[Haskell] Spam on HaskellWiki
This is beginning to annoy people. Actually, someone registered several thousand accounts (of the form XX), though almost all of them have not been used. The others have been used to add spam. I can block user accounts and IP addresses, and I can grant this privilege to others on whatever basis the Haskell community think appropriate. I have CheckUser installed (allows me to find the IP addresses of a given user, and find edits from a particular IP address), and this is also a grantable privilege. However, given that the spam is coming from quite a number of IP addresses, I suspect there is some kind of botnet involved. There is a tool called rollback that allows one-click revert of one or more sequential edits from the same user, which makes reverting spam a one-click-per-page operation. Again, this is a grantable privilege and in any case relatively harmless. However, it is only available with MediaWiki 1.9 and later, and HaskellWiki is running MediaWiki 1.5.4, so this means doing an upgrade. The current stable release is 1.13.2. -- Ashley Yakeley ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell] Spam on HaskellWiki
On Sat, 13 Dec 2008 12:10:10 +0100, Ashley Yakeley ash...@semantic.org wrote: This is beginning to annoy people. Actually, someone registered several thousand accounts (of the form XX), though almost all of them have not been used. The others have been used to add spam. I can block user accounts and IP addresses, and I can grant this privilege to others on whatever basis the Haskell community think appropriate. I have CheckUser installed (allows me to find the IP addresses of a given user, and find edits from a particular IP address), and this is also a grantable privilege. However, given that the spam is coming from quite a number of IP addresses, I suspect there is some kind of botnet involved. There is a tool called rollback that allows one-click revert of one or more sequential edits from the same user, which makes reverting spam a one-click-per-page operation. Again, this is a grantable privilege and in any case relatively harmless. However, it is only available with MediaWiki 1.9 and later, and HaskellWiki is running MediaWiki 1.5.4, so this means doing an upgrade. The current stable release is 1.13.2. I think it would be even better when the site is protected with captchas [1], like wipipedia is. http://captchas.net/ provides a free captcha service. It is too easy to create a new user account and to edit pages by means of a forum spambot [2]. -- Regards, Henk-Jan van Tuyl [1] http://en.wikipedia.org/wiki/Captcha [2] http://en.wikipedia.org/wiki/Spambot#Forum_spambots -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ -- ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] F# to ship as part of Visual Studio 2010
Hello , http://blogs.msdn.com/dsyme/archive/2008/12/10/fsharp-to-ship-as-part-of-visual-studio-2010.aspx now we can say definitely that 201x decade will be years of FP replacing OOP in programmers' minds -- Best regards, Bulat mailto:bulat.zigans...@gmail.com ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
[Haskell] Haskell Weekly News: Issue 97 - December 13, 2008
--- Haskell Weekly News http://sequence.complete.org/hwn/20081213 Issue 97 - December 13, 2008 --- Welcome to issue 97 of HWN, a newsletter covering developments in the [1]Haskell community. Lots of neat blog posts and funny quotes this week. Don't forget to keep adding [2]haiku to the wiki, and don't miss Alex McLean (yaxu)'s [3]streaming livecoding performance tonight! Announcements Spam on HaskellWiki. Ashley Yakeley [4]asked what people would like to do about the increasing amounts of spam on the Haskell wiki, and offered some suggestions. The Timber compiler 1.0.2. Johan Nordlander [5]announced the first public release of the [6]Timber compiler. Timber is a modern language for building event-driven systems, based around the notion of reactive objects. It is also a purely functional language derived from Haskell, although with a strict evaluation semantics. To try it out, just grab the [7]timberc package on Hackage. Retrospective on 2008?. Don Stewart [8]proposed the idea of a 2008 retrospective. How would you choose the 10 best new libraries, applications, blog posts, etc. of 2008? a haskell_proposals subreddit. Jason Dusek [9]announced a [10]subreddit for Haskell library proposals. The idea is that Web 2.0 will help us to allocate our collective talents more efficiently when it comes to extensions (and perhaps clue us in when our pet project is something people really want). permutation-0.2. Patrick Perry [11]announced a [12]new version of the permutation library, which includes data types for storing permutations. It implements pure and impure types, the latter which can be modified in-place. The main utility of the library is converting between the linear representation of a permutation to a sequence of swaps. This allows, for instance, applying a permutation or its inverse to an array with O(1) memory use. Data.List.Split. Brent Yorgey [13]announced the creation of a wiki page for [14]Data.List.Split, a hypothetical module containing implementations of every conceivable way of splitting lists known to man, so we no longer have to (1) argue about the 'one true' interface for a 'split' function, or (2) be embarrassed when people ask why there isn't a split function in the standard libraries. Please add code or comments! At some point it will be uploaded as a new module to Hackage. Announcing Haskell protocol-buffers version 1.2.2. Chris Kuklewicz [15]announced new versions of [16]protocol-buffers, [17]protocol-buffers-descriptor, and [18]hprotoc. Discussion A curious monad. Andrew Coppin [19]exhibited an interesting Storage monad, which (it turns out) is similar to ST. An enlightening discussion if you want to understand how ST works and the motivation behind it. Origins of '$'. George Pollard [20]asked about the origins of the $ operator (low-precedence function application) in the standard libraries, leading to some interesting history and general discussion about notation. Blog noise [21]Haskell news from the [22]blogosphere. * Jamie Brandon: [23]Zombified GMap. Jamie is determined to get his SoC generalized map library released! * Philip Wadler: [24]Informatics 1 - Fancy Dress and Competition. * Eduard - Gabriel Munteanu: [25]Learning Haskell, part 2. * Martin Sulzmann: [26]Equality, containment and intersection among regular expressions via symbolic manipulation. * Neil Mitchell: [27]mapM, mapM_ and monadic statements. * Alson Kemp: [28]A HAML parser for Haskell. * Chris Done: [29]More Haskell blogging. * Twan van Laarhoven: [30]Knight in n, part 4: tensors. Part four of Twan's enlightening series on computing knight moves. * Alex McLean: [31]Saturday night stream. All the cool kids will be watching Alex's streaming livecoding performance TONIGHT, using (among other things) a tool implemented in Haskell. * David Sankel: [32]Synchronous Events. * Lennart Augustsson: [33]The OCaml code again. * Lennart Augustsson: [34]Abstracting on, suggested solutions. * Lennart Augustsson: [35]The abstraction continues. * Conal Elliott: [36]Functional interactive behavior. * Conal Elliott: [37]Trimming inputs in functional reactive programming. * Mikael Vejdemo Johansson (Syzygy-): [38]J, or how I learned to stop worrying and love the matrix. * Conal Elliott: [39]Why classic FRP does not fit interactive behavior. * Clifford Beshers: [40]Functional Programming Marketing. * Lennart Augustsson: [41]A somewhat failed adventure in Haskell abstraction. * Joey Hess: [42]haskell and xmonad. * Andy Gill: [43]The Timber compiler 1.0.2. * Manuel M T
Re: [Haskell] F# to ship as part of Visual Studio 2010
On Sat, Dec 13, 2008 at 03:42:35PM +0300, Bulat Ziganshin wrote: Hello , http://blogs.msdn.com/dsyme/archive/2008/12/10/fsharp-to-ship-as-part-of-visual-studio-2010.aspx now we can say definitely that 201x decade will be years of FP replacing OOP in programmers' minds hehe :-) funny. do you think they'll change their the .net libraries to have functional interfaces as well? That'd be required to get OO out of the minds of users.. But there is still enough time till 2010 for that to happen? Thanks for the note. Marc Weber ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: [Haskell] Spam on HaskellWiki
ashley: This is beginning to annoy people. Actually, someone registered several thousand accounts (of the form XX), though almost all of them have not been used. The others have been used to add spam. I can block user accounts and IP addresses, and I can grant this privilege to others on whatever basis the Haskell community think appropriate. I have CheckUser installed (allows me to find the IP addresses of a given user, and find edits from a particular IP address), and this is also a grantable privilege. However, given that the spam is coming from quite a number of IP addresses, I suspect there is some kind of botnet involved. There is a tool called rollback that allows one-click revert of one or more sequential edits from the same user, which makes reverting spam a one-click-per-page operation. Again, this is a grantable privilege and in any case relatively harmless. However, it is only available with MediaWiki 1.9 and later, and HaskellWiki is running MediaWiki 1.5.4, so this means doing an upgrade. The current stable release is 1.13.2. Should we be thinking about upgrading now? I imagine there are other benefits... -- Don ___ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
Re: Suggestion: Syntactic sugar for Maps!
circularfunc:
I suggest Haskell introduce some syntactic sugar for Maps.
Python uses {this: 2, is: 1, a: 1, Map: 1}
Clojure also use braces: {:k1 1 :k2 3} where whitespace is comma but
commas are also allowed.
I find the import Data.Map and then fromList [(hello,1), (there,
2)] or the other form that I forgot(because it is to long!) to be to
long...
So why not {hello: 1, there: 2} ?
A comment from the peanut gallery:
I took circ's comment to be a suggestion that we adopt an _idiom_.
That you can non-idiomatically accomplish the same thing in Haskell by
defining some datatypes and functions doesn't seem to address the core
suggestion.
I'd rewrite circ's suggestion as follows:
A bunch of modern and popular languages use the idiom of braces for
maps (e.g. { 'a' = 1, 'b' = 2} ). Its simplicity has made maps
vital parts of most programs. Much of the world has adopted this
idiom and if Haskell adopts this syntactic sugar it will make it
easier for others to adopt Haskell.
Haskell is really interesting for a number of reasons. Map syntax
isn't one of them but map syntax sugar would make adoption of Haskell
that much easier. As I think Don S said, it's hard enough to adopt
Haskell, so let's make it easier when possible...
- Alson
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[Haskell-cafe] Missing comment highlighting in vim syntax script
Hi all,
The Haskell syntax script for vim mentions this mailing list as the
maintainer. Perhaps one of you could fix this bug.
Comments on the same line as import declarations don't get highlighted:
import A -- This comment isn't highlighted
import B {- Neither is this -}
import C {- and
this -}
I'm using this version of the syntax file: (the only version)
http://vim.svn.sourceforge.net/viewvc/vim/vim7/runtime/syntax/haskell.vim?revision=1296view=markup
Thanks,
Ori
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Re: [Haskell-cafe] Missing comment highlighting in vim syntax script
On Sat, Dec 13, 2008 at 9:10 AM, Ori Avtalion o...@avtalion.name wrote:
Comments on the same line as import declarations don't get highlighted:
import A -- This comment isn't highlighted
import B {- Neither is this -}
import C {- and
this -}
I think the way vim tries to do syntax highlighting is fundamentally
busted. That's why there are the problems like the ones you're talking
about and a million others. I plan to use vim and work on my yi
configs until I can switch. It's sad.
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[Haskell-cafe] Data.List.Split
Today yet another newbie in #haskell asked about a 'split' function for lists, and I got fed up with saying 'no one can agree on the right interface so it doesn't exist, just write it yourself', because it's a really dumb answer, even if it's true. Instead of trying to get a 'split' function added to Data.List (which will never ever happen), I thought, why not create a module Data.List.Split which contains implementations of every conceivable way to split a list? Of course, people will probably still argue over what should go in such a module, what to name the various functions, etc., but hopefully we can converge on something useful. I've created a Data.List.Split page on the wiki: http://haskell.org/haskellwiki/Data.List.Split Please add code to it! Once something useful is hashed out we can upload it to hackage. Perhaps eventually some of it can be folded into the standard libraries, but this seems like a much more lightweight way to get started. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.List.Split
A very nice initiative I must say; although the page should contain the usual explanation for why such a split method can't be universal. That is, add the same explanation you give every time; but to the page. /Gianfranco On Sat, Dec 13, 2008 at 5:30 PM, Brent Yorgey byor...@seas.upenn.edu wrote: Today yet another newbie in #haskell asked about a 'split' function for lists, and I got fed up with saying 'no one can agree on the right interface so it doesn't exist, just write it yourself', because it's a really dumb answer, even if it's true. Instead of trying to get a 'split' function added to Data.List (which will never ever happen), I thought, why not create a module Data.List.Split which contains implementations of every conceivable way to split a list? Of course, people will probably still argue over what should go in such a module, what to name the various functions, etc., but hopefully we can converge on something useful. I've created a Data.List.Split page on the wiki: http://haskell.org/haskellwiki/Data.List.Split Please add code to it! Once something useful is hashed out we can upload it to hackage. Perhaps eventually some of it can be folded into the standard libraries, but this seems like a much more lightweight way to get started. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Patience is the last resort for those unable to take action ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.List.Split
On Sat, Dec 13, 2008 at 05:39:55PM +0100, Gianfranco Alongi wrote: A very nice initiative I must say; although the page should contain the usual explanation for why such a split method can't be universal. That is, add the same explanation you give every time; but to the page. Good idea; I've added a list of possible ways to split, both to give people ideas for code to write, and to demonstrate why it's impossible to come up with one 'best' split function. vixey has already added some code, but we need more! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.List.Split
I have actually been thinking about a similar thing, but on the group subject. One can actually group things in many ways, such as groupBy (==) , so that groupBy (==) [1,2,1,2] should give [[1,1],[2,2]]. Of course other ideas are possible. On Sat, Dec 13, 2008 at 5:47 PM, Brent Yorgey byor...@seas.upenn.edu wrote: On Sat, Dec 13, 2008 at 05:39:55PM +0100, Gianfranco Alongi wrote: A very nice initiative I must say; although the page should contain the usual explanation for why such a split method can't be universal. That is, add the same explanation you give every time; but to the page. Good idea; I've added a list of possible ways to split, both to give people ideas for code to write, and to demonstrate why it's impossible to come up with one 'best' split function. vixey has already added some code, but we need more! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Patience is the last resort for those unable to take action ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 97 - December 13, 2008
--- Haskell Weekly News http://sequence.complete.org/hwn/20081213 Issue 97 - December 13, 2008 --- Welcome to issue 97 of HWN, a newsletter covering developments in the [1]Haskell community. Lots of neat blog posts and funny quotes this week. Don't forget to keep adding [2]haiku to the wiki, and don't miss Alex McLean (yaxu)'s [3]streaming livecoding performance tonight! Announcements Spam on HaskellWiki. Ashley Yakeley [4]asked what people would like to do about the increasing amounts of spam on the Haskell wiki, and offered some suggestions. The Timber compiler 1.0.2. Johan Nordlander [5]announced the first public release of the [6]Timber compiler. Timber is a modern language for building event-driven systems, based around the notion of reactive objects. It is also a purely functional language derived from Haskell, although with a strict evaluation semantics. To try it out, just grab the [7]timberc package on Hackage. Retrospective on 2008?. Don Stewart [8]proposed the idea of a 2008 retrospective. How would you choose the 10 best new libraries, applications, blog posts, etc. of 2008? a haskell_proposals subreddit. Jason Dusek [9]announced a [10]subreddit for Haskell library proposals. The idea is that Web 2.0 will help us to allocate our collective talents more efficiently when it comes to extensions (and perhaps clue us in when our pet project is something people really want). permutation-0.2. Patrick Perry [11]announced a [12]new version of the permutation library, which includes data types for storing permutations. It implements pure and impure types, the latter which can be modified in-place. The main utility of the library is converting between the linear representation of a permutation to a sequence of swaps. This allows, for instance, applying a permutation or its inverse to an array with O(1) memory use. Data.List.Split. Brent Yorgey [13]announced the creation of a wiki page for [14]Data.List.Split, a hypothetical module containing implementations of every conceivable way of splitting lists known to man, so we no longer have to (1) argue about the 'one true' interface for a 'split' function, or (2) be embarrassed when people ask why there isn't a split function in the standard libraries. Please add code or comments! At some point it will be uploaded as a new module to Hackage. Announcing Haskell protocol-buffers version 1.2.2. Chris Kuklewicz [15]announced new versions of [16]protocol-buffers, [17]protocol-buffers-descriptor, and [18]hprotoc. Discussion A curious monad. Andrew Coppin [19]exhibited an interesting Storage monad, which (it turns out) is similar to ST. An enlightening discussion if you want to understand how ST works and the motivation behind it. Origins of '$'. George Pollard [20]asked about the origins of the $ operator (low-precedence function application) in the standard libraries, leading to some interesting history and general discussion about notation. Blog noise [21]Haskell news from the [22]blogosphere. * Jamie Brandon: [23]Zombified GMap. Jamie is determined to get his SoC generalized map library released! * Philip Wadler: [24]Informatics 1 - Fancy Dress and Competition. * Eduard - Gabriel Munteanu: [25]Learning Haskell, part 2. * Martin Sulzmann: [26]Equality, containment and intersection among regular expressions via symbolic manipulation. * Neil Mitchell: [27]mapM, mapM_ and monadic statements. * Alson Kemp: [28]A HAML parser for Haskell. * Chris Done: [29]More Haskell blogging. * Twan van Laarhoven: [30]Knight in n, part 4: tensors. Part four of Twan's enlightening series on computing knight moves. * Alex McLean: [31]Saturday night stream. All the cool kids will be watching Alex's streaming livecoding performance TONIGHT, using (among other things) a tool implemented in Haskell. * David Sankel: [32]Synchronous Events. * Lennart Augustsson: [33]The OCaml code again. * Lennart Augustsson: [34]Abstracting on, suggested solutions. * Lennart Augustsson: [35]The abstraction continues. * Conal Elliott: [36]Functional interactive behavior. * Conal Elliott: [37]Trimming inputs in functional reactive programming. * Mikael Vejdemo Johansson (Syzygy-): [38]J, or how I learned to stop worrying and love the matrix. * Conal Elliott: [39]Why classic FRP does not fit interactive behavior. * Clifford Beshers: [40]Functional Programming Marketing. * Lennart Augustsson: [41]A somewhat failed adventure in Haskell abstraction. * Joey Hess: [42]haskell and xmonad. * Andy Gill: [43]The Timber compiler 1.0.2. * Manuel M T
[Haskell-cafe] Parsec and type level numerals
Hello all. I've got a puzzling Parsec problem. Perhaps the collective wisdom
of haskell-cafe can point me in the right direction.
I want to be able to parse a string of digits to a type level numeral as
described in the Number parameterized
typeshttp://okmij.org/ftp/papers/number-parameterized-types.pdfpaper.
After fiddling with the problem for a while, I'm not convinced it's
possible- it seems as though one would need to know the type of the result
before parsing, but then we wouldn't need to parse in the first place. :) My
first (simplified) approximation is as follows:
data Zero = Zero
data Succ a = Succ a
class Card t
instance Card Zero
instance (Card a) = Card (Succ a)
parseP :: (Card a) = Parser a
parseP = do { char '1'
; rest - parseP
; return $ Succ rest
}
| return Zero
I'd like for this to parse, for example, 111 into Succ Succ Succ Zero. Of
course this doesn't work because parseP is ill-typed, but I'm not sure how
to fix it. It seems that what I'm asking for is a function whose type is forall
a. (Card a) = String - a, which is problematic.
Has anyone tried this before? I'm new to using Parsec and to parsing in
general, so I apologize if this is a silly question. (Parsec is very
impressive, by the way.)
Thanks-
Nathan Bloomfield
University of Arkansas, Fayetteville
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Re: [Haskell-cafe] Parsec and type level numerals
2008/12/13 Nathan Bloomfield nblo...@gmail.com: I want to be able to parse a string of digits to a type level numeral as described in the Number parameterized types paper. Hi, I'm at UA too (bsl04). Here's a quick try. Sorry if I'm not getting what you're doing. import Text.Parsec import Text.Parsec.String data PeanoNumber = Zero | Succ PeanoNumber deriving Show parseP :: Parser PeanoNumber parseP = do char '1' rest - parseP return $ Succ rest | return Zero test = parseTest parseP 111 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A curios monad
2008/12/11 Luke Palmer lrpal...@gmail.com:
If you could guarantee that the ID of a key is globally unique, even through
different invocations of the monad (using eg. unsafePerformIO newUnique),
then you could ensure type safety and allow transport of keys between
different monads.
Well, for type-safety you don't need the entire ID of the key; you
just need a globally unique type tag. This is, of course, what
Data.Typeable provides. But you can also roll your own using Uniques:
newtype TKey a = TKey Unique deriving Eq
newTKey :: IO (TKey a)
newTKey = fmap TKey newUnique
castTKey :: TKey a - TKey b - Maybe (a - b)
castTKey (TKey u1) (TKey u2)
| u1 == u2 = Just unsafeCoerce
| otherwise = Nothing
data Key a = Key Int (TKey a) deriving (Eq, Ord)
data StoredValue = forall a. Stored (TKey a) a
type StorageMap = IntMap StoredValue
You then split up the program; one part generates TKeys for the types
in IO; then you can use those throughout the pure rest of the program
to index the types:
newKey :: TKey a - Storage (Key a)
newKey ta = do
ik - getNextFreeInt
return $ Key ik ta
-- using MaybeT:
-- newtype MaybeT m a = MaybeT { runMaybeT :: m (Maybe a) }
-- with the appropriate Monad instance
readKey :: Key a - Storage (Maybe a)
readKey (Key i t) = runMaybeT $ do
Stored tx x - MaybeT $ lookupMap i
f - MaybeT $ return (castTKey tx t)
return (f x)
-- exercises for the reader
lookupMap :: Int - Storage StoredValue
getNextFreeInt :: Storage Int
writeKey :: a - Key a - Storage ()
If you're willing to be *slightly* non-referentially transparent, you
can generate the type keys at global scope:
intTKey :: TKey Int
intTKey = unsafePerformIO newTKey
{-# NOINLINE intTKey #-}
(There have been many arguments about top level IO actions; I don't
want to get into that here!)
-- ryan
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Re: [Haskell-cafe] Parsec and type level numerals
You're almost there, but you have correctly determined the problem;
you need to know the type of the parse result in order to parse.
However, it is possible to hide the type from the parser; try writing
this function instead:
{-# LANGUAGE ExistentialQuantification #-}
data AnyCard = forall t. Card t = AnyCard t
parseP :: Parser AnyCard
Now the type-level numeral is hidden in the AnyCard existential
type. In order to use it, you need to be able to use operations that
work on any instance of Card, which means the class/instance
declarations you have so far aren't that useful. Emulating dependent
types using existentials in Haskell is never pretty!
Another option is to use a GADT to hold the type:
{-# LANGUAGE GADTs, ExistentialQuantification #-}
data GADTNum t where
GZero :: GADTNum Zero
GSucc :: GADTNum a - GADTNum (Succ a)
data AnyCard = forall t. AnyCard (GADTNum t)
Now, after the parse, you can use the structure of the GADT to
determine things about the existential type:
isTwo :: AnyCard - Maybe (Succ (Succ Zero))
isTwo (AnyCard (GSucc (GSucc GZero))) = Succ (Succ Zero)
isTwo _ = Nothing
-- ryan
2008/12/13 Nathan Bloomfield nblo...@gmail.com:
Hello all. I've got a puzzling Parsec problem. Perhaps the collective wisdom
of haskell-cafe can point me in the right direction.
I want to be able to parse a string of digits to a type level numeral as
described in the Number parameterized types paper. After fiddling with the
problem for a while, I'm not convinced it's possible- it seems as though one
would need to know the type of the result before parsing, but then we
wouldn't need to parse in the first place. :) My first (simplified)
approximation is as follows:
data Zero = Zero
data Succ a = Succ a
class Card t
instance Card Zero
instance (Card a) = Card (Succ a)
parseP :: (Card a) = Parser a
parseP = do { char '1'
; rest - parseP
; return $ Succ rest
}
| return Zero
I'd like for this to parse, for example, 111 into Succ Succ Succ Zero. Of
course this doesn't work because parseP is ill-typed, but I'm not sure how
to fix it. It seems that what I'm asking for is a function whose type is
forall a. (Card a) = String - a, which is problematic.
Has anyone tried this before? I'm new to using Parsec and to parsing in
general, so I apologize if this is a silly question. (Parsec is very
impressive, by the way.)
Thanks-
Nathan Bloomfield
University of Arkansas, Fayetteville
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Re: [Haskell-cafe] Parsec and type level numerals
2008/12/13 Nathan Bloomfield nblo...@gmail.com: I want to be able to parse a string of digits to a type level numeral as described in the Number parameterized types paper. After fiddling with the problem for a while, I'm not convinced it's possible- it seems as though one would need to know the type of the result before parsing, but then we wouldn't need to parse in the first place. :) This can be done with existential types. I think Oleg Kiselyov has an example somewhere of a parser that determines the type of its output from its input, but here's the basic idea: data SomeCard = forall a. (Card a) = SomeCard a Now you can define parseP :: Parser SomeCard Unfortunately, all you know about the value inside the SomeCard is that it's a member of the class Card, which may not be very helpful. Depending on how general you want to be, you can bundle more operations with SomeCard, or you can return a GADT that reflects the type-level natural at the value level. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A curios monad
On Thu, Dec 11, 2008 at 1:48 PM, Andrew Coppin andrewcop...@btinternet.com wrote: BTW, does anybody know how rank-N types are different from existential types? You mean the Haskell extensions? ExistentialQuantification lets you define types such as, data SomeNum = forall a. Num a = SomeNum a RankNTypes lets you nest foralls arbitrarily deep in type signatures, callCC :: ((forall b. a - m b) - m a) - m a -- this is rank-3 RankNTypes implies ExistentialQuantification (among others). -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Small haskell practical course
Hello, I've presented a small practical course[0] in EMSL[1]. Any comments are welcome. 0: http://marcot.iaaeee.org/mini-curso.pdf (Portuguese only) 1: http://emsl.softwarelivre.org/ Greetings. -- marcot http://marcot.iaaeee.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Small haskell practical course
marcot: Hello, I've presented a small practical course[0] in EMSL[1]. Any comments are welcome. 0: http://marcot.iaaeee.org/mini-curso.pdf (Portuguese only) 1: http://emsl.softwarelivre.org/ Wonderful. Maybe you can add it to the .pt section of the Haskell wiki? http://haskell.org/haskellwiki/Pt/Haskell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Small haskell practical course
Em Sáb, 2008-12-13 às 13:07 -0800, Don Stewart escreveu: marcot: Hello, I've presented a small practical course[0] in EMSL[1]. Any comments are welcome. 0: http://marcot.iaaeee.org/mini-curso.pdf (Portuguese only) 1: http://emsl.softwarelivre.org/ Wonderful. Maybe you can add it to the .pt section of the Haskell wiki? Done, thanks for the suggestion. http://haskell.org/haskellwiki/Livros_e_tutoriais -- marcot http://marcot.iaaeee.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A curios monad
David Menendez wrote: On Thu, Dec 11, 2008 at 1:48 PM, Andrew Coppin andrewcop...@btinternet.com wrote: BTW, does anybody know how rank-N types are different from existential types? You mean the Haskell extensions? ExistentialQuantification lets you define types such as, data SomeNum = forall a. Num a = SomeNum a RankNTypes lets you nest foralls arbitrarily deep in type signatures, callCC :: ((forall b. a - m b) - m a) - m a -- this is rank-3 RankNTypes implies ExistentialQuantification (among others). So how is foo :: ((forall b. a - m b) - m a) - m a different from bar :: forall b. ((a - m b) - m a) - m a then? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A curios monad
Am Sonntag, 14. Dezember 2008 00:00 schrieb Andrew Coppin: David Menendez wrote: On Thu, Dec 11, 2008 at 1:48 PM, Andrew Coppin andrewcop...@btinternet.com wrote: BTW, does anybody know how rank-N types are different from existential types? You mean the Haskell extensions? ExistentialQuantification lets you define types such as, data SomeNum = forall a. Num a = SomeNum a RankNTypes lets you nest foralls arbitrarily deep in type signatures, callCC :: ((forall b. a - m b) - m a) - m a -- this is rank-3 RankNTypes implies ExistentialQuantification (among others). So how is foo :: ((forall b. a - m b) - m a) - m a Here, the argument of foo's argument must be a polymorphic function, capable of returning an (m b) whatever b is. different from bar :: forall b. ((a - m b) - m a) - m a Here, the argument of bar's argument can have any monomorphic type (a - m b) then? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A curios monad
On Sat, Dec 13, 2008 at 3:00 PM, Andrew Coppin andrewcop...@btinternet.com wrote: So how is foo :: ((forall b. a - m b) - m a) - m a different from bar :: forall b. ((a - m b) - m a) - m a Lets use a simpler example: foo :: (forall a. a - a) - (Int, String) bar :: forall a. (a - a) - (Int, String) -- this compiles foo f = (f 1, f hello) -- this does not compile -- bar f = (f 1, f hello) -- but this does bar f = (1, hello) The difference is that the *caller* of bar chooses how to instantiate a, whereas the caller of foo must pass in a polymorphic function that foo can instantiate at whatever type it wants... even multiple different types! ident x = x plus1 x = x + 1 :: Int -- legal useFoo = foo ident -- not legal, not polymorphic -- useFoo = foo plus1 -- legal useBar = bar ident -- also legal, instantiate a in the type of bar with Int useBar2 = bar plus1 -- ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.List.Split
* On Saturday, December 13 2008, Gianfranco Alongi wrote: I have actually been thinking about a similar thing, but on the group subject. One can actually group things in many ways, such as groupBy (==) , so that groupBy (==) [1,2,1,2] should give [[1,1],[2,2]]. Of course other ideas are possible. That result happens with: sortedGroups = group . sort That composition is pretty, unlike those splitting functions. I don't know if manually fusing sort and group helps performance at all though. Making groups by comparing with the previous element, or the first element of the current group is occasionally useful: (this does the former) groupIncDiff :: (a - a - Bool) - [a] - [[a]] groupIncDiff p = uncurry (:) . foldr w ([],[]) where w n ([],a) = ([n],a) w n ((x:xs),a) | p x n = (n:x:xs,a) | otherwise = ([n],(x:xs):a) (in case somebody feels like assembling the apparently numerous was to group) On another note, is there much use of such simple library functions: does concatMap, for instance, save anything other than a couple parantheses, or does (concat . map) not necessarily get optimized into the same thing? Adam ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.List.Split
On Sun, 2008-12-14 at 00:35 -0500, Adam Vogt wrote: On another note, is there much use of such simple library functions: does concatMap, for instance, save anything other than a couple parantheses, or does (concat . map) not necessarily get optimized into the same thing Bart Massey’s results suggest very little difference: http://wiki.cs.pdx.edu/forge/concatmap.html (Yellow blobs + green crosses.) - George signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.List.Split
On Sun, 2008-12-14 at 19:46 +1300, George Pollard wrote: On Sun, 2008-12-14 at 00:35 -0500, Adam Vogt wrote: On another note, is there much use of such simple library functions: does concatMap, for instance, save anything other than a couple parantheses, or does (concat . map) not necessarily get optimized into the same thing Bart Massey’s results suggest very little difference: http://wiki.cs.pdx.edu/forge/concatmap.html (Yellow blobs + green crosses.) I should have said that, on the other hand, with stream fusion enabled, (concat . map) outperforms (concatMap) :) - George signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A curios monad
On Sat, Dec 13, 2008 at 6:00 PM, Andrew Coppin andrewcop...@btinternet.com wrote: David Menendez wrote: On Thu, Dec 11, 2008 at 1:48 PM, Andrew Coppin andrewcop...@btinternet.com wrote: BTW, does anybody know how rank-N types are different from existential types? You mean the Haskell extensions? ExistentialQuantification lets you define types such as, data SomeNum = forall a. Num a = SomeNum a RankNTypes lets you nest foralls arbitrarily deep in type signatures, callCC :: ((forall b. a - m b) - m a) - m a -- this is rank-3 RankNTypes implies ExistentialQuantification (among others). So how is foo :: ((forall b. a - m b) - m a) - m a different from bar :: forall b. ((a - m b) - m a) - m a then? Daniel Fischer already gave the short answer, I'll try explaining why someone might *want* a rank-3 signature for callCC. It involves a continuation monad, but hopefully nothing headache-inducing. The type for callCC in Control.Monad.Cont.Class is, callCC :: forall m a b. (MonadCont m) = ((a - m b) - m b) - m b You can use callCC to do very complicated things, but you can also use it as a simple short-cut escape, like the way return works in C. foo = callCC (\exit - do ... x - if something then return 'a' else exit False ... return True) The type of exit is Bool - m Char, which is fine in this example, but it means that we can only use exit to escape from computations that are producing characters. For example, we cannot write, bar = callCC (\exit - do ... x - if something then return 'a' else exit False y - if something then return 42 else exit False ... return True) Because exit would need to have the type Bool - m Char the first time and Bool - m Int the second time. But, if callCC had a rank-3 type, callCC :: forall m a. (MonadCont m) = ((forall b. a - m b) - m a) - m a then exit would have the type forall b. Bool - m b, and bar would compile just fine. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
