Re: [Haskell-cafe] efficient chop
On Sep 14, 2011, at 5:29 AM, Kazu Yamamoto (山本和彦) wrote: > Hello, > > Of course, I use ByteString or Text for real programming. But I would > like to know whether or not there are any efficient methods to remove > a tail part of a list. > > --Kazu In that case, I would prefer this version, since it is lazier: lazyChop :: String -> String lazyChop s = pref ++ if null s' then [] else (mid_sp ++ lazyChop s') where (pref,sp_suf) = break isSpace s (mid_sp,s') = span isSpace sp_suf By "lazier" I mean: *Main> chopReverse $ "hello world " ++ undefined "*** Exception: Prelude.undefined *Main> chopFoldr $ "hello world " ++ undefined "*** Exception: Prelude.undefined *Main> lazyChop $ "hello world " ++ undefined "hello world*** Exception: Prelude.undefined Daniel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] regex-applicative library needs your help! (algorithmic challenge)
* Eugene Kirpichov [2011-09-14 08:38:10+0400] > Hi, > I don't see how fallback to NFA simulation is really a failure wrt DoS > attacks. It's not exponential in time or memory, just linear memory > (in size of regex) instead of constant, and slower than DFA. Hi Eugene, thanks for pointing that out. Indeed, I now see that he uses breadth-first rather than depth-first search. Then he has the same problem as I do. I shall study his code more closely. -- Roman I. Cheplyaka :: http://ro-che.info/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANNOUNCE] Haskdogs-0.1
Re-cc'ing -cafe: On 14 September 2011 14:29, yi huang wrote: > On Wed, Sep 14, 2011 at 11:32 AM, Ivan Lazar Miljenovic > wrote: >> >> On 14 September 2011 13:27, yi huang wrote: >> > On Wed, Sep 14, 2011 at 10:18 AM, Ivan Lazar Miljenovic >> > wrote: >> >> >> >> On 14 September 2011 11:24, yi huang wrote: >> >> > Cabal compains about "Unknown build tool hasktags". >> >> > It seems not necessary to set "Build-tools: hasktags" in cabal file? >> >> >> >> cabal-install isn't capable of automatically building and installing >> >> build-tools for you. So to install haskdogs, you need to do "cabal >> >> install hasktags && cabal install haskdogs". >> > >> > I have installed hasktags, and .cabal/bin is in my PATH, i can run >> > hasktags >> > directly from shell. >> > What else did i miss? >> >> How did you specify your PATH? You can't use ~/.cabal/bin, you need >> either $HOME/.cabal/bin or the fully expanded path. > > It is $HOME/.cabal/bin , and `which hasktags' can find it without problem. > Cabal 1.10.2, ghc 7.0.4, i'm trying to look into cabal source to find the > problem. Actually... looks like you're right. I can't build it either, he appears to have hard-coded some paths in and it appears that you need some kind of magic to register a program as a build tool (that's what the error is from: hasktags isn't a registered build-tool). -- 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] regex-applicative library needs your help! (algorithmic challenge)
Hi, I don't see how fallback to NFA simulation is really a failure wrt DoS attacks. It's not exponential in time or memory, just linear memory (in size of regex) instead of constant, and slower than DFA. On Wed, Sep 14, 2011 at 1:29 AM, Roman Cheplyaka wrote: > * Chris Kuklewicz [2011-09-13 08:21:55+0100] >> I wrote regex-tdfa, the efficient (though not yet lightning fast) Posix-like >> engine. >> >> You are not the first to want an efficient Perl-like engine. The answer you >> seek flows from Russ Cox (though in C++): >> >> > http://google-opensource.blogspot.com/2010/03/re2-principled-approach-to-regular.html >> >> > http://code.google.com/p/re2/ >> >> Quoting relevant bit: >> >> > It also finds the leftmost-first match, the same match that Perl would, and >> > can return submatch information. The one significant exception is that RE2 >> > drops support for backreferences¹ and generalized zero-width assertions, >> > because they cannot be implemented efficiently. > > Hi Chris, thanks for the response. > > There's one thing about Cox's work that I don't understand. On the > page [1] he mentions that the algorithm falls back to direct NFA > simulation (search for "If all else fails" on that page). > This defeats his goal of defending against DoS attacks (the second > paragraph of that page). > > And I wouldn't be comfortable with an algorithm that is worst-case > exponential either. > > Then there's another issue: I specifically want a combinator library, > and not every automaton-based algorithm can serve this purpose in a > statically typed language (unless there's some clever trick I don't > know). > > [1]: http://swtch.com/~rsc/regexp/regexp3.html > > -- > Roman I. Cheplyaka :: http://ro-che.info/ > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] efficient chop
On 14 September 2011 13:29, Kazu Yamamoto wrote: > Hello, > > Of course, I use ByteString or Text for real programming. But I would > like to know whether or not there are any efficient methods to remove > a tail part of a list. I doubt it; lists aren't that great a data type if you want to keep manipulating the end all the time. You'd have more luck with a Sequence or some other data type. -- 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] efficient chop
Hello, Of course, I use ByteString or Text for real programming. But I would like to know whether or not there are any efficient methods to remove a tail part of a list. --Kazu From: Thomas DuBuisson Subject: Re: [Haskell-cafe] efficient chop > This was a recent question on StackOverflow: > > http://stackoverflow.com/questions/6270324/in-haskell-how-do-you-trim-whitespace-from-the-beginning-and-end-of-a-string/6270382#6270382 > > Where I started: > > If you have serious text processing needs then use the text package > from hackage. > > And concluded: > > A quick Criterion benchmark tells me that (for a particularly long > string of words with spaces and ~200 pre and post spaces) my trim > takes 1.6 ms, the trim using reverse takes 3.5ms, and Data.Text.strip > takes 0.0016 ms. > > Cheers, > Thomas > > On Tue, Sep 13, 2011 at 8:03 PM, Kazu Yamamoto wrote: >> Hello Cafe, >> >> I would like to have an efficient implementation of the chop function. >> As you guess, the chop function drops spaces in the tail of a list. >> >> chop " foo bar baz " >> -> " foo bar baz" >> >> A naive implementation is as follows: >> >> chopReverse :: String -> String >> chopReverse = reverse . dropWhile isSpace . reverse >> >> But this is not elegant. foldr version is as follows: >> >> chopFoldr :: String -> String >> chopFoldr = foldr f [] >> where >> f c [] >> | isSpace c = [] >> | otherwise = c:[] >> f c cs = c:cs >> >> But this code is slower than chopReverse in some cases. >> >> Are there any more efficient implementations of chop? Any suggestions? >> >> --Kazu >> >> ___ >> 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] efficient chop
This was a recent question on StackOverflow: http://stackoverflow.com/questions/6270324/in-haskell-how-do-you-trim-whitespace-from-the-beginning-and-end-of-a-string/6270382#6270382 Where I started: If you have serious text processing needs then use the text package from hackage. And concluded: A quick Criterion benchmark tells me that (for a particularly long string of words with spaces and ~200 pre and post spaces) my trim takes 1.6 ms, the trim using reverse takes 3.5ms, and Data.Text.strip takes 0.0016 ms. Cheers, Thomas On Tue, Sep 13, 2011 at 8:03 PM, Kazu Yamamoto wrote: > Hello Cafe, > > I would like to have an efficient implementation of the chop function. > As you guess, the chop function drops spaces in the tail of a list. > > chop " foo bar baz " > -> " foo bar baz" > > A naive implementation is as follows: > > chopReverse :: String -> String > chopReverse = reverse . dropWhile isSpace . reverse > > But this is not elegant. foldr version is as follows: > > chopFoldr :: String -> String > chopFoldr = foldr f [] > where > f c [] > | isSpace c = [] > | otherwise = c:[] > f c cs = c:cs > > But this code is slower than chopReverse in some cases. > > Are there any more efficient implementations of chop? Any suggestions? > > --Kazu > > ___ > 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] efficient chop
Hello Cafe, I would like to have an efficient implementation of the chop function. As you guess, the chop function drops spaces in the tail of a list. chop " foo bar baz " -> " foo bar baz" A naive implementation is as follows: chopReverse :: String -> String chopReverse = reverse . dropWhile isSpace . reverse But this is not elegant. foldr version is as follows: chopFoldr :: String -> String chopFoldr = foldr f [] where f c [] | isSpace c = [] | otherwise = c:[] f c cs = c:cs But this code is slower than chopReverse in some cases. Are there any more efficient implementations of chop? Any suggestions? --Kazu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Tupling functions
On Tue, Sep 13, 2011 at 10:03 PM, Chris Smith wrote: > Ah, okay... then sure, you can do this: > > class Tuple a b c | a b -> c where > tuple :: a -> b -> c > > instance Tuple (a -> b, a -> c) a (b,c) where > tuple (f,g) x = (f x, g x) This wouldn't actually work well in practice. There's no dependency between the various occurrences of "a" in the types, so unless they're already known to be the same, GHC will complain about an ambiguous instance (please excuse the silly GHCi prompt): Ok, modules loaded: Tupling. ∀x. x ⊢ tuple ((+3), show) 4 :0:1: No instance for (Tuple (a0 -> a0, a1 -> String) b0 c0) arising from a use of `tuple' Given that the class is only intended to be used where those types are equal, you really want it to unify them based on use of the tuple function. > and so on... You'll need fundeps (or type families if you prefer to > write it that way), and probably at least flexible and/or overlapping > instances, too, but of course GHC will tell you about those. I rather prefer type families in this case, both because the problem is easily expressed in "type function" style, and because it gives you an easy type equality constraint to use, rather than using arcane trickery with overlaps to force post-hoc unification. We'd probably want to do something like this: class Tuple t where type Arg t :: * type Result t :: * tuple :: t -> Arg t -> Result t instance (x1 ~ x2) => Tuple (x1 -> a, x2 -> b) where type Arg (x1 -> a, x2 -> b) = x1 type Result (x1 -> a, x2 -> b) = (a, b) tuple (f, g) x = (f x, g x) instance (x1 ~ x2, x2 ~ x3) => Tuple (x1 -> a, x2 -> b, x3 -> c) where type Arg (x1 -> a, x2 -> b, x3 -> c) = x1 type Result (x1 -> a, x2 -> b, x3 -> c) = (a, b, c) tuple (f, g, h) x = (f x, g x, h x) Used like so: Ok, modules loaded: Tupling. ∀x. x ⊢ tuple ((+2), show, (< 2)) 3 (5,"3",False) Note that not only does this avoid ambiguity, it even unifies ambiguous types that are then defaulted by the usual means. That said, I question the utility of a class like this. The boilerplate instances are tedious to write and it's not flexible in any way; tuples not being defined inductively makes them a real pain to work with unless there's a particularly good reason to do so. Something equivalent to right-nested (,) with () as a terminator is much more pleasant, and since we're deep in the pits of non-portability anyway, might as well pull out bang patterns and UNPACK pragmas if avoiding extra bottoms was the reason for using plain tuples. - C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANNOUNCE] Haskdogs-0.1
On 14 September 2011 11:24, yi huang wrote: > Cabal compains about "Unknown build tool hasktags". > It seems not necessary to set "Build-tools: hasktags" in cabal file? cabal-install isn't capable of automatically building and installing build-tools for you. So to install haskdogs, you need to do "cabal install hasktags && cabal install haskdogs". -- 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] Tupling functions
On Wed, 2011-09-14 at 13:56 +1200, Richard O'Keefe wrote: > I don't *expect* to implement anything just once. I am perfectly > happy writing as many instance declarations as I have tuple sizes > that I care about. Ah, okay... then sure, you can do this: class Tuple a b c | a b -> c where tuple :: a -> b -> c instance Tuple (a -> b, a -> c) a (b,c) where tuple (f,g) x = (f x, g x) and so on... You'll need fundeps (or type families if you prefer to write it that way), and probably at least flexible and/or overlapping instances, too, but of course GHC will tell you about those. -- Chris Smith ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Tupling functions
On 14/09/2011, at 1:44 PM, Chris Smith wrote: > On Wed, 2011-09-14 at 13:35 +1200, Richard O'Keefe wrote: >> I would like to have >> >> tuple (f1,f2) x = (f1 x, f2 x) >> tuple (f1,f2,f3)x = (f1 x, f2 x, f3 x) > There is no polymorphism across tuple structures, I know that. I know how tuples get to be instances of Ix, one instance declaration for each of (,) (,,) (,,,) > so if you absolutely > *must* have n-tuples instead of nested 2-tuples, then you just need to > implement the new functions as needed. You can't implement that only > once. I don't *expect* to implement anything just once. I am perfectly happy writing as many instance declarations as I have tuple sizes that I care about. It's just that I can't see how to get the types right, because in class Thingy t ... where tuple :: t -> a -> b b depends on t and possibly a, so instance Thingy (,,) where tuple (f,g,h) x = (f x, g x, h x) it's not an arbitrary b. Can this be done with functional dependencies? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Tupling functions
On Wed, 2011-09-14 at 13:35 +1200, Richard O'Keefe wrote: > I would like to have > > tuple (f1,f2) x = (f1 x, f2 x) > tuple (f1,f2,f3)x = (f1 x, f2 x, f3 x) > tuple (f1,f2,f3,f4) x = (f1 x, f2 x, f3 x, f4 x) > ... > > I'm aware of Control.Arrow and the &&& combinator, and I can use that > instead, but f1 &&& f2 &&& f3 doesn't have _exactly_ the type I want. > > What should I do? There is no polymorphism across tuple structures, so if you absolutely *must* have n-tuples instead of nested 2-tuples, then you just need to implement the new functions as needed. You can't implement that only once. Plenty of places in base do this, especially for instances. -- Chris Smith ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Tupling functions
I would like to have tuple (f1,f2) x = (f1 x, f2 x) tuple (f1,f2,f3)x = (f1 x, f2 x, f3 x) tuple (f1,f2,f3,f4) x = (f1 x, f2 x, f3 x, f4 x) ... I'm aware of Control.Arrow and the &&& combinator, and I can use that instead, but f1 &&& f2 &&& f3 doesn't have _exactly_ the type I want. What should I do? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] [ANNOUNCE] Haskdogs-0.1
Cabal compains about "Unknown build tool hasktags". It seems not necessary to set "Build-tools: hasktags" in cabal file? On Wed, Sep 14, 2011 at 4:39 AM, Sergey Mironov wrote: > Hi! I am pleased to announce haskdogs - project-level ctag file generator. > > haskdogs is a small shellscript-like tool which creates tag file for > entire haskell project directory. It takes into account first-level > dependencies by recursively scanning imports and adding matching > packages to the final tag list. As a result, programmer can use > his/her text editor supporting tags (vim, for example) to jump > directly to definition of any standard or foreign function he/she > uses. Note, that haskdogs calls some Unix shell commands like test or > mkdir so this tool will likely fail to work on pure Windows platforms. > > To use it, do > > 0) cabal install hasktags haskdogs && mkdir -p ~/.cabal/var/haskdogs > 1) cabal unpack TrickyProject-4.2 && cd TrickyProject-4.2 > 2) haskdogs > 3) enjoy the tagfile with references to every function > > http://hackage.haskell.org/package/haskdogs-0.1 > > Sergey > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- http://www.yi-programmer.com/blog/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Categorized Weaknesses from the State of Haskell 2011 Survey
I would appreciate is a few paragraphs in the toplevel haddock page or module that describe the general architecture and layout of the modules, as well as the typical entry points. Since the module system doesn't have a notion of private modules and it's common to re-export symbols, it can be unclear where to start, which modules to look at, and why it is the author chose that particular decomposition for the functions. Overall design and architecture is hard to get out of the code. I think the same goes for each module. It's frustrating when I want to figure out how something works, and each module just has a giant chunk of license copy-paste at the top. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell 101 on classes .... duh ..... :^)
Hi Brandon, Here is Ivan's web site. http://ivanmiljenovic.wordpress.com/ .. I have written in Haskell before ... a POSIX Realtime hackage package. It is true I am little rusty now because industry is too stubborn except in places like Silicon Valley, Wall Street, Virginia (defence industry) to use FPLs ... have to pay the bills sadly... Vasili On Tue, Sep 13, 2011 at 9:57 AM, Brandon Allbery wrote: > On Tue, Sep 13, 2011 at 00:08, Vasili I. Galchin wrote: > >> I am trying to model multigraphs but getting errors with ghci >> and can't figure out why I have a serious blind spot >> > > Why do you need to use classes for this? (Note: forget everything you > know about classes from OOP. Haskell typeclasses have approximately nothing > to do with OOP.) > > junk1.hs:19:12: >> Constructor `Arrow' should have 1 argument, but has been given 0 >> In the pattern: Arrow >> In the definition of `source': source Arrow = fst Arrow >> In the instance declaration for `Graph Arrow Int' >> > > It's asking "Arrow *what*?" You specified Arrow as taking a tuple > argument; if you want to use it here, you need to provide that argument (or > a placeholder, but in this case you clearly want the tuple). > > > source (Arrow p) = fst p > > target (Arrow p) = snd p > > Or you can use pattern matching to deconstruct the tuple as well: > > > source (Arrow (f,_)) = f > > target (Arrow (_,t)) = t > > -- > brandon s allbery allber...@gmail.com > wandering unix systems administrator (available) (412) 475-9364 vm/sms > > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Categorized Weaknesses from the State of Haskell 2011 Survey
On Sep 13, 2011, at 7:38 PM, Michael Orlitzky wrote: > >> One thing I am puzzled about, is just how extremely difficult it must >> be, to click on "Detailed documentation of the HaXml APIs" from the >> HaXml homepage, look for a moment until you see >> "Text.XML.HaXml.Parse" in the list of modules, click on it, and find, >> right at the top of the page, a function that parses a String into an >> XML document tree. > > As someone who just wants to parse an XML file, here's what happens. > First, I click on the API docs. I'm presented with a list: > >* Text > o XML >+ Text.XML.HaXml > # Text.XML.HaXml.ByteStringPP > # Text.XML.HaXml.Combinators > # DtdToHaskell >* Text.XML.HaXml.DtdToHaskell.Convert > I think you make an important point here. As a beginner myself, I am often surprised by the sparse first impression of modules that hackage offers. To a beginner, the one sentence introduction often using domain-specific language is thwarting. Compare hackage to CPAN or Sphinx documentation which present pages of examples covering all programmer-visible interfaces and the difference is clear: hackage is a module repository first and a documentation browser last. Cheers, M ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Categorized Weaknesses from the State of Haskell 2011 Survey
On 09/13/2011 05:15 PM, Malcolm Wallace wrote:
>
> I am the first to admit that HaXml's documentation is not as good as
> it could be, and I am sorry that you have had a bad experience.
Sorry for the tirade =) That was a while ago, but I definitely felt some
sympathy for the guy in the quote.
> One thing I am puzzled about, is just how extremely difficult it must
> be, to click on "Detailed documentation of the HaXml APIs" from the
> HaXml homepage, look for a moment until you see
> "Text.XML.HaXml.Parse" in the list of modules, click on it, and find,
> right at the top of the page, a function that parses a String into an
> XML document tree.
As someone who just wants to parse an XML file, here's what happens.
First, I click on the API docs. I'm presented with a list:
* Text
o XML
+ Text.XML.HaXml
# Text.XML.HaXml.ByteStringPP
# Text.XML.HaXml.Combinators
# DtdToHaskell
* Text.XML.HaXml.DtdToHaskell.Convert
* Text.XML.HaXml.DtdToHaskell.Instance
* Text.XML.HaXml.DtdToHaskell.TypeDef
# Text.XML.HaXml.Escape
# Html
* Text.XML.HaXml.Html.Generate
* Text.XML.HaXml.Html.Parse
* Text.XML.HaXml.Html.ParseLazy
* Text.XML.HaXml.Html.Pretty
# Text.XML.HaXml.Lex
# Text.XML.HaXml.Namespaces
# Text.XML.HaXml.OneOfN
# Text.XML.HaXml.Parse
# Text.XML.HaXml.ParseLazy
# Text.XML.HaXml.Posn
# Text.XML.HaXml.Pretty
# Text.XML.HaXml.SAX
# Schema
* Text.XML.HaXml.Schema.Environment
* Text.XML.HaXml.Schema.HaskellTypeModel
* Text.XML.HaXml.Schema.NameConversion
* Text.XML.HaXml.Schema.Parse
* Text.XML.HaXml.Schema.PrettyHaskell
* Text.XML.HaXml.Schema.PrimitiveTypes
* Text.XML.HaXml.Schema.Schema
* Text.XML.HaXml.Schema.TypeConversion
* Text.XML.HaXml.Schema.XSDTypeModel
# Text.XML.HaXml.ShowXmlLazy
# Text.XML.HaXml.TypeMapping
# Text.XML.HaXml.Types
# Text.XML.HaXml.Util
# Text.XML.HaXml.Validate
# Text.XML.HaXml.Verbatim
# Text.XML.HaXml.Wrappers
# Text.XML.HaXml.XmlContent
* Text.XML.HaXml.XmlContent.Haskell
* Text.XML.HaXml.XmlContent.Parser
# Xtract
* Text.XML.HaXml.Xtract.Combinators
* Text.XML.HaXml.Xtract.Lex
* Text.XML.HaXml.Xtract.Parse
Jesus! /You/ know that I want to look in Text.XML.HaXml.Parse, but /I/
don't. Let's say I choose the first link: Text.XML.HaXml. It's a list of
modules, along with their documentation. All blank! Hitting the back button.
The first thing I notice is that there seems to be specialized parser
modules for different content types, e.g. Text.XML.HaXml.Html.Parse.
Maybe I want Text.XML.HaXml.Schema.Parse? I mean, I want to parse
something with a schema, right? Nope, it's for parsing XSDs.
How about Text.XML.HaXml.Util? This looks right...
Only a small module containing some helper functions to extract xml
content - I would have added this to Types but I've put it into an
additional module - to avoid circular references (Verbatim - Types)
and it's got a function called docContent which is supposed to "Get the
main element of the document..." Great. Its type is,
docContent :: i -> Document i -> Content i
so now, to have any hope of using this function (or figure out that I'm
in the wrong place entirely), I have to go figure out what those types
are. Document has one constructor,
Document Prolog (SymTab EntityDef) (Element i) [Misc]
which leads me to,
Prolog (Maybe XMLDecl) [Misc] (Maybe DocTypeDecl) [Misc]
XMLDecl VersionInfo (Maybe EncodingDecl) (Maybe SDDecl)
type VersionInfo = String
newtype EncodingDecl = EncodingDecl String
type SDDecl = Bool
data Misc = Comment Comment | PI ProcessingInstruction
type Comment = String
type ProcessingInstruction = (PITarget, String)
type PITarget = String
data DocTypeDecl = DTD QName (Maybe ExternalID) [MarkupDecl]
data QName = N Name | QN Namespace Name
type Name = String
data Namespace = Namespace {nsPrefix :: String, nsURI :: String}
data External
Re: [Haskell-cafe] Categorized Weaknesses from the State of Haskell 2011 Survey
+1 for Heinrich Apfelmus's suggestion of cookbook recipes. In other language communities I see a lot of "quickstart" guides designed to help someone get up and running without a full understanding of what they're doing, presumably with the hope that once they get started it will provide the motivation to keep learning. But admittedly, and for good reason, learning the how without the why seems to run counter to the general mentality of the Haskell community. For widely used libraries it'd be nice to a see a supporting wiki page broken into sections like conceptual overview, how to navigate the API if it's extensive, tutorials, and cookbook recipes. Motivating the community to contribute supporting documentation could alleviate some of the burden for library writers. Frequently updated and extensive community docs can also help newcomers decide which library to start with for a given task, rather than relying purely on Hackage descriptions. I'm slowly assembling supporting docs of this kind for the libraries I use the most, and if anyone is working on something similar I'm happy to help by trying out the tutorials and giving feedback. Thanks! Eric On Tue, Sep 13, 2011 at 2:15 PM, Malcolm Wallace wrote: > > On 13 Sep 2011, at 18:59, Michael Orlitzky wrote: > > >> Malcolm Wallace and Colin Runciman's ICFP99 paper functioned well as a > >> tutorial for HaXml when I used it - maybe it is a bit out of date now? > >> HaXml is hardly a dire case. > > > > The paper is out-of-date, so it's worse than useless: you'll waste your > > time figuring out that it's wrong, and you still won't know how to do > > anything. > > > > There's not one single example anywhere that just shows you how to read > > or write a damned XML file. > > If there were anything approaching a physical manifestation of HaXml, I > > would've strangled it. > > I am the first to admit that HaXml's documentation is not as good as it > could be, and I am sorry that you have had a bad experience. > > One thing I am puzzled about, is just how extremely difficult it must be, > to click on "Detailed documentation of the HaXml APIs" from the HaXml > homepage, look for a moment until you see "Text.XML.HaXml.Parse" in the list > of modules, click on it, and find, right at the top of the page, a function > that parses a String into an XML document tree. > > It is absolutely true that finding the reverse conversion (XML tree to > String) is more obscure, being either the two-stage process of first using > "Text.XML.HaXml.Pretty" to convert to a Doc, then > "Text.PrettyPrint.HughesPJ" to render to a String; or alternatively the > one-shot conversion in "Text.XML.HaXml.Verbatim". Neither module name is as > clear as it should be for a beginner, but I can't think of better ones. > Plus, it requires some knowledge of the ecosystem, for instance that > pretty-printing is a common technique for producing textual output. > > In fact, my wish as a library author would be: please tell me what you, as > a beginner to this library, would like to do with it when you first pick it > up? Then perhaps I could write a tutorial that answers the questions people > actually ask, and tells them how to get the stuff done that they want to do. > I have tried writing documentation, but it seems that people do not know > how to find, or use it. Navigating an API you do not know is hard. I'd > like to signpost it better. > > Regards, > Malcolm > > ___ > 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] regex-applicative library needs your help! (algorithmic challenge)
* Roman Cheplyaka [2011-09-14 00:29:55+0300] > Then there's another issue: I specifically want a combinator library, > and not every automaton-based algorithm can serve this purpose in a > statically typed language (unless there's some clever trick I don't > know). Just to clarify: by "clever" trick I don't mean a "dirty" trick, like using unsafeCoerce in frisby[1]. I guess I'm just too young and naive to use that kind of stuff. Glushkov automaton is nice because it can be used to implement parsing combinators in pure Haskell + GADTs. [1]: http://hackage.haskell.org/packages/archive/frisby/0.1/doc/html/src/Text-Parsers-Frisby.html -- Roman I. Cheplyaka :: http://ro-che.info/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] regex-applicative library needs your help! (algorithmic challenge)
* Chris Kuklewicz [2011-09-13 08:21:55+0100] > I wrote regex-tdfa, the efficient (though not yet lightning fast) Posix-like > engine. > > You are not the first to want an efficient Perl-like engine. The answer you > seek flows from Russ Cox (though in C++): > > > http://google-opensource.blogspot.com/2010/03/re2-principled-approach-to-regular.html > > > http://code.google.com/p/re2/ > > Quoting relevant bit: > > > It also finds the leftmost-first match, the same match that Perl would, and > > can return submatch information. The one significant exception is that RE2 > > drops support for backreferences¹ and generalized zero-width assertions, > > because they cannot be implemented efficiently. Hi Chris, thanks for the response. There's one thing about Cox's work that I don't understand. On the page [1] he mentions that the algorithm falls back to direct NFA simulation (search for "If all else fails" on that page). This defeats his goal of defending against DoS attacks (the second paragraph of that page). And I wouldn't be comfortable with an algorithm that is worst-case exponential either. Then there's another issue: I specifically want a combinator library, and not every automaton-based algorithm can serve this purpose in a statically typed language (unless there's some clever trick I don't know). [1]: http://swtch.com/~rsc/regexp/regexp3.html -- Roman I. Cheplyaka :: http://ro-che.info/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Categorized Weaknesses from the State of Haskell 2011 Survey
On 13 Sep 2011, at 18:59, Michael Orlitzky wrote: >> Malcolm Wallace and Colin Runciman's ICFP99 paper functioned well as a >> tutorial for HaXml when I used it - maybe it is a bit out of date now? >> HaXml is hardly a dire case. > > The paper is out-of-date, so it's worse than useless: you'll waste your > time figuring out that it's wrong, and you still won't know how to do > anything. > > There's not one single example anywhere that just shows you how to read > or write a damned XML file. > If there were anything approaching a physical manifestation of HaXml, I > would've strangled it. I am the first to admit that HaXml's documentation is not as good as it could be, and I am sorry that you have had a bad experience. One thing I am puzzled about, is just how extremely difficult it must be, to click on "Detailed documentation of the HaXml APIs" from the HaXml homepage, look for a moment until you see "Text.XML.HaXml.Parse" in the list of modules, click on it, and find, right at the top of the page, a function that parses a String into an XML document tree. It is absolutely true that finding the reverse conversion (XML tree to String) is more obscure, being either the two-stage process of first using "Text.XML.HaXml.Pretty" to convert to a Doc, then "Text.PrettyPrint.HughesPJ" to render to a String; or alternatively the one-shot conversion in "Text.XML.HaXml.Verbatim". Neither module name is as clear as it should be for a beginner, but I can't think of better ones. Plus, it requires some knowledge of the ecosystem, for instance that pretty-printing is a common technique for producing textual output. In fact, my wish as a library author would be: please tell me what you, as a beginner to this library, would like to do with it when you first pick it up? Then perhaps I could write a tutorial that answers the questions people actually ask, and tells them how to get the stuff done that they want to do. I have tried writing documentation, but it seems that people do not know how to find, or use it. Navigating an API you do not know is hard. I'd like to signpost it better. Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Haskell] [ANNOUNCE] Haskdogs-0.1
Hi! I am pleased to announce haskdogs - project-level ctag file generator. haskdogs is a small shellscript-like tool which creates tag file for entire haskell project directory. It takes into account first-level dependencies by recursively scanning imports and adding matching packages to the final tag list. As a result, programmer can use his/her text editor supporting tags (vim, for example) to jump directly to definition of any standard or foreign function he/she uses. Note, that haskdogs calls some Unix shell commands like test or mkdir so this tool will likely fail to work on pure Windows platforms. To use it, do 0) cabal install hasktags haskdogs && mkdir -p ~/.cabal/var/haskdogs 1) cabal unpack TrickyProject-4.2 && cd TrickyProject-4.2 2) haskdogs 3) enjoy the tagfile with references to every function http://hackage.haskell.org/package/haskdogs-0.1 Sergey ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Question about type families
On Tue, Sep 13, 2011 at 4:58 PM, Grigory Sarnitskiy wrote:
> Is there a way to make the following code working?
>
> {-# LANGUAGE TypeFamilies #-}
>
> data family Foo a
>
> data instance (Num a) => Foo a = A a deriving Show
>
> data instance (Fractional a) => Foo a = B a deriving Show
>
>
> I want to have different constructors for 'Foo a' depending on a class of
> 'a'. Note also, that in the example above I also meant constructor A to be
> available for (Fractional a) => Foo, since in that case 'a' has Num too. How
> can I achieve it, maybe not with TypeFamilies?
Thinking further... just guessing, but maybe you want a GADT?
data Foo a where
FooN :: Num a => a -> Foo a
FooF :: Fractional a => a -> Foo a
You use FooF for Fractionals, and either one for Nums. 'a' is required
to be an instance of the class, and the instance is made available
when pattern matching on the constructor (unlike with datatype
contexts). But, as I said, automating the choice based on whether 'a'
is or is not an instance of Fractional is impossible.* You have to
specify it explicitly.
* You can probably do it with Template Haskell, but you probably don't want to.
--
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Re: [Haskell-cafe] Question about type families
On Tue, Sep 13, 2011 at 4:58 PM, Grigory Sarnitskiy wrote:
> Is there a way to make the following code working?
>
> {-# LANGUAGE TypeFamilies #-}
>
> data family Foo a
>
> data instance (Num a) => Foo a = A a deriving Show
>
> data instance (Fractional a) => Foo a = B a deriving Show
>
>
> I want to have different constructors for 'Foo a' depending on a class of
> 'a'. Note also, that in the example above I also meant constructor A to be
> available for (Fractional a) => Foo, since in that case 'a' has Num too. How
> can I achieve it, maybe not with TypeFamilies? Current error is
>
> Conflicting family instance declarations:
> data instance Foo a -- Defined at 1.hs:7:33-35
> data instance Foo a -- Defined at 1.hs:5:33-35
Directly, with current GHC? Doubly, maybe triply impossible. Type and
data families aren't allowed to overlap, and there's no way to
dispatch over whether a type is or is not a member of a class. (You
can require that it be a member, but you can't say "if not, do this
other thing"). Also, you can't give type and data families superclass
contexts the way you can classes. I haven't actually encountered this
before, but I think that what you've written here is datatype contexts
for the various instances of the data family, which means you can only
construct a 'Foo a' if the 'a' is a member of the class - but it in no
way affects which instance is chosen. Datatype contexts are considered
a misfeature, besides.[1]
Anyway. What's your wider goal?
[1] http://hackage.haskell.org/trac/haskell-prime/wiki/NoDatatypeContexts
>
> ___
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
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>
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Re: [Haskell-cafe] Categorized Weaknesses from the State of Haskell 2011 Survey
On 09/12/11 17:48, Stephen Tetley wrote: > Replying to someone's compliant in the first section: > > Malcolm Wallace and Colin Runciman's ICFP99 paper functioned well as a > tutorial for HaXml when I used it - maybe it is a bit out of date now? > HaXml is hardly a dire case. The paper is out-of-date, so it's worse than useless: you'll waste your time figuring out that it's wrong, and you still won't know how to do anything. There's not one single example anywhere that just shows you how to read or write a damned XML file. HaXml is what prompted me to start this page (bad language warning, if it ain't obvious): http://michael.orlitzky.com/articles/fuck_you.php If there were anything approaching a physical manifestation of HaXml, I would've strangled it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Question about type families
Is there a way to make the following code working?
{-# LANGUAGE TypeFamilies #-}
data family Foo a
data instance (Num a)=> Foo a = A a deriving Show
data instance (Fractional a) => Foo a = B a deriving Show
I want to have different constructors for 'Foo a' depending on a class of 'a'.
Note also, that in the example above I also meant constructor A to be available
for (Fractional a) => Foo, since in that case 'a' has Num too. How can I
achieve it, maybe not with TypeFamilies? Current error is
Conflicting family instance declarations:
data instance Foo a -- Defined at 1.hs:7:33-35
data instance Foo a -- Defined at 1.hs:5:33-35
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Re: [Haskell-cafe] Haskell 101 on classes .... duh ..... :^)
On Tue, Sep 13, 2011 at 00:08, Vasili I. Galchin wrote: > I am trying to model multigraphs but getting errors with ghci and > can't figure out why I have a serious blind spot > Why do you need to use classes for this? (Note: forget everything you know about classes from OOP. Haskell typeclasses have approximately nothing to do with OOP.) junk1.hs:19:12: > Constructor `Arrow' should have 1 argument, but has been given 0 > In the pattern: Arrow > In the definition of `source': source Arrow = fst Arrow > In the instance declaration for `Graph Arrow Int' > It's asking "Arrow *what*?" You specified Arrow as taking a tuple argument; if you want to use it here, you need to provide that argument (or a placeholder, but in this case you clearly want the tuple). > source (Arrow p) = fst p > target (Arrow p) = snd p Or you can use pattern matching to deconstruct the tuple as well: > source (Arrow (f,_)) = f > target (Arrow (_,t)) = t -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't resolve class dependences (making Boolean class)
Thank you all guys, fromBool did the trick. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't resolve class dependences (making Boolean class)
The problem is that an implementation of (===) must return a result of type b for *any* type b which is an instance of Boolean. For example, if I made data X = A | B instance Boolean X where ... then I would be able to have: eqX :: MyEq a => a -> a -> X eqX = (===) That's all fine and probably the reason why you are going through these hoops. However, look at your definition for MyEq Bool: a === b = a == b Now, "a == b" has type Bool. What would happen if I wanted an X instead? You would need something like class Boolean a where (/\) :: a -> a -> a fromBool :: Bool -> a Your instance would then become instance MyEq Bool where a === b = fromBool (a == b) You may want to take a look at the Awesome Prelude [1], which implement this and much more. Cheers! =) [1] https://github.com/tomlokhorst/AwesomePrelude -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't resolve class dependences (making Boolean class)
On 13 September 2011 23:04, Grigory Sarnitskiy wrote: > Hello! I'm trying to have a class for booleans called Boolean (the methods > are not complete): > > class MyEq a where > (===) :: (Boolean b) => a -> a -> b This means that === potentially returns _any_ instance of Boolean. Let's say for example that I define "data MyBool = T | F" and make it an instance of MyEq and Boolean. That means that T === F must be able to return either a Bool, MyBool or any other instance of Boolean that the _caller_ chooses. If this is what you want, then I suggest that you do something like: class (MyEq a) => Boolean a where (/\) :: a -> a -> a fromBool :: Bool -> a Then the instance becomes: instance MyEq Bool where x === y = fromBool $ x==y instance Boolean Bool where (/\) = (&&) fromBool = id -- 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] Can't resolve class dependences (making Boolean class)
Hello! I'm trying to have a class for booleans called Boolean (the methods are not complete): class MyEq a where (===) :: (Boolean b) => a -> a -> b class (MyEq a) => Boolean a where (/\) :: a -> a -> a instance MyEq Bool where x === y = x==y instance Boolean Bool where (/\) = (&&) However, to make Bool an instance of Boolean I need to make it an instance of MyEq first, which I can't, because to define === I need Bool to be in Boolean. Indeed the code above give the error: Could not deduce (b ~ Bool) from the context (Boolean b) bound by the type signature for === :: Boolean b => Bool -> Bool -> b at 1.hs:8:5-18 `b' is a rigid type variable bound by the type signature for === :: Boolean b => Bool -> Bool -> b at 1.hs:8:5 In the expression: x == y In an equation for `===': x === y = x == y In the instance declaration for `MyEq Bool' Failed, modules loaded: none. How can I overcome the issue? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Categorized Weaknesses from the State of Haskell 2011 Survey
Stephen Tetley wrote: Replying to someone's compliant in the first section: Malcolm Wallace and Colin Runciman's ICFP99 paper functioned well as a tutorial for HaXml when I used it - maybe it is a bit out of date now? HaXml is hardly a dire case. ... for the right audience. I guess the point is that the person complaining could not understand the existing documentation. Quote: "This type of documentation may seem to “fall out” from a mathematically-oriented understanding of the library (such as haxml’s combinator scheme, or the concept of “lenses” in fclabels), but an application programmer does not have time to work through proofs of lens properties and then figure out what they might be good for in a program. Instead, the application programmer needs cookbook-style documentation to get something up and running, and then s/he can come to understand and make use of the underlying math." I'm not sure whether it's the job of library documentation to teach mathematical understanding, but cookbook-style examples seem very valuable to me. For instance, I think that the Happstack tutorial http://happstack.com/docs/crashcourse/index.html is excellent in this regard. (Personally, a good method for writing this kind of stuff is to assume that the reader has almost zero attention span. Then, I am forced to communicate the most useful points in the first few paragraphs, because my hypothetical reader probably won't read any further than that. Of course, the resulting text will be very useful to readers with a high attention span, too.) Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] regex-applicative library needs your help! (algorithmic challenge)
I wrote regex-tdfa, the efficient (though not yet lightning fast) Posix-like engine. You are not the first to want an efficient Perl-like engine. The answer you seek flows from Russ Cox (though in C++): > http://google-opensource.blogspot.com/2010/03/re2-principled-approach-to-regular.html > http://code.google.com/p/re2/ Quoting relevant bit: > It also finds the leftmost-first match, the same match that Perl would, and > can return submatch information. The one significant exception is that RE2 > drops support for backreferences¹ and generalized zero-width assertions, > because they cannot be implemented efficiently. On 13/09/2011 06:40, Roman Cheplyaka wrote: > Please help make the regex-based parsing library efficient! > > https://github.com/feuerbach/regex-applicative/wiki/Call-For-Help > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
