Re: [Haskell-cafe] grapefruit on windows or osX
Am Sonntag, 21. Februar 2010 21:57:45 schrieb gladst...@gladstein.com: > I'm unable to get grapefruit going on osx or windows because (I think) I > can't get the underlying GTK installed. Hi, thank you for giving Grapefruit a try. Yes, you are most likely right that Gtk2Hs is the stumbling block. Grapefruit itself doesn’t do anything OS-specific, and since it works on Linux, it should also work on OS X. I strongly suggest that you try out the current development version of Grapefruit instead of the version on Hackage, since the latter is lacking a bunch of features. If you have any Grapefruit-related questions, please ask here or on the Grapefruit mailing list. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Alex Lexer: Trying to get rid of "Alex"
Hi Haskell-cafe My problem: I'm trying to obtain the current position of the lexer once it reaches the end of the file (line and row number). I'm trying to do this in a function: getEndPosition = do (a,b,c) <- alexGetInput return a Unfortunately, the type of a is 'Alex AlexPosn' instead of just 'AlexPosn' How do I strip the Alex so I'm left with just a AlexPosn object? Thanks, Amit Deshwar University of Calgary ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alex Lexer: Trying to get rid of "Alex"
On 23 February 2010 20:15, Amit Deshwar wrote: > Hi Haskell-cafe > My problem: I'm trying to obtain the current position of the lexer once it > reaches the end of the file (line and row number). > I'm trying to do this in a function: > getEndPosition = do > (a,b,c) <- alexGetInput > return a > > Unfortunately, the type of a is 'Alex AlexPosn' instead of just 'AlexPosn' > How do I strip the Alex so I'm left with just a AlexPosn object? Hi Amit, Are you sure about the type of a? It looks like you are using the "monad" wrapper, described here: http://www.haskell.org/alex/doc/html/wrappers.html If that is true, then: alexGetInput :: Alex AlexInput and type AlexInput = (AlexPosn, Char, String) >From that we can infer from your code: getEndPosition :: Alex AlexPosn and thus: a :: AlexPosn If you want to manipulate the value bound to a, you can simply apply a function to it in the body of getEndPosition, and return the result of that application (still inside the Alex type). Or you can use the function: runAlex :: String -> Alex a -> Either String a Cheers, Bernie. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsing of bytestrings with non-String errors?
On Tue, Feb 23, 2010 at 00:39, Bryan O'Sullivan wrote: > On Mon, Feb 22, 2010 at 2:38 PM, Magnus Therning > wrote: >> >> My thoughts went more like a parser type like >> >> data Parser e a = ... > > Yes, I knew that's where you were going :-) > The trouble is, you'd still have to deal with > fail :: Monad m => String -> m a > which would require your failure type to somehow accept a string. Plumbing > that in would be a little more awkward than your initial exporations suggest > :-\ > You have two problems. The first is how to construct a value of your failure > type that accepts a String parameter so that you can support users of > "fail". The second is that you might need to pass extra information to > construct your failure value when naïve code uses fail or mzero, otherwise > you will only get useful error values out quite infrequently. Yes, I suspected there'd be something I had missed. I guess it'd would require 'Parser e a' to have a 'fail' that's similar to the one in 'Maybe'. Users would then be forced to use '' to get useful error info out. Would that be an unworkable situation? >> I still haven't convinced myself that this will work though. Also, I had >> a >> look at attoparsec on bitbucket, and there are some major changes between >> 0.7 >> and 0.8. > > Even though those changes represent a major modification to the internals of > attoparsec, they shouldn't really affect what you want to do, or anything > interesting about how to do it. Ah, that's good. I think I'll have to postpone any work on this for now though, and instead implement a 'String -> MyErrorType' function for, hopefully, temporary use. I've already been sidetracked twice before ;-) /M -- Magnus Therning(OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Function to detect duplicates
Hi folks, While solving a puzzle, I was posed the problem of finding if there was no duplicates on a list. First I used: noneRepeated=null.(filter (>1)).(map length).group.sort But this seemed very unneficient, so I thought that I could detect the duplicates while sorting, and devised this: import Control.Monad import Data.Maybe noneRepeated=isNothing . (foldl merge (Just [])) . (map sort) . pairs pairs []=[] pairs [x]=[[x]] pairs (x:y:xs)=[x,y]:pairs xs sort []=Just [] sort [x]=Just [x] sort [x,y] | x>y=Just [y,x] | y>x=Just [x,y] | x==y=Nothing merge::(Eq a, Ord a) => Maybe [a]->Maybe [a]->Maybe[a] merge _ Nothing = Nothing merge Nothing _ = Nothing merge (Just []) (Just xs)=Just xs merge (Just xs) (Just [])=Just xs merge (Just (x:xs)) (Just (y:ys)) | x==y = Nothing | x>y = (Just y) +? (merge (Just (x:xs)) (Just ys)) | x___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function to detect duplicates
Hi Rafael, I assume you will perform this operation on some very large lists, or performance would not be an issue. Have you tested if your optimized version is better than your initial one? You should compare your implementation against something like this: import qualified Data.Set as Set noneRepeated :: (Ord a) => [a] -> Bool noneRepeated = accum Set.empty where accum _ [] = True accum s (x:xs) | Set.member x s = False | otherwise = accum (Set.insert x s) xs Also there is some discussion about the nub function that relates to this topic, e.g. http://buffered.io/2008/07/28/a-better-nub/. /Jonas On 23 February 2010 12:30, Rafael Gustavo da Cunha Pereira Pinto wrote: > > Hi folks, > > While solving a puzzle, I was posed the problem of finding if there was no > duplicates on a list. > > First I used: > > noneRepeated=null.(filter (>1)).(map length).group.sort > > > But this seemed very unneficient, so I thought that I could detect the > duplicates while sorting, and devised this: > > import Control.Monad > import Data.Maybe > > noneRepeated=isNothing . (foldl merge (Just [])) . (map sort) . pairs > > pairs []=[] > pairs [x]=[[x]] > pairs (x:y:xs)=[x,y]:pairs xs > > sort []=Just [] > sort [x]=Just [x] > sort [x,y] | x>y=Just [y,x] > | y>x=Just [x,y] > | x==y=Nothing > > merge::(Eq a, Ord a) => Maybe [a]->Maybe [a]->Maybe[a] > merge _ Nothing = Nothing > merge Nothing _ = Nothing > merge (Just []) (Just xs)=Just xs > merge (Just xs) (Just [])=Just xs > merge (Just (x:xs)) (Just (y:ys)) | x==y = Nothing > | x>y = (Just y) +? (merge (Just (x:xs)) > (Just ys)) > | x (Just (y:ys))) > > (+?) = liftM2 (:) > > > > My version of the merge sort returns Nothing whenever it finds two equal > entries, aborting all subsequent comparisons. > > I have a few questions for the friendly people at this cafe: > > 1) Is there any improvement I can make? > 2) Can it be parallelized (par, pseq)? > > > Best regards, > > Rafael > > ___ > 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] Profiling OpenGL applications
On Sunday, Andrew Coppin asked: > Is Thread Scope any use for profiling single-threaded programs? I used threadscope to look at eventlogs from a program that uses OpenGL to render multiple frames per second (compiled without "-threaded"). That means, there is CPU activity regularly (multiple times per second), and this can be observed via threadscope and i found it somewhat useful. There are some problems, though: 1. I can't definitely tell, which time span corresponds to CPU activity for the calculations for one frame. Is it possible to generate threadscope bookmarks from within the profiled program? (Or other events that can be shown in threadscope?) 2. The GPU activity cannot be observed. This is not a problem specific to Haskell, though. Is it even possible (with end user hardware) to get something similar to threadscope, not for CPU, but GPU activity? Any other ideas, that might help gathering information, about what's going on on the CPU(s) and the GPU? Many thanks, Sönke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Function to detect duplicates
Rafael Gustavo da Cunha Pereira Pinto wrote: > While solving a puzzle, I was posed the problem of finding if there > was no duplicates on a list. > > First I used: > > noneRepeated=null.(filter (>1)).(map length).group.sort > > But this seemed very unneficient, so I thought that I could detect the > duplicates while sorting, and devised this: > > import Control.Monad > import Data.Maybe > > noneRepeated=isNothing . (foldl merge (Just [])) . (map sort) . pairs import Data.List noneRepeated xs = xs == nub xs Greets Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://blog.ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Function to detect duplicates
Am Dienstag 23 Februar 2010 13:03:45 schrieb Ertugrul Soeylemez: > Rafael Gustavo da Cunha Pereira Pinto wrote: > > While solving a puzzle, I was posed the problem of finding if there > > was no duplicates on a list. > > > > First I used: > > > > noneRepeated=null.(filter (>1)).(map length).group.sort > > > > But this seemed very unneficient, so I thought that I could detect the > > duplicates while sorting, and devised this: > > > > import Control.Monad > > import Data.Maybe > > > > noneRepeated=isNothing . (foldl merge (Just [])) . (map sort) . pairs > > import Data.List > > noneRepeated xs = xs == nub xs Talk about inefficiency :) import Data.Set (Set) import qualified Data.Set as Set noneRepeated = go 0 Set.empty where go ct st (x:xs) | Set.size st < ct = False | otherwise = go (ct+1) (Set.insert x st) xs go ct st [] = ct == Set.size st > > > Greets > Ertugrul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Function to detect duplicates
Ertugrul: while your solution is minimalistic, Rafael deemed his ~n*log n implementation too inefficient. Thus your ~n^3 implementation is hardly an improvement... /Jonas On 23 February 2010 13:03, Ertugrul Soeylemez wrote: > Rafael Gustavo da Cunha Pereira Pinto wrote: > >> While solving a puzzle, I was posed the problem of finding if there >> was no duplicates on a list. >> >> First I used: >> >> noneRepeated=null.(filter (>1)).(map length).group.sort >> >> But this seemed very unneficient, so I thought that I could detect the >> duplicates while sorting, and devised this: >> >> import Control.Monad >> import Data.Maybe >> >> noneRepeated=isNothing . (foldl merge (Just [])) . (map sort) . pairs > > import Data.List > > noneRepeated xs = xs == nub xs > > > Greets > Ertugrul > > > -- > nightmare = unsafePerformIO (getWrongWife >>= sex) > http://blog.ertes.de/ > > > ___ > 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] Function to detect duplicates
Rafael Gustavo da Cunha Pereira Pinto writes: > First I used: > > noneRepeated=null.(filter (>1)).(map length).group.sort > But this seemed very unneficient, so I thought that I could detect the > duplicates while sorting, and devised this: [...] > 1) Is there any improvement I can make? Well - it's a bit long, don't you think? Long enough that from a cursory glance, I'd say it's in the "no obvious errors" category. How about (inspired by quicksort, as you no doubt can tell): noneRepeated [] = True noneRepeated (x:xs) = noneRepeated lt && singleton eq && noneRepeated gt where lt = filter (x) xs eq = x:filter (==x) xs singleton [_] = True singleton _ = False > 2) Can it be parallelized (par, pseq)? You could force each of the sublists in parallel, but you might lose some laziness properties, so I'd carefully benchmark it. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Function to detect duplicates
Jonas Almström Duregård wrote: > Ertugrul: while your solution is minimalistic, Rafael deemed his > ~n*log n implementation too inefficient. Thus your ~n^3 implementation > is hardly an improvement... My variant has an advantage, though. It is completely lazy, so it will take a shortcut, as soon as a duplicate is found. Depending on his application, this may be useful or not. I think the nub-based solution is the best one in general, but it's the base library implementation of nub, which is unfortunate. In fact, with a better nub implementation, this becomes an O(n * log n) time algorithm, too, but with the additional laziness advantage. The article you linked to contains such an implementation, I think. Greets Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://blog.ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Function to detect duplicates
Am Dienstag 23 Februar 2010 13:59:49 schrieb Ertugrul Soeylemez: > Jonas Almström Duregård wrote: > > Ertugrul: while your solution is minimalistic, Rafael deemed his > > ~n*log n implementation too inefficient. Thus your ~n^3 implementation > > is hardly an improvement... Not quite as bad, nub is O(n^2). > > My variant has an advantage, though. It is completely lazy, so it will > take a shortcut, as soon as a duplicate is found. Depending on his > application, this may be useful or not. > > I think the nub-based solution is the best one in general, but it's the > base library implementation of nub, which is unfortunate. In fact, with > a better nub implementation, this becomes an O(n * log n) time How can you nub in O(n*log n)? Remember, you only have Eq for nub. > algorithm, too, but with the additional laziness advantage. The article > you linked to contains such an implementation, I think. > > > Greets > Ertugrul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Proper round-trip HughesPJ/Parsec for Doubles?
Hi all, Short version: How can I pretty print and parse values of type Double such that those operations are each other's inverse? Long version: I'm writing and QuickCheck-testing a parser using the approach set out here: http://lstephen.wordpress.com/2007/07/29/parsec-parser-testing-with-quickcheck/ That is, each syntactic category gets a pretty-printer and a parser and an Arbitrary instance, and QuickCheck checks that (parse . prettyPrint) == id, basically. Somewhat unsurprisingly, this sometimes fails for floating point values (I'm using Doubles). Now, I know that floats are in some sense imprecise, and comparing for equality is fraught with peril, but it seems that if x==x then it ought to be at least _possible_ to arrange matters such that (parse . prettyPrint x) == x as well. At worst, pretty-printing the underlying binary representation!? So my feeling is that my parser could be improved. At the moment I'm working around it by defining a type class which checks for equality within some margin of error, and using that instead of Eq - but it's messier than I'd like, so I wondered if there was something obvious I'm missing. As hpaste.org seems to be down, I'll attach a code example here instead. Thanks! -Andy -- Andy Gimblett http://gimbo.org.uk/ TestParse.hs Description: Binary data ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Function to detect duplicates
>>noneRepeated xs = xs == nub xs > Not quite as bad, nub is O(n^2) You are correct of course. Still, it will probably be a bit less inefficient if the length of the lists are compared (as opposed to the elements): noneRepeated xs = length xs == length (nub xs) On 23 February 2010 14:09, Daniel Fischer wrote: > Am Dienstag 23 Februar 2010 13:59:49 schrieb Ertugrul Soeylemez: >> Jonas Almström Duregård wrote: >> > Ertugrul: while your solution is minimalistic, Rafael deemed his >> > ~n*log n implementation too inefficient. Thus your ~n^3 implementation >> > is hardly an improvement... > > Not quite as bad, nub is O(n^2). > >> >> My variant has an advantage, though. It is completely lazy, so it will >> take a shortcut, as soon as a duplicate is found. Depending on his >> application, this may be useful or not. >> >> I think the nub-based solution is the best one in general, but it's the >> base library implementation of nub, which is unfortunate. In fact, with >> a better nub implementation, this becomes an O(n * log n) time > > How can you nub in O(n*log n)? Remember, you only have Eq for nub. > >> algorithm, too, but with the additional laziness advantage. The article >> you linked to contains such an implementation, I think. >> >> >> Greets >> Ertugrul > > ___ > 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] Re: Function to detect duplicates
Am Dienstag 23 Februar 2010 14:54:36 schrieb Jonas Almström Duregård: > You are correct of course. Still, it will probably be a bit less > inefficient if the length of the lists are compared (as opposed to the > elements): > > noneRepeated xs = length xs == length (nub xs) Only if no repeated elements appear early. For xs = 1 : [1 .. 10^7], xs == nub xs will return False without noticeable delay, length xs == length (nub xs) will take VERY long. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proper round-trip HughesPJ/Parsec for Doubles?
Am Dienstag 23 Februar 2010 14:44:50 schrieb Andy Gimblett:
> Hi all,
>
> Short version: How can I pretty print and parse values of type Double
> such that those operations are each other's inverse?
>
> Long version: I'm writing and QuickCheck-testing a parser using the
> approach set out here:
>
> http://lstephen.wordpress.com/2007/07/29/parsec-parser-testing-with-quic
>kcheck/
>
> That is, each syntactic category gets a pretty-printer and a parser
> and an Arbitrary instance, and QuickCheck checks that (parse .
> prettyPrint) == id, basically. Somewhat unsurprisingly, this
> sometimes fails for floating point values (I'm using Doubles).
>
> Now, I know that floats are in some sense imprecise, and comparing for
> equality is fraught with peril, but it seems that if x==x then it
> ought to be at least _possible_ to arrange matters such that (parse .
> prettyPrint x) == x as well. At worst, pretty-printing the underlying
> binary representation!? So my feeling is that my parser could be
> improved.
Parse it as a Rational, then convert with fromRational.
I don't know whether that will always have parse . prettyPrint == id, but
it'll be much closer.
The naturalOrFloat default implementation uses
fraction= do{ char '.'
; digits <- many1 digit "fraction"
; return (foldr op 0.0 digits)
}
"fraction"
where
op d f= (f + fromIntegral (digitToInt d))/10.0
and division by 10 isn't exact with a binary representation.
>
> At the moment I'm working around it by defining a type class which
> checks for equality within some margin of error, and using that
> instead of Eq - but it's messier than I'd like, so I wondered if there
> was something obvious I'm missing.
>
> As hpaste.org seems to be down, I'll attach a code example here instead.
>
> Thanks!
>
> -Andy
>
> --
> Andy Gimblett
> http://gimbo.org.uk/
___
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[Haskell-cafe] Re: Proper round-trip HughesPJ/Parsec for Doubles?
Andy Gimblett schrieb: > Hi all, > > Short version: How can I pretty print and parse values of type Double > such that those operations are each other's inverse? Maybe you have more luck with show and read (without Parsec.Token). Your example: x = 9.91165677454629 fails because the computation performed by the parser 9.0 + 0.91165677454629 yields 9.911656774546291 Cheers Christian > Long version: I'm writing and QuickCheck-testing a parser using the > approach set out here: > > http://lstephen.wordpress.com/2007/07/29/parsec-parser-testing-with-quickcheck/ > > > That is, each syntactic category gets a pretty-printer and a parser and > an Arbitrary instance, and QuickCheck checks that (parse . prettyPrint) > == id, basically. Somewhat unsurprisingly, this sometimes fails for > floating point values (I'm using Doubles). > > Now, I know that floats are in some sense imprecise, and comparing for > equality is fraught with peril, but it seems that if x==x then it ought > to be at least _possible_ to arrange matters such that (parse . > prettyPrint x) == x as well. At worst, pretty-printing the underlying > binary representation!? So my feeling is that my parser could be improved. > > At the moment I'm working around it by defining a type class which > checks for equality within some margin of error, and using that instead > of Eq - but it's messier than I'd like, so I wondered if there was > something obvious I'm missing. > > As hpaste.org seems to be down, I'll attach a code example here instead. > > Thanks! > > -Andy > > -- > Andy Gimblett > http://gimbo.org.uk/ > > > > > > > ___ > 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] Re: Proper round-trip HughesPJ/Parsec for Doubles?
Short version: How can I pretty print and parse values of type Double such that those operations are each other's inverse? Maybe you have more luck with show and read (without Parsec.Token). Your example: x = 9.91165677454629 fails because the computation performed by the parser 9.0 + 0.91165677454629 yields 9.911656774546291 That seems to do the trick! Below, for the record, the code I've come up with (I threw away the Either Integer Double part so it's a bit simpler, also). I'm sure it can be improved, but this is passing all tests reliably, it seems. Many thanks, Christian and Daniel, for your help! Best, -Andy parseDouble :: Parser Double parseDouble = try $ do (symbol toks) "-" n <- floater return $ negate n <|> floater where toks = makeTokenParser emptyDef -- This could definitely be improved, but it's working. :-) floater :: Parser Double floater = do w <- many1 digit char '.' f <- many1 digit e <- optionMaybe $ do char 'e' -- Optional exponent part n <- option "" (char '-' >> return "-") -- Optional negation in exponent m <- many1 digit return $ n ++ m case e of Nothing -> return $ read $ w ++ "." ++ f Just e' -> return $ read $ w ++ "." ++ f ++ "e" ++ e' -- Andy Gimblett http://gimbo.org.uk/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Problems linking hsql-mysql
Hi, I have problems linking a simple test program that imports Database.HSQL.MySQL via ghc --make Test.hs. The error only occurs when importing this module of hsql-mysql-1.7.1. I pasted the building output here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=22911 (actually it was even longer but hpaste only takes 30k). When I do ghc -e main Test.hs or starting it from GHCi, everything works fine and no errors occur. So I guess all needed .lib files are there but GHC can't find them when linking (adding the flag -L"path to mysql/lib/opt" doesn't help). Anyone an idea? Best wishes, Maciej ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proper round-trip HughesPJ/Parsec for Doubles?
If you use read (reads) and show for the actual conversion it will round trip. It appears to be non-trivial since most languages and libraries get it wrong. :) -- Lennart On Tue, Feb 23, 2010 at 1:44 PM, Andy Gimblett wrote: > Hi all, > > Short version: How can I pretty print and parse values of type Double such > that those operations are each other's inverse? > > Long version: I'm writing and QuickCheck-testing a parser using the approach > set out here: > > http://lstephen.wordpress.com/2007/07/29/parsec-parser-testing-with-quickcheck/ > > That is, each syntactic category gets a pretty-printer and a parser and an > Arbitrary instance, and QuickCheck checks that (parse . prettyPrint) == id, > basically. Somewhat unsurprisingly, this sometimes fails for floating point > values (I'm using Doubles). > > Now, I know that floats are in some sense imprecise, and comparing for > equality is fraught with peril, but it seems that if x==x then it ought to > be at least _possible_ to arrange matters such that (parse . prettyPrint x) > == x as well. At worst, pretty-printing the underlying binary > representation!? So my feeling is that my parser could be improved. > > At the moment I'm working around it by defining a type class which checks > for equality within some margin of error, and using that instead of Eq - but > it's messier than I'd like, so I wondered if there was something obvious I'm > missing. > > As hpaste.org seems to be down, I'll attach a code example here instead. > > Thanks! > > -Andy > > -- > Andy Gimblett > http://gimbo.org.uk/ > > > > > > ___ > 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] Re: Proper round-trip HughesPJ/Parsec for Doubles?
For the record, here's the final improved version: float' :: TokenParser st -> GenParser Char st Double float' t = do n <- liftCtoS '-' w <- many1 digit char '.' f <- many1 digit e <- option "" $ do char 'e' n' <- liftCtoS '-' m <- many1 digit return $ concat ["e", n', m] whiteSpace t return $ read $ concat [n, w, ".", f, e] where liftCtoS a = option "" (char a >> return [a]) Thanks for all the help, again. -Andy -- Andy Gimblett http://gimbo.org.uk/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems linking hsql-mysql
Hi Maciej, I will try to reproduce the error -- could you send me your both *.cabal files (for hsql & hsql-mysql), if you have changed anything, and your system configuration. Is this extremely urgent? I ask this, as these days exactly the end phase of the projects of about 100 beginner Haskell students, which I am the one to look after. So I am in a little of slow motion regarding other things... ;-) But in case you are in emergency, please let me know... At first sight, I would say it looks like a configuration problem... ;-) Cheers, Nick Maciej Podgurski wrote: Hi, I have problems linking a simple test program that imports Database.HSQL.MySQL via ghc --make Test.hs. The error only occurs when importing this module of hsql-mysql-1.7.1. I pasted the building output here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=22911 (actually it was even longer but hpaste only takes 30k). When I do ghc -e main Test.hs or starting it from GHCi, everything works fine and no errors occur. So I guess all needed .lib files are there but GHC can't find them when linking (adding the flag -L"path to mysql/lib/opt" doesn't help). Anyone an idea? Best wishes, Maciej ___ 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] Re: sendfile leaking descriptors on Linux?
On Feb 21, 2010, at 20:17 , Jeremy Shaw wrote: The PS3 does do something though. If we were doing a write *and* read select on the socket, the read select would wakeup. So, it is trying to notify us that something has happened, but we are not seeing it because we are only looking at the write select(). Earlier the OP claimed this would happen within a few minutes if he seeked in a movie. If it's that reproducible, it should be easy to capture a tcpdump and attach it to an email (or pastebin it), allowing us to determine what really happens. Also, Donn, you are incorrect about invalidating premises; we know the connection is going away, we can infer it's not going away normally, that's why there have been comments about it sending a FIN and dropping the connection entirely (bypassing the shutdown handshake), or sending an RST, etc. (I'd also be interested in finding out if OpenSolaris or FreeBSD has the same problem, but that may be too difficult to test easily. I still find it highly unlikely that loss of a connection only wakes the read end in general, and would absolutely not be surprised if this were some odd corner case in the Linux TCP stack. Sadly, I don't have a PS3 (yet, if ever) and I don't know of any streaming software for non-hacked Wiis.) -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: sendfile leaking descriptors on Linux?
Quoth "Brandon S. Allbery KF8NH" , > On Feb 21, 2010, at 20:17 , Jeremy Shaw wrote: >> The PS3 does do something though. If we were doing a write *and* >> read select on the socket, the read select would wakeup. So, it is >> trying to notify us that something has happened, but we are not >> seeing it because we are only looking at the write select(). > > Earlier the OP claimed this would happen within a few minutes if he > seeked in a movie. If it's that reproducible, it should be easy to > capture a tcpdump and attach it to an email (or pastebin it), allowing > us to determine what really happens. > > Also, Donn, you are incorrect about invalidating premises; we know the > connection is going away, we can infer it's not going away normally, > that's why there have been comments about it sending a FIN and > dropping the connection entirely (bypassing the shutdown handshake), > or sending an RST, etc. That's what I'm saying - it clearly is not a full close, i.e., going away normally per protocol. With luck maybe the packets will show that something does happen at a wire protocol level, and there will be a way to recognize the event at the `user land' level and plug that into the event loop. My prediction is that on the contrary, the transition between functional and defunct will not be not announced in any way by the peer, but that's just guessing. It would be a lot less interesting. Donn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: sendfile leaking descriptors on Linux?
On Feb 23, 2010, at 23:47 , Donn Cave wrote: My prediction is that on the contrary, the transition between functional and defunct will not be not announced in any way by the peer, but that's just guessing. It would be a lot less interesting. But that's not the issue. The *kernel* is clearly detecting it; the problem is it's only being reported for the *read* end of the socket, whereas sendfile() (correctly) only cares about, and therefore only registers interest in, the *write* end. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Optimizing hash array mapped tries
On Feb 22, 2010, at 02:15 , Edward Z. Yang wrote: * i-Full-update essentially copies a 32-size vector, with a change to one element. I think I am getting brutally punished for this, in terms of both memory usage as well as runtime. What I'm curious is whether or not this is intrinsic to the algorithm, or if it's something special that GHC is doing. IIRC this is intrinsic to the way GHC modifies and garbage-collects array modifications. There's been discussion on -cafe about it. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC RTS question
On Feb 22, 2010, at 03:36 , Roman Cheplyaka wrote:
* Anthony Cowley [2010-02-21 14:15:00-0500]
#! /usr/bin/env bash
./prog --RTS $*
./prog --RTS "$@"
Otherwise it will work wrong if arguments contain quoted field
separators (e.g. spaces).
#! /bin/sh
./prog --RTS ${1+"$@"}
The longer specification above should work with whatever /bin/sh is
around, whether it's Solaris /sbin/sh, FreeBSD's sh, general Linux
bash, Debian/Ubuntu dash, etc.
--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com
system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu
electrical and computer engineering, carnegie mellon universityKF8NH
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Re: [Haskell-cafe] Linux ghci vs Windows ghci
On Feb 21, 2010, at 06:27 , Donghee Nah wrote: I'm using Windows 7 32bit Host OS(ghc 6.8.3) and Virtualbox Archlinux Guest OS(ghc 6.8.4) I feel that ghci code executing speed in guest os is 1.5~2x faster than host os My guess is that GHC (and the GHC RTS) on win32 is using a POSIX emulation layer supplied by mingw32 for all system calls, introducing extra overhead. Unfortunately, I don't think we have enough Windows- familiar folks with enough understanding of the GHC RTS to optimize it for the native Windows API. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [offtopic] UNIX Shell (was: GHC RTS question)
* Brandon S. Allbery KF8NH [2010-02-24 00:02:12-0500]
> On Feb 22, 2010, at 03:36 , Roman Cheplyaka wrote:
> >* Anthony Cowley [2010-02-21 14:15:00-0500]
> >>#! /usr/bin/env bash
> >>./prog --RTS $*
> >
> > ./prog --RTS "$@"
> >
> >Otherwise it will work wrong if arguments contain quoted field
> >separators (e.g. spaces).
>
>
> #! /bin/sh
> ./prog --RTS ${1+"$@"}
>
> The longer specification above should work with whatever /bin/sh is
> around, whether it's Solaris /sbin/sh, FreeBSD's sh, general Linux
> bash, Debian/Ubuntu dash, etc.
Are you referring to some Solaris shell bug?
Under POSIX these constructs seem to be equivalent.
"If there are no positional parameters, the expansion of '@' shall
generate zero fields, even when '@' is double-quoted."
--
Roman I. Cheplyaka :: http://ro-che.info/
"Don't let school get in the way of your education." - Mark Twain
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