- Haskell-Cafe - Haskell.org

flipped IO sequence
by Cetin Sert 02 Oct '08

02 Oct '08

warn :: String → IO Int warn = return 1 << putStrLn -- causes an error -- = \msg → return 1 << putStrLn msg -- works just fine -- = \msg → putStrLn msg >> return 1 -- works just fine (<<) :: Monad m ⇒ m b → m a → m b b << a = a >>= \_ → b Why do I get this compile-time error?? How can one define << ? cetin@linux-d312:~/lab/test/qths/p> ghc -fglasgow-exts -O2 -o d64x --make demo2.hs system.hs [1 of 2] Compiling Netman.System ( system.hs, system.o ) system.hs:23:14: No instance for (Num (IO Int)) arising from the literal `1' at system.hs:23:14 Possible fix: add an instance declaration for (Num (IO Int)) In the first argument of `return', namely `1' In the first argument of `(<<)', namely `return 1' In the expression: return 1 << putStrLn

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(A little humour)
by Andrew Coppin 02 Oct '08

02 Oct '08

Apparently C++ lets you overload the arithmetic operators, the assignment operator, the initialisation and destruction operators, the pointer dereference operator, the memory allocation operator, and even the function call operator. o_O But only _Haskell_ lets you overload the ";" operator! ;-) [I believe they call this "ha ha, only serious" humour...]

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cabal upgrade
by Achim Schneider 02 Oct '08

02 Oct '08

% cabal update Downloading package list from server 'http://hackage.haskell.org/packages/archive' % cabal install pureMD5 All requested packages already installed. Nothing to do. % cabal install pureMD5-0.2.4 Downloading 'pureMD5-0.2.4'... [...] Well, I might be spoiled by portage but shouldn't there be a thing like cabal upgrade pureMD5 and cabal upgrade --all ? -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited.

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The Haskell Platform
by Galchin, Vasili 02 Oct '08

02 Oct '08

Hello, I probably missed some details for which I apologize. My feeling is that "periodically" the "haskell platform server" should attempt to rebuild the Haskell library. Any library that fails to rebuild then the "maintainer" of that library should be notified, e.g. email, pager(;^)), .... Kind regards, Vasili

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Haskell, GHC, and ABI
by Sean Leather 02 Oct '08

02 Oct '08

> Dynamic linking doesn't solve all the problems, we still have the problem > that GHC does a lot of cross-module inlining, regardless of whether dynamic > linking is used. However, I really would like to have a way to have > complete control over what is exposed across a package boundary. We need > this not just for licensing reasons, but also for making a dynamic library > with a fixed ABI, so it can be upgraded later. > > Incedentally the lack of this feature is one reason I've not being rushing > to get shared libraries into GHC. They're just not that useful unless you > can upgrade a library independently of the things it depends on. > I completely agree. Having a fixed ABI that survives library changes and compiler upgrades is an important factor in achieving a useful system. Incidentally, I perused http://hackage.haskell.org/trac/ghc/wiki/DynamicLinking and didn't see much about this here. Is there some notes or a plan for reaching this goal with GHC (or any other Haskell compiler)? Sean

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Re: [Haskell-cafe] Version 0.4.3 of happs-tutorial is a HAppS job board, done in HAppS.
by Thomas Hartman 01 Oct '08

01 Oct '08

Oh, the whole point of this was to put preview of the latest chapters I've been working on. The new stuff is at http://happstutorial.com:5002/ So far there's an introduction to macid, macid data safety and backups, and using utf8 data with happs. I'm particularly intereted in hearing what the happs devs and others have to say on the topic of keeping data safe: http://happstutorial.com:5002/tutorial/macid-data-safety Thomas. 2008/9/30 John Melesky <john(a)phaedrusdeinus.org>: > Thomas, > > The tutorial site seems to be unreachable or otherwise down. > > I know the modern programming landscape is fast-moving, HAppS is new and > constantly changing, so i probably should have grabbed the content when you > posted it, but perhaps keeping it up for more than a day and a half might be > good? :-) > > -john melesky > > > On Sep 28, 2008, at 6:36 PM, Thomas Hartman wrote: > >> Hello, world. >> >> In Version 4 of the ongoing self-demoing HAppS Tutorial, we implement >> a HAppS job board using HAppS. >> >> demo: http://happstutorial.com:5001 >> >> install: sudo cabal install happs-tutorial >> >> darcs head: darcs get http://code.haskell.org/happs-tutorial >> >> There aren't any new lessons compared to the last release, but the >> code is much cleaner, and... well... the web site actually does >> something. >> >> Coming soon, lessons on form processing and HAppS State. >> >> Enjoy! >> >> Thomas. >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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Re: [Haskell-cafe] Class Quantification
by Bas van Dijk 01 Oct '08

01 Oct '08

On Wed, Oct 1, 2008 at 3:01 AM, Reiner Pope <reiner.pope(a)gmail.com> wrote: > I believe there is no way to simply express this "abstraction over classes", > but the Scrap your boilerplate with class[1] paper discusses this same > problem and present a workaround by defining the class's dictionary of > methods as an explicit type. > > What follows is the code to implement their workaround for your example. > > First some fairly standard extensions: > >> {-# LANGUAGE Rank2Types, EmptyDataDecls, FlexibleInstances, KindSignatures >> #-} > > And some more controversial, but necessary ones: > >> {-# LANGUAGE UndecidableInstances, OverlappingInstances #-} >> >> module Cls where >> > > The working bla function. Unfortunately, the "pseudoclass" cls needs > to have its type explicitly named, hence the (uninhabited) Proxy type. > >> bla :: forall cls a c d. (Sat (cls c), Sat (cls d)) => Proxy cls -> >> (forall b. Sat (cls b) => a -> b) -> a -> (c,d) >> bla _ f x = (f x, f x) > > Again, testFoo and testBar unfortunately have to name which dictionary type > to use, via the Proxy. > >> testFoo = bla (undefined :: Proxy NumD) fromInteger 1 :: (Int,Float) >> testBar = bla (undefined :: Proxy ReadD) read "1" :: (Int,Float) > > The Sat class, straight from SYB: > >> class Sat a where >> dict :: a >> data Proxy (cxt :: * -> *) > > The explicit dictionary construction for the Read class: > >> data ReadD a = ReadD { readsPrecD :: Int -> ReadS a } >> instance (Read a) => Sat (ReadD a) where >> dict = ReadD readsPrec >> instance (Sat (ReadD a)) => Read a where >> readsPrec = readsPrecD dict > > The explicit dictionary construction for the Num class: > >> data NumD a = NumD { plusD :: a -> a -> a, >> timesD :: a -> a -> a, >> negateD :: a -> a, >> absD :: a -> a, >> signumD :: a -> a, >> fromIntegerD :: Integer -> a } >> instance (Num a) => Sat (NumD a) where >> dict = NumD (+) (*) negate abs signum fromInteger > > We define these fake Eq,Show instances just to make the > Num instance valid. It would be longer, but not more > difficult, to genuinely encode the (Eq,Show)=>Num hierarchy. > >> instance (Sat (NumD a)) => Show a where {} >> instance (Sat (NumD a)) => Eq a where {} >> instance (Sat (NumD a)) => Num a where >> (+) = plusD dict >> (*) = timesD dict >> negate = negateD dict >> abs = absD dict >> signum = signumD dict >> fromInteger = fromIntegerD dict > > [1] http://homepages.cwi.nl/~ralf/syb3/ Sections 3.2 and 4.1 > > On Wed, Oct 1, 2008 at 9:01 AM, Bas van Dijk <v.dijk.bas(a)gmail.com> wrote: >> >> On Tue, Sep 30, 2008 at 11:25 PM, Sean Leather <sean.leather(a)gmail.com> >> wrote: >> > But perhaps you're looking for potentially unknown classes? >> >> Yes indeed. >> >> Thanks, >> >> Bas >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe > > Nice! The explicit passing of the proxy type is indeed unfortunate but it's nice that the type of your 'bla' is almost identical to mine: > bla :: forall cls a c d. (Sat (cls c), Sat (cls d)) => Proxy cls -> (forall b. Sat (cls b) => a -> b) -> a -> (c,d) > bla :: forall cls. (cls c, cls d) => (forall b. cls b => a -> b) -> a -> (c, d) Thanks, Bas

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tutorial site back up Re: [Haskell-cafe] Version 0.4.3 of happs-tutorial is a HAppS job board, done in HAppS.
by Thomas Hartman 01 Oct '08

01 Oct '08

Well, at least I know people are trying to read the tutorial :) I'll say a few words about what happened. The underlying problem is that HAppS dies unpredictably because of problems in the haskell network library, a but I reported at http://code.google.com/p/happs/issues/detail?id=40 I wrote a cron job to restart my server when it dies, but I recently tweaked the job in order to serve the "head" version as well as what is on hackage, and the tweak broke the cron job's functionality. (fixed now -- at least, I hope it's fixed.) To be honest I don't really understand the underlying problem in the haskell network library, but it would be great if somebody who does could fix this. Thomas. 2008/9/30 John Melesky <john(a)phaedrusdeinus.org>: > Thomas, > > The tutorial site seems to be unreachable or otherwise down. > > I know the modern programming landscape is fast-moving, HAppS is new and > constantly changing, so i probably should have grabbed the content when you > posted it, but perhaps keeping it up for more than a day and a half might be > good? :-) > > -john melesky > > > On Sep 28, 2008, at 6:36 PM, Thomas Hartman wrote: > >> Hello, world. >> >> In Version 4 of the ongoing self-demoing HAppS Tutorial, we implement >> a HAppS job board using HAppS. >> >> demo: http://happstutorial.com:5001 >> >> install: sudo cabal install happs-tutorial >> >> darcs head: darcs get http://code.haskell.org/happs-tutorial >> >> There aren't any new lessons compared to the last release, but the >> code is much cleaner, and... well... the web site actually does >> something. >> >> Coming soon, lessons on form processing and HAppS State. >> >> Enjoy! >> >> Thomas. >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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postmortem question about xmonad
by minh thu 01 Oct '08

01 Oct '08

Hi, I'd like to know, now that time got by a bit, what the writers of the X monad think about the use of the ReaderT/WriterT/IO brought to them (to isolate Configuration data and dynamic data and glue them together with IO). Are you happy of it, did it make things easier or not, would you do it again ? Thanks a lot, Thu

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state monad and continuation monads ...
by Galchin, Vasili 01 Oct '08

01 Oct '08

Hello, I would like to read 1) pedagogical examples of State monad and the Continuation monad 2) library usage of these monads .... Regards, Vasili

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ANNOUNCE: graphviz-2008.9.20
by Ivan Miljenovic 01 Oct '08

01 Oct '08

The latest version of Matthew Sackman's Haskell bindings to Graphviz [1] are now available on Hackage [2]. The reason there's a new release only two weeks after the previous one is that I've made some extensions to it (hence why I'm writing the announcement) that Matthew has kindly included. Since Matthew doesn't recall writing an announcement for graphviz before, here is a brief synopsis of what it does. The Graphviz program is probably _the_ way of drawing graphs (note: this is graph-theory graphs, not function plotting). As it stands, there are currently at least four different Haskell bindings available for Graphviz that I've managed: * The inbuilt Graphviz module in FGL [3] * graphviz (which this announcement is for) * dotgen [4] * A really simple generator by Duncan Coutts [5] In addition to this, the following utilities on Hackage output graphs in Graphviz's .dot format (either using one of the above libraries or their own parser): * prof2dot : converts profiling information to .dot [custom, I think] [6] * flow2Dot : convert textual descriptions to .dot [also custom, I think] [7] * graphmod : draw the dependencies between Haskell modules [uses dotgen] [8] As it can be seen, there's a plethora of possible ways of creating .dot graphs in Haskell. What seperates the graphviz package from the others is: * It uses FGL graphs, rather than passing through lists of nodes and edges manually (of course, if you're not doing any other graph-related activity you might not want to use an FGL graph), whilst providing more control than the default FGL module. * A large list of attributes that can be used are available: http://hackage.haskell.org/packages/archive/graphviz/2008.9.20/doc/html/Dat… * A "sane" interface that provides a large degree of customizability (don't specify the attributes manually for each node/edge/etc., just pass through a function that will create the attribute you want). * Limited parsing of .dot format (note that as yet it can't convert a parsed DotGraph into an FGL graph). * The graphToGraph function allows you to pass a graph through Graphviz and then extract out positional information and combine it with the original graph. There are some things things that graphviz can't do, such as drawing undirected graphs and clusters (which dotgen can)... at least until now. The changes that I have made provide the additional functionality to graphviz: * Differentiate between undirected and directed graphs. Whilst FGL represents undirected graphs with a directed graph by duplicating all edges (an undirected edge {1,2} is represented by the two edges (1,2) and (2,1)), you don't really want to draw a graph this way. Furthermore, many reports say that graphviz's "neato" command is better at drawing undirected graphs than the normal "dot" command is. Thus, graphviz will now draw only one edge out of every directed pair. To do so, however, requires that the edge labels are an instance of Ord: if this is a problem for you, please contact either Matthew or myself and we'll see what else we can do (this is required because it's assumed that if two edges (1,2) and (2,1) are meant to represent the undirected edge {1,2}, then their labels must be the same). * Add clustering support. Graphs can be drawn (but as yet not parsed) to provide nested clustering support to arbitrary depth. To do so, you need to provide a function (LNode a -> NodeCluster c a), where NodeCluster is the following recursive data type that indicates in which subcluster a node in the graph belongs: data NodeCluster c a = N (LNode a) | C c (NodeCluster c a) The c type represents the cluster label, and is the parameter by which cluster attributes are assigned. Note that c has to be an instance of Ord. Clusters are not parseable, because there's no clear way of how to convert a cluster to an FGL graph. The interface for graphviz remains unchanged, so you can safely upgrade to this version. Here is an example function of how the library can be used to draw an FGL graph to a (very plain) Graphviz graph (well, it will convert it to the DotGraph datatype, which when shown produces the .dot graph code): graphviz :: (Graph g, Show a, Ord b, Show b) => String -> g a b -> DotGraph graphviz title g = graphToDot g attrs nattrs eattrs where attrs = [Label title] nattrs (_,a) = [Label (show a)] eattrs (_,_,b) = [Label (show b)] Enjoy! [1] http://graphviz.org/ [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphviz [3] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fgl [4] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dotgen [5] http://haskell.org/~duncan/WriteDotGraph.hs [6] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/prof2dot [7] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/flow2dot [8] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphmod -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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Re: [Haskell-cafe] Class Quantification
by Bas van Dijk 01 Oct '08

01 Oct '08

On Tue, Sep 30, 2008 at 11:25 PM, Sean Leather <sean.leather(a)gmail.com> wrote: > But perhaps you're looking for potentially unknown classes? Yes indeed. Thanks, Bas

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Re: [Haskell-cafe] System.Process
by Donn Cave 01 Oct '08

01 Oct '08

Quoth David Roundy <droundy(a)darcs.net>: ... | My point was that which of these is correct entirely depends on what | your input is. It's often a huge (and security-bug-prone) chore to | escape all those shell characters, and so in many cases it's much | nicer to execute an external program direcly without invoking a | shell. That's true, and in the other cases - when you want the shell to process the command line - you should be able to invoke it. I'm not looking at the source code (nor even running my example, since I don't have ghc handy), but the basic difference is not "runCommand parses the arguments", but "runCommand [only] invokes the shell". If you want runProcess to invoke the shell: runProcess "/bin/sh" ["-c", commandLine] ... (... ought to be ["sh", "-c" commandLine], but the way I remember it ghc gratuitously prevents you from specifying argv 0.) Donn Cave, donn(a)avvanta.com [I just sifted this thread out of ca. 300 spams and stuff, so please pardon me if this has already been mentioned in another followup.]

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Re: [Haskell-cafe] Class Quantification
by Sean Leather 01 Oct '08

01 Oct '08

> Now I would like to generalise 'foo' and 'bar' to 'bla' so that I can > write: > > testBla1 = bla fromInteger 1 :: (Int, Float) > testBla2 = bla read "1" :: (Int, Float) > > My question is how to define 'bla'. > > I can write: > > > bla :: (forall b. a -> b) -> a -> (c, d) > > bla f x = (f x, f x) > > But then 'testBla1' gives the following expected error: > > Could not deduce (Num b) from the context () > arising from a use of `fromInteger' > > [...] > > So, somehow I need to quantify over the type class. > > bla :: forall cls. (cls c, cls d) => (forall b. cls b => a -> b) -> a -> > (c, d) > > But this isn't legal. > > Is there another way of defining 'bla'? > The simple, from-the-gut answer involves the enumeration of all the classes that you need in the context. > bla :: (Read c, Read d, Num c, Num d) => (forall b. (Read b, Num b) => a -> b) -> a -> (c, d) > bla f x = (f x, f x) But perhaps you're looking for potentially unknown classes? Sean

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Distributing Haskell binaries as OSX App Bundles
by Stephen 01 Oct '08

01 Oct '08

I wrote a command-line program recently for a friend in haskell. However, he's far away and not particularly computer literate. I sent him the raw binaries, but they came up with errors about not being able to find libgmp stuff. So then I thought I should probably be able to somehow distribute all the stuff together in a .app bundle. However, the only experience I have of doing this sort of stuff before is via xcode. What's the best way to go about this? It just occurred to me now that maybe cmake is the way to go? Any advice that might save me some time would be really appreciated. Cheers, Stephen

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Haskell versus F#, OCaml, et. al. ...
by Galchin, Vasili 01 Oct '08

01 Oct '08

Hello, Frank mode on ... ;^) In terms of functionality, where is Haskell superior vs inferior to ML, Caml, OCaml, F#, Erlang, etc.? E.g. in terms of library functionality? Regards, Vasili

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GHC, names of inferred type variables
by Shiqi Cao 01 Oct '08

01 Oct '08

Hi, Error messages from GHC contain inferred type variables, is there anyway to find out which term an inferred type variable is for(if the term exists)? Thanks, Shiqi

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Class Quantification
by Bas van Dijk 01 Oct '08

01 Oct '08

Hello, I was writing some Haskell when I stumbled on the following problem: With the following language extension... > {-# LANGUAGE RankNTypes #-} ... it's possible to define 'foo' and 'bar' like so: > foo :: (Num c, Num d) => (forall b. Num b => a -> b) -> a -> (c, d) > foo f x = (f x, f x) > bar :: (Read c, Read d) => (forall b. Read b => a -> b) -> a -> (c, d) > bar f x = (f x, f x) Which allows us to write: > testFoo = foo fromInteger 1 :: (Int, Float) > testBar = bar read "1" :: (Int, Float) Now I would like to generalise 'foo' and 'bar' to 'bla' so that I can write: testBla1 = bla fromInteger 1 :: (Int, Float) testBla2 = bla read "1" :: (Int, Float) My question is how to define 'bla'. I can write: > bla :: (forall b. a -> b) -> a -> (c, d) > bla f x = (f x, f x) But then 'testBla1' gives the following expected error: Could not deduce (Num b) from the context () arising from a use of `fromInteger' Possible fix: add (Num b) to the context of the polymorphic type `forall b. a -> b' In the first argument of `bla', namely `fromInteger' In the expression: bla fromInteger 1 :: (Int, Float) In the definition of `testBla1': testBla1 = bla fromInteger 1 :: (Int, Float) And 'testBla2' gives a similar error complaining that it can't deduce (Read b) from the context. So, somehow I need to quantify over the type class. bla :: forall cls. (cls c, cls d) => (forall b. cls b => a -> b) -> a -> (c, d) But this isn't legal. Is there another way of defining 'bla'? Thanks, Bas

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Re: [Haskell-cafe] not able to compile Happy GLR examples
by brianalexander1＠cableone.net 30 Sep '08

30 Sep '08

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Red-Blue Stack
by Matthew Eastman 30 Sep '08

30 Sep '08

Hey guys, This is probably more of a question about functional programming than it is about Haskell, but hopefully you can help me out. I'm new to thinking about things in a functional way so I'm not sure what the best way to do some things are. I'm in a data structures course right now, and the assignments for the course are done in Java. I figured it'd be fun to try and implement them in Haskell as well. The part of the assignment I'm working on is to implement a RedBlueStack, a stack where you can push items in as either Red or Blue. You can pop Red and Blue items individually, but the stack has to keep track of the overall order of items. i.e. popping Blue in [Red, Red, Blue, Red, Blue] would give [Red, Red, Blue] All push and pop operations on the stack have to be done in O(1) time. It was easy to do in Java since you can just keep track of everything with a few pointers, but it took a while to get the Haskell version working. Maybe I'm just not used to the functional way of doing things. I originally had this: data RBSItem a = Red a | Blue a data RedBlueStack a = RBS { red :: [RBSItem a], blue :: [RBSItem a], overall :: [RBSItem a] } But there was no way to keep popping in O(1) time because I would have to walk through the overall list when removing items. I eventually came up with: data ShowColour = PlusRed | MinusRed | PlusBlue | MinusBlue data RedBlueStack a = RBS { red :: [a], blue :: [a], order :: [ShowColour] } popRed :: RedBlueStack a -> RedBlueStack a popRed (RBS (r:rs) b o) = RBS rs b (MinusRed : o) popRed rbs@(RBS [] _ _) = rbs -- As an aside here, would it be better to put "popRed = id" for the catch-all in popRed instead of what I have? -- I don't know proper Haskell coding style yet. remUseless :: [ShowColour] -> [ShowColour] remUseless order@(x:xs) | x == MinusRed = remShowColour PlusRed xs | x == MinusBlue = remShowColour PlusBlue xs | otherwise = order where remShowColour r (c:cs) | c == r = cs | otherwise = c : remShowColour r cs remShowColour _ [] = error "Incorrect Stack Order" So instead of walking through the overall list, I just have to add a MinusRed or MinusBlue to the order list. This makes the pop and push functions operate in O(1) time, but it seems a bit excessive, because whenever the overall order of the stack is needed (e.g. printing the stack) I need to clean up the order list. I was just wondering whether this is the best way to implement something like this, keeping track of changes made instead of making the changes. If anyone has any ideas for other ways of implementing this I'd love to see them. I didn't take into account that Haskell is lazy. Will that have any effect on the running time? Probably not for a simple program like this, but for larger ones and more complex data structures and algorithms, I'm guessing it would? Thanks, Matt

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'par' - why has it the type a -> b -> b ?
by Henning Thielemann 30 Sep '08

30 Sep '08

What is the reason for implementing parallelism with 'par :: a -> b -> b'? Analogy to 'seq'? I thought parallelism would be introduced most naturally by a function which does two computations in parallel and puts together their results after completion. Say > par2 :: (a -> b -> c) -> (a -> b -> c) to be used like > par2 (+) expensiveComputationA expensiveComputationB I assume that par2 can be implemented this way: > par2 f x y = > f x (par x y) ?

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announcing darcs 2.1.0pre2
by Eric Kow 30 Sep '08

30 Sep '08

Hi everybody, The second pre-release of darcs 2.1 (formerly known as 2.0.3) is now available at http://darcs.net/darcs-2.1.0pre2.tar.gz We have increased the version number since the last pre-release because we are adopting an important new behaviour: The darcs initialize command now creates darcs-2 format repositories by default This will help new repositories to benefit from the improved handling of duplicate patches and to avoid the exponential time conflicts problem. Upcoming release schedule ------------------------- 2008-10-03: darcs 2.1.0pre3 2008-10-10: darcs 2.1.0 Work remaining -------------- * http://bugs.darcs.net/issue971 (Petr Ročkai) When using hashed or repositories, allow darcs check to deal with filenames that differ only in case when run on a case-insensitive filesystem. Petr has done 90% of the work for this -- he has implemented this for darcs repair -- so this shall largely be a question of refactoring. * http://bugs.darcs.net/issue1003 Allow darcs-transfer mode to deal with a specific set of missing files (namely _darcs/format) so that users can benefit from ssh connection sharing even if the remote end uses an old-fashioned repository. In the meantime, a simple workaround is to touch the _darcs/format file in the remote repoistory * http://bugs.darcs.net/issue1078 Fix a corner case in paths handling that makes darcs overly cautious if the repository is a symbolic link * http://bugs.darcs.net/issue1026 Improve the error messages for 'bug in get_extra' errors, which can happen if darcs is fooled into thinking that two patches are the same. Changes since the last pre-release ---------------------------------- * User Experience: Do not allow users to add files to a darcs repository if their filenames would be considered invalid under Windows. This can be overridden with the --reserved-ok flag (issue53, Eric Kow) * Bug Fix: Do not leave behind a half-gotten directory if darcs get fails (issue1041, Vlad Dogaru, David Roundy) * User Experience: notice when you are trying to pull from a seemingly unrelated repository, that is one with a sufficiently different history. This can be overridden with the --allow-unrelated-repos flag (Dmitry Kurochkin, David Roundy) * Bug Fix: Fix hang after a user input error (for example, EOF) (Judah Jacobson) * Quality Assurance: Improvements to documentation and online help (Simon Michael) -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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Re: Haddock + Hoogle == Javadoc on steroids
by Simon Michael 30 Sep '08

30 Sep '08

Taking this to haskell-cafe.. http://joyful.com/repos/darcs-sm/api-doc is a mashup of haddock, hoogle and hscolour (and darcsweb, darcs-graph - see http://joyful.com/repos) It's rough but quite useful - a few minutes here gave me a much better understanding of the big picture of darcs code. By alternating shift & enter in the contents pane I could browse quickly through all modules. Improvement: one could do a lot of useful magic with javascript. But it would be more powerful to improve the tools, eg I'd like if haddock had frames/no-frames built in and hoogle could be made to work in either case. I haven't had time to work on this, currently I hard-code the target in hoogle and munge the haddock output slightly (see recent patch in darcs-unstable). As you say it would be great to keep improving this area and baking it into our tools and infrastructure. Highly accessible and efficient docs and code browsing tools help a lot! On Sep 27, 2008, at 1:49 PM, Jason Dagit wrote: > Simon, > > I'm wondering if you could find a way to make it "trivial" for people using cabal to combine haddock and hoogle the way you have for darcs? > > Some ideas: > 1) Depend entirely on cabal for the auto setup of things > 2) Provide the framed interface on your webpage also has a layout in emacs (so people can use either web or emacs) > 3) Package it so that people just 'cabal install hoodock && hoddock ./src' and then they are done for 90% of cases > 4) Provide demos for darcs and something else large like GHC > > What do you think? If you need help with it, I'm sure there are tons of people on Haskell-Cafe that would really dig this and help you with it. > > Thanks, I love it! > Jason Thanks! -Simon

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Re: [Haskell-cafe] Re: Version 0.4.3 of happs-tutorial is a HAppS job board, done in HAppS.
by Thomas Hartman 30 Sep '08

30 Sep '08

The executable needs the templates in the same directory to work correctly. Copy the happs-tutorial.tar.gz file from whereever cabal put it -- probably somewhere under .cabal if you're on linux. Untar it, cd into the directory, compile and run in there. Should work. I'll revise the tutorial instructions to make this clearer, thanks for the feedback. Thomas. 2008/9/29 Anton Tayanovskyy <anton.tayanovskyy(a)gmail.com>: > Hello Thomas, > > After doing > > sudo cabal install happs-tutorial > > I got HappS to build which is really a great improvement (about a year > ago I could not build HappS). It also installed happs-tutorial > executable. > > Now, the executable runs, but when I try to access the server over HTTP, I get: > > IO Error: Just "templates/base.st" -- does not exist > > Also, on my system I can't locate base.st nor hackInGhci.sh mentioned > in the online tutorial. Actually, I somehow fail to make sense of this > page: > > http://www.happstutorial.com/tutorial/run-tutorial-locally > > After the Cabal install, I'm lost. Maybe it's just me not seeing > something obvious, but in that case it still gives you a good sample > of your target audience, us webmonkeys :) > > If that helps, I'm on Fedora 9, GHC 8.3. > > Thanks. > > > --Anton > > > On Mon, Sep 29, 2008 at 5:25 PM, Thomas Hartman <tphyahoo(a)gmail.com> wrote: >> Someone on reddit pointed out that many firewalls block 5001 so I >> moved to vanilla http port 80. >> >> http://www.happstutorial.com >> >> >> >> 2008/9/29 Thomas Hartman <tphyahoo(a)gmail.com>: >>> Hello, world. >>> >>> In Version 4 of the ongoing self-demoing HAppS Tutorial, we implement >>> a HAppS job board using HAppS. >>> >>> demo: http://happstutorial.com:5001 >>> >>> install: sudo cabal install happs-tutorial >>> >>> darcs head: darcs get http://code.haskell.org/happs-tutorial >>> >>> There aren't any new lessons compared to the last release, but the >>> code is much cleaner, and... well... the web site actually does >>> something. >>> >>> Coming soon, lessons on form processing and HAppS State. >>> >>> Enjoy! >>> >>> Thomas. >>> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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Re: [Haskell-cafe] Re: Haddock + Hoogle == Javadoc on steroids
by Sean Leather 30 Sep '08

30 Sep '08

> > Hi Neil.. my apologies, my nightly cron script clobbered it. Please try > now, same url: http://joyful.com/repos/darcs-sm/api-doc > It seems the "Contents" link embeds the outer frame into the right-hand side inner frame. Otherwise, it looks nice! Sean

1 0

The container problem
by Andrew Coppin 30 Sep '08

30 Sep '08

Take a look around you. Haskell provides several sorts of container. We have: Data.List Data.Set Data.Map Data.Hashtable Data.ByteString Data.Sequence Data.Array Data.Tree Data.IntSet Data.IntMap ... In other words, we have *a lot* of different data containers. And yet, each one provides its own unique API. To anybody used to OO languages, that sounds pretty crazy. In something like Java or Smalltalk or Eiffel, you have an abstract class that represents "container", and maybe a seperate one for "ordered container", and then concrete subclasses for each kind of container. Each one may add a few unique methods of its own, but basically all the containers have a uniform API, and you can write functions that work for any arbitrary [ordered] container. In Haskell, you can't do this. Why is that? To me, it seems that there are two sticking points: 1. Historical reasons. 2. The Haskell '98 type system. (1) is obviously solvable. (2) is harder. Some containers can contain *any* type of data. Haskell permits parametric polymorphism, so this is no problem: Data.List.map :: (a -> b) -> [a] -> [b] Other containers only support *one* type of data: Data.ByteString.Char8.map :: (Char -> Char) -> ByteString -> ByteString The type has a different kind, and the function parameter's type is more constrained. Yet still this poses no problem. However... now try writing a class that both of these functions could be methods of. Good luck with that, by the way... This is AFAIK also the reason why, e.g., Set is *not* an instance of Monad; you can't write a valid instance. The type checker won't have it. To ears accustomed to the OO way, all this makes it sound like Haskell's type system sucks. (Which is rich, because in half the OO languages, you can't write a type-safe container that works for arbitrary element types in the first place! Haskell is a Big Win here.) If I understand this correctly, to solve this problem you need either Functional Dependencies or Associated Types. Is that correct? I also gather that "FDs have problems" - although I have no idea what those problems are. Everybody's hoping that ATs will fix this, but ATs are still kinda new. (Are they even fully implemented in GHC yet?) Can anybody correct/expand on this state of affires? I just want to make sure I understand our position correctly...

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[Haskell-cafe] Version 0.4.3 of happs-tutorial is a HAppS job board, done in HAppS.
by Thomas Hartman 30 Sep '08

30 Sep '08

Hello, world. In Version 4 of the ongoing self-demoing HAppS Tutorial, we implement a HAppS job board using HAppS. demo: http://happstutorial.com:5001 install: sudo cabal install happs-tutorial darcs head: darcs get http://code.haskell.org/happs-tutorial There aren't any new lessons compared to the last release, but the code is much cleaner, and... well... the web site actually does something. Coming soon, lessons on form processing and HAppS State. Enjoy! Thomas.

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not able to compile Happy GLR examples
by brianalexander1＠cableone.net 30 Sep '08

30 Sep '08

2 1

ANNOUNCE: Graphalyze-0.1
by Ivan Miljenovic 30 Sep '08

30 Sep '08

I'd like to announce the initial release of my graph-theoretic analysis library, Graphalyze [1], the darcs repo for which is also available [2]. This is a pre-release of the library that I'm writing for my mathematics honours thesis, "Graph-Theoretic Analysis of the Relationships in Discrete Data". I'll also be releasing a tool that uses this library to analyse the structure of Haskell code, that I'm tentatively calling SourceGraph. As it stands, the library has a number of algorithms included, some of which I've developed from scratch (e.g. clique finder), and others are implementations of published algorithms (mainly the two clustering algorithms). The code is meant to be more readable than efficient, and I wanted to explore ways of developing algorithms that match more closely the way graphs work (which makes FGL a much nicer fit than matrix-based or list-based graph data structures). This library is only a pre-release, as whilst everything in there works (at least it does for me), I'd like to get some feedback from the community, especially since this is my first ever released solo piece of code (I've coded assignments, and worked on projects with others, but have never released anything that I've been solely responsible for before). In particular, have I written the .cabal file correctly? Also, I'd like advice on something else: the part of the library that I'd like to develop still is the reporting framework. The end goal of the library is for the user to specify which algorithms they want applied to their data, and then the library produces a document with the results. This document is _not_ meant to be machine readable. As such, I can think of three options: 1) Plain text, with graphs either in seperate image files (using graphviz) or else as plaintext (FGL's show function). 2) Generate LaTeX code. 3) Generate Pandoc [3] compatible Markdown, and let the user convert it into whatever format they prefer. I'm not a big fan of option 1), as it is probably the most unreadable in general. I'd like to use Pandoc, as it is theoretically possible to convert it to numerous other filetypes, however with inline linking there's still no way (at least I can find) to have images scaled to the correct size automatically. So unless I pre-scale the images, using option 3) and then converting to PDF via LaTex generation of the Markdown sources is probably out. As such, what would you all prefer to read as a documentation-style report of your software? 1) A PDF via LaTeX, which has the advantage of being printable and all in one file 2) HTML via Pandoc, which lets you have the images linked separately from the document, and thus no need to shrink them down (they can stay at the natively generated size, and thus easier to zoom in, etc.). Finally, I'll be giving my honours talk on this next Monday. So if you're in Brisbane on 6 October and interested, it'll be on at 2PM at the University of Queensland (where as part of it I'll be explaining to mathematicians why Haskell is a great language to use for mathematics... or at least trying to!). [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze [2] http://code.haskell.org/Graphalyze/ [3] http://johnmacfarlane.net/pandoc -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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Code.haskell.org down
by Mitchell, Neil 29 Sep '08

29 Sep '08

Hi, For me, it seems that code.haskell.org is down. Is this the case for other people as well? It seems code.haskell.org regularly looses connectivity for me :-( Thanks Neil ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================

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about logical computation
by z_axis 29 Sep '08

29 Sep '08

hi, friends I am a Haskell newbie however i like it very much. After starting learn haskell, i donot find the corresponding "&", "|" , "~", "<<", ">>" logical computation of C language. Sincerely! -------------- z_axis 2008-09-29

3 2

TH error
by Tim Newsham 29 Sep '08

29 Sep '08

I'm goofing with TH and I have my program mostly done: http://hpaste.org/10713 If I have the "$(deriveBinary ''MyData)" line commented out it prints out what looks to me like correct code. I can even paste it into a program and it compiles. However, when the line isn't commented out I get an error I don't understand: test.hs:1:0: Illegal data constructor name: `x' When splicing generated code into the program There are two places in my code I use "x" in splices that could be causing the problem: g <- [| getWord8 >>= \x -> $(caseE [| x |] gcases') |] and put x = $(caseE [| x |] (map return ps)) |] but I don't understand why these might be causing errors (if they are indeed the cause). Using -ddump-splices doesn't help since it seems to hit the error before dumping splices. What's going on here? Tim Newsham http://www.thenewsh.com/~newsham/

3 2

bug in number reading?
by Jason Dusek 29 Sep '08

29 Sep '08

Maybe I'm missing something, but this doesn't seem right... -- _jsn :; ghc -e '10e4' <interactive>:1:0: Warning: Defaulting the following constraint(s) to type `Double' `Fractional a' arising from a use of `it' at <interactive>:1:0-3 In the first argument of `print', namely `it' In the expression: print it In a stmt of a 'do' expression: print it 100000.0 it :: forall t. (Fractional t) => t

4 4

yi compiles but does not launches
by Ahn, Ki Yung 29 Sep '08

29 Sep '08

I wanted to try out yi after seeing it demonstrated in the Haskell symposium. So, I installed cabal as described here http://hackage.haskell.org/trac/hackage/wiki/CabalInstall I am using Debian unstable with debian distributed GHC 6.8.2.x but it seems that yi requries GHC 6.8.3 to compile. So, I manually installed GHC 6.8.3 using the binary distribution from ghc homepage. When I install yi with "cabal install yi" it succeeds and installs yi version 0.4.6 However, when I run yi it starts but immediately get stuck with the following error message: Custom yi ("/home/kyagrd/.yi/yi-i386-linux") could not be launched! The custom file yi-i386-linux does not exist and I don't have any idea what that is. Same thing happens with the development version 0.4.7 from darcs repository. I did this from complete scratch. I removed the .cabal and .ghc directory and started from scratch in a clean state. If anyone have succeeded using yi in Debian unstable please let me know how you got around from this problem. -- Ahn, Ki Yung

2 1

[m..n] question
by Richard A. O'Keefe 28 Sep '08

28 Sep '08

Erlang's equivalent of [m..n] is lists:seq(M, N), which is currently defined to raise an exception when N < M. In particular, lists:seq(1, N) returns a list of length N when N > 0, but not when N = 0. I'm currently arguing that lists:seq(1, 0) should be [], not an exception. Oddly enough, I'm being beaten over the head with Haskell, of all things. In Haskell, "The sequence enumFromTo e1 e3 is the list [e1,e1+1,e1+2,...e3]. The list is empty if e1 > e3." It is being claimed that the reason for this is that "exceptions are problematic" in Hasell, so the Haskell designers went out of their way to make this function total whether it made sense or not. I am currently suggesting that it's to keep the specification (for integers) simple: "[m..n] is the set of integers x such that m<=x<=n, listed in ascending order". There's also the nice equivalence between [m..n] and takeWhile (<= n) [m..]. Unfortunately, no such "abstract" characterisation of [m..n] is mentioned in the report, and the takeWhile connection is inferred from numericEnumFromTo. Does anyone remember why the definition of enumFromTo is the way it is? -- If stupidity were a crime, who'd 'scape hanging?

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Re: [Haskell] Symposium videos
by Don Stewart 28 Sep '08

28 Sep '08

Malcolm.Wallace: > Guerilla videos of the Haskell Symposium 2008 presentations. Enjoy. Now on haskell.org, http://haskell.org/haskellwiki/Video_presentations/Haskell_Symposium_2008 Great work Malcolm!!

2 1

TH code for deriving Binary and NFData instances
by Tim Newsham 28 Sep '08

28 Sep '08

Here's some TH code for automatically deriving Data.Binary and Control.Parallel.Strategies.NFData instances: http://www.thenewsh.com/~newsham/store/DeriveBinary.hs Tim Newsham http://www.thenewsh.com/~newsham/

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Re: Haskell-Cafe Digest, Vol 61, Issue 49
by Mark Snyder 28 Sep '08

28 Sep '08

whoops! wow, wrong message to reply to... please disregard the previous. Apologies, ~Mark Snyder ----- Original Message ---- From: "haskell-cafe-request(a)haskell.org" <haskell-cafe-request(a)haskell.org> To: haskell-cafe(a)haskell.org Sent: Thursday, September 25, 2008 12:13:22 PM Subject: Haskell-Cafe Digest, Vol 61, Issue 49 Send Haskell-Cafe mailing list submissions to haskell-cafe(a)haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/haskell-cafe or, via email, send a message with subject or body 'help' to haskell-cafe-request(a)haskell.org You can reach the person managing the list at haskell-cafe-owner(a)haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Haskell-Cafe digest..." Today's Topics: 1. RE: Injecting Haskell into C (Simon Peyton-Jones) 2. Re: Haskell board game (Ryan Ingram) 3. Re: Am I doing it right? (Achim Schneider) 4. Re: if - then - else layout (Jules Bean) 5. Re: if - then - else layout (Achim Schneider) 6. Re: Distributing Haskell binaries as OSX App Bundles (Christian Maeder) 7. Re: if - then - else layout (Achim Schneider) 8. Re: if - then - else layout (Achim Schneider) 9. announcing darcs 2.1.0pre2 (Eric Kow) 10. Re: pure Haskell database (jean-christophe mincke) 11. Re: pure Haskell database (Achim Schneider) 12. Re: pure Haskell database (Marc Weber) 13. Re[2]: [Haskell-cafe] pure Haskell database (Bulat Ziganshin) 14. Re: Google Android (Adam Langley) 15. Re: Google Android (Maarten Hazewinkel) 16. Where is OpenGL loadMatrix ? (minh thu) 17. Re: Where is OpenGL loadMatrix ? ( Krzysztof Skrz?tnicki ) 18. Re: Where is OpenGL loadMatrix ? (Achim Schneider) 19. Re: Re: Where is OpenGL loadMatrix ? (minh thu) 20. StateWriter: a monad-writing exercise (Anthony LODI) 21. Re: StateWriter: a monad-writing exercise (Henning Thielemann) 22. Re: Re: Where is OpenGL loadMatrix ? (Bit Connor) 23. Re: Re: Where is OpenGL loadMatrix ? (minh thu) 24. Re: Where is OpenGL loadMatrix ? (Achim Schneider) 25. Re: pure Haskell database (Manlio Perillo) 26. Microsoft's Craig Mundie outlines the future of computing (Lihn, Steve) 27. GHC 6.10, OS X, Fink and CPPFLAGS (Svein Ove Aas) 28. Re: Climbing up the shootout... (Ketil Malde) 29. Problem with existential quantification (Eric) ---------------------------------------------------------------------- Message: 1 Date: Thu, 25 Sep 2008 08:32:44 +0100 From: Simon Peyton-Jones <simonpj(a)microsoft.com> Subject: RE: [Haskell-cafe] Injecting Haskell into C To: Anatoly Yakovenko <aeyakovenko(a)gmail.com>, "roma(a)ro-che.info" <roma(a)ro-che.info> Cc: haskell <haskell-cafe(a)haskell.org> Message-ID: <638ABD0A29C8884A91BC5FB5C349B1C32D766E2F96(a)EA-EXMSG-C334.europe.corp.microsoft.com> Content-Type: text/plain; charset="us-ascii" Anatoly I have not been following the details, but would you consider writing up your example on the GHC user guide Wiki? http://haskell.org/haskellwiki/GHC/Using_the_FFI It's a very good way to share your experience with others. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe- | bounces(a)haskell.org] On Behalf Of Anatoly Yakovenko | Sent: 24 September 2008 22:42 | To: roma(a)ro-che.info | Cc: haskell | Subject: Re: [Haskell-cafe] Injecting Haskell into C | | you'll find this example really helpfull | | | ---------- Forwarded message ---------- | From: Claude Heiland-Allen <claudiusmaximus(a)goto10.org> | Date: 2008/6/5 | Subject: Re: [Haskell-cafe] example of FFI FunPtr | To: "Galchin, Vasili" <vigalchin(a)gmail.com> | Cc: haskell <haskell-cafe(a)haskell.org> | | | Galchin, Vasili wrote: | > | > Hello, | > | > I want to model a Haskell function that is a callback from C. I have | > only found one example in the unix package's Semaphore.hsc, which | apparently | > is not used. I want to be able to marshall a Haskell function that is a | > first class citizen residing in a Haskell data type and pass to a C | function | > via FFI. Are there examples of this? | | Attached is a simple example. | | The main thing to note is 'foreign import ccall "wrapper"' which gives | you a factory for turning Haskell functions into foreign function | pointers. | | More information: | | http://www.cse.unsw.edu.au/~chak/haskell/ffi/ | | | Claude | -- | http://claudiusmaximus.goto10.org | | | CallBacker: CallBacker.hs callerback.c callerback.h | ghc -O2 -Wall -fffi -o CallBacker CallBacker.hs callerback.c | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------ Message: 2 Date: Thu, 25 Sep 2008 01:09:02 -0700 From: "Ryan Ingram" <ryani.spam(a)gmail.com> Subject: Re: [Haskell-cafe] Haskell board game To: "Rafael C. de Almeida" <almeidaraf(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <2f9b2d30809250109g3f0a2359s31a003c515549875(a)mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Bertram has put together a peg solitaire game using gtk2hs with Prompt for control: http://int-e.home.tlink.de/haskell/solitaire.tar.gz It's a good read and probably a good starting point for other board games. -- ryan On Wed, Sep 24, 2008 at 7:04 PM, Rafael C. de Almeida <almeidaraf(a)gmail.com> wrote: > Hello, > > I'm interested in doing a simple board game on haskell. For that I want > to be able to draw stuff like the possible player movements and I want > to be able to display very simple animations. I want to know what > graphical interface library you suggest to me. > > I have almost no prior experience with graphical interfaces of any kind, > so I rather start with something easy and straightforward. I have no > need for great performance or anything like that. I'd like if it runs on > windows with much trouble, that is, it'll be easy to package it for > windows without requiring the user to install anything besides my game. > > My first thought was to use GTK's gtkTable, but I'm unsure how easy it > is to make it work on windows. Beside that, I'm not sure it would be the > easiest API for me to use. > > []'s > Rafael > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > ------------------------------ Message: 3 Date: Thu, 25 Sep 2008 10:41:38 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: Am I doing it right? To: haskell-cafe(a)haskell.org Message-ID: <20080925104138.02079514@solaris> Content-Type: text/plain; charset=US-ASCII Daniel Fischer <daniel.is.fischer(a)web.de> wrote: > The fast searching function on ByteStrings has already been written > for you :) > That's in ghc 6.8.3, which is not in gentoo but only in the haskell overlay, which means that all blame goes to the gentoo maintainers for being utterly out of date. The KMP import works like a charm. findSubstring is only defined for strict bytestrings... try running those benchmarks again, this time on data bigger than your ram. Not to mention that it's deprecated. The really interesting topic is hacking Parsec to use KMP search on "manyTill anyChar (try string match), or rather any recursive try involving combinators that can calculate the position for the next candidate match as a side effect. PS: Thank you for not pointing out that my original code crashes on B.tail B.empty in some cases, or even just that it can't replace overlapping matches at all. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 4 Date: Thu, 25 Sep 2008 09:45:12 +0100 From: Jules Bean <jules(a)jellybean.co.uk> Subject: Re: [Haskell-cafe] if - then - else layout To: leledumbo <leledumbo_cool(a)yahoo.co.id> Cc: haskell-cafe(a)haskell.org Message-ID: <48DB4F98.9000804(a)jellybean.co.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed leledumbo wrote: > consider this partial program: > if n>5 then > putStrLn "big" > else > putStrLn "small" > > this works fine in hugs, but in ghc I must change it to: > if n>5 > then > putStrLn "big" > else > putStrLn "small" Actually both of those are valid expressions. And they both work in hugs and ghc. The question I imagine you're asking involves layout mode: do if n>5 then putStrLn "big" else putStrLn "small" this is shorthand for do { if n > 5 then putStrLn "big" ; else putStrLn "small" } which is a syntax error. A statement in a do block cannot begin with the keyword "else". If you indent the else a bit further than it counts and a continuation of the enclosing expression (beginning with if) so it desugars to do { if n > 5 then putStrLn "big" else putStrLn "small" } which is fine. Haskell' is apparently going to include a hack to permit this case. I think that's a poor decision, because including a hack to the layout rule makes it harder to understand and explain the layout rule. Jules ------------------------------ Message: 5 Date: Thu, 25 Sep 2008 10:48:21 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: if - then - else layout To: haskell-cafe(a)haskell.org Message-ID: <20080925104821.09da2a93@solaris> Content-Type: text/plain; charset=US-ASCII "Brandon S. Allbery KF8NH" <allbery(a)ece.cmu.edu> wrote: > I think Hugs is violating the Haskell98 layout rules. > One could argue that GHC should, too. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 6 Date: Thu, 25 Sep 2008 11:04:00 +0200 From: Christian Maeder <Christian.Maeder(a)dfki.de> Subject: [Haskell-cafe] Re: Distributing Haskell binaries as OSX App Bundles To: Stephen <analytic(a)gmail.com> Cc: Haskell-Cafe(a)haskell.org Message-ID: <48DB5400.4060804(a)dfki.de> Content-Type: text/plain; charset=ISO-8859-1 Stephen wrote: > I wrote a command-line program recently for a friend in haskell. > However, he's far away and not particularly computer literate. I sent > him the raw binaries, but they came up with errors about not being able > to find libgmp stuff. So then I thought I should probably be able to I usually link in libgmp.a statically. This happens automatically if libgmp.a resides in ghc's libdir (just copy it) Cheers Christian ------------------------------ Message: 7 Date: Thu, 25 Sep 2008 11:12:26 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: if - then - else layout To: haskell-cafe(a)haskell.org Message-ID: <20080925111226.67482196@solaris> Content-Type: text/plain; charset=US-ASCII Jules Bean <jules(a)jellybean.co.uk> wrote: > do > if n>5 then > putStrLn "big" > else > putStrLn "small" > > this is shorthand for > > do { if n > 5 then putStrLn "big" ; else putStrLn "small" } > > which is a syntax error. A statement in a do block cannot begin with > the keyword "else". > > Haskell' is apparently going to include a hack to permit this case. I > think that's a poor decision, because including a hack to the layout > rule makes it harder to understand and explain the layout rule. > There's no need to hack the layout rule, you're even giving pointers to the solution. Something like this: if p = do (_, c, a) <- get put (b, c, a) mzero then c = do (b, _, a) <- get put (b, c, a) mzero else a = do (b, c, _) <- get put (b, c, a) mzero end = do (b, c, a) <- get return if p then a else c Advantages are obvious: Order doesn't really matter anymore, as in then "get away" else "or else" if i tell you to end Furthermore, this scheme supports logical comments, a rare kind of control structure enabling mindboggingly diverse rapid prototyping options: if i knew what i want to do if i knew how to do it then i'd have written the next line much earlier if i wrote this line then i don't need to remove the other lines else where in other languages i'd have to do that end -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 8 Date: Thu, 25 Sep 2008 11:20:58 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: if - then - else layout To: haskell-cafe(a)haskell.org Message-ID: <20080925112058.46e0c095@solaris> Content-Type: text/plain; charset=US-ASCII Achim Schneider <barsoap(a)web.de> wrote: > if i knew how to do it Sorry, apparent mistake, besides confusing b (bool) with p (predicate): if p _ c = do (_, _, a) <- get put (p, c, a) mzero -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 9 Date: Thu, 25 Sep 2008 10:32:27 +0100 From: Eric Kow <kowey(a)darcs.net> Subject: [Haskell-cafe] announcing darcs 2.1.0pre2 To: darcs-users(a)darcs.net Cc: haskell-cafe(a)haskell.org Message-ID: <20080925093227.GG301(a)Macintosh.local> Content-Type: text/plain; charset="utf-8" Hi everybody, The second pre-release of darcs 2.1 (formerly known as 2.0.3) is now available at http://darcs.net/darcs-2.1.0pre2.tar.gz We have increased the version number since the last pre-release because we are adopting an important new behaviour: The darcs initialize command now creates darcs-2 format repositories by default This will help new repositories to benefit from the improved handling of duplicate patches and to avoid the exponential time conflicts problem. Upcoming release schedule ------------------------- 2008-10-03: darcs 2.1.0pre3 2008-10-10: darcs 2.1.0 Work remaining -------------- * http://bugs.darcs.net/issue971 (Petr Ročkai) When using hashed or repositories, allow darcs check to deal with filenames that differ only in case when run on a case-insensitive filesystem. Petr has done 90% of the work for this -- he has implemented this for darcs repair -- so this shall largely be a question of refactoring. * http://bugs.darcs.net/issue1003 Allow darcs-transfer mode to deal with a specific set of missing files (namely _darcs/format) so that users can benefit from ssh connection sharing even if the remote end uses an old-fashioned repository. In the meantime, a simple workaround is to touch the _darcs/format file in the remote repoistory * http://bugs.darcs.net/issue1078 Fix a corner case in paths handling that makes darcs overly cautious if the repository is a symbolic link * http://bugs.darcs.net/issue1026 Improve the error messages for 'bug in get_extra' errors, which can happen if darcs is fooled into thinking that two patches are the same. Changes since the last pre-release ---------------------------------- * User Experience: Do not allow users to add files to a darcs repository if their filenames would be considered invalid under Windows. This can be overridden with the --reserved-ok flag (issue53, Eric Kow) * Bug Fix: Do not leave behind a half-gotten directory if darcs get fails (issue1041, Vlad Dogaru, David Roundy) * User Experience: notice when you are trying to pull from a seemingly unrelated repository, that is one with a sufficiently different history. This can be overridden with the --allow-unrelated-repos flag (Dmitry Kurochkin, David Roundy) * Bug Fix: Fix hang after a user input error (for example, EOF) (Judah Jacobson) * Quality Assurance: Improvements to documentation and online help (Simon Michael) -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

2 1

Notes on the future of Haskell from ICFP
by Bryan O'Sullivan 27 Sep '08

27 Sep '08

Here's a writeup I posted from the conference floor this afternoon: http://www.serpentine.com/blog/2008/09/26/some-notes-on-the-future-of-haske…

3 2

Building DLLs
by Andrew Coppin 27 Sep '08

27 Sep '08

OK, so a GHC question: Apparently at some point, GHC used to support DLLs. And then it stopped working. And then it may or may not have been brought back again... Does anybody know exactly what the status of this is? Is it currently working or broken? If it's working, what can and can't you use it for? And how do you work it? ;-) Thanks.

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Re: haskell blas bindings: does iomatrix gemv transposing of matrix a?
by Patrick O'Regan Perry 27 Sep '08

27 Sep '08

Hi Anatoly, I made the decision to make "herm" an O(1) operation. This means you don't have to pass transpose arguments to the multiplication routines. When you do, for example: > let a = listMatrix (2,3) [1..6] > x = listVector 2 [1, -1] > in herm a <*> x this gets implemented as a call to gemv with transa set to "ConjTrans". BLAS actually supports "NoTrans", "Trans", and "ConjTrans". For real data types, "Trans" is the same as "ConjTrans". For complex data types, they are different. Unfortunately, it is impossible to call a routine with "Trans" in the blas bindings. I explicitly did not want people to have to pass extra parameters to indicate transpose/conjugacy information, and I wanted "conjugate transpose" to be an O(1) operation. Ideally, "transpose" would be O(1), as well. However, since BLAS doesn't have an option to conjugate the input matrix but not transpose it, only one of "herm" and "trans" can be O(1). I think in hmatrix, "trans" is O(1), but not "herm". Patrick p.s. I've been busy with other work lately, and I probably won't make a release soon, but I did a pretty big overhaul of the library to support operations in the ST monad. For impure operations, the functions of all the operations are mostly the same, but the types are all different. (For pure operations, there are only minor changes.) If you want the development version, you can get the darcs repo at http://stat.stanford.edu/~patperry/code/blas . The new version is pretty typeclass-heavy, since that's the only way I know how to support both ST and IO. Consequently, there have been some performance regressions. I have some optimization ideas (in the "TODO") file, but I do not have time to implement them right now. If you or anyone else would like to help with this or anything else, I would be glad to have you aboard the development "team". ----- Original Message ----- From: "Anatoly Yakovenko" <aeyakovenko(a)gmail.com> To: patperry(a)stanford.edu Cc: "haskell" <haskell-cafe(a)haskell.org> Sent: Tuesday, September 16, 2008 8:46:02 PM GMT -05:00 US/Canada Eastern Subject: haskell blas bindings: does iomatrix gemv transposing of matrix a? Hey Patric, Thanks for your great work on the blas bidnings. I have a question on gemv. I thought its possible for blas to transpose the input matrix before doing the multiplication. Is it possible to do that with the haskell bindings? Or am I mistaken in how gemv is used Thanks, Anatoly

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Python's big challenges, Haskell's big advantages?
by Don Stewart 27 Sep '08

27 Sep '08

http://www.heise-online.co.uk/open/Shuttleworth-Python-needs-to-focus-on-fu… "cloud computing, transactional memory and future multicore processors" Get writing that multicore, STM, web app code! -- Don

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Kind-of-off-Topic: Random thoughts on language design
by Rafael Gustavo da Cunha Pereira Pinto 27 Sep '08

27 Sep '08

Hi all, TGIF! And since it is friday, I started thinking on some alternatives to program PIC processors... I don't know how many of you are familiar with the PIC family of microcontrollers <http://www.microchip.com/>. They are RISC controllers with a wide range of complexity, starting on 8-bit and up to 32-bit, but the architecture is basically the same: - RISC - Register based (from 20-16k general purpose registers) - Limited hardware call stack. While studying Haskell, the functional bug bit me and I realized that this architecture is somewhat not well suited for traditional compilers. I suddenly started thinking on how one could implement some kind of declarative language that could easy the programming of those beasts. One of the approaches I thought was to use a block based programming (like Simulink), defining "atomic" operations that would be wired together. Do you think a compiler for this "block language" could this be implemented in Haskell? What about using the Arrow monads? Best Regards -- Rafael Gustavo da Cunha Pereira Pinto Electronic Engineer, MSc.

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Software and morals (Was: Re: Hmm, what license to use?)
by Achim Schneider 27 Sep '08

27 Sep '08

> [topic drifting to discussion of the geneva convention] Jonathan Cast <jonathanccast(a)fastmail.fm> wrote: > software Well, there indeed has been a judgement that a certain military programmer can't be disciplined for disobeying an order to program a specific software on the reason that he can't consciously allow the possibility of it being used to help the US military in Iraq. http://en.wikipedia.org/wiki/Florian_Pfaff -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited.

1 0

MetaHDBC paper
by Mads Lindstrøm 26 Sep '08

26 Sep '08

Hi all, In May I started a Haskell-cafe discussions[1], where I proposed using Template Haskell to do type-safe database access. The idea got well received and turned into the MetaHDBC library[2]. Concurrently with development I also wrote a paper describing MetaHDBC. I have never writing a paper before, and I therefore tried to imitate the best by following Simon PJ's slides and video about writing papers in [3]. A draft of the paper can be found here [4]. Your opportunity to influence the paper is large, as my limited paper-writing experience means I have little preconception about what a good paper looks like. I would especially like comments about the overall quality of the paper, can it be called scientific and comments about anything I could do to improve the paper. And remember, if commenting, honest is better than polite. Greetings, Mads Lindstrøm [1] http://www.nabble.com/Using-Template-Haskell-to-make-type-safe-database-acc… [2] http://www.haskell.org/haskellwiki/MetaHDBC [3] http://research.microsoft.com/~simonpj/papers/giving-a-talk/giving-a-talk.h… [4] http://lindstroem.files.wordpress.com/2008/09/metahdbc.pdf

5 5

Problem with existential quantification
by Eric 26 Sep '08

26 Sep '08

Dear all, I've written a function with the following type: build :: Bifunctor s => (forall b. (s a b -> b) -> b) -> Fix s a When I try to compile I get the following error: Illegal polymorphic or qualified type: forall b. (s a b -> b) -> b In the type signature for `build': build :: (Bifunctor s) => (forall b. (s a b -> b) -> b) -> Fix s a What's happening? E.M.

3 3

ANN: datapacker 1.0.1
by John Goerzen 26 Sep '08

26 Sep '08

Hi everyone, I'm finding Haskell to be a really handy language for writing programs designed to be used from shell scripts of late. hpodder, twidge, and datapacker are al on Hackage. I released dataacker 1.0.1 recently. It's about one fifth the size of a close competitor written in another language. And it has more useful features, IMHO ;-) http://changelog.complete.org/posts/760-New-version-of-datapacker.html

2 1

if - then - else layout
by leledumbo 26 Sep '08

26 Sep '08

consider this partial program: if n>5 then putStrLn "big" else putStrLn "small" this works fine in hugs, but in ghc I must change it to: if n>5 then putStrLn "big" else putStrLn "small" -- View this message in context: http://www.nabble.com/if---then---else-layout-tp19663006p19663006.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: Haskell-Cafe Digest, Vol 61, Issue 49
by Mark Snyder 26 Sep '08

26 Sep '08

Ed, I'm here until about 5:30 today, so pretty much any time until then should be fine. Fridays I'm stuck in office hours or teaching in Eaton from 10am-5pm, so today is probably a better bet. Lambda is supposed to be at 2:30pm, but it seems like nobody is really going to be there (there's no topic and a lot of people are missing), so that's probably not a timing concern, but it's the only one I can think of. ~Mark ----- Original Message ---- From: "haskell-cafe-request(a)haskell.org" <haskell-cafe-request(a)haskell.org> To: haskell-cafe(a)haskell.org Sent: Thursday, September 25, 2008 12:13:22 PM Subject: Haskell-Cafe Digest, Vol 61, Issue 49 Send Haskell-Cafe mailing list submissions to haskell-cafe(a)haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/haskell-cafe or, via email, send a message with subject or body 'help' to haskell-cafe-request(a)haskell.org You can reach the person managing the list at haskell-cafe-owner(a)haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Haskell-Cafe digest..." Today's Topics: 1. RE: Injecting Haskell into C (Simon Peyton-Jones) 2. Re: Haskell board game (Ryan Ingram) 3. Re: Am I doing it right? (Achim Schneider) 4. Re: if - then - else layout (Jules Bean) 5. Re: if - then - else layout (Achim Schneider) 6. Re: Distributing Haskell binaries as OSX App Bundles (Christian Maeder) 7. Re: if - then - else layout (Achim Schneider) 8. Re: if - then - else layout (Achim Schneider) 9. announcing darcs 2.1.0pre2 (Eric Kow) 10. Re: pure Haskell database (jean-christophe mincke) 11. Re: pure Haskell database (Achim Schneider) 12. Re: pure Haskell database (Marc Weber) 13. Re[2]: [Haskell-cafe] pure Haskell database (Bulat Ziganshin) 14. Re: Google Android (Adam Langley) 15. Re: Google Android (Maarten Hazewinkel) 16. Where is OpenGL loadMatrix ? (minh thu) 17. Re: Where is OpenGL loadMatrix ? ( Krzysztof Skrz?tnicki ) 18. Re: Where is OpenGL loadMatrix ? (Achim Schneider) 19. Re: Re: Where is OpenGL loadMatrix ? (minh thu) 20. StateWriter: a monad-writing exercise (Anthony LODI) 21. Re: StateWriter: a monad-writing exercise (Henning Thielemann) 22. Re: Re: Where is OpenGL loadMatrix ? (Bit Connor) 23. Re: Re: Where is OpenGL loadMatrix ? (minh thu) 24. Re: Where is OpenGL loadMatrix ? (Achim Schneider) 25. Re: pure Haskell database (Manlio Perillo) 26. Microsoft's Craig Mundie outlines the future of computing (Lihn, Steve) 27. GHC 6.10, OS X, Fink and CPPFLAGS (Svein Ove Aas) 28. Re: Climbing up the shootout... (Ketil Malde) 29. Problem with existential quantification (Eric) ---------------------------------------------------------------------- Message: 1 Date: Thu, 25 Sep 2008 08:32:44 +0100 From: Simon Peyton-Jones <simonpj(a)microsoft.com> Subject: RE: [Haskell-cafe] Injecting Haskell into C To: Anatoly Yakovenko <aeyakovenko(a)gmail.com>, "roma(a)ro-che.info" <roma(a)ro-che.info> Cc: haskell <haskell-cafe(a)haskell.org> Message-ID: <638ABD0A29C8884A91BC5FB5C349B1C32D766E2F96(a)EA-EXMSG-C334.europe.corp.microsoft.com> Content-Type: text/plain; charset="us-ascii" Anatoly I have not been following the details, but would you consider writing up your example on the GHC user guide Wiki? http://haskell.org/haskellwiki/GHC/Using_the_FFI It's a very good way to share your experience with others. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe- | bounces(a)haskell.org] On Behalf Of Anatoly Yakovenko | Sent: 24 September 2008 22:42 | To: roma(a)ro-che.info | Cc: haskell | Subject: Re: [Haskell-cafe] Injecting Haskell into C | | you'll find this example really helpfull | | | ---------- Forwarded message ---------- | From: Claude Heiland-Allen <claudiusmaximus(a)goto10.org> | Date: 2008/6/5 | Subject: Re: [Haskell-cafe] example of FFI FunPtr | To: "Galchin, Vasili" <vigalchin(a)gmail.com> | Cc: haskell <haskell-cafe(a)haskell.org> | | | Galchin, Vasili wrote: | > | > Hello, | > | > I want to model a Haskell function that is a callback from C. I have | > only found one example in the unix package's Semaphore.hsc, which | apparently | > is not used. I want to be able to marshall a Haskell function that is a | > first class citizen residing in a Haskell data type and pass to a C | function | > via FFI. Are there examples of this? | | Attached is a simple example. | | The main thing to note is 'foreign import ccall "wrapper"' which gives | you a factory for turning Haskell functions into foreign function | pointers. | | More information: | | http://www.cse.unsw.edu.au/~chak/haskell/ffi/ | | | Claude | -- | http://claudiusmaximus.goto10.org | | | CallBacker: CallBacker.hs callerback.c callerback.h | ghc -O2 -Wall -fffi -o CallBacker CallBacker.hs callerback.c | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe ------------------------------ Message: 2 Date: Thu, 25 Sep 2008 01:09:02 -0700 From: "Ryan Ingram" <ryani.spam(a)gmail.com> Subject: Re: [Haskell-cafe] Haskell board game To: "Rafael C. de Almeida" <almeidaraf(a)gmail.com> Cc: haskell-cafe(a)haskell.org Message-ID: <2f9b2d30809250109g3f0a2359s31a003c515549875(a)mail.gmail.com> Content-Type: text/plain; charset=ISO-8859-1 Bertram has put together a peg solitaire game using gtk2hs with Prompt for control: http://int-e.home.tlink.de/haskell/solitaire.tar.gz It's a good read and probably a good starting point for other board games. -- ryan On Wed, Sep 24, 2008 at 7:04 PM, Rafael C. de Almeida <almeidaraf(a)gmail.com> wrote: > Hello, > > I'm interested in doing a simple board game on haskell. For that I want > to be able to draw stuff like the possible player movements and I want > to be able to display very simple animations. I want to know what > graphical interface library you suggest to me. > > I have almost no prior experience with graphical interfaces of any kind, > so I rather start with something easy and straightforward. I have no > need for great performance or anything like that. I'd like if it runs on > windows with much trouble, that is, it'll be easy to package it for > windows without requiring the user to install anything besides my game. > > My first thought was to use GTK's gtkTable, but I'm unsure how easy it > is to make it work on windows. Beside that, I'm not sure it would be the > easiest API for me to use. > > []'s > Rafael > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > ------------------------------ Message: 3 Date: Thu, 25 Sep 2008 10:41:38 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: Am I doing it right? To: haskell-cafe(a)haskell.org Message-ID: <20080925104138.02079514@solaris> Content-Type: text/plain; charset=US-ASCII Daniel Fischer <daniel.is.fischer(a)web.de> wrote: > The fast searching function on ByteStrings has already been written > for you :) > That's in ghc 6.8.3, which is not in gentoo but only in the haskell overlay, which means that all blame goes to the gentoo maintainers for being utterly out of date. The KMP import works like a charm. findSubstring is only defined for strict bytestrings... try running those benchmarks again, this time on data bigger than your ram. Not to mention that it's deprecated. The really interesting topic is hacking Parsec to use KMP search on "manyTill anyChar (try string match), or rather any recursive try involving combinators that can calculate the position for the next candidate match as a side effect. PS: Thank you for not pointing out that my original code crashes on B.tail B.empty in some cases, or even just that it can't replace overlapping matches at all. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 4 Date: Thu, 25 Sep 2008 09:45:12 +0100 From: Jules Bean <jules(a)jellybean.co.uk> Subject: Re: [Haskell-cafe] if - then - else layout To: leledumbo <leledumbo_cool(a)yahoo.co.id> Cc: haskell-cafe(a)haskell.org Message-ID: <48DB4F98.9000804(a)jellybean.co.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed leledumbo wrote: > consider this partial program: > if n>5 then > putStrLn "big" > else > putStrLn "small" > > this works fine in hugs, but in ghc I must change it to: > if n>5 > then > putStrLn "big" > else > putStrLn "small" Actually both of those are valid expressions. And they both work in hugs and ghc. The question I imagine you're asking involves layout mode: do if n>5 then putStrLn "big" else putStrLn "small" this is shorthand for do { if n > 5 then putStrLn "big" ; else putStrLn "small" } which is a syntax error. A statement in a do block cannot begin with the keyword "else". If you indent the else a bit further than it counts and a continuation of the enclosing expression (beginning with if) so it desugars to do { if n > 5 then putStrLn "big" else putStrLn "small" } which is fine. Haskell' is apparently going to include a hack to permit this case. I think that's a poor decision, because including a hack to the layout rule makes it harder to understand and explain the layout rule. Jules ------------------------------ Message: 5 Date: Thu, 25 Sep 2008 10:48:21 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: if - then - else layout To: haskell-cafe(a)haskell.org Message-ID: <20080925104821.09da2a93@solaris> Content-Type: text/plain; charset=US-ASCII "Brandon S. Allbery KF8NH" <allbery(a)ece.cmu.edu> wrote: > I think Hugs is violating the Haskell98 layout rules. > One could argue that GHC should, too. -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 6 Date: Thu, 25 Sep 2008 11:04:00 +0200 From: Christian Maeder <Christian.Maeder(a)dfki.de> Subject: [Haskell-cafe] Re: Distributing Haskell binaries as OSX App Bundles To: Stephen <analytic(a)gmail.com> Cc: Haskell-Cafe(a)haskell.org Message-ID: <48DB5400.4060804(a)dfki.de> Content-Type: text/plain; charset=ISO-8859-1 Stephen wrote: > I wrote a command-line program recently for a friend in haskell. > However, he's far away and not particularly computer literate. I sent > him the raw binaries, but they came up with errors about not being able > to find libgmp stuff. So then I thought I should probably be able to I usually link in libgmp.a statically. This happens automatically if libgmp.a resides in ghc's libdir (just copy it) Cheers Christian ------------------------------ Message: 7 Date: Thu, 25 Sep 2008 11:12:26 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: if - then - else layout To: haskell-cafe(a)haskell.org Message-ID: <20080925111226.67482196@solaris> Content-Type: text/plain; charset=US-ASCII Jules Bean <jules(a)jellybean.co.uk> wrote: > do > if n>5 then > putStrLn "big" > else > putStrLn "small" > > this is shorthand for > > do { if n > 5 then putStrLn "big" ; else putStrLn "small" } > > which is a syntax error. A statement in a do block cannot begin with > the keyword "else". > > Haskell' is apparently going to include a hack to permit this case. I > think that's a poor decision, because including a hack to the layout > rule makes it harder to understand and explain the layout rule. > There's no need to hack the layout rule, you're even giving pointers to the solution. Something like this: if p = do (_, c, a) <- get put (b, c, a) mzero then c = do (b, _, a) <- get put (b, c, a) mzero else a = do (b, c, _) <- get put (b, c, a) mzero end = do (b, c, a) <- get return if p then a else c Advantages are obvious: Order doesn't really matter anymore, as in then "get away" else "or else" if i tell you to end Furthermore, this scheme supports logical comments, a rare kind of control structure enabling mindboggingly diverse rapid prototyping options: if i knew what i want to do if i knew how to do it then i'd have written the next line much earlier if i wrote this line then i don't need to remove the other lines else where in other languages i'd have to do that end -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 8 Date: Thu, 25 Sep 2008 11:20:58 +0200 From: Achim Schneider <barsoap(a)web.de> Subject: [Haskell-cafe] Re: if - then - else layout To: haskell-cafe(a)haskell.org Message-ID: <20080925112058.46e0c095@solaris> Content-Type: text/plain; charset=US-ASCII Achim Schneider <barsoap(a)web.de> wrote: > if i knew how to do it Sorry, apparent mistake, besides confusing b (bool) with p (predicate): if p _ c = do (_, _, a) <- get put (p, c, a) mzero -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or broadcasting of this signature prohibited. ------------------------------ Message: 9 Date: Thu, 25 Sep 2008 10:32:27 +0100 From: Eric Kow <kowey(a)darcs.net> Subject: [Haskell-cafe] announcing darcs 2.1.0pre2 To: darcs-users(a)darcs.net Cc: haskell-cafe(a)haskell.org Message-ID: <20080925093227.GG301(a)Macintosh.local> Content-Type: text/plain; charset="utf-8" Hi everybody, The second pre-release of darcs 2.1 (formerly known as 2.0.3) is now available at http://darcs.net/darcs-2.1.0pre2.tar.gz We have increased the version number since the last pre-release because we are adopting an important new behaviour: The darcs initialize command now creates darcs-2 format repositories by default This will help new repositories to benefit from the improved handling of duplicate patches and to avoid the exponential time conflicts problem. Upcoming release schedule ------------------------- 2008-10-03: darcs 2.1.0pre3 2008-10-10: darcs 2.1.0 Work remaining -------------- * http://bugs.darcs.net/issue971 (Petr Ročkai) When using hashed or repositories, allow darcs check to deal with filenames that differ only in case when run on a case-insensitive filesystem. Petr has done 90% of the work for this -- he has implemented this for darcs repair -- so this shall largely be a question of refactoring. * http://bugs.darcs.net/issue1003 Allow darcs-transfer mode to deal with a specific set of missing files (namely _darcs/format) so that users can benefit from ssh connection sharing even if the remote end uses an old-fashioned repository. In the meantime, a simple workaround is to touch the _darcs/format file in the remote repoistory * http://bugs.darcs.net/issue1078 Fix a corner case in paths handling that makes darcs overly cautious if the repository is a symbolic link * http://bugs.darcs.net/issue1026 Improve the error messages for 'bug in get_extra' errors, which can happen if darcs is fooled into thinking that two patches are the same. Changes since the last pre-release ---------------------------------- * User Experience: Do not allow users to add files to a darcs repository if their filenames would be considered invalid under Windows. This can be overridden with the --reserved-ok flag (issue53, Eric Kow) * Bug Fix: Do not leave behind a half-gotten directory if darcs get fails (issue1041, Vlad Dogaru, David Roundy) * User Experience: notice when you are trying to pull from a seemingly unrelated repository, that is one with a sufficiently different history. This can be overridden with the --allow-unrelated-repos flag (Dmitry Kurochkin, David Roundy) * Bug Fix: Fix hang after a user input error (for example, EOF) (Judah Jacobson) * Quality Assurance: Improvements to documentation and online help (Simon Michael) -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

1 0

StateWriter: a monad-writing exercise
by Anthony LODI 26 Sep '08

26 Sep '08

Hello haskell-cafe, In my application I have a complex state threaded through long computation chains, and I need a way to log all state changes (so that the evolving state can be animated/replayed somewhere else). Initially I tried combining State and Writer monads but this allows for the possibility to change the state, and forget to write a log entry, etc. So I decided to write a separate monad, StateWriter l s, that takes a state-modifying function, l->s->s (l is an ADT for all the allowable state transitions), an initial state s, and only allows s to change by appending 'l' log entries inside the monad. The net result is that I should have read-only access to the current state inside the monad, and all state transitions should be logged (by going through the one function, the log entries serve as witnesses to all state transitions). Anyway, here's my (very rough!) first stab at the problem. This is the first time I've tried writing a monad so any comments/critiques are much appreciated. Also, about the 'StateWriter' idea in general: am I just (poorly?) reimplementing something obvious? Is it unlikely to scale well on real-world problems? Is there some way to combine the existing State and Writer monads to avoid having to do this? If there's nothing seriously wrong here, I was thinking my next step would be to try changing the lists to monoids (like in the Writer monad), and then to try writing a transformer version of the whole thing. Cheers, - Anthony LODI ================================================================================ {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances #-} newtype StateWriter l s a = StateWriter { _runSWriter :: (l -> s -> s) -> [l] -> s -> (a, [l], s) } instance Monad (StateWriter l s) where return a = StateWriter $ \_ ls s -> (a, ls, s) (StateWriter x) >>= f = StateWriter $ \fn ls s -> let (v, ls', s') = x fn ls s in _runSWriter (f v) fn ls' s' class MonadStateWriter m l s | m -> l s where put :: l -> m () get :: m s instance MonadStateWriter (StateWriter l s) l s where put l = StateWriter $ \fn ls s -> ((), ls ++ [l], fn l s) get = StateWriter $ \fn ls s -> (s, ls, s) runSWriter :: StateWriter l s a -> (l -> s -> s) -> s -> (a, [l], s) runSWriter sw fn = _runSWriter sw fn [] -------------------------------------------------------------------------------- data Ops = Inc | Dec deriving (Show) test :: StateWriter Ops Int String test = do put Inc put Inc put Inc val <- get let op = if val == 3 then Dec else Inc put op return "done" stateFn :: Ops -> Int -> Int stateFn Inc s = s + 1 stateFn Dec s = s - 1 runtest = runSWriter test stateFn 0 -- ("done",[Inc,Inc,Inc,Dec],2)

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