[Haskell-cafe] Re: What do _you_ want to see in FGL?
Ivan Lazar Miljenovic schrieb:
- Having a separate parameter (using associated types?) for the node
type rather than just using Int.
Just Int for nodes was disappointing. It should have been at least a
newtype. I would vote against these experimental features like
associated types or MPTC and FD.
I prefer plain type parameters for data types, but that does not fit
well together with type classes.
* Better fundamental data structures: one of the things that has always
annoyed me about FGL is how much it uses tuples; I propose re-defining
the Context type to be a record-based data structure. Also, usage of
Sets, Maps, etc. where applicable.
Right, these tuples annoyed me, too. (If this changes, it will break a
lot of our existing code, though.)
I also did not like the list of links, that let me redefine the context
data type (although it does not fit well into the current class):
newtype Gr a b = Gr { convertToMap :: Map.IntMap (GrContext a b) }
data GrContext a b = GrContext
{ nodeLabel :: a
, nodeSuccs :: Map.IntMap [b]
, loops :: [b]
, nodePreds :: Map.IntMap [b] }
http://trac.informatik.uni-bremen.de:8080/hets/browser/trunk/Common/Lib/Graph.hs
Maybe Ord b should be required for edge labels b (in order to use
sets), although it may make sense to have many edges with the same label
between the same two nodes. However, for this special case the user
could provide an additional index or a counter.
* Data.Graph.Inductive.Monad: does anyone actually use this?
I did not use it. (I've got no opinion about the other points you made.)
Cheers Christian
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[Haskell-cafe] Re: What do _you_ want to see in FGL?
Christian Maeder christian.mae...@dfki.de writes: Ivan Lazar Miljenovic schrieb: - Having a separate parameter (using associated types?) for the node type rather than just using Int. Just Int for nodes was disappointing. It should have been at least a newtype. This then loses you all of the advantages of using Int (pre-defined data type with known space usage, ordering, etc. and the ability to use IntMap and IntSet which out-perform the normal ones). I would vote against these experimental features like associated types or MPTC and FD. I prefer plain type parameters for data types, but that does not fit well together with type classes. Why don't you like extensions? I used to feel the same way, but then someone pointed out to me that just because Haskell98 doesn't have them doesn't mean they aren't good/useful, and we should be coding for _modern_ Haskell. * Better fundamental data structures: one of the things that has always annoyed me about FGL is how much it uses tuples; I propose re-defining the Context type to be a record-based data structure. Also, usage of Sets, Maps, etc. where applicable. Right, these tuples annoyed me, too. (If this changes, it will break a lot of our existing code, though.) All of my proposals will break existing code though, but I believe for the better. We can't be afraid to innovate/change our libraries, otherwise they can't improve. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What do _you_ want to see in FGL?
Hi, Primarily I want to see in FGL: documentation, documentation and more documentation. The library has lots of undocumented functions (especially the queries, e.g. http://hackage.haskell.org/packages/archive/fgl/5.4.2.2/doc/html/Data-Graph-Inductive-Query-DFS.html has no documentation at all), and the only reference is the original paper. I've seen several people who didn't read the paper (or didn't read the right bits) get confused by the inductive way the graph is constructed, when they try to de-construct it. I would also like to see the library reduced in size/scope if possible; there's a lot of modules in FGL, but all I've ever used are D.G.I.Graph, D.G.I.Tree, D.G.I.Graphviz and D.G.I.Query.DFS. I consider this to probably be the most common usage of the library by others too (if you throw in D.G.I.Query.BFS). So by the sounds of it, if you split Graphviz and Query off to separate libraries, I probably only use the core module. Ivan Lazar Miljenovic wrote: Here are some ideas that I have regarding FGL: * Better fundamental data structures: one of the things that has always annoyed me about FGL is how much it uses tuples; I propose re-defining the Context type to be a record-based data structure. Also, usage of Sets, Maps, etc. where applicable. I think this is worth doing, even if it does break code. If you're doing Context, you may as well do LNode and LEdge too. * Data.Graph.Inductive.Monad: does anyone actually use this? No, now that I look at it, it's not what I would expect. It seems to be a lot of operations that could be constructed by sticking liftM before the normal operations. For example: nodesM :: GraphM m gr = m (gr a b) - m [Node] I would have thought the useful operations for graphs and monads would have been something more like: nodesM :: GraphM m gr = gr (m a) (m b) - m [Node] On that node, I would like to see some instances for the graph types: particularly Functor, Foldable and Traversable, for both (Gr a) and (Flip Gr b) -- where Flip is http://hackage.haskell.org/packages/archive/TypeCompose/latest/doc/html/Control-Compose.html#t:Flip or http://hackage.haskell.org/packages/archive/category-extras/latest/doc/html/Control-Functor-Combinators-Flip.html If you put FGL in a repository somewhere, I might be able to find some time to write those instances and perhaps contribute a bit of documentation (no promises, though!). Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: What do _you_ want to see in FGL?
Ivan Lazar Miljenovic schrieb: I would vote against these experimental features like associated types or MPTC and FD. I prefer plain type parameters for data types, but that does not fit well together with type classes. Why don't you like extensions? I used to feel the same way, but then someone pointed out to me that just because Haskell98 doesn't have them doesn't mean they aren't good/useful, and we should be coding for _modern_ Haskell. My feeling is, that the last words about fancy type class extension are not spoken yet. Already the simple classes have disadvantages (wrt multiple instances), that i.e. parameterized modules solve differently (but maybe also not good enough, yet). Parametrized data types, hofs, purity, etc. are proven concepts also found in other functional languages that I prefer to stick to. Cheers Christian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] happstack/SOAP
Hi - I'm looking for an example/demo happstack server that handles SOAP requests. - Thanks, J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What do _you_ want to see in FGL?
Hello Ivan
What would your thoughts be on freezing FGL as it is and putting
changes into a new package FGL2 or NewFGL?
The implementation technique for FGL is independently interesting;
Martin Erwig expanded on it in other papers ('Metamorphic
Programming') but no one else seems to have picked up on it. As I
think there is more mileage in the idiom and hopefully someone will
pick up on it at some point, it would be nice if it survives in the
code.
Best wishes
Stephen
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RE: [Haskell-cafe] London HUG domain expired
From: sefer@gmail.com [mailto:sefer@gmail.com] On Behalf Of Yitzchak Gale On Fri, Apr 23, 2010 at 1:24 PM, Bayley, Alistair wrote: Looks like the London HUG domain (londonhug.net) registration has expired. Neil Bartlett was the registrant. Neil: do you plan to renew? The whois database reports: Domain name: LONDONHUG.NET This domain name is up for auction for a limited time. To place a bid, visit: http://www.namejet.com And it appears that someone has already placed a $75 bid. The domain should be renewed promptly, before the grace period expires. Probably the best option, but can anyone other than Neil do this? If not, does anyone know if Neil is reachable? (could try his phone number listed in the whois record, but that seems a little invasive). Alistair * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Broken ghc documentation links
To reproduce: 1) Look for data IO on Hoogle, e.g. http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html#t%3AIO 2) Click source, which redirects to http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC-Types.html#IO 3) Observe a Not Found page Is there anyone interested in fixing this? Bye, Lenny___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Ada-style ranges
Hi list, how would you describe Ada's ranges in Haskell's typesystem? http://en.wikibooks.org/wiki/Ada_Programming/Types/range I feel, you can not because this is a runtime property. Bye, Lenny___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?
Dear all, Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when installing packages with an unqualified base requirement? Example: $ cabal install -v fad --reinstall [snip] Resolving dependencies... selecting fad-1.0 (hackage) selecting base-3.0.3.2 (installed) and 4.2.0.0 (installed) and discarding syb-0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.2 and 0.2.1 [snip] Configuring fad-1.0... Dependency base ==3.0.3.2: using base-3.0.3.2 [snip] [1 of 1] Compiling Numeric.FAD ( Numeric/FAD.hs, dist/build/Numeric/FAD.o ) Numeric/FAD.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. [snip] Thanks, Bjorn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Unicode strings and runCommand / runProcess
Actually, the behavior of openFile when given a String with characters 0xFF is also completely undocumented. I am not sure what it does with that. It should probably be the same as runCommand, whatever it is. Actually, the behaviour of openFile is known to be platform-dependent. According to Simon Marlow, Be careful with FilePaths. On Windows they are interpreted as Unicode, on Unix they are interpreted as [Word8], by taking the low 8 bits of each Char. So if you always encode FilePaths to UTF-8, that will break on Windows. Fixing FilePaths is a high priority. The last sentence gives me some hope. http://ghcmutterings.wordpress.com/2009/09/30/heads-up-what-you-need-to-know-about-unicode-io-in-ghc-6-12-1/#comment-61 But truncation makes impossible to pass non ASCII strings portably. They should be encoded there is no easy way to do so. Actually problem is use of strings. String is sequence of _characters_ and program talk to outside world using sequence of bytes. I think that right (but impossible) way to solve this problem is to use separate data types for file path, command line arguments. I think that Strings should be used _only_ for characters (code points). Using the same data type for encoded/truncated data is dangerous. Most of the current problems with Unicode is due to the fact that Strings could turn out to be anything (are not strictly typed from this point of view). Hence, the runtime checks and hacks like isUTF8Encoded :: String - Bool, encodeString :: String - String and decodeString :: String - String... So I absolutely support that truncating is wrong. Expecting encoded data in Strings is wrong too. So the only option (except changing the standard library and introducing a new type for FilePath), is to do all necessary conversions inside openFile and similar functions. I think there are two alternatives. One is to encode/decode strings using current locale and provide [Word8] based variants. Main problem is that seeming innocent actions like getting directory content could crash program (exception ) Actually, any IO action is unpredictible. So trying to get directory contents can produce an error (for various reasons, e.g. permission denied). If it reports an error when there are filenames not presentable in the current locale (e.g. contain invalid UTF-8 sequences in UTF-8 locale), the problem is likely to be the wrong locale settings. What's the problem with an exception? I think [Word8] variants for those who wants to deal with such cases (guess file system encoding etc.) is enough. Another options is to provide function to encode/decode strings. This is ugly and mix strings which hold characters and string which hold bytes and completely unhaskellish but it seems there is no good solution. This is ugly, because it's impossible to know if a String is already encoded or not. This is ugly because application code will be polluted with conditional compilation to be cross-platform (or worse, people will forget to write cross-platform code in _some_ cases). Also truncation could have security implications. It makes almost impossible to escape dangerous characters robustly. Consider following code. This is more matter of speculations than real threat but nevertheless: Nice example. It shows that escaping should be the last step. S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What do _you_ want to see in FGL?
Stephen Tetley stephen.tet...@gmail.com writes:
What would your thoughts be on freezing FGL as it is and putting
changes into a new package FGL2 or NewFGL?
That's another possibility. However, I was planning on keeping the
fundamental layout and design of FGL. I quite like and have used the
inductive approach of graph construction/deconstruction in my own code;
I just plan on updating/modernising the layout and design (after all,
large all-in-one packages are _so_ pre-Hackage :p).
Whilst freezing it is an option, I feel that this will lead to the same
problems that we already face with mtl: most people agree/know that the
approach/design is bad, but we keep using it because there's no (one)
viable alternative to be used (and thus mtl stays in the Platform, which
means more people use it, and thus we have this vicious cycle). By
using the same name we can break this cycle: there is no implicit
loyalty to an old package that people still use because its familiar
(of course, this leaves it open to the problems with QuickCheck and
Parsec, yet they are being resolved and more and more people are moving
to QuickCheck-2 and Parsec-3).
The implementation technique for FGL is independently interesting;
Martin Erwig expanded on it in other papers ('Metamorphic
Programming') but no one else seems to have picked up on it. As I
think there is more mileage in the idiom and hopefully someone will
pick up on it at some point, it would be nice if it survives in the
code.
Hmmm I haven't come across Metamorphic Programming before, will
have to have a read through it (which isn't that appealing at the
moment, since I'm in the middle of the literature review section of my
PhD :s).
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Broken ghc documentation links
So, the problem is that there are broken links _in Hoogle_; have you thought about contacting the author Neil Mitchell directly? hask...@kudling.de hask...@kudling.de writes: To reproduce: 1) Look for data IO on Hoogle, e.g. http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html#t%3AIO 2) Click source, which redirects to http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC-Types.html#IO 3) Observe a Not Found page Is there anyone interested in fixing this? -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?
Bjorn Buckwalter bjorn.buckwal...@gmail.com writes: Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when installing packages with an unqualified base requirement? Example: You mean cabal-install rather than Cabal. The reason that base-3 is chosen is because many of these old libraries won't build with base-4; as such, if no upper bound restriction is found on the base package then base-3 is chosen as it is more likely to work than base-4 (there were a _lot_ of breakages when base-4 first came out with 6.10.1). $ cabal install -v fad --reinstall [snip] Resolving dependencies... selecting fad-1.0 (hackage) selecting base-3.0.3.2 (installed) and 4.2.0.0 (installed) and discarding syb-0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.2 and 0.2.1 [snip] Configuring fad-1.0... Dependency base ==3.0.3.2: using base-3.0.3.2 [snip] [1 of 1] Compiling Numeric.FAD ( Numeric/FAD.hs, dist/build/Numeric/FAD.o ) Numeric/FAD.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. [snip] -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ada-style ranges
On 04/26/2010 12:50 PM, hask...@kudling.de wrote:
Hi list,
how would you describe Ada's ranges in Haskell's typesystem?
http://en.wikibooks.org/wiki/Ada_Programming/Types/range
Hi Lenny,
can non-constant expressions be given as arguments to 'range'? If not, then
what about a opaque wrapper type?
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module Range1 (Range1, fromRange1, mkBounded, mkRange1) where
newtype Range1 = Range1 { fromRange1 :: Integer }
deriving (Eq, Num, Ord, Show)
instance Bounded Range1 where
minBound = Range1 $ -5
maxBound = Range1 $ 10
mkBounded :: (Bounded a, Ord a) = (b - a) - b - Maybe a
mkBounded f x = case f x of
y | minBound = y y = maxBound - Just y
| otherwise - Nothing
mkRange1 :: Integer - Maybe Range1
mkRange1 = mkBounded Range1
-- Steffen
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Fwd: Re: [Haskell-cafe] Broken ghc documentation links
FYI -- Ursprüngliche Nachricht -- Von: hask...@kudling.de hask...@kudling.de An: Ivan Lazar Miljenovic ivan.miljeno...@gmail.com Cc: Neil Mitchell ndmitch...@gmail.com Datum: 26. April 2010 um 13:45 Betreff: Re: [Haskell-cafe] Broken ghc documentation links Hi, So, the problem is that there are broken links _in Hoogle_; have you thought about contacting the author Neil Mitchell directly? While the URL http://www.haskell.org/hoogle/ contains the word Hoogle, the URL http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude.html#t%3AIO does not and it does no mention Hoogle on the page either. How did you determine that the latter is related to Hoogle? Bye, Lnny___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?
On Mon, Apr 26, 2010 at 19:38, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Bjorn Buckwalter bjorn.buckwal...@gmail.com writes: Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when installing packages with an unqualified base requirement? Example: You mean cabal-install rather than Cabal. The reason that base-3 is chosen is because many of these old libraries won't build with base-4; as such, if no upper bound restriction is found on the base package then base-3 is chosen as it is more likely to work than base-4 (there were a _lot_ of breakages when base-4 first came out with 6.10.1). I see, I guess that's pragmatic although the deprecation warning is unfortunate. (I'm aware of the cabal-install versus Cabal distinction, but I understand that cabal-install uses Cabal to resolve dependencies; thus I assumed Cabal was the culprit.) Thanks, Bjorn $ cabal install -v fad --reinstall [snip] Resolving dependencies... selecting fad-1.0 (hackage) selecting base-3.0.3.2 (installed) and 4.2.0.0 (installed) and discarding syb-0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.2 and 0.2.1 [snip] Configuring fad-1.0... Dependency base ==3.0.3.2: using base-3.0.3.2 [snip] [1 of 1] Compiling Numeric.FAD ( Numeric/FAD.hs, dist/build/Numeric/FAD.o ) Numeric/FAD.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. [snip] -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Broken ghc documentation links
Am Montag 26 April 2010 13:36:22 schrieb Ivan Lazar Miljenovic: So, the problem is that there are broken links _in Hoogle_; No, hoogle just sends you to http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Prelude.html#t%3AIO , which does exist. It's the 'Source' link in the haddocks that sends you to the 404 Not Found. It's the same with my local docs, I think it's haddock that got confused by the move of the IO definition from base to ghc-prim. have you thought about contacting the author Neil Mitchell directly? hask...@kudling.de hask...@kudling.de writes: To reproduce: 1) Look for data IO on Hoogle, e.g. http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Prelude .html#t%3AIO 2) Click source, which redirects to http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC -Types.html#IO 3) Observe a Not Found page Is there anyone interested in fixing this? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?
Bjorn Buckwalter bjorn.buckwal...@gmail.com writes: On Mon, Apr 26, 2010 at 19:38, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Bjorn Buckwalter bjorn.buckwal...@gmail.com writes: Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when installing packages with an unqualified base requirement? Example: [snip] The reason that base-3 is chosen is because many of these old libraries won't build with base-4; as such, if no upper bound restriction is found on the base package then base-3 is chosen as it is more likely to work than base-4 (there were a _lot_ of breakages when base-4 first came out with 6.10.1). I see, I guess that's pragmatic although the deprecation warning is unfortunate. The deprecation warning is due to GHC 6.12; this is a not-so-subtle hint to package maintainers to fix their code up, and to users to poke the maintainers of packages they use to do so! -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] and [] = True; or [] = False
Dear all, Does it make good sense that 'and []' returns 'True' and 'or []' returns 'False'? The Haskell Road to Logic, Maths and Programming says so: The function or takes a list of truth values and returns True if at least one member of the list equals True, while and takes a list of truth values and returns True if all members of the list equal True. Should the conjunction of all elements of [] count as true or false? As true, for it is indeed (trivially) the case that all elements of [] are true. So the identity element for conjunction is True. Should the disjunction of all elements of [] count as true or false? As false, for it is false that [] contains an element which is true. Therefore, the identity element for disjunction is False. While the above reasoning is fine, and allows straight-forward implementations, it isn't extremely convincing. In particular, it isn't clear that, while simple, the definitions of the first paragraph are the most sensible. Perhaps one of the more mathematically versed readers on the Cafe could enlighten me? What got me thinking about this was the apparently incorrect intuition that 'and xs' would imply 'or xs'. Thanks, Bjorn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] and [] = True; or [] = False
Bjorn Buckwalter wrote: Dear all, Does it make good sense that 'and []' returns 'True' and 'or []' returns 'False'? The Haskell Road to Logic, Maths and Programming says so: The function or takes a list of truth values and returns True if at least one member of the list equals True, while and takes a list of truth values and returns True if all members of the list equal True. Should the conjunction of all elements of [] count as true or false? As true, for it is indeed (trivially) the case that all elements of [] are true. So the identity element for conjunction is True. Should the disjunction of all elements of [] count as true or false? As false, for it is false that [] contains an element which is true. Therefore, the identity element for disjunction is False. While the above reasoning is fine, and allows straight-forward implementations, it isn't extremely convincing. In particular, it isn't clear that, while simple, the definitions of the first paragraph are the most sensible. Perhaps one of the more mathematically versed readers on the Cafe could enlighten me? The empty sum is regarded to be zero. The empty product is equal to one. The empty conjunction is True. The empty disjunction is False. The reason for this is that these are the neutral elements, i.e. 0 + x = x 1 * x = x True AND x = x False OR x = x This allows some laws to hold also in degenerate cases, and it is quite useful in general to accept these conventions. An example of such a law is (∀ x : x ∈ A : P(x)) ∧ (∀ x : x ∈ B : P(x)) == (∀ x : x ∈ A ∪ B : P(x)). This also works if A or B is empty, provided that we say that the empty conjunction is true. In Haskell, we now have that (and xs) (and ys) == and (xs ++ ys), even if xs or ys is the empty list. Cheers, Jochem -- Jochem Berndsen | joc...@functor.nl ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] and [] = True; or [] = False
Well, what's the sum of an empty list? Seems naturally that it's 0, but why? Let's say that sum [] = x. If we take two lists, say, l1 = [1,2,3] and l2 = [4,5], then sum l1 + sum l2 = 6 + 9 = 15 = sum [1,2,3,4,5] = sum (l1 ++ l2) We expect it to be the case even if one of the lists is empty, so x + 9 = sum [] + sum l2 = to be expected = sum ([] ++ l2) = sum l2 = 9 Therefore, x = 0. With and we have the same thing: and [] = x Let l1 = [True, True], l2 = [True, False] and l1 and l2 = True False = False = and [True, True, True, False] = and (l1 ++ l2) x True = and [] and l1 = to be expected = and ([] ++ l1) = and l1 = True Therefore, x = True. Bjorn Buckwalter wrote: Dear all, Does it make good sense that 'and []' returns 'True' and 'or []' returns 'False'? The Haskell Road to Logic, Maths and Programming says so: The function or takes a list of truth values and returns True if at least one member of the list equals True, while and takes a list of truth values and returns True if all members of the list equal True. Should the conjunction of all elements of [] count as true or false? As true, for it is indeed (trivially) the case that all elements of [] are true. So the identity element for conjunction is True. Should the disjunction of all elements of [] count as true or false? As false, for it is false that [] contains an element which is true. Therefore, the identity element for disjunction is False. While the above reasoning is fine, and allows straight-forward implementations, it isn't extremely convincing. In particular, it isn't clear that, while simple, the definitions of the first paragraph are the most sensible. Perhaps one of the more mathematically versed readers on the Cafe could enlighten me? What got me thinking about this was the apparently incorrect intuition that 'and xs' would imply 'or xs'. Thanks, Bjorn ___ 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] and [] = True; or [] = False
Am Montag 26 April 2010 14:15:40 schrieb Bjorn Buckwalter: Dear all, Does it make good sense that 'and []' returns 'True' and 'or []' returns 'False'? The Haskell Road to Logic, Maths and Programming says so: The function or takes a list of truth values and returns True if at least one member of the list equals True, while and takes a list of truth values and returns True if all members of the list equal True. Should the conjunction of all elements of [] count as true or false? As true, for it is indeed (trivially) the case that all elements of [] are true. So the identity element for conjunction is True. Should the disjunction of all elements of [] count as true or false? As false, for it is false that [] contains an element which is true. Therefore, the identity element for disjunction is False. While the above reasoning is fine, and allows straight-forward implementations, it isn't extremely convincing. In particular, it isn't clear that, while simple, the definitions of the first paragraph are the most sensible. Perhaps one of the more mathematically versed readers on the Cafe could enlighten me? It's necessary for and (xs ++ ys) == and xs and ys and or (xs ++ ys) == or xs || or ys It's the same reason why sum [] == 0 and product [] == 1. What got me thinking about this was the apparently incorrect intuition that 'and xs' would imply 'or xs'. Unless xs is empty Thanks, Bjorn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?
On Mon, Apr 26, 2010 at 20:07, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Bjorn Buckwalter bjorn.buckwal...@gmail.com writes: On Mon, Apr 26, 2010 at 19:38, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Bjorn Buckwalter bjorn.buckwal...@gmail.com writes: Why does cabal seem to prefer base-3.0.3.2 over base-4.2.0.0 when installing packages with an unqualified base requirement? Example: [snip] The reason that base-3 is chosen is because many of these old libraries won't build with base-4; as such, if no upper bound restriction is found on the base package then base-3 is chosen as it is more likely to work than base-4 (there were a _lot_ of breakages when base-4 first came out with 6.10.1). I see, I guess that's pragmatic although the deprecation warning is unfortunate. The deprecation warning is due to GHC 6.12; this is a not-so-subtle hint to package maintainers to fix their code up, and to users to poke the maintainers of packages they use to do so! Understood, but in this case the warning seems misdirected since fad does not restrict itself to base-3.*... So what would be the fix, to set an upper bound on base? Is the general recommendation that all packages should specify upper bounds on all dependencies (if so why doesn't Cabal tell us?)? I can see that this would make some sense as a package might be broken by an API change in its dependencies. On the other hand I can also see it causing headaches occasionally... Thanks, Bjorn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] and [] = True; or [] = False
Forgot about this one: Bjorn Buckwalter wrote: What got me thinking about this was the apparently incorrect intuition that 'and xs' would imply 'or xs'. No. See, and is very close to for all, and or is similarly close to exists. For example, the statement all crows are black means just this crow is black AND this one too AND another one on the tree is also black AND... etc. Now, obviously, all real dragons can fly. But it doesn't mean there is such thing as a real dragon. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?
Am Montag 26 April 2010 14:32:03 schrieb Bjorn Buckwalter: So what would be the fix, to set an upper bound on base? Is the general recommendation that all packages should specify upper bounds on all dependencies (if so why doesn't Cabal tell us?)? Yes, that's the general recommendation. (upper and lower bounds) I can see that this would make some sense as a package might be broken by an API change in its dependencies. Exactly. That's why bounds on the versions of the dependencies are a good thing. On the other hand I can also see it causing headaches occasionally... Yes, but probably less headaches than packages eternally breaking because of API changes in the dependencies. Thanks, Bjorn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does cabal select base-3.0.3.2 when base-4.2.0.0 is available?
Bjorn Buckwalter bjorn.buckwal...@gmail.com writes: So what would be the fix, to set an upper bound on base? The fix is to have the maintainer check whether or not the package builds with base-4 (you can do this the old manual way using runhaskell Setup.hs). If it does, then specify that it does so, e.g.: base 5 The upper bound is needed (and Hackage now enforces this) because too many packages have this same problem: the maintainers blindly assume that the package will build for all time, and then it dies the next time a new major version of the base package is released. Note that some people cheat by having dependencies like base 10 as Hackage will accept this because there is indeed an upper bound, but this just causes problems in the future (Don Stewart had base 5 for a release of ghc-core which then failed to build with base-4). Is the general recommendation that all packages should specify upper bounds on all dependencies (if so why doesn't Cabal tell us?)? This is the eventual goal and is why Duncan Coutts is pushing the Package Versioning Policy (http://www.haskell.org/haskellwiki/Package_versioning_policy) as you can tell from the version (if it is followed correctly) when the API has changed in a backwards-incompatible fashion. At the moment, however, Hackage - not Cabal - enforces the requirement on the base package for all new packages uploaded. This isn't made compulsory for all package dependencies as 1) it is base dependencies that typically cause most of the breakages and 2) not all packages follow the PVP and thus doing this doesn't always make sense (e.g. some packages use a date-based versioning system for some reason). I can see that this would make some sense as a package might be broken by an API change in its dependencies. On the other hand I can also see it causing headaches occasionally... Right, see the recent thread started by John Goerzon The instability of Haskell libraries which is in part to do with this problem. At the moment when a dependency has a major version update but is still buildable by your package you have to create a new release to let it use that updated dependency, which is a pain and isn't always done promptly by maintainers. Possibly the best way towards fixing this is the proposal to take the Cabal files outside of the tarballs and distribute them separately; that way they can be edited without affecting the tarball in question (thus making them even more like Gentoo's ebuild or Arch's PKGBUILD files). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] and [] = True; or [] = False
Bjorn Buckwalter wrote: Dear all, Does it make good sense that 'and []' returns 'True' and 'or []' returns 'False'? It's certainly what I would expect it to do, based on several ways of thinking. 1: If we define the function using explicit recursion: and (x:xs) = x and xs Therefore and [] has to be True. Similar logic for or. 2: My instinct is to consider and = all (== True), while or = any (== True). It's even clearer to me that all [] = True and any [] = False (similiar to Miguel's post). Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] and [] = True; or [] = False
Ok Guys, you've convinced me thrice within ten minutes of posing my question. The quality of the mailing list is just ridiculous! ;) And Miguel, thanks for the follow-up regarding for all and exists – it's an excellent analogy and easy to remember! On Mon, Apr 26, 2010 at 20:23, Jochem Berndsen joc...@functor.nl wrote: Bjorn Buckwalter wrote: Dear all, Does it make good sense that 'and []' returns 'True' and 'or []' returns 'False'? The Haskell Road to Logic, Maths and Programming says so: The function or takes a list of truth values and returns True if at least one member of the list equals True, while and takes a list of truth values and returns True if all members of the list equal True. Should the conjunction of all elements of [] count as true or false? As true, for it is indeed (trivially) the case that all elements of [] are true. So the identity element for conjunction is True. Should the disjunction of all elements of [] count as true or false? As false, for it is false that [] contains an element which is true. Therefore, the identity element for disjunction is False. While the above reasoning is fine, and allows straight-forward implementations, it isn't extremely convincing. In particular, it isn't clear that, while simple, the definitions of the first paragraph are the most sensible. Perhaps one of the more mathematically versed readers on the Cafe could enlighten me? The empty sum is regarded to be zero. The empty product is equal to one. The empty conjunction is True. The empty disjunction is False. The reason for this is that these are the neutral elements, i.e. 0 + x = x 1 * x = x True AND x = x False OR x = x This allows some laws to hold also in degenerate cases, and it is quite useful in general to accept these conventions. An example of such a law is (∀ x : x ∈ A : P(x)) ∧ (∀ x : x ∈ B : P(x)) == (∀ x : x ∈ A ∪ B : P(x)). This also works if A or B is empty, provided that we say that the empty conjunction is true. In Haskell, we now have that (and xs) (and ys) == and (xs ++ ys), even if xs or ys is the empty list. Cheers, Jochem -- Jochem Berndsen | joc...@functor.nl ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Broken ghc documentation links
Daniel Fischer daniel.is.fisc...@web.de writes: Am Montag 26 April 2010 13:36:22 schrieb Ivan Lazar Miljenovic: So, the problem is that there are broken links _in Hoogle_; No, hoogle just sends you to http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Prelude.html#t%3AIO , which does exist. It's the 'Source' link in the haddocks that sends you to the 404 Not Found. It's the same with my local docs, I think it's haddock that got confused by the move of the IO definition from base to ghc-prim. Yeah, as I've said I mis-read the initial problem (I've fielded a few queries recently regarding Hoogle not pointing to the 6.12.2 docs and initially thought this was another one). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Installing ghc in an OpenSolaris Zone
Hello, has anyone yet managed to install ghc (6.10.4) into an OpenSolaris zone? Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The instability of Haskell libraries
On 04/25/2010 03:47 PM, Ivan Lazar Miljenovic wrote: So you recommend having packages specifically for instances? My main problem with this is if you want a custom variant of that instance. Let's take FGL graphs for example with instances for QuickCheck's Arbitrary class. Maybe you want arbitrary graphs that are simple, or maybe multiple edges are fine. Even when considering Arbitrary instances for something like String you may wish to have a custom variant that makes sense for what you're testing. My conclusion: it is not possible to have hard-and-fast conclusions for things like this :p I'm inclined to agree. As an example, there is the convertible library. It grew out of the need to make an easy way to map Haskell to database types in HDBC, and these days is a more general way to convert from one type to another. I provide a bunch of Convertible instances, but they are in separate modules, and thus can be omitted if a person doesn't want the instances. As an example: what's the correct way to convert a Double to an Integer? As an example, Prelude defines at least 4: ceiling, floor, truncate, and round. Now, in a certain sense, Convertible is designed for people that don't care which is used. (And yes, that is a perfectly valid answer in some cases.) But if you want your own, you can simply not import the numeric Convertible instances. It would, however, be nice if the language allowed you to override default instances with the code in your own package. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: graphviz 2999.9.0.0
I'm pleased to announce the latest version of my graphviz library that provides Haskell bindings to the Graphviz graph visualisation suite. There are numerous changes in this release, the most important of which are: * graphviz now has an FAQ and an improved README as well as its own homepage: http://projects.haskell.org/graphviz/ (as prompted by Eric Kow). * Add support for record labels; values are automatically escaped/unescaped. The `Record` and `MRecord` shapes have been added for use with these labels. Requested by Minh Thu and Eric Kow. * Add support for HTML-like values (this replaces the wrong and completely broken URL datatype). Strings are automatically escaped/unescaped. * Various parsing improvements (including a slight parsing speed increase!). In particular, graphviz is now able to parse almost all Dot graphs found on my system (including samples shipped with Graphviz, Linux kernel documentation and various other package documentations). A list of the breakages and why: * /usr/share/sgml/docbook/xsl-stylesheets/roundtrip/template.dot seems to be a binary file and thus can't be read. * /usr/share/graphviz/graphs/directed/Latin1.gv uses Latin1 encoding; at the moment graphviz uses the system's locale encoding (or whatever GHC 6.10 defaults to). * /usr/share/doc/boost-*/html/libs/graph/example/graphviz_test.dot (various boost versions) has subgraphs in edges; graphviz currently can't cope with these. * /usr/src/linux-2.6.33-gentoo-r1/Documentation/blockdev/drbd/drbd-connection-state-overview.dot uses incorrect syntax for the minlen attribute (it is meant to be an integer but actually contains a floating point value). The plans for the next release (which I don't plan on even starting for a while) are to focus on improving printing and parsing performance, using a state-based printer and parser (as part of Dot syntax is state-based) and force usage of UTF-8 (via text or utf8-string). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANNOUNCE: graphviz 2999.9.0.0
A few things I forgot to mention in my haste to get this out: 1) I was planning on having a tutorial-style blog post where I'd use graphviz to parse an manipulate the output ghc-pkg dot; however I've been busier than I expected recently and figured it'd be better to get this release out and do this later. 2) The website was developed with the help of John MacFarlane; at the moment I'm using the CSS he uses for Pandoc's homepage, but I plan on updating that during the week (again, better to get it out now and fix it later). And with that, I need to sleep. Having a public holiday to get this finished in was nice, but it didn't help with my sleep deprivation :s On 26 April 2010 23:46, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: I'm pleased to announce the latest version of my graphviz library that provides Haskell bindings to the Graphviz graph visualisation suite. There are numerous changes in this release, the most important of which are: * graphviz now has an FAQ and an improved README as well as its own homepage: http://projects.haskell.org/graphviz/ (as prompted by Eric Kow). * Add support for record labels; values are automatically escaped/unescaped. The `Record` and `MRecord` shapes have been added for use with these labels. Requested by Minh Thu and Eric Kow. * Add support for HTML-like values (this replaces the wrong and completely broken URL datatype). Strings are automatically escaped/unescaped. * Various parsing improvements (including a slight parsing speed increase!). In particular, graphviz is now able to parse almost all Dot graphs found on my system (including samples shipped with Graphviz, Linux kernel documentation and various other package documentations). A list of the breakages and why: * /usr/share/sgml/docbook/xsl-stylesheets/roundtrip/template.dot seems to be a binary file and thus can't be read. * /usr/share/graphviz/graphs/directed/Latin1.gv uses Latin1 encoding; at the moment graphviz uses the system's locale encoding (or whatever GHC 6.10 defaults to). * /usr/share/doc/boost-*/html/libs/graph/example/graphviz_test.dot (various boost versions) has subgraphs in edges; graphviz currently can't cope with these. * /usr/src/linux-2.6.33-gentoo-r1/Documentation/blockdev/drbd/drbd-connection-state-overview.dot uses incorrect syntax for the minlen attribute (it is meant to be an integer but actually contains a floating point value). The plans for the next release (which I don't plan on even starting for a while) are to focus on improving printing and parsing performance, using a state-based printer and parser (as part of Dot syntax is state-based) and force usage of UTF-8 (via text or utf8-string). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] maling-list manager in haskell?
Hi, is there a mailing-list manager written in haskell? Best regards Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Broken ghc documentation links
Am Montag 26 April 2010 15:15:03 schrieb Ivan Lazar Miljenovic: Daniel Fischer daniel.is.fisc...@web.de writes: Am Montag 26 April 2010 13:36:22 schrieb Ivan Lazar Miljenovic: So, the problem is that there are broken links _in Hoogle_; No, hoogle just sends you to http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Pre lude.html#t%3AIO , which does exist. It's the 'Source' link in the haddocks that sends you to the 404 Not Found. It's the same with my local docs, I think it's haddock that got confused by the move of the IO definition from base to ghc-prim. Yeah, as I've said I mis-read the initial problem (I've fielded a few queries recently regarding Hoogle not pointing to the 6.12.2 docs and initially thought this was another one). Yes, I sent the reply before your second reply hit my inbox. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Order of arguments to GCC when building SDL on Windows with Cabal
Hello, I've been trying for a while to build the SDL haskell library on windows. People have told me it worked for them, but I can't get to work for the life of me. I have the latest Haskell Platform, I think more or less the latest MINGW and MSYS tools. I'm on Windows 7 64 bits. I installed the SDL library without hassle, and the samples work. It's only the haskell library that's bothering me. I've modified the .cabal file as indicated for Windows (extra-include-dirs, extra-lib-dirs), and runhaskell Setup configure. But then runhaskell Setup build fails with: Preprocessing library SDL-0.5.9... dist\build\Graphics\UI\SDL\General_hsc_make.o:General_hsc_make.c:(.text +0x29): m ultiple definition of `main' d:/dev/mingw/bin/../lib/gcc/mingw32/4.5.0/../../../ libmingw32.a(main.o):main.c:( .text+0x0): first defined here D:\dev\SDL-1.2.14\lib/libSDLmain.a(SDL_win32_main.o): In function `console_main' : /Users/hercules/trunk/SDL-1.2/./src/main/win32/SDL_win32_main.c:315: undefined r eference to `SDL_main' collect2: ld returned 1 exit status linking dist\build\Graphics\UI\SDL\General_hsc_make.o failed command was: d:\dev\MinGW\bin\gcc.exe -LD:\dev\SDL-1.2.14\lib -L/usr/ lib -lmingw 32 -lSDLmain -lSDL -mwindows -LD:\dev\haskell\HaskellPlatform \2010.1.0.0\base-4. 2.0.0 -lwsock32 -luser32 -lshell32 -LD:\dev\haskell\HaskellPlatform \2010.1.0.0\i nteger-gmp-0.2.0.0 -LD:\dev\haskell\HaskellPlatform\2010.1.0.0\ghc- prim-0.2.0.0 -LD:\dev\haskell\HaskellPlatform\2010.1.0.0 -LD:\dev\haskell \HaskellPlatform\201 0.1.0.0/gcc-lib -lm -lwsock32 -LD:\dev\haskell\HaskellPlatform \2010.1.0.0 dist\b uild\Graphics\UI\SDL\General_hsc_make.o -o dist\build\Graphics\UI\SDL \General_hs c_make.exe (I have the same error with the gcc inside the Haskell Platform, the same error running in a windows shell without MSYS on the path, in the MSYS bash with MSYS on the path). And I figured out what's wrong with that line after thinking for a while (as in, several days...): basically the line says something like gcc sdl-flags file.o -o file.exe. If I revert the order of the arguments and run gcc file.o -o file.exe sdl-flags, it works! The gcc documentation explains that the libraries are searched in the order they appear (http://gcc.gnu.org/onlinedocs/gcc/Link-Options.html), so to put the libraries you depend on after the code that has the dependencies. And I can see that building the SDL samples indeed puts the .c file before the sdl linker flags. So this seems to be my problem. What's the solution? 1. I've done something stupid or forgot some essential MINGW tool that would make my system not dependent on the order of the arguments to gcc? I've tried with gcc 3.4.5 and gcc 4.5.0, same result. 2. I can hack somewhere (where???) the command passed on to GCC when building? Maybe some voodoo in the cabal file? 3. I can get runhaskell Setup build to only dump the commands it's going to run, modify them in my favorite text editor and run them manually (as said above, I've managed to create the first exe required but build insists on rebuilding it even if present) 4. ...? The fact that some people managed seem to point with a problem with my config, but it's seems reasonnably clean to me, and I've even managed to install wxWidgets and wxHaskell... Any help appreciated! -- JP Moresmau http://jpmoresmau.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bulk Synchronous Parallel
Hi Aaron, On 21.04.2010 20:29, Aaron D. Ball wrote: Unfortunately, Eden is one of the examples I had in mind when referring to distributed Haskell projects as overly complicated and [for practical purposes] dead. Their last release available for download was in 2006. Their beta is available upon request, which doesn't raise my confidence in the level of active development or openness of the project. You're partly right. The development of the Eden system itself has been neglected for a time. Mostly because Jost Berthold (the main system programmer) finished his PhD and left Marburg (and has only limited spare time with his new job). The remaining members of the Eden group here were mostly language users and language developers, not system implementors. No one really opted to take over responsibility... However, this is changing right now. We are actively merging the Eden runtime and that of the GpH language (as both need basically the same features) to get a new runtime based on GHC 6.12 (and GHC HEAD). This runtime, while still in beta state, is already usable. However, building it is currently still a bit too complicated to bother end users with it. So, if your complicated is referring to this, you are right. We hope to simplify this and to have a usable release in the near future. If your complicated was targetting the use of the Eden language itself, however, I object! They just had a hackathon in St Andrews, http://hackage.haskell.org/trac/ghc/wiki/HackPar they don't seem to have even a source code repository yet, and they appear to be bogged down in that complexity I mentioned. Of course, a source code repository for Eden always existed. The new repository was meant for the merged version of Eden/GpH. And that exists as well. The Eden webpage will be updated as soon as we have a pre-release of the 6.12 branch. Best regards, Thomas Horstmeyer (Eden group Marburg) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haddock infix constructors in markup
Hi all, If I have the following data type: data Expr = Num Int | Expr :+: Expr | Expr :-: Expr Haddock handles the infix constructors, and generates a very nice output (html in this case) However when I try to reference to one of the infix constructors in the markup of other functions it fails to hyperlink. -- | If the input is 'Num' does magic, if it is ':+:' does even more magic! someFunc :: Expr - Expr In the output of this markup, the 'Num' is hyperlinked but the ':+:' is not. Is there a different syntax for infix constructors (and for infix functions presumably) or does haddock simple lack this feature? Best, -- Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haddock infix constructors in markup
Am Montag 26 April 2010 18:15:02 schrieb Ozgur Akgun: Hi all, If I have the following data type: data Expr = Num Int | Expr :+: Expr | Expr :-: Expr Haddock handles the infix constructors, and generates a very nice output (html in this case) However when I try to reference to one of the infix constructors in the markup of other functions it fails to hyperlink. -- | If the input is 'Num' does magic, if it is ':+:' does even more magic! someFunc :: Expr - Expr In the output of this markup, the 'Num' is hyperlinked but the ':+:' is not. Is there a different syntax for infix constructors (and for infix functions presumably) or does haddock simple lack this feature? Infix functions work fine (try referring to e.g. '' in the haddock comment), but infix constructors apparently not. Best, ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fwd: Mancoosi International Solver Competition
This looks interesting: an international competition of solvers for package/component installation and upgrade problems. http://www.mancoosi.org/misc-2010/ (deadline: June 10) Is the underlying package dependency model the same as cabal's? If (nearly) so, then cabal's solver could enter the competition - if it wins, then fine; if not, then it could be replaced by the winner :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)
On Apr 23, 2010, at 2:59 PM, Thomas Hartman wrote: So, you might need to -- upgrade hsx -- make sure that the upgraded trhsx executable is the one being executed by cabal install hsx (maybe deleting/temporarily moving other trhsx exes) Unfortunately, this suggestion didn't work out for me. I read through all the relevant GHC documentation I could find -- I didn't see a way to set a specific path for GHC to search through for binaries. Whether I moved trhsx or not, the error was the same. But it's the only trhsx on my system. I've upgraded through every version of hsx that is compatible with Happstack, and tried every hsp that is compatible with Happstack. I've built Cabal-install, removed it, used the Arch package; tried global/user installs for Happstack; did a darcs get on the official Happstack repo, and tried to build using its build script, on a fresh GHC install; and other stuff that I guess didn't make much sense. It always broke in the same place: [ a...@kizaru:~/ ]$ cabal install hsp-0.4.5 Resolving dependencies... Configuring hsp-0.4.5... Preprocessing library hsp-0.4.5... Building hsp-0.4.5... ghc: could not execute: trhsx cabal: Error: some packages failed to install: hsp-0.4.5 failed during the building phase. The exception was: ExitFailure 1 The strange thing about it (that I noticed) is that GHC reports failing during the building phase instead of the preprocessing phase. Maybe this is just an artifact of the logging system, but it seems like GHC is doing something strange. If I increase the verbosity, (near the end) I get: *** Haskell pre-processor: trhsx src/HSP/HJScript.hs /tmp/ghc6345_0/ghc6345_6.hscpp /tmp/ ghc6345_0/ghc6345_0.hspp *** Deleting temp files: Deleting: /tmp/ghc6345_0/ghc6345_0.hspp /tmp/ghc6345_0/ ghc6345_6.hscpp /tmp/ghc6345_0/ghc6345_5.hscpp /tmp/ghc6345_0/ ghc6345_4.hscpp /tmp/ghc6345_0/ghc6345_3.hscpp /tmp/ghc6345_0/ ghc6345_2.hscpp /tmp/ghc6345_0/ghc6345_1.hscpp /tmp/ghc6345_0/ ghc6345_0.hscpp Warning: deleting non-existent /tmp/ghc6345_0/ghc6345_0.hspp *** Deleting temp dirs: Deleting: /tmp/ghc6345_0 ghc: could not execute: trhsx /usr/bin/ghc returned ExitFailure 1 cabal: Error: some packages failed to install: hsp-0.4.5 failed during the building phase. The exception was: ExitFailure 1 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The instability of Haskell libraries
On Apr 26, 2010, at 09:33 , John Goerzen wrote: It would, however, be nice if the language allowed you to override default instances with the code in your own package. Many other languages refer to this kind of thing as monkey patching and warn against it because of the problems it causes. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: What do _you_ want to see in FGL?
I'm a fan of making FGL more record-based, but definitely keeping the inductive graph style. My own biggest gripe with previous versions of FGL was that the graph implementations were severely underoptimized. In particular, PatriciaTree left open a *lot* of optimization. Ivan, would you like to set up a darcs repo for FGL-Prime or something at code.haskell.org, and start cracking? I'm really excited for this project. Louis Wasserman wasserman.lo...@gmail.com http://profiles.google.com/wasserman.louis ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Rank-2 polymorphism and overloading
Hello all, I'm having difficulties understanding rank-2 polymorphism in combination with overloading. Consider the following contrived definition: f :: (forall a . Eq a = a - a - Bool) - Bool f eq = eq True True Then, we pass f both an overloaded function and a regular polymorphic function: x :: forall a . Eq = a - a - Bool x = \x y - x == y y :: forall a . a - a - Bool y = \x y - True g :: (Bool, Bool) g = (f x, f y) Could someone explain to me, or point me to some reading material, why g is correctly typed? I understand that x's type is what f expects, but why does y's polymorphic type fulfill the overloaded type of f's argument? I can imagine that it is justified since f's argument type is more restrictive than y's type. However, it requires y to throw away the provided dictionary under the hood, which seems counter intuitive to me. Regards, Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Halp: wacky FFI problems
Hey, I'm trying to do some funky things with the FFI, and I'm clueless enough with C that I could use some help. In particular, I'm trying to bind to the glpk library in a multithreaded style. It's not normally thread-safe, but somebody suggested how to make it safe here http://www.mail-archive.com/help-g...@gnu.org/msg04021.html. I have no idea how to integrate this with FFI-style bindings. A single-threaded set of bindings that I've written is here: http://hackage.haskell.org/package/glpk-hs I'm trying to figure out how to integrate FFI bindings with pthreads, and yadda yadda, and I'm pretty clueless. Any suggestions? Louis Wasserman wasserman.lo...@gmail.com http://profiles.google.com/wasserman.louis ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Rank-2 polymorphism and overloading
Thomas van Noort wrote: Hello all, I'm having difficulties understanding rank-2 polymorphism in combination with overloading. Consider the following contrived definition: f :: (forall a . Eq a = a - a - Bool) - Bool f eq = eq True True Then, we pass f both an overloaded function and a regular polymorphic function: x :: forall a . Eq = a - a - Bool x = \x y - x == y y :: forall a . a - a - Bool y = \x y - True g :: (Bool, Bool) g = (f x, f y) Could someone explain to me, or point me to some reading material, why g is correctly typed? I understand that x's type is what f expects, but why does y's polymorphic type fulfill the overloaded type of f's argument? I can imagine that it is justified since f's argument type is more restrictive than y's type. However, it requires y to throw away the provided dictionary under the hood, which seems counter intuitive to me. f requires a function that is able to compute, for two values of type a (which instantiates Eq), a Boolean. y certainly fulfills that requirement: it does not even require that the values are of a type instantiating Eq. This is also well-typed and might or might not be enlightening: z :: forall a. Eq a = a - a - Bool z = y g :: (Bool, Bool) g = (f x, f z) -- note the use of z here instead of y Jochem -- Jochem Berndsen | joc...@functor.nl ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Rank-2 polymorphism and overloading
Am Montag 26 April 2010 19:52:23 schrieb Thomas van Noort: Hello all, I'm having difficulties understanding rank-2 polymorphism in combination with overloading. Consider the following contrived definition: f :: (forall a . Eq a = a - a - Bool) - Bool f eq = eq True True Then, we pass f both an overloaded function and a regular polymorphic function: x :: forall a . Eq = a - a - Bool x = \x y - x == y y :: forall a . a - a - Bool y = \x y - True g :: (Bool, Bool) g = (f x, f y) Could someone explain to me, or point me to some reading material, why g is correctly typed? I understand that x's type is what f expects, but why does y's polymorphic type fulfill the overloaded type of f's argument? I can imagine that it is justified since f's argument type is more restrictive than y's type. Yes, y's type is more general than the type required by f, hence y is an acceptable argument for f - even z :: forall a b. a - b - Bool is. However, it requires y to throw away the provided dictionary under the hood, which seems counter intuitive to me. Why? y doesn't need the dictionary, so it just ignores it. Regards, Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] The Poor Man's PVP-Checking Tool
Hi, The issue of a tool to help with checking packages against the Package Versioning Policy (PVP: http://www.haskell.org/haskellwiki/Package_versioning_policy) has come up several times on this list, and it seems to be a generally wanted tool. One of the things desired in such a tool is the ability to check what has been added/changed/removed in the latest version of a package, to help see what kind of version bump is needed according to the PVP. This could also be used to check if past releases have obeyed the PVP. A proper way to build this tool is to parse the types of everything involved (functions, data types, and instances), and check them for being the same (given that the type parameters may have been renamed, or a definition substituted for a synonym and so on). I have instead hacked together a tool in an hour or so that roughly does the job. It uses Perl, which I haven't written for a long time, because that was quickest -- if this bothers you, pretend its a crazy Haskell EDSL or something :-). I've attached the Perl script. It combines the command-line tools diff and sort with a tiny bit of manual processing along with the Haskell tool cabal-install, and brings them to bear on the output of haddock --hoogle, which already nicely spits out the types of all functions, data types and instances in your library. It looks for differences in the output between two package versions, and tells you what version bump it thinks you need. It errs on the conservative side, I believe -- it should never miss a bump when it's needed, but you may sometimes get a false alarm if you've made a harmless change. As an example, let's take the recent stm release. You run the Perl script with the name and version of both package versions (if you omit the version, it should use the latest): n...@beast ~: perl cmp.perl stm-2.1.2.0 stm-2.1.1.2 Warning: The documentation for the following packages are not installed. No links will be generated to these packages: ffi-1.0, rts-1.0 Warning: The documentation for the following packages are not installed. No links will be generated to these packages: ffi-1.0, rts-1.0 25a26 Control.Concurrent.STM.TVar:readTVarIO :: TVar a - IO a 39c40 @version 2.1.1.2 --- @version 2.1.2.0 Given previous version number A.B.C.D: It seems you have added something. You must increase C (or A or B) For those who can read diff, you get the diff. At the bottom, the tool works out the required bump; here something was added so C must be increased, and we can see that the package did just that. Let's take another example from my latest development version of my CHP library; here I run the command with one argument (chp, which means the latest version on Hackage): n...@banshee ~/work/chp: perl cmp.perl chp Warning: The documentation for the following packages are not installed. No links will be generated to these packages: rts-1.0 Control/Concurrent/CHP/Alt.hs:116:9: Warning: orphan instance: instance Alternative CHP Warning: The documentation for the following packages are not installed. No links will be generated to these packages: rts-1.0 6a7 Control.Concurrent.CHP.Alt:instance Alternative CHP 82d82 Control.Concurrent.CHP.Channels.Creation:class ChannelTuple t 88,92d87 Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) = ChannelTuple (Chan r w a, Chan r w a) Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) = ChannelTuple (Chan r w a, Chan r w a, Chan r w a) Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) = ChannelTuple (Chan r w a, Chan r w a, Chan r w a, Chan r w a) Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) = ChannelTuple (Chan r w a, Chan r w a, Chan r w a, Chan r w a, Chan r w a) Control.Concurrent.CHP.Channels.Creation:instance (Channel r w) = ChannelTuple (Chan r w a, Chan r w a, Chan r w a, Chan r w a, Chan r w a, Chan r w a) 102d96 Control.Concurrent.CHP.Channels.Creation:newChannels :: (ChannelTuple t, MonadCHP m) = m t 149c143 Control.Concurrent.CHP.Monad:class (MonadIO m) = MonadCHP m --- Control.Concurrent.CHP.Monad:class (Monad m) = MonadCHP m 155a150 Control.Concurrent.CHP.Monad:foreverP :: CHP a - CHP b 156a152 Control.Concurrent.CHP.Monad:liftIO_CHP :: IO a - CHP a 160a157 Control.Concurrent.CHP.Monad:process :: String - a - a 164a162 Control.Concurrent.CHP.Monad:subProcess :: String - a - a 169c167 Control.Concurrent.CHP.Parallel:data (Monad m, MonadCHP m) = ForkingT m a --- Control.Concurrent.CHP.Parallel:data ForkingT m a 173d170 Control.Concurrent.CHP.Parallel:instance (MonadIO m) = MonadIO (ForkingT m) 175c172 Control.Concurrent.CHP.Parallel:instance MonadTrans ForkingT --- Control.Concurrent.CHP.Parallel:liftForking :: (Monad m) = m a - ForkingT m a 239c236 @version 2.1.0.1 --- @version 2.2.0 Given previous version number A.B.C.D: It seems you have added, removed or changed some instances. You must
Re: [Haskell-cafe] Haddock infix constructors in markup
2010/4/26 Daniel Fischer daniel.is.fisc...@web.de: Am Montag 26 April 2010 18:15:02 schrieb Ozgur Akgun: Hi all, If I have the following data type: data Expr = Num Int | Expr :+: Expr | Expr :-: Expr Haddock handles the infix constructors, and generates a very nice output (html in this case) However when I try to reference to one of the infix constructors in the markup of other functions it fails to hyperlink. -- | If the input is 'Num' does magic, if it is ':+:' does even more magic! someFunc :: Expr - Expr In the output of this markup, the 'Num' is hyperlinked but the ':+:' is not. Is there a different syntax for infix constructors (and for infix functions presumably) or does haddock simple lack this feature? Infix functions work fine (try referring to e.g. '' in the haddock comment), but infix constructors apparently not. Yes, I actually fixed this a few weeks ago in Haddock's lexer. Colon was just not included in the character set for identifiers. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Rank-2 polymorphism and overloading
On 26-4-2010 20:13, Jochem Berndsen wrote: Thomas van Noort wrote: ... f requires a function that is able to compute, for two values of type a (which instantiates Eq), a Boolean. y certainly fulfills that requirement: it does not even require that the values are of a type instantiating Eq. This is also well-typed and might or might not be enlightening: z :: forall a. Eq a = a - a - Bool z = y g :: (Bool, Bool) g = (f x, f z) -- note the use of z here instead of y I find your example of z more intuitive as it is z that does not provide its dictionary to y, but throws it away explicitly. This in contrast to y that is provided a dictionary but throws it away implicitly. Regards, Thomas Jochem ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Rank-2 polymorphism and overloading
On 26-4-2010 20:12, Daniel Fischer wrote: Am Montag 26 April 2010 19:52:23 schrieb Thomas van Noort: ... Yes, y's type is more general than the type required by f, hence y is an acceptable argument for f - even z :: forall a b. a - b - Bool is. That's what I thought. I've just never seen such a notion of a more general type involving overloading before. However, it requires y to throw away the provided dictionary under the hood, which seems counter intuitive to me. Why? y doesn't need the dictionary, so it just ignores it. Sure, but y's type explicitly mentions that it doesn't want a dictionary, so why would you provide one to it? Regards, Thomas Regards, Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)
Hello, Does trying to install hsp-0.5.1 work any better? - jeremy On Apr 26, 2010, at 12:27 PM, Alexander Solla wrote: On Apr 23, 2010, at 2:59 PM, Thomas Hartman wrote: So, you might need to -- upgrade hsx -- make sure that the upgraded trhsx executable is the one being executed by cabal install hsx (maybe deleting/temporarily moving other trhsx exes) Unfortunately, this suggestion didn't work out for me. I read through all the relevant GHC documentation I could find -- I didn't see a way to set a specific path for GHC to search through for binaries. Whether I moved trhsx or not, the error was the same. But it's the only trhsx on my system. I've upgraded through every version of hsx that is compatible with Happstack, and tried every hsp that is compatible with Happstack. I've built Cabal-install, removed it, used the Arch package; tried global/user installs for Happstack; did a darcs get on the official Happstack repo, and tried to build using its build script, on a fresh GHC install; and other stuff that I guess didn't make much sense. It always broke in the same place: [ a...@kizaru:~/ ]$ cabal install hsp-0.4.5 Resolving dependencies... Configuring hsp-0.4.5... Preprocessing library hsp-0.4.5... Building hsp-0.4.5... ghc: could not execute: trhsx cabal: Error: some packages failed to install: hsp-0.4.5 failed during the building phase. The exception was: ExitFailure 1 The strange thing about it (that I noticed) is that GHC reports failing during the building phase instead of the preprocessing phase. Maybe this is just an artifact of the logging system, but it seems like GHC is doing something strange. If I increase the verbosity, (near the end) I get: *** Haskell pre-processor: trhsx src/HSP/HJScript.hs /tmp/ghc6345_0/ghc6345_6.hscpp /tmp/ ghc6345_0/ghc6345_0.hspp *** Deleting temp files: Deleting: /tmp/ghc6345_0/ghc6345_0.hspp /tmp/ghc6345_0/ ghc6345_6.hscpp /tmp/ghc6345_0/ghc6345_5.hscpp /tmp/ghc6345_0/ ghc6345_4.hscpp /tmp/ghc6345_0/ghc6345_3.hscpp /tmp/ghc6345_0/ ghc6345_2.hscpp /tmp/ghc6345_0/ghc6345_1.hscpp /tmp/ghc6345_0/ ghc6345_0.hscpp Warning: deleting non-existent /tmp/ghc6345_0/ghc6345_0.hspp *** Deleting temp dirs: Deleting: /tmp/ghc6345_0 ghc: could not execute: trhsx /usr/bin/ghc returned ExitFailure 1 cabal: Error: some packages failed to install: hsp-0.4.5 failed during the building phase. The exception was: ExitFailure 1 ___ 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] Run haskell program in emacs without typing main in the ghci buffer.
Hello, Is it possible to run haskell program in emacs without typing main in the ghci buffer? Assuming main function exists of course. Or, maybe automate sending main\n string to ghci buffer input. In other words, I want edit/run/see result style session. Thanks in advance, Zura -- View this message in context: http://old.nabble.com/Run-haskell-program-in-emacs-without-typing-%22main%22-in-the-ghci-buffer.-tp28368541p28368541.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)
On Apr 26, 2010, at 12:30 PM, Jeremy Shaw wrote: Does trying to install hsp-0.5.1 work any better? I hadn't tried it, since it forces hsx-0.7 to install. But I gave it a shot, and it fails the same way: [ a...@kizaru:~/ ]$ cabal install hsp-0.5.1 Resolving dependencies... Configuring hsp-0.5.1... Preprocessing library hsp-0.5.1... Building hsp-0.5.1... ghc: could not execute: trhsx cabal: Error: some packages failed to install: hsp-0.5.1 failed during the building phase. The exception was: ExitFailure 1 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haddock infix constructors in markup
So, how can we make use of this fix? On 26 April 2010 19:47, David Waern david.wa...@gmail.com wrote: 2010/4/26 Daniel Fischer daniel.is.fisc...@web.de: Am Montag 26 April 2010 18:15:02 schrieb Ozgur Akgun: Hi all, If I have the following data type: data Expr = Num Int | Expr :+: Expr | Expr :-: Expr Haddock handles the infix constructors, and generates a very nice output (html in this case) However when I try to reference to one of the infix constructors in the markup of other functions it fails to hyperlink. -- | If the input is 'Num' does magic, if it is ':+:' does even more magic! someFunc :: Expr - Expr In the output of this markup, the 'Num' is hyperlinked but the ':+:' is not. Is there a different syntax for infix constructors (and for infix functions presumably) or does haddock simple lack this feature? Infix functions work fine (try referring to e.g. '' in the haddock comment), but infix constructors apparently not. Yes, I actually fixed this a few weeks ago in Haddock's lexer. Colon was just not included in the character set for identifiers. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haddock infix constructors in markup
Am Montag 26 April 2010 22:05:48 schrieb Ozgur Akgun: So, how can we make use of this fix? My guess: $ cabal install haddock-2.7.2 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)
Alexander Solla a...@2piix.com writes: On Apr 26, 2010, at 12:30 PM, Jeremy Shaw wrote: Does trying to install hsp-0.5.1 work any better? I hadn't tried it, since it forces hsx-0.7 to install. But I gave it a shot, and it fails the same way: [ a...@kizaru:~/ ]$ cabal install hsp-0.5.1 Resolving dependencies... Configuring hsp-0.5.1... Preprocessing library hsp-0.5.1... Building hsp-0.5.1... ghc: could not execute: trhsx cabal: Error: some packages failed to install: hsp-0.5.1 failed during the building phase. The exception was: ExitFailure 1 Is $HOME/.cabal/bin on your $PATH? G -- Gregory Collins g...@gregorycollins.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)
On Apr 26, 2010, at 1:23 PM, Gregory Collins wrote: Is $HOME/.cabal/bin on your $PATH? Argh. I had ~/.cabal/bin in my $PATH instead of $HOME/.cabal/bin. I'm still not sure what the semantic difference is in this use case, but one ($HOME) works and the other (~/) doesn't. Thanks everybody ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Build problems (hsp, trhsx, ultimately Happstack)
Am Montag 26 April 2010 22:23:42 schrieb Gregory Collins: Alexander Solla a...@2piix.com writes: On Apr 26, 2010, at 12:30 PM, Jeremy Shaw wrote: Does trying to install hsp-0.5.1 work any better? I hadn't tried it, since it forces hsx-0.7 to install. But I gave it a shot, and it fails the same way: [ a...@kizaru:~/ ]$ cabal install hsp-0.5.1 Resolving dependencies... Configuring hsp-0.5.1... Preprocessing library hsp-0.5.1... Building hsp-0.5.1... ghc: could not execute: trhsx cabal: Error: some packages failed to install: hsp-0.5.1 failed during the building phase. The exception was: ExitFailure 1 Is $HOME/.cabal/bin on your $PATH? G He said it is. That would've been too easy. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: FRP for game programming / artifical life simulation
2010/4/25 Patai Gergely patai_gerg...@fastmail.fm: (in my own FRP experiments I have an update thread and a render thread). I wonder how to nicely deal with state that requires communication with the outer world, even though it is functional at heart. For instance, if you want to change a vertex buffer or a texture or whatever during the update, how do you organise your code? Do you maintain separate pure and impure state information blocks? I don't have a vertex buffers or texture in my update loop. These are low level details, left to the render loop. Indeed I maintained a pure information block in the update. If you really wanted to have low-level access in the update loop, I wouldn't know how to do that, although keeping two copies could work. Now my experiments were really simple 2D games, so not really state of the art. Deciding between push and pull according to profiling results is a nice idea. :) It might be too expensive to do it adaptively during runtime (the overhead might easily distort the results and thus render them invalid), but treating it as just a flag could give us an interesting architecture to play with. Yes, I see it more in the line of profile based optimization, where a compiler performs static optimization based on a previous profile. I kind of abandoned the FRP thing because Haskell just feels a bit too complicated/abstract for me. It might also be that for the average person to learn Haskell really well, one needs a mentor. I would love to follow courses about it actually :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News?
Hi all, I haven't seen a Haskell Weekly News in a while. Is there anything I can do to help? -deech ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] and [] = True; or [] = False
On Apr 27, 2010, at 12:15 AM, Bjorn Buckwalter wrote: Dear all, Does it make good sense that 'and []' returns 'True' and 'or []' returns 'False'? YES! There is no other behaviour that would make sense. You wouldn't expect sum [] to return anything but 0, would you? What got me thinking about this was the apparently incorrect intuition that 'and xs' would imply 'or xs'. Only if not (null xs). See also Lisp and Scheme, where (AND) - true, (OR) - false, and look up the behaviour of ∀ and ∃ in a logic book. (∀x∈s)p(x) does NOT imply (∃x∈s)p(x) because s might be empty. (This is where the modern ∀ and ∃ part company with Aristotelian logic. In syllogisms, all unicorns are white does not count as true unless there is at least one unicorn.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: What do _you_ want to see in FGL?
On 27 April 2010 03:39, Louis Wasserman wasserman.lo...@gmail.com wrote: I'm a fan of making FGL more record-based, but definitely keeping the inductive graph style. Definitely. My own biggest gripe with previous versions of FGL was that the graph implementations were severely underoptimized. In particular, PatriciaTree left open a lot of optimization. Wouldn't know much about the optimisation side of things; when I've used FGL graphs before they usually weren't the bottleneck in my program. Ivan, would you like to set up a darcs repo for FGL-Prime or something at code.haskell.org, and start cracking? I'm really excited for this project. Sure, let's take these preliminary discussions off-list. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Run haskell program in emacs without typing main in the ghci buffer.
On 27 April 2010 05:43, Zura_ x...@gol.ge wrote: Is it possible to run haskell program in emacs without typing main in the ghci buffer? Assuming main function exists of course. Or, maybe automate sending main\n string to ghci buffer input. In other words, I want edit/run/see result style session. This is probably possible if you have enough elisp-fu (which I don't, but have a look at Flymake Haskell). If so, it would be better to have this as a different emacs keybinding rather than the default haskell-load-file one, as 1) you won't always have a main action and 2) you won't always want to _run_ your main action (e.g. it launches nuclear missiles and you don't want to run that when you're just testing your countdown function...). However, by using :main in the ghci session you have a bit more control as it allows you to specify command-line flags and inputs, which running just main doesn't. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haddock infix constructors in markup
On 27 April 2010 02:15, Ozgur Akgun ozgurak...@gmail.com wrote: data Expr = Num Int | Expr :+: Expr | Expr :-: Expr [snip] -- | If the input is 'Num' does magic, if it is ':+:' does even more magic! someFunc :: Expr - Expr In the output of this markup, the 'Num' is hyperlinked but the ':+:' is not. I would hazard a guess that the Num hyperlink points to the Num typeclass in the Prelude rather than your Num constructor. As for your infix constructor, I have no idea. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Weekly News?
Hehe, Mostly, at the moment, as I mentioned to Deech, what is holding me up is trying to get HWN and 7 classes worth of finals and papers done. This is the last two weeks of my last semester, but it should be all done soon. I hope to get HWN out shortly after it's all finished up. I shall return! /Joe On Apr 26, 2010, at 7:54 PM, Ivan Miljenovic wrote: On 27 April 2010 08:08, aditya siram aditya.si...@gmail.com wrote: Hi all, I haven't seen a Haskell Weekly News in a while. Is there anything I can do to help? My guess is do John's marking, etc. for him so that he has some time to do the HWN! We also want him to avoid this situation: http://ro-che.info/ccc/06.html :p -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Weekly News?
On 27 April 2010 10:08, Joe Fredette jfred...@gmail.com wrote: I hope to get HWN out shortly after it's all finished up. I shall return! As long as you don't end up copying the Gentoo situation where the Gentoo Weekly News died, was resurrected (not sure how many times), was converted to the Gentoo Monthly News to make it simpler, and then became the Gentoo Never News (hey, GNN sounds kinda catchy, though not as good as C :p). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Weekly News?
Most certainly, the HWN is easy to put together, it's just a little time consuming, the weekly schedule is just enough under a normal 40- hour courseload. When that number jumps into the high billions (as it did this last semester), it becomes someone more difficult to fit in. HWN will always be HWN, at least as long as I can keep it that way. :D /Joe On Apr 26, 2010, at 8:17 PM, Ivan Miljenovic wrote: On 27 April 2010 10:08, Joe Fredette jfred...@gmail.com wrote: I hope to get HWN out shortly after it's all finished up. I shall return! As long as you don't end up copying the Gentoo situation where the Gentoo Weekly News died, was resurrected (not sure how many times), was converted to the Gentoo Monthly News to make it simpler, and then became the Gentoo Never News (hey, GNN sounds kinda catchy, though not as good as C :p). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proper Handling of Exceptional IEEE Floating Point Numbers
On 24/04/2010, at 22:42, Roman Leshchinskiy wrote: On 24/04/2010, at 22:06, Barak A. Pearlmutter wrote: I was thinking of this: data T = T Double deriving ( Eq, Ord ) ... GHC basically produces instance Ord T where compare (T x) (T y) = compare x y t u = compare t u == LT That is indeed what it does. Which is a plain old bug, since it leads to inconsistent behaviour between wrapped vs unwrapped values. *Main T (0/0) == T (0/0) False *Main T (0/0) T (0/0) False *Main T (0/0) T (0/0) True *Main (0/0) (0/0) False Urgh. You're right, I hadn't thought of this. Would you care to submit a bug report? I submitted one but on further reflection, this is not so simple. Let's look at pairs as an example. At the moment, () is implemented basically like this: (a,b) (c,d) = case compare a c of LT - False EQ - compare b d GT - True Of course, this means that (0/0,'a') (0/0,'a'). So we could change the implementation: (a,b) (c,d) = a c || (a == c b d) But now we compare a to c twice which is very bad for, say, ([Int],Int). Clearly, we want to use the first definition but it leads to inconsistent results for Doubles. I don't see how to solve this while keeping IEEE semantics of silent NaNs. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Run haskell program in emacs without typing main in the ghci buffer.
Zura_ x...@gol.ge writes: Hello, Is it possible to run haskell program in emacs without typing main in the ghci buffer? Assuming main function exists of course. Or, maybe automate sending main\n string to ghci buffer input. In other words, I want edit/run/see result style session. Assuming you're using haskell-mode, does M-x inferior-haskell-load-and-run do what you want? You can of course define a shortcut for it: (define-key haskell-mode-map \C-l 'inferior-haskell-load-and-run) If you don't want to load the file, just run main: (defun haskell-main () (interactive) (inferior-haskell-send-command (inferior-haskell-process) :main)) (This a very simple version; there're many possible variations; for instance, adding (swith-to-haskell) at the end). HTH, jao ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Abstracted File Library?
Hello, I'm implementing a command which manipulates files both on Unix/Mac and Windows. I was very surprised because there is not getStatusChangeTime function. So, I wrote it with CPP. http://github.com/kazu-yamamoto/Mew/blob/master/bin/hs/Stat.hs Another problem is that since '\\' is used as the file separator of Windows, I cannot use regular expression naturally for file path. In many programming languages, '/' is only file separator for programmers. And my friend, who is an expert of Windows API, says to me that Windows API allows '/' as a file separator. Why don't we use '/' on Windows, too? Are there any abstracted file library to solve these problems? Or should I start to write such a library? --Kazu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Abstracted File Library?
Excerpts from Kazu Yamamoto (山本和彦)'s message of Tue Apr 27 04:59:46 +0200 2010: Hello, I'm implementing a command which manipulates files both on Unix/Mac and Windows. I was very surprised because there is not getStatusChangeTime function. So, I wrote it with CPP. http://github.com/kazu-yamamoto/Mew/blob/master/bin/hs/Stat.hs Another problem is that since '\\' is used as the file separator of Windows, I cannot use regular expression naturally for file path. In Clarify this, please. Used by who? The user may enter \\ which is valid on Windows. Both Cabal and filepath libraries do have functions operating on filepath strings. Eg filepath can split them. I agree that / is valid on Windows. So before working on user input you have to sanitize paths by replacing \\ by / Are there any abstracted file library to solve these problems? Or should I start to write such a library? Which functions should this library have? I'm pretty sure that filepath already has most functions you need. You may want to patch it so that it's using / on Windows when assembling paths form lists of directory names. Marc Weber ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Abstracted File Library?
Hello, Clarify this, please. Used by who? It is by System.FilePath. Windows: combine home bob == home\\bob Both Cabal and filepath libraries do have functions operating on filepath strings. Eg filepath can split them. I'm want to use regular expressions for results of 'combine', for instance. Are there any abstracted file library to solve these problems? Or should I start to write such a library? Which functions should this library have? isSymbolicLink, linkCounts, etc. I'm pretty sure that filepath already has most functions you need. Not really at least to me. --Kazu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Abstracted File Library?
Hi Kazu, I don't have a ghc Windows installation at the moment so I can't test. filepath has functions such as normalise and equalFilePath. Have a look at splitPath which is using pathSeparators which allows both \\ and / on Windows. filpath is using \\ to join pathes though. So appling normalise on filepath on Windowsn will result in having paths containing \\ only. This will still not help you writing your regex unless you replace / by \\ on Windows. It's easy to write [\\/] in regex to catch both. So maybe a normalisePosix function should be added which always returns / ? The fast way which would work for you only is making pathSeparator return / only. Then you're done but your code will not be portable.. Including a local copy of filepath for exactly this reason could be an option for you. isSymbolicLink, linkCounts, etc. Don't know about them.. Marc Weber ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Curl UTF8
On 2010-04-23, Khudyakov Alexey alexey.sklad...@gmail.com wrote: В сообщении от 23 апреля 2010 02:36:07 Rickard Karlsson написал: Hi, I'm trying to download a file in UTF-8 with libcurl(1.3.5) and GHC 6.12: import Network.Curl u = http://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt; main = curlGetString u [] = putStrLn . snd Which doesn't print the characters correctly. If i read the file from local storage with getFile it is displayed properly. I think curl knows nothing about encoding and convert one byte to one Char and getFile uses new IO which uses system locale to choose encoding. Then clearly curl should not return Strings, but byte arrays. Of course, curl can very well look at the headers which in this case do specify UTF-8, and so perhaps it should do the translation itself. -- Aaron Denney -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: The instability of Haskell libraries
On 2010-04-24, John Goerzen jgoer...@complete.org wrote: It is a funny thing, because our fundamental libraries *have* had time to settle down, in a sense. In another sense, I must say that the innovations we have seen recently have been sorely needed and are unquestionably a good thing. Overall, agreed. It still makes it a pain to write to the current standard, because it is moving. Unicode support in IO, This was just a bugfix in GHC, made more painful by people writing code dependent on the old behaviour. I guess this is the price of failing to avoid success, to borrow Simon's phrase. And again, not entirely bad. I despair that a better Numeric hierarchy will never make it into Haskell. -- Aaron Denney -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The instability of Haskell libraries
On 27 April 2010 14:55, Aaron Denney wno...@ofb.net wrote: I despair that a better Numeric hierarchy will never make it into Haskell. I think the reason it hasn't is because I for one still haven't seen a fully implemented such hierarchy that's worth using. Then again, most of my numerical calculations are very basic; yay for combinatorics! :p -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: The instability of Haskell libraries
On Apr 27, 2010, at 00:55 , Aaron Denney wrote: I despair that a better Numeric hierarchy will never make it into Haskell. I thought the main reason for that was that nobody could agree on a better hierarchy that was actually usable. (Nobody wants to chain 10 typeclasses together to get work done.) -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
