] - [(String, Int)] occurenceCount' [] _ = [(, 0)] why not occurrenceCount' [] _ = [] ? occurenceCount' (u:us) xs = [(u, occurenceCount u xs)] ++ occurenceCount' us xs But it can be done shorter: import qualified Data.Map as Map import Data.List occurrenceCount'' :: Ord a = [a] - [(a,Int)] occurrenceCount'' xs = Map.toList $ foldl' (\mp x - Map.insertWith' (+) x 1 mp) Map.empty xs No need to get the unique elements up front. Please remember i've only been playing with Haskell for three afternoons now and i'm happy that the above code is working correctly. However i've got three questions: 1) occurenceCount' [] _ = [(, 0)] is plain ugly and also adds a useless tuple to the end result. Is there a better way to solve this? 2) I'm forcing elements into a singleton list on two occasions, both in my unique function and in my occurenceCount' function. Once again this seems ugly and I'm wondering if there is a better solution. Use (:), e.g. unique (x:xs) = x : unique (filter (/= x) xs) 3) The whole process as i'm doing it now feels pretty imperatively (been working for years as a Java / PHP programmer). I've got this feeling that the occurenceCount' function could be implemented using a mapping function. What ways are there to make this more functional? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Collecting MonadError errors generically
Leon, In order to avoid the short-circuiting behaviour, it might help you to work in terms of Applicatives instead of Monads. For example, in my error-message package I have the following instance: instance (Monoid e) = Applicative (Either e) where pure = Right (*) (Left error2) (Left error1) = Left (error1 `mappend` error2) (*) (Left error) _ = Left error (*) _ (Left error) = Left error (*) (Right function) (Right argument) = Right (function argument) This allows me to write liftA2 (,) calculation1 calculation2 so that both calculations are always run and the errors are collected together. This contrasts with liftM2 (,) calculation1 calculation2 which halts if calculation1 and doesn't even bother to run calculation2. Cheers, Greg On 07/13/10 15:08, Leon Grynszpan wrote: Hello, This is my first post to the Haskell Café, and I'm hoping the issue I'm tackling here isn't one that's been thoroughly explored elsewhere. If that's the case, I'll apologize in advance for my insufficient google chops. Otherwise, here goes... I do a lot of work within the error monad. Having read Eric Kidd's blog on error reporting in Haskell (http://www.randomhacks.net/articles/2007/03/10/haskell-8-ways-to-report-errors), I'm always a bit paranoid about dealing with errors in the most generic, flexible way possible. As a result, a lot of the functions I use that could result in errors have signatures along these lines: couldThrowError :: (Error e, MonadError e m) = t1 - t2 - m t3 The way I figure it, this means that I can use these functions within any particular MonadError, which keeps me happy if I decide to change implementations at any particular point during development. Usually, I use these couldThrowError functions in a standard do block. Something along the lines of: couldThrowError :: (Error e, MonadError e m) = t1 - t2 - m t3 couldThrowError = do x - processWithPossibleError t1 y - processWithPossibleError t2 ... return (z :: t3) Things stay generic at this level. I can still choose any MonadError implementation I want, and if any of the computations in the do block throws an Error, the whole function short-circuits. Often enough, however, I don't want this kind of short-circuiting behavior. What I want, instead, is to run a whole bunch of computations that may throw errors. If there are any errors, I want to collect them all into one big master error. If not, I want a list of results. Here's an example of usage: couldThrowError :: (Error e, MonadError e m) = t1 - m t2 getParams :: (Error e, MonadError e m) = [t1] -- m [t2] getParams = groupErrors . map couldThrowError I found it pretty easy to implement groupErrors for Either String: groupErrors :: (Error e, MonadError e m) = [Either String a] - m [a] groupErrors eithers = case partitionEithers eithers of ([], xs) - return xs (es, _) - strError $ unlines es The problem, though, is that running this function now causes type inference to provide Either String as my MonadError implementation. If any of the potential error sources are dealing with a different concrete implementation, I'm stuck! It would be nice if I could stay generic. I made an effort at this that you can see below, but it strikes me as very awkward. collectErrors :: (Monoid e, Error e, MonadError e m) = m a - m [a] - m [a] collectErrors m1 m2 = do m1r - (m1 `catchError` (\e1 - (m2 `catchError` (\e2 - throwError $ mappend e1 e2)) throwError e1)) m2r - m2 return $ m1r : m2r groupErrors' :: (Monoid e, Error e, MonadError e m) = [m a] - m [a] groupErrors' = foldr collectErrors (return []) As you can see, I now require an error type that implements monoid. An example I've tested is: newtype ErrorString = ES String deriving (Read, Show, Eq, Ord, Error) instance Monoid ErrorString where mempty = ES mappend (ES s1) (ES s2) = ES $ s1 `mappend` \n `mappend` s2 This seems to work, but something strikes me as being very hackish here. Maybe it's just that collectErrors looks very ugly, and in Haskell my intuition tells me that what looks ugly on the surface is often ugly down below. I suspect that I might really not be approaching this problem the right way, but after a lot of time spent wrestling with it, I'm eager to read your suggestions. Is there a better way to do groupErrors, or should I be looking at an entirely different philosophy? Thanks, Grynszpan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org
Re: [Haskell-cafe] lists of arbitrary depth
On Jul 13, 2010, at 9:00 PM, Christopher Done wrote: On 13 July 2010 10:58, vadali shlomivak...@gmail.com wrote:\ i want to define a function which takes as a parameter a list which can contain other lists, eg. [1,[2,3],[4,[5,6]]] What would the type of a list like that be? What you _can_ do is data List_Or t = Item t | List [List_Or t] deriving (Eq, Ord, Show) and have a list like ell :: List_Or Int ell = List [Item 1, List [Item 2, Item 3], List [Item 4, List [Item 5, Item 6]]] how would i define a function that can iterate through the items so (in this example) iter1 = 1 iter2 = [2,3] iter3 = [4,[5,6]] Then you can write functions like iter n (List x) = head (drop (n-1) x) with examples *Main iter 1 ell Item 1 *Main iter 2 ell List [Item 2,Item 3] *Main iter 3 ell List [Item 4,List [Item 5,Item 6]] ( can i do that without using the Tree data type? ) This basically _is_ a tree data type, even if not THE Tree data type. That's because nested lists are trees. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lambda calculus and equational logic
On Jul 14, 2010, at 1:51 AM, Ben Lippmeier wrote: Replacing equals by equals usually doesn't change anything. What kind of equality do you use for getChar :: IO Char ? The usual one: getChar = getChar. It's a pure value. If I find [getChar,getChar] in a program, I can safely replace it by let g = getChar in [g,g]. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] ANNOUNCE: jhc 0.7.4
wren is half right: at the level of Unixy APIs (and this includes anything that goes on in a Terminal window and anything that you will be doing from Haskell) you use UTF8, but OSX APIs --- that is, Carbon and Cocoa --- use UTF16. So for the purposes of ghc/jhc OSX is UTF8, but if someone wrote a fully native Cocoa-based runtime it would use UTF16. (Compare Win32 APIs to mingw APIs; very similar situation.) I guess the question here is what it _means_ to say that the standard encoding is UTF-8 or UTF-16 or anything else. I took it to be an *external* property: what is the expected/best supported encoding for *user* data. By that criterion, the only standard encoding for Mac OS X 5 would appear to be UTF-8; it did not come with any support for *user* data in UTF-16. If the question means what is the encoding used by the kernel, or by the native interfaces to the kernel, that gets a different answer. I've now lost track: what did the original poster mean? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] ANNOUNCE: Haskell 2010 Report (final)
On Tue, Jul 13, 2010 at 10:24:00AM +0100, Simon Marlow wrote: Well, a main useful case is that I can do -phaskell98 and -phaskell2010 at the same time. So I can make the default jhc behavior be the union of the two languages easily. That works in GHC too: the modules of those two packages don't overlap. That is partly because we never moved Prelude from base to haskell98. But don't you still have to have things directly declare they depend on 'base' then in order to get 'Prelude'? The extra dependency on the implementation specific 'base' because you want both haskell98 and haskell2010 is what I am trying to avoid. But suppose the Haskell 2010 Prelude had some differences from the Haskell 98 Prelude - then a direct re-export wouldn't work, and you'd be stuck with conflicts again. So my main point is that while direct re-exports avoid conflicts sometimes, they're not a general solution, and eventually you run into the same problems again. There are differences between several Haskell 2010 modules and the equivalent base modules, so you won't be able to use re-exports for those. Yeah, jhc really doesn't have a good solution for that. Something I was thinking about was 'union' modules, like, if you include two libraries that both export Data.List, you get the union of both of what they export with conflicts being reported lazily (though, instance conflicts will likely have to be reported strictly). It may help in some cases, but again, is not a general solution. (and I can imagine it would be confusing if it happened when people wern't expecting it...) Hmm.. maybe. Jhc doesn't have PackageImports, the idea being that you re-export modules rather than importing them from a specific package and exporting their interface. So, it sort of shifts the effort from the interface makers to the implementors, as in, the Haskell 98 Prelude will actually have to be in a module called Compat.Haskell98.Prelude and just re-exported by the 'haskell98' and 'haskell2010' modules. I don't think the difference is as fundamental as you make out. In Haskell you can already write Yeah, I don't think they are really that different in capabilities. Though, Jhc currently has a restriction that module names (real modules, not re-exported ones) cannot ever conflict, even if hidden, so there is a big difference in expressibility at the moment, but that is mainly due to what I consider a bug in jhc, or a misfeature at best. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: New FGL naming survey
Thank you for all the people who have voted; we so far have 42 results in about 12 hours. Some indication of the results so far: * 62% prefer inductive-graphs * 62% have indicated that they use fgl or do some graph-related stuff (no correlation, just an interesting coincidence; I have not as yet done the number crunching to tell what the most popular name is for people that actually use fgl or other graph stuff). * Someone stated that ponies smell sweaty... not sure how that's relevant, but OK. * At least two people prefer the new name as it isn't an acronym (one because acronyms aren't needed and the term functional is redundant, the other because the term graph isn't directly in the package name). * Martin Erwig himself said that he thinks we should keep using the name fgl. So, keep the votes coming in (I actually didn't expect this many already)! On 14 July 2010 00:24, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Whether or not the new FGL that Thomas Bereknyei and I are working on should keep the name was a semi-hot issue when we first mentioned the fact that we were working on a new version about a month ago. As such, I've created a survey here to try and find out what the Haskell community overall thinks we should call it: https://spreadsheets.google.com/viewform?formkey=dGpzMmFnUWY3Uktodk5wdHlLQk5kT1E6MA More info can be found on the actual survey page. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com -- 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] Re: Please report any bug of gtk2hs-0.11.0!
Short version of this post: Looks like the intsall depends on alex and that dependencies doesn't appear to be handled, i.e. I had to install alex before proceeding. why do is it called gtk2hs if you are actually installing package gtk ;-) Where's the demo directory ?! Moral of the story: don't forget to install -dev version of the necessary libraries. For me that was libpango1.0-dev, libgtk2.0-dev and libglib2.0-dev. The long version: I have a debian system and I expect the problems I found to be relatively common. Hope this is useful. First I found that I needed package alex. then i was able to cabal install gtk2hs-buildtools however cabal install gtk didn't work: Configuring glib-0.11.0... setup: The pkg-config package glib-2.0 is required but it could not be found. cabal: Error: some packages failed to install: gio-0.11.0 depends on glib-0.11.0 which failed to install. glib-0.11.0 failed during the configure step. The exception was: ExitFailure 1 gtk-0.11.0 depends on glib-0.11.0 which failed to install. pango-0.11.0 depends on glib-0.11.0 which failed to install. cabal install glib Configuring glib-0.11.0... setup: The pkg-config package glib-2.0 is required but it could not be found. cabal: Error: some packages failed to install: glib-0.11.0 failed during the configure step. The exception was: ExitFailure 1 now it's not obvious to me at this point if it's referencing a cabal package glib-2.0 or the unix libs. But I'm going to guess it's actually the unix libs. I do have the unix libs installed : ii libglib2.0-0 2.24.1-1 The GLib library of C routines However I remembered that annoying little thing that there is always those darn -dev versions of the lib that you need when you actually want to compile against libraries. So I installed it and got farther along, crashing on pango. Turns out it's the same problem. So install libpango1.0-dev and continue... Stopped again on gtk+, aka gtk libgtk2.0-dev. Installed it, and trudged on. I noticed that the install process stays at this point for a long time: Preprocessing library gtk-0.11.0... But it does eventually continue, and it even completes successfully ! Strangely, at this point, I find that I don't know that I actually have gtk2hs installed. I know that this sound kinda dumb, but I just did cabal install gtk, right ? I immediately tried cabal install gtk2hs, which said no such library, and realized that gtk was it :-) So I'd like to run a demo to make sure things are installed properly. Running the demos. -- To get started, you can compile and run one of the programs that reside in the demo/ directory in the respective packages. For example: ~/gtk2hs/gtk/demo/hello:$ make But after the installation the demo directory is nowhere to be found. Do you need to pull it in with darcs ?? Brian On Tue, 13 Jul 2010 11:42:26 +0200 Christian Maeder christian.mae...@dfki.de wrote: Andy Stewart schrieb: Hi all, We plan to release bug fix version : gtk2hs-0.11.1 Please report any bug of gtk2hs-0.11.0, we will fix it before release gtk2hs-0.11.1 I'm looking forward for this bug-fix release (since gtk2hs-0.11.0 did not work for me). Because I've almost missed this message I reply to gtk2hs-us...@lists.sourceforge.net, too. Christian We plan to add many new APIs in gtk2hs-0.12.0, so gtk2hs-0.11.1 will be the last stable version with current APIs. Thanks for your help! -- Andy ___ 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] Re: Please report any bug of gtk2hs-0.11.0!
On 14 July 2010 14:52, bri...@aracnet.com wrote: Short version of this post: Looks like the intsall depends on alex and that dependencies doesn't appear to be handled, i.e. I had to install alex before proceeding. Yes, cabal-install isn't able to cope with the build-tools dependencies. why do is it called gtk2hs if you are actually installing package gtk ;-) The overall meta-project is called gtk2hs, and all these libraries used to come together in one big package called gtk2hs. Where's the demo directory ?! Does it say there's one? -- 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
