Re: [Haskell-cafe] lazy A-star search
Anton, I think the mapM inside searchBy is incorrect. You're threading state between exploration of different branches, which you I think shouldn't be doing. 30.10.2011, в 19:44, Anton Kholomiov anton.kholom...@gmail.com написал(а): I'm misunderstanding astar. I've thought that 'whole route'-heuristic will prevent algorithm from going in circles. The more you circle around the more the whole route distance is. Thank you for showing this. Here is an updated version. searchBy function contains a state. State value accumulates visited nodes: -- | Heuristic search. Nodes are visited from smaller to greater. searchBy :: Ord b = (a - b) - (a - a - Ordering) - Tree a - [a] searchBy f heur t = evalState (searchBy' f heur t) S.empty searchBy' :: Ord b = (a - b) - (a - a - Ordering) - Tree a - State (S.Set b) [a] searchBy' f heur (Node v ts) = get = phi where phi visited | S.member (f v) visited = return [] | otherwise = put (S.insert (f v) visited) (v :) . foldr (mergeBy heur) [] $ mapM (searchBy' f heur) ts I need to add function Ord b = (a - b). It converts tree nodes into visited nodes. I'm using it for saving distance-values alongside with nodes in astar algorithm. In attachment you can find algorithm with your example. 2011/10/27 Ryan Ingram ryani.s...@gmail.com Also, this wasn't clear in my message, but the edges in the graph only go one way; towards the top/right; otherwise the best path is ABCDEHIJ :) On Thu, Oct 27, 2011 at 10:48 AM, Ryan Ingram ryani.s...@gmail.com wrote: You're missing one of the key insights from A-star (and simple djikstra, for that matter): once you visit a node, you don't have to visit it again. Consider a 5x2 2d graph with these edge costs: B 1 C 1 D 1 E 9 J 1 1 1 1 1 A 2 F 2 G 2 H 2 I with the start node being A, the target node being J, and the heuristic being manhattan distance. Your search will always try to take the top route, on every node along the bottom path, even though you visit every node along the top route in your first try at reaching the goal. You need a way to mark that a node is visited and remove it from future consideration, or else you're wasting work. A-star will visit the nodes in the order ABCDE FGHIJ; your algorithm visits the nodes in the order ABCDE FCDE GDE HE IJ. -- ryan On Sat, Oct 22, 2011 at 5:28 AM, Anton Kholomiov anton.kholom...@gmail.com wrote: Recently I was looking for an A-star search algorithm. I've found a package but I couldn't understand the code. Then I saw some blogposts but they were difficult to understand too. I thought about some easier solution that relies on laziness. And I've come to this: Heuristic search is like depth-first search but solutions in sub-trees are concatenated with mergeBy function, that concatenates two list by specific order: module Search where import Control.Applicative import Data.Function(on) import Control.Arrow(second) import Data.Tree -- | Heuristic search. Nodes are visited from smaller to greater. searchBy :: (a - a - Ordering) - Tree a - [a] searchBy heur (Node v ts) = v : foldr (mergeBy heur) [] (searchBy heur $ ts) -- | Merge two lists. Elements concatenated in specified order. mergeBy :: (a - a - Ordering) - [a] - [a] - [a] mergeBy _ a [] = a mergeBy _ []b = b mergeBy p (a:as)(b:bs) | a `p` b == LT= a : mergeBy p as (b:bs) | otherwise = b : mergeBy p bs (a:as) Now we can define specific heuristic search in terms of searchBy: -- | Heuristic is distance to goal. bestFirst :: Ord h = (a - h) - (a - [a]) - a - [a] bestFirst dist alts = searchBy (compare `on` dist) . unfoldTree (\a - (a, alts a)) -- | A-star search. -- Heuristic is estimated length of whole path. astar :: (Ord h, Num h) = (a - h) - (a - [(a, h)]) - a - [a] astar dist alts s0 = fmap fst $ searchBy (compare `on` astarDist) $ unfoldTree gen (s0, 0) where astarDist (a, d) = dist a + d gen (a, d) = d `seq` ((a, d), second (+d) $ alts a) I'm wondering is it effective enough? Anton ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Search.hs ___ 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] Hackage feature request: E-mail author when a package breaks
Hey everyone, I have uploaded a number of small packages to Hackage that I no longer actively use so that I don't find out immediately when a new version of GHC has broken them. Since Hackage is going to the trouble of finding out when a package no longer builds anyway, could it have a feature where when a working package breaks with a new version of GHC the author is automatically e-mailed? This would make me (and probably others) a lot more likely to notice and proactively fix broken packages. (Heck, I wouldn't even necessarily mind being nagged about it from time to time. :-) ) Cheers, Greg___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] blog software in Haskell?
Hi, I just upgraded my server, and set up everything again. Except wordpress, as 1) I'm not too fond of its user interface, and 2) it's a big pile of PHP, difficult to keep updated, and basically a disaster waiting to happen (and in fact, it was hacked at one point). Before I enable it again, is there any alternatives I should consider? Preferably written in Haskell, of course, but other suggestions welcome as well. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] blog software in Haskell?
On Mon, Oct 31, 2011 at 11:14 AM, Ketil Malde ke...@malde.org wrote: Hi, I just upgraded my server, and set up everything again. Except wordpress, as 1) I'm not too fond of its user interface, and 2) it's a big pile of PHP, difficult to keep updated, and basically a disaster waiting to happen (and in fact, it was hacked at one point). Before I enable it again, is there any alternatives I should consider? Preferably written in Haskell, of course, but other suggestions welcome as well. Hi, Have a look at Hakyll[1] [1]: http://jaspervdj.be/hakyll/ Mihai ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Amazon AWS storage best to use with Haskell?
Hi, Please share your experience / ideas on AWS storage most friendly to Haskell. So far I store my data mostly in Data.Map structures serialized to text files with write / read functions. Now I was requested to move my app and data to Amazon cloud. As far as I know there are two main storage types that Amazon provides: S3 - basic block storage and SimpleDB ( http://docs.amazonwebservices.com/AmazonSimpleDB/latest/GettingStartedGuide/ ) Questions: 1) I would like to continue working with my data using abstractions similar to the ones that Data.Map provides. Any ideas how to iterate and modify SimpleDB records in a similar powerful way as provided by Data.Map? Or maybe S3? 2) It would be great to do development and testing offline without actually connecting to AWS S3 / SimpleDB. Are there any AWS simulators + Haskell libraries that will allow to do such an offline development? 3) Any experience / ideas with Haskell libs for NoSQL, not AWS-native, storages, that will run well both offline and in AWS? 4) My code processes hundreds of messages. Every message is processed in exactly the same way as the others. So the code can be easily parallelized. Any Haskell frameworks that will allow me to run this code in a simple concurrency model? Thanks! Dmitri ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Organizing big repository
This is not evident in hte documentation, but Leksah does these things for you if you add your packages to the workspace list.. It is necessary to use the background compilation option, that is, set by default. Alberto 2011/10/27 Konstantin Litvinenko to.darkan...@gmail.com I am trying to understand how to organize my code and edit-compile-run cycles. I can't figure out how to setup environment in such why that when I build some program using cabal, cabal will rebuild program dependencies if some was changed. I don't want to configure/build/install manually. Having program 'foo' depends on lib 'bar' I want to edit some files in 'bar' than build 'foo' and get 'bar' rebuilt and 'foo' rebuilt/relink. How can I do this? __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://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] Fwd: Organizing big repository
This is not evident in hte documentation, but Leksah does these things for you if you add your packages to the workspace list.. It is necessary to use the background compilation option, that is, set by default. Alberto 2011/10/27 Konstantin Litvinenko to.darkan...@gmail.com I am trying to understand how to organize my code and edit-compile-run cycles. I can't figure out how to setup environment in such why that when I build some program using cabal, cabal will rebuild program dependencies if some was changed. I don't want to configure/build/install manually. Having program 'foo' depends on lib 'bar' I want to edit some files in 'bar' than build 'foo' and get 'bar' rebuilt and 'foo' rebuilt/relink. How can I do this? __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://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] is Haskell missing a non-instantiating polymorphic case?
On 23 October 2011 06:48, Adam Megacz meg...@cs.berkeley.edu wrote: The title might be a bit more provocative than necessary. I'm starting to suspect that there are very useful aspects of the parametricity of System F(C) which can't be taken advantage of by Haskell in its current state. To put it briefly, case-matching on a value of type (forall n . T n) forces one to instantiate the n, even though the branch taken within the case cannot depend on n (parametricity). I wonder if you can write eta-expansion for a product type containing an existential given your extension? If I have: data Id a = Id a I can currently write: eta x = Id (case x of Id x - x) And I have that eta x != _|_ for all x. But if I have: data Exists = forall a. Exists a Then I can't write the equivalent eta-expansion: eta x = Exists (case x of Exists x - x) The closest I can get is: eta x = Exists (case x of Exists x - unsafeCoerce x :: ()) I'm not sure if you can do this with your extension but it smells plausible. Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to implement digital filters using Arrows
Hi John, Thanks for all your help. I've been studying your suggested code: type FilterAu b c = Automaton (-) b c liftAu :: ((x,FilterState s)-(y,FilterState s)) - FilterState s - FilterAu x y liftAu f s0 = proc x - do rec (y,s') - arr f - (x,s) s - delay s0 - s' returnA - y runAutomaton is a bit cumbersome, so define a custom run function that takes a list runAuto a [] = [] runAuto (Automaton f) (x:xs) = let (y,a) = f xt in y:runAuto a xs as well as the various instance definitions for Automaton. I think I understand how the `returnA' in the last line of your `liftAu' function is getting translated by those instance definitions into: c where c = Automaton ( arr id arr (const c) ) and, furthermore, how that is passing the supplied `y' into the first element of the resulting couple. However, I don't understand how the recursively defined `c' is capturing the modified filter state and preserving it for the next call. It seems like the Automaton being referred to by `c' is a newly constructed entity, which knows nothing about the current state of the running Automaton. Any help in understanding this would be greatly appreciated. Thanks! -db ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lazy A-star search
The last implementation is type-driven, so I'm trying to understand it myself now in the light of your remark. Do you mean that the problem is this: to mergeBy things together I need to add the nodes to the set of visited nodes first? So I'm adding nodes to visited set before I've chosen the best node. 31 октября 2011 г. 9:05 пользователь Eugene Kirpichov ekirpic...@gmail.comнаписал: Anton, I think the mapM inside searchBy is incorrect. You're threading state between exploration of different branches, which you I think shouldn't be doing. 30.10.2011, в 19:44, Anton Kholomiov anton.kholom...@gmail.com написал(а): I'm misunderstanding astar. I've thought that 'whole route'-heuristic will prevent algorithm from going in circles. The more you circle around the more the whole route distance is. Thank you for showing this. Here is an updated version. searchBy function contains a state. State value accumulates visited nodes: -- | Heuristic search. Nodes are visited from smaller to greater. searchBy :: Ord b = (a - b) - (a - a - Ordering) - Tree a - [a] searchBy f heur t = evalState (searchBy' f heur t) S.empty searchBy' :: Ord b = (a - b) - (a - a - Ordering) - Tree a - State (S.Set b) [a] searchBy' f heur (Node v ts) = get = phi where phi visited | S.member (f v) visited = return [] | otherwise = put (S.insert (f v) visited) (v :) . foldr (mergeBy heur) [] $ mapM (searchBy' f heur) ts I need to add function Ord b = (a - b). It converts tree nodes into visited nodes. I'm using it for saving distance-values alongside with nodes in astar algorithm. In attachment you can find algorithm with your example. 2011/10/27 Ryan Ingram ryani.s...@gmail.com Also, this wasn't clear in my message, but the edges in the graph only go one way; towards the top/right; otherwise the best path is ABCDEHIJ :) On Thu, Oct 27, 2011 at 10:48 AM, Ryan Ingram ryani.s...@gmail.comwrote: You're missing one of the key insights from A-star (and simple djikstra, for that matter): once you visit a node, you don't have to visit it again. Consider a 5x2 2d graph with these edge costs: B 1 C 1 D 1 E 9 J 1 1 1 1 1 A 2 F 2 G 2 H 2 I with the start node being A, the target node being J, and the heuristic being manhattan distance. Your search will always try to take the top route, on every node along the bottom path, even though you visit every node along the top route in your first try at reaching the goal. You need a way to mark that a node is visited and remove it from future consideration, or else you're wasting work. A-star will visit the nodes in the order ABCDE FGHIJ; your algorithm visits the nodes in the order ABCDE FCDE GDE HE IJ. -- ryan On Sat, Oct 22, 2011 at 5:28 AM, Anton Kholomiov anton.kholom...@gmail.com wrote: Recently I was looking for an A-star search algorithm. I've found a package but I couldn't understand the code. Then I saw some blogposts but they were difficult to understand too. I thought about some easier solution that relies on laziness. And I've come to this: Heuristic search is like depth-first search but solutions in sub-trees are concatenated with mergeBy function, that concatenates two list by specific order: module Search where import Control.Applicative import Data.Function(on) import Control.Arrow(second) import Data.Tree -- | Heuristic search. Nodes are visited from smaller to greater. searchBy :: (a - a - Ordering) - Tree a - [a] searchBy heur (Node v ts) = v : foldr (mergeBy heur) [] (searchBy heur $ ts) -- | Merge two lists. Elements concatenated in specified order. mergeBy :: (a - a - Ordering) - [a] - [a] - [a] mergeBy _ a [] = a mergeBy _ []b = b mergeBy p (a:as)(b:bs) | a `p` b == LT= a : mergeBy p as (b:bs) | otherwise = b : mergeBy p bs (a:as) Now we can define specific heuristic search in terms of searchBy: -- | Heuristic is distance to goal. bestFirst :: Ord h = (a - h) - (a - [a]) - a - [a] bestFirst dist alts = searchBy (compare `on` dist) . unfoldTree (\a - (a, alts a)) -- | A-star search. -- Heuristic is estimated length of whole path. astar :: (Ord h, Num h) = (a - h) - (a - [(a, h)]) - a - [a] astar dist alts s0 = fmap fst $ searchBy (compare `on` astarDist) $ unfoldTree gen (s0, 0) where astarDist (a, d) = dist a + d gen (a, d) = d `seq` ((a, d), second (+d) $ alts a) I'm wondering is it effective enough? Anton ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Search.hs ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe
Re: [Haskell-cafe] Hackage feature request: E-mail author when a package breaks
On Mon, Oct 31, 2011 at 12:08 AM, Gregory Crosswhite gcrosswh...@gmail.comwrote: I have uploaded a number of small packages to Hackage that I no longer actively use so that I don't find out immediately when a new version of GHC has broken them. Since Hackage is going to the trouble of finding out when a package no longer builds anyway, could it have a feature where when a working package breaks with a new version of GHC the author is automatically e-mailed? This would make me (and probably others) a lot more likely to notice and proactively fix broken packages. (Heck, I wouldn't even necessarily mind being nagged about it from time to time. :-) ) If done well I think this is a good idea. Currently I have my buildbot email me whenever a package breaks (although the bot doesn't automatically install new GHCs). -- Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Figures 6 and 7 from `Programming with Arrows'?
Does anyone have figures 6 and 7, as well as the intervening unnumbered figure, from `Programming with Arrows'? Thanks, -db ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hackage feature request: E-mail author when a package breaks
Gregory Crosswhite wrote: could [Hackage] have a feature where when a working package breaks with a new version of GHC the author is automatically e-mailed? This would be nice. However, there would have to be a way for it to be turned on and off by the author. (Spam is not nice.) Thanks, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Amazon AWS storage best to use with Haskell?
On Mon, Oct 31, 2011 at 6:50 PM, John Lenz l...@math.uic.edu wrote: 4) My code processes hundreds of messages. Every message is processed in exactly the same way as the others. So the code can be easily parallelized. Any Haskell frameworks that will allow me to run this code in a simple concurrency model? Yes, there are many options. http://www.haskell.org/**haskellwiki/GHC/Concurrencyhttp://www.haskell.org/haskellwiki/GHC/Concurrency John, thanks for detailed reply! I am looking at Haskell Concurrency wiki, but can not figure out which framework - STM, sparks, threads, etc. Amazon AWS will be able to scale? As far as I know, to scale CPU and program memory in Amazon, all you can ask from AWS is to start some number of additional extra VMs. Every VM contains a complete image of your OS and executables, all images are exactly the same. That's fine with me as currently all my workflow tasks are performed by separately compiled Haskell executables communicating via regular files. So to reformulate my question: - Does any Haskell framework exist that allow to orchestrate separate processes (NOT threads that share the same process memory)? On the other hand, in case there is a way to make Amazon AWS to scale Haskell STM, sparks, threads, etc. - I would happily rewrite my Haskell code to use these frameworks. So my second question: - Is there a way to make Amazon AWS to scale Haskell STM, sparks, threads or any other Haskell concurrency frameworks? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Monad.Reader Issue 19
On Wed, Oct 26, 2011 at 4:24 PM, Bas van Dijk v.dijk@gmail.com wrote: I have one question regarding your use of atomicModifyIORef: x - atomicModifyIORef ref (\_ - (tmstr, ())) x `seq` return () Can't you write that as just: writeIORef ref tmstr? If you're not using the previous value of the IORef there's no chance of inconsistency. From the documentation at http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-IORef.html : IORef operations may appear out-of-order to another thread, ... ... atomicModifyIORef acts as a barrier to reordering. Multiple atomicModifyIORef operations occur in strict program order. Based on this description, it seems that atomicModifyIORef is safer for writing to an IORef than writeIORef when there are multiple threads reading and writing it. If my assessment is correct, I think Data.IORef should have an atomicWriteIORef :: IORef a - a - IO () function to clarify this. I'm not completely sure about this myself. Could someone confirm this? Moreover, it'd be nice if there were writeIORef' and atomicModifyIORef' functions that force the value. Doing so would help people avoid making the mistake described by the author. It's a really common mistake. - Joey ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] blog software in Haskell?
On 31 October 2011 22:14, Ketil Malde ke...@malde.org wrote: I just upgraded my server, and set up everything again. Except wordpress, as 1) I'm not too fond of its user interface, and 2) it's a big pile of PHP, difficult to keep updated, and basically a disaster waiting to happen (and in fact, it was hacked at one point). Before I enable it again, is there any alternatives I should consider? Preferably written in Haskell, of course, but other suggestions welcome as well. http://gitit.net/ ...has git and darcs storage. http://www.haskell.org/haskellwiki/Web/Content_Management There is also orchid: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/orchid-0.0.6 https://github.com/sebastiaanvisser/orchid https://github.com/sebastiaanvisser/orchid-doc which I recall was quite pretty, but I cannot find an online demo. Alistair ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hackage feature request: E-mail author when a package breaks
On 31 October 2011 17:22, Yitzchak Gale g...@sefer.org wrote: Gregory Crosswhite wrote: could [Hackage] have a feature where when a working package breaks with a new version of GHC the author is automatically e-mailed? This would be nice. However, there would have to be a way for it to be turned on and off by the author. (Spam is not nice.) How about sending an email to haskell-package-packate-name@haskell.org, and then people can join that mailing list if they are interested in that sort of stuff? Mailman is good at doing subscribe and unsubscribe. Alexander ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Amazon AWS storage best to use with Haskell?
On Mon, Oct 31, 2011 at 6:50 PM, John Lenz l...@math.uic.edu wrote: CouchDB works great, although I decided to go with SimpleDB since then it is amazon's problem to scale and allocate disk and so forth, which I like better. For couchdb, you can use my package couchdb-enumerator on hackage. Regarding CouchDB. So far I have my records keyed by Id and stored in Data.Map which I serialize to text file. Using Data.Map functions I do many operations with these records including mapping functions over keys and values, accumulation, lookup, intersection, union etc. When I move this data to CouchDB and start using couchdb-enumerator to work with it, how natural will it be to implement all these functions that I use from Data.Map? Or maybe it makes more sense to store my serialized Data.Map as a blob in CouchDB? And do not use views or similar CouchDB / SimpleDB interfaces at all? Just retrieve necessary blob and deserialize it to Data.Map, update and then store modified blob to CouchDB again? It would be great if somebody had time to implement Data.List, Data.Map, etc on top of generic NoSQL DB interface with specific instances for CouchDB, SimpleDB, etc. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Amazon AWS storage best to use with Haskell?
For distributed execution you can look at the recent work on CloudHaskell: https://github.com/jepst/CloudHaskell http://groups.google.com/group/cloudhaskell As for a programming model -- Philip Trinder et. al have a version of monad-par that works in a distributed way over CloudHaskell, likewise CloudHaskell itself provides a simple Task layer. For a NOSQL layer -- I'm looking for the answer to that same question myself! We've been experimenting with Cassandra (used via the hscassandra package based in turn on cassandra-thrift). Already it's clear that there are many areas that need work. The Haskell code generated by Thrift itself has a lot of room for improvement (for the intrepid hacker: cycles there would be well-spent). We haven't tried CouchDB yet. Please keep us posted on what you find. I don't know if any one has a clean way for hooking a simple Haskell-ish interface (e.g. Data.Map) up to a persistence layer. But it seems like there have been a bunch of papers on database supported haskell and the like. One of them must have solved this! http://hackage.haskell.org/package/DSH Cheers, -Ryan On Mon, Oct 31, 2011 at 4:53 PM, dokondr doko...@gmail.com wrote: On Mon, Oct 31, 2011 at 6:50 PM, John Lenz l...@math.uic.edu wrote: CouchDB works great, although I decided to go with SimpleDB since then it is amazon's problem to scale and allocate disk and so forth, which I like better. For couchdb, you can use my package couchdb-enumerator on hackage. Regarding CouchDB. So far I have my records keyed by Id and stored in Data.Map which I serialize to text file. Using Data.Map functions I do many operations with these records including mapping functions over keys and values, accumulation, lookup, intersection, union etc. When I move this data to CouchDB and start using couchdb-enumerator to work with it, how natural will it be to implement all these functions that I use from Data.Map? Or maybe it makes more sense to store my serialized Data.Map as a blob in CouchDB? And do not use views or similar CouchDB / SimpleDB interfaces at all? Just retrieve necessary blob and deserialize it to Data.Map, update and then store modified blob to CouchDB again? It would be great if somebody had time to implement Data.List, Data.Map, etc on top of generic NoSQL DB interface with specific instances for CouchDB, SimpleDB, etc. ___ 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] How to implement digital filters using Arrows
On 1/11/2011 1:35 AM, Captain Freako wrote: you need to study ArrowLoop and understand that. In the code rec (y,s')- arr f - (x,s) s- delay s0 - s' the state is 'captured' in the recursive binding. i.e. just like in real circuits the output state s is threaded back as an input. The recursive binding is just sugar for the application of the loop combinator. The signature of the loop combinator is loop :: arrow (input, feedback) (output, feedback) - arrow input output with the loop combinator (with which recursive arrow bindings are defined) the function could have been defined as... liftAu f s0 = loop (second (delay s0) arr f ) the delay is neccessary to break the recursion. i.e. to calculate the next output and state the previous state is used. liftAu :: ((x,FilterState s)-(y,FilterState s)) - FilterState s - FilterAu x y liftAu f s0 = proc x - do rec (y,s')- arr f - (x,s) s- delay s0 - s' returnA - y I think I understand how the `returnA' in the last line of your `liftAu' function is getting translated by those instance definitions into: c where c = Automaton ( arr id arr (const c) ) and, furthermore, how that is passing the supplied `y' into the first element of the resulting couple. However, I don't understand how the recursively defined `c' is capturing the modified filter state and preserving it for the next call. It seems like the Automaton being referred to by `c' is a newly constructed entity, which knows nothing about the current state of the running Automaton. Any help in understanding this would be greatly appreciated. Thanks! -db ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Amazon AWS storage best to use with Haskell?
On Tue, Nov 1, 2011 at 12:07 AM, Ryan Newton rrnew...@gmail.com wrote: ... For a NOSQL layer -- I'm looking for the answer to that same question myself! We've been experimenting with Cassandra (used via the hscassandra package based in turn on cassandra-thrift). Already it's clear that there are many areas that need work. The Haskell code generated by Thrift itself has a lot of room for improvement (for the intrepid hacker: cycles there would be well-spent). Any example code of using hscassandra package would really help! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lazy A-star search
On Sun, Oct 30, 2011 at 8:44 AM, Anton Kholomiov anton.kholom...@gmail.comwrote: I'm misunderstanding astar. I've thought that 'whole route'-heuristic will prevent algorithm from going in circles. The more you circle around the more the whole route distance is. Sort of. Consider the tree in my example graph: A -1- B -1- C -1- D -1- E -9- J -2- F -1- C -1- D -1- E -9- J -2- G -1- D -1- E -9- J -2- H -1- E -9- J -2- I -1- J There's no circling going on as you depth-first search this tree, even though you are wasting time visiting the same node multiple times. However, the thing you know with A*/djikstra is this: If I have visited a node, there is no shorter path to that node. So any time I encounter that node again, I must have at least as long of a path, and so any later nodes along that path can't be any better along this path. Effectively, you are pruning the tree: A -1- B -1- C -1- D -1- E -9- J *** -2- F -1- C *** -2- G -1- D *** -2- H -1- E *** -2- I -1- J GOAL (*** = pruned branches) since the second time you visit C, you know the first path was faster, so there is no reason to continue to visit D/E again. This is even more noticable in graphs with multidirectional edges, as the tree is infinitely deep at every cycle. I wonder if there is a way to represent this more directly as tree-pruning. It's weird, because you are pruning the tree based on visiting other branches of the tree. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] arr considered harmful
I know it's a bit of an 'intentionally provocative' title, but with the recent discussions on Arrows I thought it timely to bring this up. Most of the conversion from arrow syntax into arrows uses 'arr' to move components around. However, arr is totally opaque to the arrow itself, and prevents describing some very useful objects as arrows. For example, I would love to be able to use the arrow syntax to define objects of this type: data Circuit a b where Const :: Bool - Circuit () Bool Wire :: Circuit a a Delay :: Circuit a a And :: Circuit (Bool,Bool) Bool Or :: Circuit (Bool,Bool) Bool Not :: Circuit Bool Bool Then :: Circuit a b - Circuit b c - Circuit a c Pair :: Circuit a c - Circuit b d - Circuit (a,b) (c,d) First :: Circuit a b - Circuit (a,c) (b,c) Swap :: Circuit (a,b) (b,a) AssocL :: Circuit ((a,b),c) (a,(b,c)) AssocR :: Circuit (a,(b,c)) ((a,b),c) Loop :: Circuit (a,b) (a,c) - Circuit b c etc. Then we can have code that examines this concrete data representation, converts it to VHDL, optimizes it, etc. However, due to the presence of the opaque 'arr', there's no way to make this type an arrow without adding an 'escape hatch' Arr :: (a - b) - Circuit a b which breaks the abstraction: circuit is supposed to represent an actual boolean circuit; (Arr not) is not a valid circuit because we've lost the information about the existence of a 'Not' gate. The arrow syntax translation uses arr to do plumbing of variables. I think a promising project would be to figure out exactly what plumbing is needed, and add those functions to a sort of 'PrimitiveArrow' class. All of these plumbing functions are trivially implemented in terms of 'arr', when it exists, but if it doesn't, it should be possible to use the arrow syntax regardless. -- ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] arr considered harmful
Have you seen Adam Megacz's work on generalized arrows? I think he proposes to kill arr and has done a decent amount of work on it. On Mon, Oct 31, 2011 at 8:33 PM, Ryan Ingram ryani.s...@gmail.com wrote: I know it's a bit of an 'intentionally provocative' title, but with the recent discussions on Arrows I thought it timely to bring this up. Most of the conversion from arrow syntax into arrows uses 'arr' to move components around. However, arr is totally opaque to the arrow itself, and prevents describing some very useful objects as arrows. For example, I would love to be able to use the arrow syntax to define objects of this type: data Circuit a b where Const :: Bool - Circuit () Bool Wire :: Circuit a a Delay :: Circuit a a And :: Circuit (Bool,Bool) Bool Or :: Circuit (Bool,Bool) Bool Not :: Circuit Bool Bool Then :: Circuit a b - Circuit b c - Circuit a c Pair :: Circuit a c - Circuit b d - Circuit (a,b) (c,d) First :: Circuit a b - Circuit (a,c) (b,c) Swap :: Circuit (a,b) (b,a) AssocL :: Circuit ((a,b),c) (a,(b,c)) AssocR :: Circuit (a,(b,c)) ((a,b),c) Loop :: Circuit (a,b) (a,c) - Circuit b c etc. Then we can have code that examines this concrete data representation, converts it to VHDL, optimizes it, etc. However, due to the presence of the opaque 'arr', there's no way to make this type an arrow without adding an 'escape hatch' Arr :: (a - b) - Circuit a b which breaks the abstraction: circuit is supposed to represent an actual boolean circuit; (Arr not) is not a valid circuit because we've lost the information about the existence of a 'Not' gate. The arrow syntax translation uses arr to do plumbing of variables. I think a promising project would be to figure out exactly what plumbing is needed, and add those functions to a sort of 'PrimitiveArrow' class. All of these plumbing functions are trivially implemented in terms of 'arr', when it exists, but if it doesn't, it should be possible to use the arrow syntax regardless. -- ryan ___ 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] arr considered harmful
On Mon, Oct 31, 2011 at 10:33 PM, Ryan Ingram ryani.s...@gmail.com wrote: The arrow syntax translation uses arr to do plumbing of variables. I think a promising project would be to figure out exactly what plumbing is needed, and add those functions to a sort of 'PrimitiveArrow' class. All of these plumbing functions are trivially implemented in terms of 'arr', when it exists, but if it doesn't, it should be possible to use the arrow syntax regardless. There are already generalized arrows [1]. Is that what you are looking for? Cheers, [1] http://www.cs.berkeley.edu/~megacz/garrows/ -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] arr considered harmful
This seems basically what I'm talking about, except even more hardcore. I think mostly what I'm suggesting is that the GHC arrow preprocessor to compile to something like generalized arrows, by default, with current Arrows as a special case. -- ryan On Mon, Oct 31, 2011 at 5:48 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Mon, Oct 31, 2011 at 10:33 PM, Ryan Ingram ryani.s...@gmail.com wrote: The arrow syntax translation uses arr to do plumbing of variables. I think a promising project would be to figure out exactly what plumbing is needed, and add those functions to a sort of 'PrimitiveArrow' class. All of these plumbing functions are trivially implemented in terms of 'arr', when it exists, but if it doesn't, it should be possible to use the arrow syntax regardless. There are already generalized arrows [1]. Is that what you are looking for? Cheers, [1] http://www.cs.berkeley.edu/~megacz/garrows/ -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] arr considered harmful
Ryan Ingram writes: Most of the conversion from arrow syntax into arrows uses 'arr' to move components around. However, arr is totally opaque to the arrow itself, and prevents describing some very useful objects as arrows. For example, I would love to be able to use the arrow syntax to define objects of this type: data Circuit a b where Const :: Bool - Circuit () Bool Wire :: Circuit a a Delay :: Circuit a a And :: Circuit (Bool,Bool) Bool Or :: Circuit (Bool,Bool) Bool Not :: Circuit Bool Bool Then :: Circuit a b - Circuit b c - Circuit a c Pair :: Circuit a c - Circuit b d - Circuit (a,b) (c,d) First :: Circuit a b - Circuit (a,c) (b,c) Swap :: Circuit (a,b) (b,a) AssocL :: Circuit ((a,b),c) (a,(b,c)) AssocR :: Circuit (a,(b,c)) ((a,b),c) Loop :: Circuit (a,b) (a,c) - Circuit b c etc. Then we can have code that examines this concrete data representation, converts it to VHDL, optimizes it, etc. However, due to the presence of the opaque 'arr', there's no way to make this type an arrow without adding an 'escape hatch' Arr :: (a - b) - Circuit a b which breaks the abstraction: circuit is supposed to represent an actual boolean circuit; (Arr not) is not a valid circuit because we've lost the information about the existence of a 'Not' gate. If you require the circuit to be parametric in the value types, you can limit the types of function you can pass to arr to simple plumbing. See the netlist example at the end of my Fun of Programming slides (http://www.soi.city.ac.uk/~ross/papers/fop.html). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Amazon AWS storage best to use with Haskell?
Any example code of using hscassandra package would really help! I'll ask my student. We may have some simple examples. Also, I have no idea as to their quality but I was pleasantly surprised to find three different amazon related packages on Hackage (simply by searching for the word Amazon in the package list). http://hackage.haskell.org/package/hS3 http://hackage.haskell.org/package/hSimpleDB http://hackage.haskell.org/package/aws It would be great to know if these work. -Ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ghc 7.2.1 Generics problem
Hi, I do not know why, my ghc 7.2.1 does not seem to support DeriveRepresentable. I compiled the ghc 7.2.1 myself by ghc 7.0.4. All options default. $ ghc Types/TopTalkerRecord.hs Types/TopTalkerRecord.hs:2:14: Unsupported extension: DeriveRepresentable $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.2.1 -- 竹密岂妨流水过 山高哪阻野云飞 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
