Re: [Haskell-cafe] Monads with The contexts?
http://en.pk.paraiso-lang.org/Haskell/Monad-Gaussian What do you think? Will this be a good approach or bad? I don't think it is a Monad (or even restricted monad, see below). Suppose G a is a `Gaussian' monad and n :: G Double is a random number with the Gaussian (Normal distribution). Then (\x - x * x) `fmap` n is a random number with the chi-square distribution (of the degree of freedom 1). Chi-square is _not_ a normal distribution. Perhaps a different example is clearer: (\x - if x 0 then 1.0 else 0.0) `fmap` n has also the type G Double but obviously does not have the normal distribution (since that random variable is discrete). There are other problems Let's start with some limitation; we restrict ourselves to Gaussian distributions and assume that the standard deviations are small compared to the scales we deal with. That assumption is not stated in types and it is hard to see how can we enforce it. Nothing prevents us from writing liftM2 n n in which case the variance will no longer be small compared with the mean. Just a technical remark: The way G a is written, it is a so-called restricted monad, which is not a monad (the adjective `restricted' is restrictive here). http://okmij.org/ftp/Haskell/types.html#restricted-datatypes ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal install fails due to recent HUnit
On Wed, Jul 18, 2012 at 05:51:51PM -0600, Richard G. wrote: What's the best way to fix this? I can see two options: - Move the test stanzas to a different Cabal file, allowing users to perform the tests with a little fiddling. - Remove the conditional statements from the test stanzas, which may break compatibility with some compilers and interpreters. Is there another option? I think it is preferable to have a test section in the main cabal file. Just an idea: What about having just a single test suite that *depends on the library*? I think that way the test suit would not require any conditionals, but you could not test with different optimization levels anymore. We could then add a Makefile/script that configures, builds and tests with the different optimization levels. This approach also has the advantage, that we are testing exactly the same thing (the library!) that the user is going to use. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Probabilistic programming [Was: Monads with The contexts?]
Exercise: how does the approach in the code relate to the approaches to sharing explained in http://okmij.org/ftp/tagless-final/sharing/sharing.html Chapter 3 introduces an implicit impure counter, and Chapter 4 uses a database that is passed around. let_ in Chapter 5 of sharing.pdf realizes the sharing with sort of continuation-passing style.The unsafe counter works across the module (c.f. counter.zip) but is generally unpredictable... The reason sharing has the type m a - m (m a) rather than m a - m a is the fact new calculations to share may be created dynamically. Therefore, we need a supply of keys (gensym). We count on the monad m to provide the supply. However, top-level computations (bound to top-level identifiers) are created only once, at the initialization time. Therefore, a static assignment of identifiers will suffice. The static assignment is similar to the manual label assignment technique -- the first technique described Sec 3 of the sharing.pdf paper. John T. O'Donnell has automated this manual assignment using TH. Now I'm on to the next task; how we represent continuous probability distributions? The existing libraries: Seemingly have restricted themselves to discrete distributions, or at least providing Random support for Monte-Carlo simulations. I must warn that although it is ridiculously easy to implement MonadProb in Haskell, the result is not usable. Try to implement HMM with any of the available MonadProb and see how well it scales. (Hint: we want the linear time scaling as we evolve the model -- not exponential). There is a *huge* gap between a naive MonadProb and something that could be used even for passingly interesting problems. We need support for so-called `variable elimination'. We need better sampling procedures: rejection sampling is better forgotten. Finally, GHC is actually not a very good language system for probabilistic programming of generative-model--variety. See http://okmij.org/ftp/Haskell/index.html#memo-off for details. To give you the flavor of difficulties, consider a passingly interesting target tracking problem: looking at a radar screen and figuring out how many planes are there and where they are going: http://okmij.org/ftp/kakuritu/index.html#blip Since the equipment is imperfect, there could be a random blip on the radar that corresponds to no target. If we have a 10x10 screen and 2% probability of a noise blip in every of the 100 `pixels', we get the search space of 2^100 -- even before we get to the planes and their stochastic equations of motion. Hansei can deal with the problem -- and even scale linearly with time. I don't think you can make a monad out of Gaussian distributions. That is not to say that monads are useless in these problems -- monads are useful, but at a different level, to build a code for say, MCMC (Monte Carlo Markov Chain). It this this meta-programming approach that underlies Infer.net http://research.microsoft.com/en-us/um/cambridge/projects/infernet/ and Avi Pfeffer's Figaro http://www.cs.tufts.edu/~nr/cs257/archive/avi-pfeffer/figaro.pdf I should point out Professor Sato of Toukyou Tech, who is the pioneer in the probabilistic programming http://sato-www.cs.titech.ac.jp/sato/ http://sato-www.cs.titech.ac.jp/en/publication/ You can learn from him all there is to know about probabilistic programming. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fwd: hackage compile failure with QuickCheck 2.5
On Wed, Jul 18, 2012 at 09:35:52AM +0100, Erik Hesselink wrote: I don't think you can install this package on 7.4. As Andres said, it requires containers 0.5, but ghc 7.4's base libraries (in this case, template-haskell) use containers 0.4, and can't be reinstalled. I guess your best bet is to use sbv-2.1, which depends on containers = 0.3, or to unpack it and see if you can loosen the containers dependency and see if it still works with 0.4 So the moral of this story is that libraries should avoid depending on features of the containers package that have not yet been released with GHC. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Need help with learning Parsec
Dear gentle Haskellers,
I was trying to whet my Haskell by trying out Parsec today to try and parse
out XML. Here's the code I cam up with -
I wanted some help with the gettext parser that I've written. I had to do
a dummy char ' ') in there just to satisfy the many used in the xml
parser. I'd appreciate it very much if someone could give me some feedback.
data XML = Node String [XML]
| Body String deriving Show
gettext = do
x - many (letter | digit )
if (length x) 0 then
return (Body x)
else (char ' ' (return $ Body ))
xml :: Parser XML
xml = do {
name - openTag
; innerXML - many innerXML
; endTag name
; return (Node name innerXML)
}
innerXML = do
x - (try xml | gettext)
return x
openTag :: Parser String
openTag = do
char ''
content - many (noneOf )
char ''
return content
endTag :: String - Parser String
endTag str = do
char ''
char '/'
string str
char ''
return str
h1 = parse xml aA/a
h2 = parse xml abA/b/a
h3 = parse xml abc/c/b/a
h4 = parse xml ab/bc/c/a
Regards,
Kashyap
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Re: [Haskell-cafe] Need help with learning Parsec
Am 19.07.2012 14:53, schrieb C K Kashyap:
Dear gentle Haskellers,
I was trying to whet my Haskell by trying out Parsec today to try and
parse out XML. Here's the code I cam up with -
I wanted some help with the gettext parser that I've written. I had to
do a dummy char ' ') in there just to satisfy the many used in the
xml parser. I'd appreciate it very much if someone could give me some
feedback.
You don't want empty bodies! So use many1 in gettext.
gettext = fmap Body $ many1 $ letter | digit
If you have spaces in your bodies, skip them or allow them with
noneOf .
HTH Christian
data XML = Node String [XML]
| Body String deriving Show
gettext = do
x - many (letter | digit )
if (length x) 0 then
return (Body x)
else (char ' ' (return $ Body ))
xml :: Parser XML
xml = do {
name - openTag
; innerXML - many innerXML
; endTag name
; return (Node name innerXML)
}
innerXML = do
x - (try xml | gettext)
return x
openTag :: Parser String
openTag = do
char ''
content - many (noneOf )
char ''
return content
endTag :: String - Parser String
endTag str = do
char ''
char '/'
string str
char ''
return str
h1 = parse xml aA/a
h2 = parse xml abA/b/a
h3 = parse xml abc/c/b/a
h4 = parse xml ab/bc/c/a
Regards,
Kashyap
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Re: [Haskell-cafe] Need help with learning Parsec
Am 19.07.2012 14:53, schrieb C K Kashyap: innerXML = do x - (try xml | gettext) return x Omit try (and return). xml always starts with whereas gettext never does. C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need help with learning Parsec
gettext = (many1 $ noneOf ) = (return . Body)
works for your case.
On Thu, Jul 19, 2012 at 6:37 PM, Christian Maeder
christian.mae...@dfki.dewrote:
Am 19.07.2012 14:53, schrieb C K Kashyap:
Dear gentle Haskellers,
I was trying to whet my Haskell by trying out Parsec today to try and
parse out XML. Here's the code I cam up with -
I wanted some help with the gettext parser that I've written. I had to
do a dummy char ' ') in there just to satisfy the many used in the
xml parser. I'd appreciate it very much if someone could give me some
feedback.
You don't want empty bodies! So use many1 in gettext.
gettext = fmap Body $ many1 $ letter | digit
If you have spaces in your bodies, skip them or allow them with
noneOf .
HTH Christian
data XML = Node String [XML]
| Body String deriving Show
gettext = do
x - many (letter | digit )
if (length x) 0 then
return (Body x)
else (char ' ' (return $ Body ))
xml :: Parser XML
xml = do {
name - openTag
; innerXML - many innerXML
; endTag name
; return (Node name innerXML)
}
innerXML = do
x - (try xml | gettext)
return x
openTag :: Parser String
openTag = do
char ''
content - many (noneOf )
char ''
return content
endTag :: String - Parser String
endTag str = do
char ''
char '/'
string str
char ''
return str
h1 = parse xml aA/a
h2 = parse xml abA/b/a
h3 = parse xml abc/c/b/a
h4 = parse xml ab/bc/c/a
Regards,
Kashyap
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Re: [Haskell-cafe] Need help with learning Parsec
Am 19.07.2012 15:14, schrieb Christian Maeder: Am 19.07.2012 14:53, schrieb C K Kashyap: innerXML = do x - (try xml | gettext) return x Omit try (and return). xml always starts with whereas gettext never does. I was wrong, you do not want to swallow an endTag as openTag. openTag should start with: try $ char '' notFollowedBy (char '/') and endTag should start with: try $ string / C. C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need help with learning Parsec
On Thu, Jul 19, 2012 at 06:45:05PM +0530, Sai Hemanth K wrote: gettext = (many1 $ noneOf ) = (return . Body) You can simplify this to: import Control.Applicative hiding ((|)) gettext = Body $ many1 (noneOf ) And some of your other parsers can be simplified as well: innerXML = xml | gettext openTag :: Parser String openTag = char '' * many (noneOf ) * char '' endTag :: String - Parser String endTag str = string / * string str * char '' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need help with learning Parsec
gettext = Body $ many1 (noneOf ) Note that this is the same as: gettext = Body `fmap` many1 (noneOf ) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need help with learning Parsec
On Thu, Jul 19, 2012 at 03:34:47PM +0200, Simon Hengel wrote: openTag :: Parser String openTag = char '' * many (noneOf ) * char '' endTag :: String - Parser String endTag str = string / * string str * char '' Well yes, modified to what Christian Maeder just suggested. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need help with learning Parsec
Am 19.07.2012 15:26, schrieb Christian Maeder: Am 19.07.2012 15:14, schrieb Christian Maeder: Am 19.07.2012 14:53, schrieb C K Kashyap: innerXML = do x - (try xml | gettext) return x Omit try (and return). xml always starts with whereas gettext never does. I was wrong, you do not want to swallow an endTag as openTag. openTag should start with: try $ char '' notFollowedBy (char '/') and endTag should start with: try $ string / Strictly, the try in endTag is not necessary (only in openTag) C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to add constraint to .cabal?
On Thu, Jul 19, 2012 at 09:37:52AM +0800, Magicloud Magiclouds wrote: Hi, Say I have a package that only appends --constraint=template-haskell==2.7.0.0 --constraint=warp-tls==1.2.1 could I install it. Now I want to release the package, then how could I have these constraint into the .cabal so the user would not get troubled? Using the build-depends field. See http://www.haskell.org/cabal/users-guide/developing-packages.html#build-information -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need help with learning Parsec
Am 19.07.2012 15:41, schrieb Simon Hengel: On Thu, Jul 19, 2012 at 03:34:47PM +0200, Simon Hengel wrote: openTag :: Parser String openTag = char '' * many (noneOf ) * char '' if you disallow empty tags and / within tags, then you can avoid the notFollowedBy construct by: openTag = try (char '' * many1 (noneOf /)) * char '' C. endTag :: String - Parser String endTag str = string / * string str * char '' Well yes, modified to what Christian Maeder just suggested. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need help with learning Parsec
Thank you so much ... I've updated my monad version here - https://github.com/ckkashyap/LearningPrograms/blob/master/Haskell/Parsing/xml_1.hshttps://github.com/ckkashyap/LearningPrograms/blob/master/Haskell/Parsing/xml_2.hs and the Applicative version here - https://github.com/ckkashyap/LearningPrograms/blob/master/Haskell/Parsing/xml_2.hs The applicative version however does not seem to work. Is there a good tutorial that I can look up for Parsec - I am checking out http://legacy.cs.uu.nl/daan/download/parsec/parsec.html but I am looking for a tutorial where a complex parser would be built ground up. Next I'd like to take care of escaped angular brackets. Regards, Kashyap On Thu, Jul 19, 2012 at 7:40 PM, Christian Maeder christian.mae...@dfki.dewrote: Am 19.07.2012 15:41, schrieb Simon Hengel: On Thu, Jul 19, 2012 at 03:34:47PM +0200, Simon Hengel wrote: openTag :: Parser String openTag = char '' * many (noneOf ) * char '' if you disallow empty tags and / within tags, then you can avoid the notFollowedBy construct by: openTag = try (char '' * many1 (noneOf /)) * char '' C. endTag :: String - Parser String endTag str = string / * string str * char '' Well yes, modified to what Christian Maeder just suggested. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
