- Haskell-Cafe - Haskell.org

Haskell wiki account request response time
by Howard B. Golden 04 Mar '19

04 Mar '19

Hi Michal, You requested a Haskell wiki account at Fri, 1 Mar 2019 16:08:10 +0100 > Date: Fri, 1 Mar 2019 16:08:10 +0100 > From: Miguel <m.i(a)gmx.at> > To: wiki-account-request(a)haskell.org > Subject: wiki-account-request > oo_miguel Then, 8 minutes, 25 seconds later, you sent this message to Haskell-Cafe: > From: m.i at gmx.at (Miguel) > Date: Fri, 1 Mar 2019 16:16:35 +0100 > Subject: [Haskell-cafe] wiki-account-request > Message-ID: <20190301151635.kkpq2m4x7fkbftqj(a)megaloman.softwarefools.com> > Hi, > Not receiving any response from the other channel I hereby request a > wiki.haskell.org account with the preferred username: "oo_miguel" > Thanks in Advance, > Michal Idziorek > Ref: > https://wiki.haskell.org/index.php?title=Special:UserLogin > "If you would like an account please email 'wiki-account-request' > (at the domain haskell dot org) or, if you find that unresponsive, > on the haskell-cafe mailing list." At Fri, 1 Mar 2019 18:36:00 +0100, Henk-Jan_van_Tuyl created your account. This was 2 hours and 28 minutes after your initial request. Generally, we create accounts within 24 hours of their request, often much sooner. All of us who create accounts are volunteers. We create accounts manually to prevent spam. Regards, Howard

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PR to "double-conversion"
by Иван Николаев 02 Mar '19

02 Mar '19

Hi Bryan! May I ask you to take a look at my PR to your double-conversion library? I’ve made it about six months ago and sent you an email. A few days ago I updated it. In the PR mentioned above I’m adding several things which need your attention: 1. Conversion to bytestring and text builder. 2. Conversion of Float (using type family, but without performance degrading). 3. More benchmarks. 4. Update of the original double-conversion library. Now a bunch of 20k doubles is converted to strict bytestring in 5-8 ms using bytestring builder instead of >200-300ms using just bytestring. Cheers, Rinat

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ANN: hledger-1.14
by Simon Michael 02 Mar '19

02 Mar '19

I'm pleased to announce the release of hledger 1.14! Thank you release contributors Jakob Schöttl and Jakub Zárybnický. hledger is a robust, cross-platform plain text accounting tool, for tracking money, time, stocks, cryptocurrencies or any other commodity, using double-entry accounting, private or shared plain text files, revision control, and command-line, curses or web UIs. Find out more at http://hledger.org and http://plaintextaccounting.org. Release notes summary: ---------------------- Inclusive balance assertions, commodities command, --invert option, JSON get/add support in hledger-web. For full details, see http://hledger.org/release-notes. Getting started: ---------------- All install methods are described at http://hledger.org/download . (system packages, windows binaries, docker, nix, cabal, stack, hledger-install bash script..) Some of these might take a few days to become up to date. Tutorials and all docs and support options are linked at http://hledger.org . Get help via chat in #hledger on Freenode: http://irc.hledger.org Or connect via Matrix: http://riot.hledger.org New and old users, contributors, sponsors, positive/negative feedback, always welcome! Best, -Simon

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wiki-account-request
by Miguel 01 Mar '19

01 Mar '19

Hi, Not receiving any response from the other channel I hereby request a wiki.haskell.org account with the preferred username: "oo_miguel" Thanks in Advance, Michal Idziorek Ref: https://wiki.haskell.org/index.php?title=Special:UserLogin "If you would like an account please email 'wiki-account-request' (at the domain haskell dot org) or, if you find that unresponsive, on the haskell-cafe mailing list."

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show in monad
by Damien Mattei 01 Mar '19

01 Mar '19

just for tracing the monad i have this : import Control.Monad import Data.Ratio import Data.List (all) import Debug.Trace newtype Prob a = Prob { getProb :: [(a,Rational)] } deriving Show instance Functor Prob where fmap f (Prob xs) = trace " Functor Prob " Prob $ map (\(x,p) -> (f x,p)) xs t flatten :: Prob (Prob a) -> Prob a flatten (Prob xs) = trace (" flatten " ++ show xs) Prob $ concat $ map multAll xs where multAll (Prob innerxs,p) = trace " multAll " map (\(x,r) -> (x,p*r)) innerxs instance Applicative Prob where pure = trace " Applicative Prob return " return (<*>) = trace " Applicative Prob ap " ap instance Monad Prob where return x = trace " Monad Prob return " Prob [(x,1%1)] m >>= f = trace " Monad Prob >>= " flatten (fmap f m) fail _ = trace " Monad Prob fail " Prob [] {- instance Applicative Prob where pure a = Prob [(a,1%1)] Prob fs <*> Prob as = Prob [(f a,x*y) | (f,x) <- fs, (a,y) <- as] instance Monad Prob where Prob as >>= f = Prob [(b,x*y) | (a,x) <- as, let Prob bs = f a, (b,y) <- bs] -} in this : flatten :: Prob (Prob a) -> Prob a flatten (Prob xs) = trace (" flatten " ++ show xs) Prob $ concat $ map multAll xs where multAll (Prob innerxs,p) = trace " multAll " map (\(x,r) -> (x,p*r)) innerxs i have this error: [1 of 1] Compiling Main ( monade.hs, interpreted ) monade.hs:22:43: error: • No instance for (Show a) arising from a use of ‘show’ Possible fix: add (Show a) to the context of the type signature for: flatten :: forall a. Prob (Prob a) -> Prob a • In the second argument of ‘(++)’, namely ‘show xs’ In the first argument of ‘trace’, namely ‘(" flatten " ++ show xs)’ In the expression: trace (" flatten " ++ show xs) Prob | 22 | flatten (Prob xs) = trace (" flatten " ++ show xs) | ^^^^^^^ Failed, no modules loaded. how can i implement a show for xs ? regards, damien

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qtHaskell
by David Harley 28 Feb '19

28 Feb '19

I've made a new version of qtHaskell - version 1.1.10.1 available at the following site: http://www.isptech.co.uk/qtHaskell/download.html It comprises bindings to about 50 Qt modules and includes a version of Asteroids which uses functional reactive programming and some code running in a non-IO based monad, plus a Qt based version of Threadscope (qts). The installation of a code set of this sort can be tricky, it builds using a combination of cabal, qmake and make controled from perl. I wish it were simpler, but in most cases: ./build lite -jx will build all modules required for the demos and examples. It has currently only been tested on Linux hence, the build script which used to work on Windows will probably not work without some modification. I'll get around to that if there's any interest. It has also only been tested against regular builds of Qt 5.11/5.12 build from the qt-everywhere-src-5.11/12.x codesets. Good luck with any building and testing of qtHaskell-1.1.10.1, and I'd be delighted to get any feedback David Harley

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rounding and undefined behavior
by Matt Peddie 28 Feb '19

28 Feb '19

Hi cafe, It's been my general impression that when neither Haskell nor C defines behavior in a particular situation, the behavior nonetheless matches. I was surprised to observe Prelude Data.Int> round (4294967295 :: Double) :: Int16 -1 when #include <stdio.h> #include <inttypes.h> int main(void) { double d = 4294967295; int16_t r = (int16_t) d; printf("%"PRId16"\n", r); return 0; } yields 0 when compiled and run. As far as I can tell, neither language defines what this result should be, so neither is doing anything wrong here. But I was surprised that they differ; does anyone know why Haskell's rounding operation behaves the way it does (maybe there is some historical reason)? Or can someone perhaps point me to a standards document I missed that states how the language must round out-of-bounds inputs? Regards Matt Peddie

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example of monad from http://learnyouahaskell.com not working
by Damien Mattei 27 Feb '19

27 Feb '19

i'm trying this example (see code below) from : http://learnyouahaskell.com/for-a-few-monads-more#making-monads when trying to compile this: import Data.Ratio newtype Prob a = Prob { getProb :: [(a,Rational)] } deriving Show instance Functor Prob where fmap f (Prob xs) = Prob $ map (\(x,p) -> (f x,p)) xs thisSituation :: Prob (Prob Char) thisSituation = Prob [( Prob [('a',1%2),('b',1%2)] , 1%4 ) ,( Prob [('c',1%2),('d',1%2)] , 3%4) ] flatten :: Prob (Prob a) -> Prob a flatten (Prob xs) = Prob $ concat $ map multAll xs where multAll (Prob innerxs,p) = map (\(x,r) -> (x,p*r)) innerxs instance Monad Prob where return x = Prob [(x,1%1)] m >>= f = flatten (fmap f m) fail _ = Prob [] l1 = Prob [('a',2%3),('b',1%3)] multAllExt :: (Prob a, Rational) -> [(a, Rational)] multAllExt (Prob innerxs,p) = map (\(x,r) -> (x,p*r)) innerxs --Main> :type multAllExt --multAllExt :: (Prob a, Rational) -> [(a, Rational)] --Main> multAllExt (l1,1 % 4) --[('a',1 % 6),('b',1 % 12)] i get this error: GHCi, version 8.4.3: http://www.haskell.org/ghc/ :? for help Prelude> :load monade.hs [1 of 1] Compiling Main ( monade.hs, interpreted ) monade.hs:21:10: error: • No instance for (Applicative Prob) arising from the superclasses of an instance declaration • In the instance declaration for ‘Monad Prob’ | 21 | instance Monad Prob where | ^^^^^^^^^^ Failed, no modules loaded. it fails when i add the last part of the example: instance Monad Prob where return x = Prob [(x,1%1)] m >>= f = flatten (fmap f m) fail _ = Prob [] seems the Monad needs an instance of the Applicative to be instanciated... what is wrong? regards, Damien

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Haskell.Org accepted for GSoC 2019
by Jasper Van der Jeugt 26 Feb '19

26 Feb '19

Hi all, We're very excited to announce that Haskell.Org has been accepted [1] into the Google Summer of Code 2019 program [2]. We hope that, like last year, it will lead to a whole range of improvements to the Haskell ecosystem, and to new faces joining our community! We would like to thank everyone who submitted ideas -- this is a key part of being accepted into GSoC. Now, here's the near term timeline: - Today - March 25: Potential student participants discuss application ideas with mentors - March 25 - April 9: Students can submit applications - May 6: Accepted student proposals announced At this point, we're looking for both students and extra mentors. We would like to assign at least two mentors to each project if possible, so the students get the support they deserve. Additional ideas for projects are still welcome! There's a lot of information on our Summer of Haskell page [3]. If there are any students who are not sure where to begin, feel free to reach out to us directly [4]! [1]: https://summerofcode.withgoogle.com/organizations/5556388114202624/ [2]: https://summerofcode.withgoogle.com/ [3]: https://summer.haskell.org/ [4]: https://summer.haskell.org/contact.html Warm regards Jasper Van der Jeugt on behalf of the Haskell.Org Committee

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generics-sop equivalent of everywhere/mkT?
by Scott Michel 26 Feb '19

26 Feb '19

Before I cut down my code to a test case, are there any examples of a generics-sop equivalent of syb's everywhere/mkT? What's the way to operate on a product, replace the "I" argument with a compatible argument and walk back through the isomorphism, i.e. "to $ <something> $ from". I'm hacking on a Z80 system emulator (TRS-80 Model I system, more specifically). There are a couple of places where it'd be smoother in the disassembler to transform the disassembled instruction sequence (converting addresses to labels) before output. Consequently, cutting down code to an example is a bit painful -- examples would help. -scooter

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