Re: [Haskell-cafe] Categorical description of systems with dependent types
On 12/2/10 4:47 PM, Iavor Diatchki wrote: Hi, You have it exactly right, and I don't think that there's a particularly deep reason to prefer the one over the other. It seems that computer science people tend to go with the (product-function) terminology, while math people seem to prefer the (sum-product) version, but it is all largely a matter of taste. The product=function,sum=pair terminology comes from a certain interpretation of dependent types in set theory. I believe this originated with Per Martin-Löf's work, though I don't have any citations on hand. That terminology conflicts with the standard product=pair,sum=either terminology of functional languages, however. So folks from a functional background tend to prefer: dependent function, dependent product, sum; whereas folks from a set-theoretic background tend to prefer product, sum, /union. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type families again
On Thu, 2 Dec 2010, Robert Greayer wrote:
On Thu, Dec 2, 2010 at 4:39 PM, Antoine Latter wrote:
On Thu, Dec 2, 2010 at 3:29 PM, Andrew Coppin
wrote:
What we /can't/ do is define a polymorphic map function. One might try to do
something like
class Functor f where
type Element f :: *
fmap :: (Element f2 ~ y) => (x -> y) -> f -> f2
instance Functor [x] where
type Element [x] = x
fmap = map
However, this fails. Put simply, the type for fmap fails to specify that f
and f2 must be /the same type of thing/, just with different element types.
The trouble is, after spending quite a bit of brainpower, I literally cannot
think of a way of writing such a constraint. Does anybody have any
suggestions?
Does this do what you need?
http://hackage.haskell.org/packages/archive/rmonad/0.6/doc/html/Control-RMonad.html#t:RFunctor
Antoine
I think this doesn't handle the ByteString case (wrong kind). Here's
another mostly unsatisfactory (injectivity issues) solution that may
possibly not even work though it does compile:
I spent a while looking at this a couple of months ago after a similar
question. What I came up with is below; I haven't got as far as
deciding whether or how to incorporate this into rmonad. Also, the Const
type actually already exists in Control.Applicative.
Cheers,
Ganesh
{-# LANGUAGE GADTs, TypeFamilies, MultiParamTypeClasses, FlexibleInstances,
ScopedTypeVariables, RankNTypes #-}
module Control.RMonad.Wibble where
import Control.RMonad
import Data.ByteString (ByteString)
import qualified Data.ByteString as BS
import qualified Data.ByteString.Char8 as BSC
import Data.Suitable
import GHC.Word (Word8)
-- Part I
-- a little warmup: ByteStrings
-- We have two choices for BSWrapper. Either make
-- it a GADT, which means we can leave out the match on the
-- argument constraints below, or make it a H98 phantom.
-- The second option seems cleaner and more symmetric.
-- It also means we can us newtype to avoid runtime overhead.
-- data BSWrapper a where
-- BSWrapper :: ByteString -> BSWrapper Word8
newtype BSWrapper a = BSWrapper ByteString
data instance Constraints BSWrapper a = (a ~ Word8) => BSConstraints
instance Suitable BSWrapper Word8 where
constraints = BSConstraints
instance RFunctor BSWrapper where
-- We could also use withResConstraints by rearranging the arguments to mymap
so Constraints is last
fmap = mymap constraints constraints
where mymap :: forall x y . Constraints BSWrapper x -> Constraints BSWrapper y -> (x
-> y) -> BSWrapper x -> BSWrapper y
mymap BSConstraints BSConstraints f (BSWrapper x) = BSWrapper (BS.map
f x)
-- Part II
-- OK, now let's generalise:
-- Having a class here rather than a plain type family isn't really necessary,
-- but it feels natural
class SingletonContainer c where
type ContainedType c :: *
-- data SingletonWrapper c a where
-- SingletonWrapper :: SingletonContainer c => c -> SingletonWrapper c
(ContainedType c)
-- This is just a generic Const type. Is there a standard one somewhere else?
newtype SingletonWrapper c a = SingletonWrapper c
data instance Constraints (SingletonWrapper c) a = (a ~ ContainedType c) =>
SingletonConstraints
-- important to use the type equality constraint here instead of inlining it
-- on the RHS, as otherwise instance resolution would get stuck
instance (a ~ ContainedType c) => Suitable (SingletonWrapper c) a where
constraints = SingletonConstraints
class SingletonContainer c => Mappable c where
lmap :: (ContainedType c -> ContainedType c) -> c -> c
instance Mappable c => RFunctor (SingletonWrapper c) where
fmap = mymap constraints constraints
where mymap :: forall x y
. Constraints (SingletonWrapper c) x
-> Constraints (SingletonWrapper c) y
-> (x -> y)
-> SingletonWrapper c x
-> SingletonWrapper c y
mymap SingletonConstraints SingletonConstraints f (SingletonWrapper
x) = SingletonWrapper (lmap f x)
-- so, why is Word8 the blessed instance? Why not Char (from
Data.ByteString.Char8)?
instance SingletonContainer ByteString where
type ContainedType ByteString = Word8
-- Part III
-- and finally, let's try to generalise the Singleton concept:
-- using the Const concept again...
newtype Const a b = Const a
instance Show a => Show (Const a b) where
show (Const x) = show x
data instance Constraints (Const ByteString) a =
(a ~ Word8) => BSConstraintsWord8
| (a ~ Char) => BSConstraintsChar
instance Suitable (Const ByteString) Word8 where
constraints = BSConstraintsWord8
instance Suitable (Const ByteString) Char where
constraints = BSConstraintsChar
instance RFunctor (Const ByteString) where
fmap = mymap constraints constraints
where mymap :: forall x y
. Constraints (Const ByteString) x
-> Constraints (Const ByteString) y
-> (x -> y) -> Const ByteString x -> Const ByteString y
Re: [Haskell-cafe] Digests
2010/12/4 Permjacov Evgeniy : >> near cryptographic) security. To quote Wikipedia again: "The avalanche >> effect is evident if, when an input is changed slightly (for example, >> flipping a single bit) the output changes significantly (e.g., half >> the output bits flip)." > This simply means, that active set of bits must be at least of the size > of final value and value to be added must be added somehow to every byte > in active set. The simplest way to do it is multiplication of vector > [active-state-bits++current-byte] and some matrix of size [resulting > bytes count|resulting bytes count + 1] (of cource, not in floating-point > math, but, for example, using modulo-256 arithmetic or even hand-coded > tables for "mul" and "sum"). This, of course, means, that byte-streaming > hashes needs some initial seed (that must be paired with resulting value > to check) and that every byte will cause much operations to perform, > resulting in poor performance. So, the conclusion is: byte-streaming > hashes are possible, but because of requirements definitly will have > poor performance, much worse then block ones. Am I correct? I think you are correct. PS The note about matrices is interesting one. The total matrix should be dense, but we could factor it. For example, by multiplying two N wide and M wide band matrices we will get (N+M) wide band matrix. You are free to choose multiplication and addition operations, like addition could be XOR and multiplication could be ROTATE_LEFT (like in RC5). I did a little experiment: http://thesz.mskhug.ru/svn/cryptomatrix/ Just to demonstrate interesting properties of your suggestion. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Digests
On 12/03/2010 11:40 AM, Serguey Zefirov wrote: > 2010/12/3 Permjacov Evgeniy : */me wrote it into to_read list. The problem is, however, that block ciphers are quite unfriendly to plain word8 streams. It is not a deadly problem, but i'd like to avoid block collections. >>> All one-way hashes do block collections. This is unavoidable. >> Why ? Is there some math behind this proposition ? > This is hard - to add single byte into the sum with cryptographic (or > near cryptographic) security. To quote Wikipedia again: "The avalanche > effect is evident if, when an input is changed slightly (for example, > flipping a single bit) the output changes significantly (e.g., half > the output bits flip)." This simply means, that active set of bits must be at least of the size of final value and value to be added must be added somehow to every byte in active set. The simplest way to do it is multiplication of vector [active-state-bits++current-byte] and some matrix of size [resulting bytes count|resulting bytes count + 1] (of cource, not in floating-point math, but, for example, using modulo-256 arithmetic or even hand-coded tables for "mul" and "sum"). This, of course, means, that byte-streaming hashes needs some initial seed (that must be paired with resulting value to check) and that every byte will cause much operations to perform, resulting in poor performance. So, the conclusion is: byte-streaming hashes are possible, but because of requirements definitly will have poor performance, much worse then block ones. Am I correct? > http://en.wikipedia.org/wiki/Avalanche_effect > > This is true for hashes too. Hash should change about half of the > random output bits when single bit of input changes. Especially if you > aim to tamper-proof hashes. You have to have that property on every > round of hashing, because you don't know when to stop. For bytes, you > have to guarantee that you get an avalanche effect for every byte - it > means, that you have to transform your entire block plus input byte in > an expensive way. MD5 and all other hashes have internal state of > various size, they all keep input blocks to make hashing transform > less expensive. > > Fast methods like sum-modulo-poly (CRC variants) or linear > congruential generators do not have good avalanche property when used > for stream hashing or encryption. Even their combination (one in ZIP > encryption) wasn't strong enough. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bifold: a simultaneous foldr and foldl
On 12/01/10 21:35, Larry Evans wrote:
> On 11/30/10 13:43, Noah Easterly wrote:
[snip]
>> Thanks, Larry, this is some interesting stuff.
>>
>> I'm not sure yet whether Q is equivalent - it may be, but I haven't been
>> able to thoroughly grok it yet.
>>
[snip]
>
> Hi Noah,
>
> The attached is my attempt at reproducing your code and also
> contains an alternative attempt at emulating the code in
> section 12.5 of:
>
> http://www.thocp.net/biographies/papers/backus_turingaward_lecture.pdf
>
The attached code is a revision of my previous if_recur attempt
at emulated the section 12.5 code. This revision added the i
function from the seciton 12.5 (instead of delegating that
task to the h function). The 2nd attachment shows the output.
It shows that by modifying the args to if_recur, you can
reproduce the output from foldl or foldr.
{-
Purpose:
create a function, if_recur, like the f in section 12.5 of:
[BAC77]
http://www.thocp.net/biographies/papers/backus_turingaward_lecture.pdf
-}
module IfRecur where
-- {*if_recur
if_recur :: state_down
-> (state_down -> Bool)
-> (state_down -> state_down)
-> (state_down -> state_saved)
-> ((state_saved,state_up) -> state_up)
-> (state_down -> state_up)
-> state_up
if_recur state_now -- current state
recur_ -- continue recursion?
then_down -- ::state_down -> state_down
save_state -- ::state_down -> state_saved
now_up -- ::((state_saved,state_up)->state_up
else_ -- ::state_down -> state_up
{- The following table shows the corresponndence
between the f in section 12.5 of [BAC77]
and the arguments to this function:
[BAC77] [if_recur]
=== ==
p recur_
g else_
j then_down
i save_state
h now_up
-}
= if recur_ state_now
then now_up
( save_state state_now
, if_recur (then_down state_now)
recur_
then_down
save_state
now_up
else_
)
else else_ state_now
-- }*if_recur
{--}
palindrome :: [a] -> [a]
palindrome x = if_recur
(x,[]) --state_now
(not.null.fst) --recur_
(\(sn,cd) -> (tail sn,(head sn):cd)) --then_down
(\(sn,cd) -> head sn) --save_state
(\(ss,cu) -> ss:cu) --now_up
(\(sn,cd) -> cd) --else_
if_recur_foldl :: [a] -> [a]
if_recur_foldl x = if_recur
(x,[]) --state_now
(not.null.fst) --recur_
(\(sn,cd) -> (tail sn,(head sn):cd)) --then_down
(\(sn,cd) -> ()) --save_state
(\(ss,cu) -> cu) --now_up
(\(sn,cd) -> cd) --else_
if_recur_foldr :: [a] -> [a]
if_recur_foldr x = if_recur
(x,[]) --state_now
(not.null.fst) --recur_
(\(sn,cd) -> (tail sn,cd)) --then_down
(\(sn,cd) -> head sn) --save_state
(\(ss,cu) -> ss:cu) --now_up
(\(sn,cd) -> cd) --else_
test = sequence
[ print "palindrome [1,2,3]:"
, print (palindrome [1,2,3])
, print "if_recur_foldl [1,2,3]:"
, print (if_recur_foldl [1,2,3])
, print "(foldl (flip(:)) [] [1,2,3]):"
, print (foldl (flip(:)) [] [1,2,3])
, print "if_recur_foldr [1,2,3]:"
, print (if_recur_foldr [1,2,3])
, print "(foldr (:) [] [1,2,3]):"
, print (foldr (:) [] [1,2,3])
]
{--}
/home/evansl/prog_dev/haskell/my-code $ ghci IfRecur.hs
GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling IfRecur ( IfRecur.hs, interpreted )
Ok, modules loaded: IfRecur.
*IfRecur> test
"palindrome [1,2,3]:"
[1,2,3,3,2,1]
"if_recur_foldl [1,2,3]:"
[3,2,1]
"(foldl (flip(:)) [] [1,2,3]):"
[3,2,1]
"if_recur_foldr [1,2,3]:"
[1,2,3]
"(foldr (:) [] [1,2,3]):"
[1,2,3]
[(),(),(),(),(),(),(),(),(),()]
*IfRecur>
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Re: [Haskell-cafe] Digests
I may be missing something, but it is not clear to me if you want cryptographic security. If you do, then the only safe choice is to use a standard algorithm (or block cipher construction, perhaps). Sorry if that's already what you are discussing - I don't know whether there are any established algorithms that mix in a byte at a time. (though the argument that they are aiming for avalanche properties is pretty strong). (The history of the submissions to the SHA3 contest http://csrc.nist.gov/groups/ST/hash/sha-3/index.html shows it's not easy for even the experts to get it right, and that it can take a long time for problems to be noticed, even if you can convince tons of other experts to look over an algorithm) If you don't want cryptographic security, there may are probably cheap things you could consider. Brandon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] In what language...?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 11/28/10 08:47 , Florian Weimer wrote: > * Gregory Collins: > >> * Andrew Coppin: >>> Hypothesis: The fact that the average Haskeller thinks that this >>> kind of dense cryptic material is "pretty garden-variety" notation >>> possibly explains why normal people think Haskell is scary. >> >> That's ridiculous. You're comparing apples to oranges: using Haskell >> and understanding the underlying theory are two completely different >> things. > > I could imagine that the theory could be quite helpful for accepting > nagging limitations. I'm not an experienced Haskell programmer, > though, but that's what I noticed when using other languages. Yes and no; for example, it's enough to know that System F (the type system used by GHC) can't describe dependent types, without needing to know *why*. A brief overview is more useful in this case. This is true of most of the ML-ish languages: they're based on rigorous mathematical principles, but those principles are sufficiently high level that there isn't a whole lot of point in teaching them as part of teaching the languages. The concepts behind other languages are rarely based in anything quite as high level, and moreover often take structural rather than mathematical form, so understanding them *does* help. (An example of this is C++ templates; as I understand it, there *is* mathematics behind them, but many of their behaviors come from their structure rather than the math.) - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkz5ROsACgkQIn7hlCsL25VdGQCeLuDo6HS8sfnFG1EuA4oDO56y 5soAoLexEtjRKYIVFFCpWk86u0/woZGF =Fn2e -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HStringTemplate and syb-with-class usage
I've seen questions on using HStringTemplate with syb-with-class on the list before, but haven't seen this issue addressed. I'm hoping it's a noob issue, and, therefore, thought I would check with the list before spending too much time digging around for solutions. I'm attempting to use HStringTemplate with the syb-with-class support. I've made sure HStringTemplate is installed with 'syb-with-class=True'. 'genericToSElem' is always failing on the 'True =' guard with an error of "Unable to serialize the primitive type [...]" with whatever primitive Haskell type I've included in my ADT; for example, "Unable to serialize the primitive type 'Prelude.Int'". I've made sure to include 'Text.StringTemplate.GenericWithClass', 'Data.Generics.SYB.WithClass.Basics', and 'Data.Generics.SYB.WithClass.Derive', and to derive instances of the 'Typeable' and 'Data' classes with '$(derive [''Test])', where 'Test' is my test ADT. This makes me think that the overloaded 'toSElem' functions defined by the instances in 'Text.StringTemplate.Instances' are not being called? A cursory comparison to RJson, which the HStringTemplate syb-with-class solution is based on, didn't lead me to any obvious differences that I was missing. For reference, my current configuration is (Sorry, it's an older configuration, but the one I'm stuck with for now) GHC 6.10.4 (Mac OS X 10.6.4, Intel) HStringTemplate 0.6.3 syb-with-class0.6 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Emacs mode for Happy?
I'm planning on using Happy for my compiler construction class this quarter. The only problem so far is that emacs keeps trying to mangle my .y files because it assumes I mean them for yacc. Is there an emacs mode for Happy or is it maybe time to also buckle down to learning elisp and write one myself? -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Question about TagSoup
I really wouldn't use tag soup for this. Haskell has libraries specifically
for XML processing which might be better suited to your needs.
On Fri, Dec 3, 2010 at 5:59 AM, David Virebayre
> wrote:
> Hello café,
>
> I have seen tutorials about extracting information from a tag soup, but I
> have a different use case:
> I want to read a xml file, find a tag, change its content, and write the
> xml file back.
>
> This is an example of the files
>
>
> http://ns.adobe.com/AdobeInDesign/idml/1.0/packaging"; DOMVersion="7.0">
> StoryTitle="$ID/" AppliedNamedGrid="n">
> OpticalMarginSize="12" FrameType="TextFrameType"
> StoryOrientation="Horizontal" StoryDirection="LeftToRightDirection"/>
> IncludeAllResources="false"/>
> AppliedParagraphStyle="ParagraphStyle/prix">
> AppliedCharacterStyle="CharacterStyle/$ID/[No character style]">
>zzznba5
>
>
>
>
>
> Assuming I want to change the content of the "Content" tag, this is what I
> came up with (simplified), I'm using direct recursion. Is there a better way
> ?
>
> ts = do
> soup <- parseTags `fmap` readFile "idml/h00/Stories/Story_ub9fad.xml"
> writeFile "test" $ renderTagsOptions renderOptions{optMinimize = const
> True}
> $ modif soup
>
> modif [] = []
> modif (x@(TagOpen "Content" []):TagText _m : xs) = x : TagText "modified"
> : modif xs
> modif (x:xs) = x : modif xs
>
> David.
>
> ___
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>
>
--
Alex R
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[Haskell-cafe] getErrorStatus in HXT
Hi, I have some problems with the error processing in HXT. Here is a trivial example: e <- runX (transformDoc [] someRules src dst) transformDoc cfg rules src dst = configSysVars cfg >>> readDocument [] src >>> rules >>> -- some transformations writeDocument [] dst >>> getErrStatus I would expect "e" to contain an error value >= c_err for the case where any of the processing steps in transformDoc fails. But it does not, even with an io error on writeDocument. I guess I misunderstand "getErrStatus" in some way. Any idea? Thanks, Tobias ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Most images broken on haskellwiki pages
This was because, for some odd reason, the images were stored using absolute URLs and not real wikilinks. I've fixed most of them on that page. Edward ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Most images broken on haskellwiki pages
Thanks to Edward Z Yang - the problem has gone. The point is that I used raw URLs to include these images, but I should have used [[Image:MyImage.png]]. 3 декабря 2010 г. 15:22 пользователь Eugene Kirpichov написал: > 2010/12/3 Thomas Schilling : >> Should be fixed. PDF previews are currently broken, but images should be >> fine. > Unfortunately they aren't. Please take a look at > http://www.haskell.org/haskellwiki/Timeplot . > >> >> 2010/12/3 Eugene Kirpichov : >>> Hello, >>> >>> Any news on this one? >>> >>> >>> >>> 01.12.2010, в 11:53, Yitzchak Gale написал(а): >>> Eugene Kirpichov wrote: > I looked at a couple pages of mine... > and looks > like the vast majority of images are not displaying. This probably has to do with moving the wiki to the new server during the past few days. I forwarded your email to the admin team there for them to have a look. Regards, Yitz >>> >>> ___ >>> Haskell-Cafe mailing list >>> Haskell-Cafe@haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >> >> >> >> -- >> Push the envelope. Watch it bend. >> > > > > -- > Eugene Kirpichov > Senior Software Engineer, > Grid Dynamics http://www.griddynamics.com/ > -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Most images broken on haskellwiki pages
2010/12/3 Thomas Schilling : > Should be fixed. PDF previews are currently broken, but images should be > fine. Unfortunately they aren't. Please take a look at http://www.haskell.org/haskellwiki/Timeplot . > > 2010/12/3 Eugene Kirpichov : >> Hello, >> >> Any news on this one? >> >> >> >> 01.12.2010, в 11:53, Yitzchak Gale написал(а): >> >>> Eugene Kirpichov wrote: I looked at a couple pages of mine... and looks like the vast majority of images are not displaying. >>> >>> This probably has to do with moving the wiki to the >>> new server during the past few days. I forwarded your >>> email to the admin team there for them to have a look. >>> >>> Regards, >>> Yitz >> >> ___ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > > -- > Push the envelope. Watch it bend. > -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Most images broken on haskellwiki pages
Should be fixed. PDF previews are currently broken, but images should be fine. 2010/12/3 Eugene Kirpichov : > Hello, > > Any news on this one? > > > > 01.12.2010, в 11:53, Yitzchak Gale написал(а): > >> Eugene Kirpichov wrote: >>> I looked at a couple pages of mine... >>> and looks >>> like the vast majority of images are not displaying. >> >> This probably has to do with moving the wiki to the >> new server during the past few days. I forwarded your >> email to the admin team there for them to have a look. >> >> Regards, >> Yitz > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Push the envelope. Watch it bend. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] haskell.org migration complete
On 02/12/2010 23:48, Claus Reinke wrote: The haskell.org server migration is now complete. Please let us know if you have any problems. Beginning this week, the majority of mails from haskell.org lists seem to end up in my ISP's spam filter. That would be Yahoo! - I wonder whether others here have seen a similar effect when checking their spam filters? I don't know whether this is caused by the migration, but it made me wonder about something I recalled reading about whitelisting mailing list senders with ISPs, and a little search found the following: http://en.wikipedia.org/wiki/Whitelist http://help.yahoo.com/l/us/yahoo/mail/postmaster/basics/ http://help.yahoo.com/l/us/yahoo/mail/postmaster/forms_index.html http://help.yahoo.com/l/us/yahoo/mail/postmaster/bulkv2.html http://www.novablog.info/2008/10/21/5-simple-steps-to-improving-e-mail-deliverability/ So it might be related to the new server. Is whitelisting something the mailing list hosting service should deal with, or is that left to the customer? I'm fairly sure GMail at least whitelists haskell.org, because I get spam sent via the -ow...@haskell.org aliases that invariably ends up in my inbox, apparently bypassing GMail's usually very good spam filtering. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Question about TagSoup
Hello café,
I have seen tutorials about extracting information from a tag soup, but I
have a different use case:
I want to read a xml file, find a tag, change its content, and write the xml
file back.
This is an example of the files
http://ns.adobe.com/AdobeInDesign/idml/1.0/packaging"; DOMVersion="7.0">
zzznba5
Assuming I want to change the content of the "Content" tag, this is what I
came up with (simplified), I'm using direct recursion. Is there a better way
?
ts = do
soup <- parseTags `fmap` readFile "idml/h00/Stories/Story_ub9fad.xml"
writeFile "test" $ renderTagsOptions renderOptions{optMinimize = const
True}
$ modif soup
modif [] = []
modif (x@(TagOpen "Content" []):TagText _m : xs) = x : TagText "modified" :
modif xs
modif (x:xs) = x : modif xs
David.
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Re: [Haskell-cafe] Digests
2010/12/3 Permjacov Evgeniy : >>> */me wrote it into to_read list. The problem is, however, that block >>> ciphers are quite unfriendly to plain word8 streams. It is not a deadly >>> problem, but i'd like to avoid block collections. >> All one-way hashes do block collections. This is unavoidable. > Why ? Is there some math behind this proposition ? This is hard - to add single byte into the sum with cryptographic (or near cryptographic) security. To quote Wikipedia again: "The avalanche effect is evident if, when an input is changed slightly (for example, flipping a single bit) the output changes significantly (e.g., half the output bits flip)." http://en.wikipedia.org/wiki/Avalanche_effect This is true for hashes too. Hash should change about half of the random output bits when single bit of input changes. Especially if you aim to tamper-proof hashes. You have to have that property on every round of hashing, because you don't know when to stop. For bytes, you have to guarantee that you get an avalanche effect for every byte - it means, that you have to transform your entire block plus input byte in an expensive way. MD5 and all other hashes have internal state of various size, they all keep input blocks to make hashing transform less expensive. Fast methods like sum-modulo-poly (CRC variants) or linear congruential generators do not have good avalanche property when used for stream hashing or encryption. Even their combination (one in ZIP encryption) wasn't strong enough. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Digests
On 12/03/2010 10:48 AM, Serguey Zefirov wrote: > 2010/12/3 Permjacov Evgeniy : >>> Most of the time you can get away with usual block ciphers (and even >>> with weaker parameters). There is a scheme that transforms block >>> cipher into hash function: >>> http://en.wikipedia.org/wiki/CRHF#Hash_functions_based_on_block_ciphers >> */me wrote it into to_read list. The problem is, however, that block >> ciphers are quite unfriendly to plain word8 streams. It is not a deadly >> problem, but i'd like to avoid block collections. > All one-way hashes do block collections. This is unavoidable. Why ? Is there some math behind this proposition ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
