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I have a question
by Eunsu Kim 07 May '16

07 May '16

Hi I don’t want to receive this mail anymore. what should do? thanks

2 1

Re: [Haskell-cafe] Code critique request
by Michael Litchard 06 May '16

06 May '16

Thank you David, for taking all that time on my project. I got so much more than I was expecting. I take it my concern was focused in the wrong place? Time-space complexity of mapM fibb is okay? On Fri, May 6, 2016 at 1:37 PM, David McBride <toad3k(a)gmail.com> wrote: > A lot of your functions return Either FizError a when they obviously can't > have an error? I prefer to keep the functions as pure as they can be, and > then lift them into Either in the few cases where I'd need them to be in > that type. > > How about fibb :: Integer -> Integer, fizzbuzz :: Integer -> Text, then > in the above code: > mapM (Right <$> fizzbuzz) =<< ... =<< mapM (Right <$> fibb) =<< ... > > This also greatly simplifies many of your tests and benchmarks. For > example src-test/PropTests/Fibonacci.hs, testfib changes from > > testfib n = > case (fibb n) of > Left _ -> False > Right n' -> isFib n' > > to > > testfib = isFib . fibb > > in src-test/UnitTests/Fibonacci.hs, fibs changes from > > fibs = [Right 1,Right 1,Right 2,Right 3,Right 5,Right 8,Right 13,Right > 21,Right 34,Right 55] > > to > > fibs = [1,1,2,3,5,8,13,21,34,55] > > among others. > > In fizzbuzz, I would, instead of converting it to maybe and then using > fromMaybe, use the option function from semigroups which is the option > equivalent to maybe, and contains all the functionality of fromMaybe. > fizzbuzz :: Integer -> Text > fizzbuzz i = option (show i) id fizzbuzz' > > Your type annotation on c = 2 and subsequent comments are unnecessary if > fibb has a type annotation, which it does. I would also recommend adding > types for divs and fib' as the types are non obvious and I had to use > typeholes to find them. > > In fibb, I would change map (toEnum . fromIntegral) to map (>0) (or /= > 0). It is easier to understand, faster, and will not blow up on negative > numbers (I realize there can't be, but it was not obvious to me). > > You wrote an unfoldl, but I'm pretty sure you could replace that with > reverse (unfoldr ...). Due to the fact that you are appending with (++) in > your implementation anyways, it is much more efficient. My final version > of fibb looks like this, and passes your tests. > fibb = snd . foldl' fib' (1, 0) . map (>0) . reverse . unfoldr divs > > boolToEither can be written with an if statement instead of case > boolToEither bool a b = if bool then Right b else Left a > > Stylistically, I would put argument validation into src-exe and into the > main function, allowing it to bail with an argument error before ever > getting to your fizzbuzz code, which should not concern itself with program > argument validation. I realize you are intending to demonstrate monads > using either in your blog, so carry on if that's the case. > > Some general advice I would give, is that if a function isn't doing as > little as it can, try pulling out some of the stuff it doesn't need to do > out into a shallower part of your program. > > For example, when I look at the fibb where fib' function, fib' :: (a, a) > -> Bool -> (a, a), where depending on the bool, and nothing else, it does > two completely different things. Maybe it should be two different > functions, with the bool checking outside? I'm not familiar enough with > what you are trying to do to say that that can be done, but that is my > first instinct. > > As to the structure of your project, it looks great. I may have learned a > few things... > > > On Fri, May 6, 2016 at 2:29 PM, Michael Litchard <michael(a)schmong.org> > wrote: > >> I've got this fizzbuzz project I am using for a blog series, among other >> things. In this version, the fizzbuzz function is fed from a Fibonacci >> generator. I'm particularly concerned with the efficiency of the Fibonacci >> generator, but all scrutiny is welcomed. >> >> I'll included a link to the entire project, but below are the parts I >> think would be sufficient to spot trouble with how I am generating >> Fibonacci numbers. >> >> -- Driver function performs following-- (1) checks that input is proper-- (2) creates integer list for fibonacci generator-- (3) calculates first x in fibonnaci sequence-- (4) generates fizzbuzz output using (3) >> >> fizzBuzzFib :: [Text] -> Either FizzError [Text] >> fizzBuzzFib str = >> mapM fizzbuzz =<< >> mapM fibb =<< -- Possible problem here(\x -> Right [1 .. x]) =<< >> convertToPInt =<< >> mustHaveOne str >> >> fibb :: Integer -> Either FizzError Integer >> fibb n = Right $ snd . foldl' fib' (1, 0) . map (toEnum . fromIntegral) $ unfoldl divs n >> where >> unfoldl f x = >> case f x of >> Nothing -> [] >> Just (u, v) -> unfoldl f v ++ [u] >> >> divs 0 = Nothing >> divs k = Just (uncurry (flip (,)) (k `divMod` 2)) >> >> fib' (f, g) p >> | p = (f*(f+c*g), f^c + g^c) >> | otherwise = (f^c+g^c, g*(c*f-g)) >> where >> c :: Integer -- See codebase for reasons >> c = 2 >> >> The whole project, for your critiquing eye:https://github.com/mlitchard/swiftfizz >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> >> >

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Code critique request
by Michael Litchard 06 May '16

06 May '16

I've got this fizzbuzz project I am using for a blog series, among other things. In this version, the fizzbuzz function is fed from a Fibonacci generator. I'm particularly concerned with the efficiency of the Fibonacci generator, but all scrutiny is welcomed. I'll included a link to the entire project, but below are the parts I think would be sufficient to spot trouble with how I am generating Fibonacci numbers. -- Driver function performs following-- (1) checks that input is proper-- (2) creates integer list for fibonacci generator-- (3) calculates first x in fibonnaci sequence-- (4) generates fizzbuzz output using (3) fizzBuzzFib :: [Text] -> Either FizzError [Text] fizzBuzzFib str = mapM fizzbuzz =<< mapM fibb =<< -- Possible problem here(\x -> Right [1 .. x]) =<< convertToPInt =<< mustHaveOne str fibb :: Integer -> Either FizzError Integer fibb n = Right $ snd . foldl' fib' (1, 0) . map (toEnum . fromIntegral) $ unfoldl divs n where unfoldl f x = case f x of Nothing -> [] Just (u, v) -> unfoldl f v ++ [u] divs 0 = Nothing divs k = Just (uncurry (flip (,)) (k `divMod` 2)) fib' (f, g) p | p = (f*(f+c*g), f^c + g^c) | otherwise = (f^c+g^c, g*(c*f-g)) where c :: Integer -- See codebase for reasons c = 2 The whole project, for your critiquing eye:https://github.com/mlitchard/swiftfizz

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Trouble building library with cabal-install 1.24
by Amy de Buitléir 06 May '16

06 May '16

I'm trying to use cabal-install 1.24. To start fresh, I removed ~/.cabal and ~/.ghc, and then used the old cabal(-install) executable to do cabal update and cabal install cabal-install. Unfortunately, it seems that cabal-install is building everything except my library! $ cabal --version cabal-install version 1.24.0.0 compiled using version 1.24.0.0 of the Cabal library $ ghc --version The Glorious Glasgow Haskell Compilation System, version 7.10.3 $ cat cabal.project.local tests: True program-options ghc-options: -Werror $ cabal new-build --enable-test -v Project settings changed, reconfiguring... creating /home/eamybut/néal/creatur/dist-newstyle creating /home/eamybut/néal/creatur/dist-newstyle/cache creating /home/eamybut/.cabal/store/ghc-7.10.3 Reading installed packages... /usr/local/ghc-7.10.3/bin/ghc-pkg dump '--package-db=/home/eamybut/.cabal/store/ghc-7.10.3/package.db' -v0 /usr/local/ghc-7.10.3/bin/ghc --print-libdir -Werror In order, the following will be built: cond-0.4.1.1 (lib:cond) (requires build) primitive-0.6.1.0 (lib:primitive) (requires build) random-1.1 (lib:random) (requires build) MonadRandom-0.4.2.3 (lib:MonadRandom) (requires build) regex-base-0.93.2 (lib:regex-base) (requires build) regex-posix-0.95.2 (lib:regex-posix) (requires build) tf-random-0.5 (lib:tf-random) (requires build) QuickCheck-2.8.2 (lib:QuickCheck) (requires build) xml-1.3.14 (lib:xml) (requires build) test-framework-0.8.1.1 (lib:test-framework) (requires build) test-framework-hunit-0.3.0.2 (lib:test-framework-hunit) (requires build) test-framework-quickcheck2-0.3.0.3 (lib:test-framework-quickcheck2) (requires build) creatur-5.9.12 (lib:creatur test:creatur-tests) *test (first run) creating /home/eamybut/néal/creatur/dist-newstyle/build creating /home/eamybut/néal/creatur/dist-newstyle/tmp Extracting /home/eamybut/.cabal/packages/hackage.haskell.org/cond/0.4.1.1/cond-0.4.1.1.tar. gz to /home/eamybut/néal/creatur/dist-newstyle/tmp/cond-4543... Extracting Extracting Extracting /home/eamybut/.cabal/packages/hackage.haskell.org/primitive/0.6.1.0/primitive-0. 6.1.0.tar.gz /home/eamybut/.cabal/packages/hackage.haskell.org/random/1.1/random-1.1.tar.gz /home/eamybut/.cabal/packages/hackage.haskell.org/regex-base/0.93.2/regex-base-0 .93.2.tar.gz Updating cond.cabal with the latest revision from the index. to /home/eamybut/néal/creatur/dist-newstyle/tmp/primitive-4543... to /home/eamybut/néal/creatur/dist-newstyle/tmp/random-4543... to /home/eamybut/néal/creatur/dist-newstyle/tmp/regex-base-4543... creating dist Updating primitive.cabal with the latest revision from the index. Updating random.cabal with the latest revision from the index. Updating regex-base.cabal with the latest revision from the index. Configuring cond-0.4.1.1... creating dist creating dist creating dist /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- configure Configuring primitive-0.6.1.0... Configuring random-1.1... Configuring regex-base-0.93.2... --verbose=2 --builddir=dist --ghc --prefix=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b82b24 b34eb8efb77ce69172f7e29c5da408121c1e840e7bca --bindir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b82b24 b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/bin /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- configure /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- configure /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- configure --libdir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b82b24 b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/lib --verbose=2 --builddir=dist --ghc --verbose=2 --builddir=dist --ghc --verbose=2 --builddir=dist --ghc --libsubdir= --prefix=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d5514a8 7874afe52df39e3953f43ebb68440dbf31be727064e02c914 --prefix=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b303e6 d2667f43890fe97c8ce038e14ab1c9b19e493af5c1 --prefix=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc118558 645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d --libexecdir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b8 2b24b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/libexec --bindir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d5514a8 7874afe52df39e3953f43ebb68440dbf31be727064e02c914/bin --bindir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b303e6 d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/bin --bindir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc118558 645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/bin --datadir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b82b2 4b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/share --libdir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d5514a8 7874afe52df39e3953f43ebb68440dbf31be727064e02c914/lib --libdir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b303e6 d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/lib --libdir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc118558 645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/lib --datasubdir= --libsubdir= --libsubdir= --libsubdir= --docdir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b82b24 b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/share/doc --libexecdir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d55 14a87874afe52df39e3953f43ebb68440dbf31be727064e02c914/libexec --libexecdir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b3 03e6d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/libexec --libexecdir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc11 8558645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/libexec --htmldir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b82b2 4b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/share/doc/html --datadir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d5514a 87874afe52df39e3953f43ebb68440dbf31be727064e02c914/share --datadir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b303e 6d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/share --datadir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc11855 8645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/share --haddockdir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b8 2b24b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/share/doc/html --datasubdir= --datasubdir= --datasubdir= --sysconfdir=/home/eamybut/.cabal/store/ghc-7.10.3/cond-0.4.1.1-d6f8f52c204603b8 2b24b34eb8efb77ce69172f7e29c5da408121c1e840e7bca/etc --docdir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d5514a8 7874afe52df39e3953f43ebb68440dbf31be727064e02c914/share/doc --docdir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b303e6 d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/share/doc --docdir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc118558 645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/share/doc --enable-library-vanilla --enable-library-profiling --enable-shared --htmldir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d5514a 87874afe52df39e3953f43ebb68440dbf31be727064e02c914/share/doc/html --htmldir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b303e 6d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/share/doc/html --htmldir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc11855 8645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/share/doc/html --disable-executable-dynamic --disable-profiling --profiling-detail=default --haddockdir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d55 14a87874afe52df39e3953f43ebb68440dbf31be727064e02c914/share/doc/html --haddockdir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b3 03e6d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/share/doc/html --haddockdir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc11 8558645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/share/doc/html --library-profiling-detail=default --enable-optimization --disable-debug-info --sysconfdir=/home/eamybut/.cabal/store/ghc-7.10.3/primitive-0.6.1.0-b7ddd297d55 14a87874afe52df39e3953f43ebb68440dbf31be727064e02c914/etc --sysconfdir=/home/eamybut/.cabal/store/ghc-7.10.3/random-1.1-b26d9915a884bbc1b3 03e6d2667f43890fe97c8ce038e14ab1c9b19e493af5c1/etc --sysconfdir=/home/eamybut/.cabal/store/ghc-7.10.3/regex-base-0.93.2-b143cb5bc11 8558645f7ba3efa292084e0faa0371afb4065baebdd6202d7600d/etc --disable-library-for-ghci --disable-split-objs --disable-executable-stripping --enable-library-vanilla --enable-library-profiling --enable-shared --enable-library-vanilla --enable-library-profiling --enable-shared --enable-library-vanilla --enable-library-profiling --enable-shared --disable-library-stripping --package-db=clear --package-db=global --disable-executable-dynamic --disable-profiling --profiling-detail=default --disable-executable-dynamic --disable-profiling --profiling-detail=default --disable-executable-dynamic --disable-profiling --profiling-detail=default --package-db=/home/eamybut/.cabal/store/ghc-7.10.3/package.db --library-profiling-detail=default --enable-optimization --disable-debug-info --library-profiling-detail=default --enable-optimization --disable-debug-info --library-profiling-detail=default --enable-optimization --disable-debug-info --ipid=cond-0.4.1.1-d6f8f52c204603b82b24b34eb8efb77ce69172f7e29c5da408121c1e840e 7bca --disable-library-for-ghci --disable-split-objs --disable-executable-stripping --disable-library-for-ghci --disable-split-objs --disable-executable-stripping --disable-library-for-ghci --disable-split-objs --disable-executable-stripping --dependency=base=base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d --disable-library-stripping --package-db=clear --package-db=global --disable-library-stripping --package-db=clear --package-db=global --disable-library-stripping --package-db=clear --package-db=global --disable-tests --disable-coverage --exact-configuration --disable-benchmarks --package-db=/home/eamybut/.cabal/store/ghc-7.10.3/package.db --package-db=/home/eamybut/.cabal/store/ghc-7.10.3/package.db --package-db=/home/eamybut/.cabal/store/ghc-7.10.3/package.db --with-ghc=/usr/local/ghc-7.10.3/bin/ghc --ipid=primitive-0.6.1.0-b7ddd297d5514a87874afe52df39e3953f43ebb68440dbf31be7270 64e02c914 --ipid=random-1.1-b26d9915a884bbc1b303e6d2667f43890fe97c8ce038e14ab1c9b19e493af5 c1 --flags=splitbase --flags=newbase --with-ghc-pkg=/usr/local/ghc-7.10.3/bin/ghc-pkg --ghc-option=-Werror --dependency=base=base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d --dependency=base=base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d --ipid=regex-base-0.93.2-b143cb5bc118558645f7ba3efa292084e0faa0371afb4065baebdd6 202d7600d --dependency=ghc-prim=ghc-prim-0.4.0.0-6cdc86811872333585fa98756aa7c51e --dependency=time=time-1.6-3b93b66397d7b7d84c3a87826ae1549fc4e47935065267f486fdc 3425d250cd5 --dependency=array=array-0.5.1.0-960bf9ae8875cc30355e086f8853a049 --dependency=transformers=transformers-0.5.2.0-c4818cc3cc5467e714fd3fd12dcbf7740 9ca3ca7292b47a5830cfcb4fb5911e2 --disable-tests --disable-coverage --exact-configuration --disable-benchmarks --dependency=base=base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d Redirecting build log to {handle: /home/eamybut/.cabal/logs/cond-0.4.1.1.log} --disable-tests --disable-coverage --exact-configuration --disable-benchmarks --with-ghc=/usr/local/ghc-7.10.3/bin/ghc --dependency=bytestring=bytestring-0.10.6.0-9a873bcf33d6ce2fd2698ce69e2c1c66 --with-ghc=/usr/local/ghc-7.10.3/bin/ghc --with-ghc-pkg=/usr/local/ghc-7.10.3/bin/ghc-pkg --ghc-option=-Werror --dependency=containers=containers-0.5.6.2-59326c33e30ec8f6afd574cbac625bbb --with-ghc-pkg=/usr/local/ghc-7.10.3/bin/ghc-pkg --ghc-option=-Werror --dependency=mtl=mtl-2.2.1-f8863ab628c53078d6adbcf7634212242d99bcdf1c73497f1131e 24fcafd4187 --disable-tests --disable-coverage --exact-configuration --disable-benchmarks Redirecting build log to {handle: /home/eamybut/.cabal/logs/random-1.1.log} --with-ghc=/usr/local/ghc-7.10.3/bin/ghc Redirecting build log to {handle: --with-ghc-pkg=/usr/local/ghc-7.10.3/bin/ghc-pkg --ghc-option=-Werror /home/eamybut/.cabal/logs/primitive-0.6.1.0.log} Redirecting build log to {handle: /home/eamybut/.cabal/logs/regex-base-0.93.2.log} Building regex-base-0.93.2... /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- build --verbose=2 --builddir=dist Redirecting build log to {handle: /home/eamybut/.cabal/logs/regex-base-0.93.2.log} Building random-1.1... /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- build --verbose=2 --builddir=dist Redirecting build log to {handle: /home/eamybut/.cabal/logs/random-1.1.log} Building primitive-0.6.1.0... /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- build --verbose=2 --builddir=dist Redirecting build log to {handle: /home/eamybut/.cabal/logs/primitive-0.6.1.0.log} Building cond-0.4.1.1... /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- build --verbose=2 --builddir=dist Redirecting build log to {handle: /home/eamybut/.cabal/logs/cond-0.4.1.1.log} Extracting /home/eamybut/.cabal/packages/hackage.haskell.org/xml/1.3.14/xml-1.3.14.tar.gz to /home/eamybut/néal/creatur/dist-newstyle/tmp/xml-4543... Updating xml.cabal with the latest revision from the index. creating dist Configuring xml-1.3.14... /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- configure --verbose=2 --builddir=dist --ghc --prefix=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b38458e7 afa38083e761daf4b6cf823ee2a31d1d5bba8de548 --bindir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b38458e7 afa38083e761daf4b6cf823ee2a31d1d5bba8de548/bin --libdir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b38458e7 afa38083e761daf4b6cf823ee2a31d1d5bba8de548/lib --libsubdir= --libexecdir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b384 58e7afa38083e761daf4b6cf823ee2a31d1d5bba8de548/libexec --datadir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b38458e 7afa38083e761daf4b6cf823ee2a31d1d5bba8de548/share --datasubdir= --docdir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b38458e7 afa38083e761daf4b6cf823ee2a31d1d5bba8de548/share/doc --htmldir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b38458e 7afa38083e761daf4b6cf823ee2a31d1d5bba8de548/share/doc/html --haddockdir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b384 58e7afa38083e761daf4b6cf823ee2a31d1d5bba8de548/share/doc/html --sysconfdir=/home/eamybut/.cabal/store/ghc-7.10.3/xml-1.3.14-b04f5878120533b384 58e7afa38083e761daf4b6cf823ee2a31d1d5bba8de548/etc --enable-library-vanilla --enable-library-profiling --enable-shared --disable-executable-dynamic --disable-profiling --profiling-detail=default --library-profiling-detail=default --enable-optimization --disable-debug-info --disable-library-for-ghci --disable-split-objs --disable-executable-stripping --disable-library-stripping --package-db=clear --package-db=global --package-db=/home/eamybut/.cabal/store/ghc-7.10.3/package.db --ipid=xml-1.3.14-b04f5878120533b38458e7afa38083e761daf4b6cf823ee2a31d1d5bba8de5 48 --dependency=base=base-4.8.2.0-0d6d1084fbc041e1cded9228e80e264d --dependency=bytestring=bytestring-0.10.6.0-9a873bcf33d6ce2fd2698ce69e2c1c66 --dependency=text=text-1.2.2.1-ba97440de9fbd614cd8b02c1d9fda7e9073a288481e7e539c 2629ac910e67bf4 --disable-tests --disable-coverage --exact-configuration --disable-benchmarks --with-ghc=/usr/local/ghc-7.10.3/bin/ghc --with-ghc-pkg=/usr/local/ghc-7.10.3/bin/ghc-pkg --ghc-option=-Werror Redirecting build log to {handle: /home/eamybut/.cabal/logs/xml-1.3.14.log} Building xml-1.3.14... /home/eamybut/.cabal/bin/cabal act-as-setup --build-type=Simple -- build --verbose=2 --builddir=dist Redirecting build log to {handle: /home/eamybut/.cabal/logs/xml-1.3.14.log} That's the last line. No mention of actually building creatur (my library). $ find dist-newstyle dist-newstyle dist-newstyle/tmp dist-newstyle/cache dist-newstyle/cache/source-hashes dist-newstyle/cache/improved-plan dist-newstyle/cache/plan.json dist-newstyle/cache/compiler dist-newstyle/cache/elaborated-plan dist-newstyle/cache/solver-plan dist-newstyle/cache/config dist-newstyle/build $ find dist dist $ cabal info creatur * creatur (library) Synopsis: Framework for artificial life experiments. Versions available: 4.2.0, 4.3.2, 4.3.3, 5.7.3, 5.8.0, 5.8.2, 5.9.9, 5.9.10, 5.9.11 (and 51 others) Versions installed: [ Not installed ] . . . I'm using the same cabal file I've used with sandboxes.

2 3

GHC.Prim: Resizable Multidimensional array
by Jake 06 May '16

06 May '16

I'm trying to create a resizable multidimensional array using the primitive array stuff in GHC.Prim. I see that the only resizable array is the ByteArray#, but the only array that supports multidimensionality is the ArrayArray# as far as I can tell. I have groups of 4 Double#s that I want to have a resizable array of, so only really the "first dimension" needs to be resizable. I was thinking if there was a way to get the pointer of a SmallArray# as an Addr# I could use the ability of ByteArray#s to store Addr#s. The other option I was considering was to simply have a mapping similar to the ones provided by Data.Ix that maps pairs of numbers to a single index, and in that way use a single ByteArray# to store everything. However, because this will be a fairly large array it seems like it is a much better idea to avoid allocating and reallocating that humongous chunk of memory when I can keep it spread out in smaller chunks by storing pointers to smaller arrays in the larger array. But maybe that isn't an important consideration? Thanks, Jake

1 0

Taking over cmdtheline
by Gregory Crosswhite 06 May '16

06 May '16

The package cmdtheline has not been updated since Apr 30, 2013, and it is broken with the current version of GHC; it needs to have its upper bound on transformers bumped. I tried contacting the author three months ago and three weeks ago to ask him to fix the package, but I received no response. I contacted him one more time one week ago to tell him that I intended to take over the package, and still I received no response. Thus, following the instructions on Hackage for taking over a package, I am officially stating my intent to take over this package so that I can fix it. Cheers, Greg

2 1

Fwd: Problem logging in GHC Trac
by Юрий Сыровецкий (Yuriy Syrovetskiy) 05 May '16

05 May '16

Hello I enter my login and password at https://ghc.haskell.org/trac/ghc/login and get: Internal Server Error Please contact the server administrator, webmaster@localhost Who is responsible for the site? Who can fix it? -- Yuriy Syrovetskiy, http://cblp.su

1 0

Is Haskell IO inherently slower than C?
by Jake 05 May '16

05 May '16

I'm trying to write a program in Haskell that writes a large file at the end, and it seems like that output alone is taking way longer than it should. I don't understand why Haskell shouldn't be able to write data as quickly as C, so I wrote two test files: -- Test.hs import Control.Loop import Data.ByteString.Builder import System.IO main :: IO () main = numLoop 0 1000000 $ \_ -> hPutBuilder stdout $ char7 ' ' // test.c #include <stdio.h> int main() { int i; for (i = 0; i < 1000000; i++) { fprintf(stdout, " "); } return 0; } I compiled them both with -O2, and ran them redirecting their outputs to /dev/null. For the Haskell version I got times aroudn 0.3 seconds, while the C version was around 0.03. Is there any reason why in simple IO the Haskell version would be slower by an order of magnitude?

5 8

Cabal confusion. Modules not being exposed still accessible for testing.
by Michael Litchard 04 May '16

04 May '16

I use reactive-banana <https://github.com/HeinrichApfelmus/reactive-banana/blob/master/reactive-ba…> as an example. My question is how can Reactive.Banana.Internal.Combinators be testable from Reactive.Banana.Test.Plumbing? My misunderstanding is that only modules named in the exposed-modules stanza could be imported. Could someone clear up my misunderstanding?

2 2

ANN: stack-1.1.0
by Emanuel Borsboom 04 May '16

04 May '16

See haskellstack.org for installation and upgrade instructions. Release notes: - Added Ubuntu 16.04 LTS (xenial) Apt repo. - No longer uploading new versions to Fedora 21 repo. Behavior changes: - Snapshot packages are no longer built with executable profiling. See #1179 <https://github.com/commercialhaskell/stack/issues/1179>. - stack init now ignores symlinks when searching for cabal files. It also now ignores any directory that begins with . (as well as dist dirs) - before it would only ignore .git, .stack-work, and dist. - The stack executable is no longer built with -rtsopts. Before, when -rtsopts was enabled, stack would process +RTS options even when intended for some other program, such as when used with stack exec -- prog +RTS. See #2022 <https://github.com/commercialhaskell/stack/issues/2022>. - The stack path --ghc-paths option is deprecated and renamed to --programs. --compiler is added, which points directly at the compiler used in the current project. --compiler-bin points to the compiler’s bin dir. - For consistency with the $STACK_ROOT environment variable, the stack path --global-stack-root flag and the global-stack-root field in the output of stack path are being deprecated and replaced with the stack-root flag and output field. Additionally, the stack root can now be specified via the --stack-root command-line flag. See #1148 <https://github.com/commercialhaskell/stack/issues/1148>. - stack sig GPG-related sub-commands were removed (folded into upload and sdist) - GPG signing of packages while uploading to Hackage is now the default. Use upload --no-signature if you would rather not contribute your package signature. If you don’t yet have a GPG keyset, read this blog post on GPG keys <https://fpcomplete.com/blog/2016/04/stack-security-gnupg-keys> We can add a stack.yaml config setting to disable signing if some people desire it. We hope that people will sign. Later we will be adding GPG signature verification options. - stack build pkg-1.2.3 will now build even if the snapshot has a different package version - it is treated as an extra-dep. stack build local-pkg-1.2.3 is an error even if the version number matches the local package #2028 <https://github.com/commercialhaskell/stack/issues/2028>. - Having a nix: section no longer implies enabling nix build. This allows the user to globally configure whether nix is used (unless the project overrides the default explicitly). See #1924 <https://github.com/commercialhaskell/stack/issues/1924>. - Remove deprecated valid-wanted field. - Docker: mount home directory in container #1949 <https://github.com/commercialhaskell/stack/issues/1949>. - Deprecate --local-bin-path instead --local-bin. - stack image: allow absolute source paths for add. Other enhancements: - stack haddock --open [PACKAGE] opens the local haddocks in the browser. - Fix too much rebuilding when enabling/disabling profiling flags. - stack build pkg-1.0 will now build pkg-1.0 even if the snapshot specifies a different version (it introduces a temporary extra-dep) - Experimental support for --split-objs added #1284 <https://github.com/commercialhaskell/stack/issues/1284>. - git packages with submodules are supported by passing the --recursive flag to git clone. - When using hpack <https://github.com/sol/hpack>, only regenerate cabal files when hpack files change. - hpack files can now be used in templates - stack ghci now runs ghci as a separate process #1306 <https://github.com/commercialhaskell/stack/issues/1306> - Retry when downloading snapshots and package indices - Many build options are configurable now in stack.yaml: build: library-profiling: true executable-profiling: true haddock: true haddock-deps: true copy-bins: true prefetch: true force-dirty: true keep-going: true test: true test-arguments: rerun-tests: true additional-args: ['-fprof'] coverage: true no-run-tests: true bench: true benchmark-opts: benchmark-arguments: -O2 no-run-benchmarks: true reconfigure: true cabal-verbose: true - A number of URLs are now configurable, useful for firewalls. See #1794 <https://github.com/commercialhaskell/stack/issues/1884>. - Suggest causes when executables are missing. - Allow --omit-packages even without --solver. - Improve the generated stack.yaml. - Improve ghci results after :load Main module collision with main file path. - Only load the hackage index if necessary #1883 <https://github.com/commercialhaskell/stack/issues/1883>, #1892 <https://github.com/commercialhaskell/stack/issues/1892>. - init: allow local packages to be deps of deps #1965 <https://github.com/commercialhaskell/stack/issues/1965>. - Always use full fingerprints from GPG #1952 <https://github.com/commercialhaskell/stack/issues/1952>. - Default to using gpg2 and fall back to gpg #1976 <https://github.com/commercialhaskell/stack/issues/1976>. - Add a flag for —verbosity silent. - Add haddock --open flag #1396 <https://github.com/commercialhaskell/stack/issues/1396>. Bug fixes: - Package tarballs would fail to unpack. #1884 <https://github.com/commercialhaskell/stack/issues/1884>. - Fixed errant warnings about missing modules, after deleted and removed from cabal file #921 <https://github.com/commercialhaskell/stack/issues/921> #1805 <https://github.com/commercialhaskell/stack/issues/1805>. - Now considers a package to dirty when the hpack file is changed #1819 <https://github.com/commercialhaskell/stack/issues/1819>. - Nix: cancelling a stack build now exits properly rather than dropping into a nix-shell #1778 <https://github.com/commercialhaskell/stack/issues/1778>. - allow-newer: true now causes --exact-configuration to be passed to Cabal. See #1579 <https://github.com/commercialhaskell/stack/issues/1579> . - stack solver no longer fails with InvalidRelFile for relative package paths including ... See #1954 <https://github.com/commercialhaskell/stack/issues/1954>. - Ignore emacs lock files when finding .cabal #1897 <https://github.com/commercialhaskell/stack/issues/1897>. - Use lenient UTF-8 decode for build output #1945 <https://github.com/commercialhaskell/stack/issues/1945>. - Clear index cache whenever index updated #1962 <https://github.com/commercialhaskell/stack/issues/1962>. - Fix: Building a container image drops a .stack-work dir in the current working (sub)directory #1975 <https://github.com/commercialhaskell/stack/issues/1975>. - Fix: Rebuilding when disabling profiling #2023 <https://github.com/commercialhaskell/stack/issues/2023>. ------------------------------ Thanks to all our contributors for this release: - Beerend Lauwers @beerendlauwers <https://github.com/beerendlauwers> - Chris Done @chrisdone <https://github.com/chrisdone> - Christian Hoener zu Siederdissen - @CthulhuDen <Https://Github.Com/CthulhuDen> - Emanuel Borsboom @borsboom <https://github.com/borsboom> - Erik Stevenson @narrative <https://github.com/narrative> - @fmap <https://github.com/fmap> - Greg @myfreeweb <https://github.com/myfreeweb> - Harendra Kumar @harendra-kumar <https://github.com/harendra-kumar> - Luigy Leon @luigy <https://github.com/luigy> - @malteneuss <https://github.com/malteneuss> - Mark Karpov @mrkkrp <https://github.com/mrkkrp> - Martin Dehnel-Wild @mpdehnel <https://github.com/mpdehnel> - Mathieu Boespflug @mboes <https://github.com/mboes> - Michael Sloan @mgsloan <https://github.com/mgsloan> - Michael Snoyman @snoyberg <https://github.com/snoyberg> - Noon van der Silk @silky <https://github.com/silky> - Oleg Grenrus @phadej <https://github.com/phadej> - Paul Rouse @paul-rouse <https://github.com/paul-rouse> - Rob Rix @robrix <https://github.com/robrix> - Simon Hengel @sol <https://github.com/sol> - Simon Jakobi @sjakobi <https://github.com/sjakobi> - Taylor Fausak @tfausak <https://github.com/tfausak> - @tejon <https://github.com/tejon> - Tim Dysinger @dysinger <https://github.com/dysinger> - Tobias Kortkamp @t6 <https://github.com/t6> - Tristan Webb @drwebb <https://github.com/drwebb> - Yuji Yamamoto @igrep <https://github.com/igrep> - Yuriy Syrovetskiy @cblp <https://github.com/cblp> - Yves Parès (Ywen) @YPares <Https://Github.Com/YPares> And thanks as always to the 150+ contributors to past releases!

2 1

ANN: monad-ste-0.1.0.0
by Carter Schonwald 04 May '16

04 May '16

hello All, I took the time this evening to clean up some work that came out of a larger project and have made a corresponding release to hackage monad-ste is sibling to ST that provides efficient abortive errors using GHC's exception machinery as well as handy machinery like being a PrimMonad and PrimBase instance! (and take heed, you cannot catch ) hackage: https://hackage.haskell.org/package/monad-ste-0.1.0.0 github: https://github.com/cartazio/monad-ste also thanks Brian Schroeder, Joel Burget and Duncan Coutts for providing invaluable feedback, debugging and the like for this library enjoy! -Carter

1 0

Call for Papers: OCL and Textual Modeling Tools and Textual Model Transformations (OCL 2016) - Submit Your Paper Until July 17, 2016
by Achim D. Brucker 04 May '16

04 May '16

(Apologies for duplicates) CALL FOR PAPERS 16th International Workshop on OCL and Textual Modeling Co-located with ACM/IEEE 19th International Conference on Model Driven Engineering Languages and Systems (MODELS 2016) October 2-4, 2016, Saint-Malo, France (TBC) http://oclworkshop.github.io Modeling started out with UML and its precursors as a graphical notation. Such visual representations enable direct intuitive capturing of reality, but some of their features are difficult to formalize and lack the level of precision required to create complete and unambiguous specifications. Limitations of the graphical notations encouraged the development of text-based modeling languages that either integrate with or replace graphical notations for modeling. Typical examples of such languages are OCL, textual MOF, Epsilon, and Alloy. Textual modeling languages have their roots in formal language paradigms like logic, programming and databases. The goal of this workshop is to create a forum where researchers and practitioners interested in building models using OCL or other kinds of textual languages can directly interact, report advances, share results, identify tools for language development, and discuss appropriate standards. In particular, the workshop will encourage discussions for achieving synergy from different modeling language concepts and modeling language use. The close interaction will enable researchers and practitioners to identify common interests and options for potential cooperation. Topics of interest include (but are not limited to) =================================================== - Mappings between textual modeling languages and other languages or formalisms - Algorithms, evaluation strategies and optimizations in the context of textual modeling languages for -- validation, verification, and testing, -- model transformation and code generation, -- meta-modeling and DSLs, and -- query and constraint specifications - Alternative graphical/textual notations for textual modeling languages - Evolution, transformation and simplification of textual modeling expressions - Libraries, templates and patterns for textual modeling languages - Tools that support textual modeling languages (e.g., verification of OCL formulae, runtime monitoring of invariants) - Complexity results for textual modeling languages - Quality models and benchmarks for comparing and evaluating textual modeling tools and algorithms - Successful applications of textual modeling languages - Case studies on industrial applications of textual modeling languages - Experience reports -- usage of textual modeling languages and tools in complex domains, -- usability of textual modeling languages and tools for end-users - Empirical studies about the benefits and drawbacks of textual modeling languages - Innovative textual modeling tools - Comparison, evaluation and integration of modeling languages - Correlation between modeling languages and modeling tasks This year, we particularly encourage submissions describing tools that support - in a very broad sense - textual modeling languages (if you have implemented OCL.js to run OCL in a web browser, this is the right workshop to present your work) as well as textual model transformations. Venue ===== The workshop will be organized as a part of MODELS 2016 Conference in Saint-Malo, France. It continues the series of OCL workshops held at UML/MODELS conferences: York (2000), Toronto (2001), San Francisco (2003), Lisbon (2004), Montego Bay (2005), Genova (2006), Nashville (2007), Toulouse (2008), Denver (2009), Oslo (2010), Zurich (2011, at the TOOLs conference), 2012 in Innsbruck, 2013 in Miami, 2014 in Valencia, Spain, and 2015 in Ottawa, Canada. Similar to its predecessors, the workshop addresses both people from academia and industry. The aim is to provide a forum for addressing integration of OCL and other textual modeling languages, as well as tools for textual modeling, and for disseminating good practice and discussing the new requirements for textual modeling. Workshop Format =============== The workshop will include short (about 15 min) presentations, parallel sessions of working groups, and sum-up discussions. Submissions =========== Two types of papers will be considered: * short contributions (between 6 and 8 pages) describing new ideas, innovative tools or position papers. * full papers (between 12 and 16 pages) in LNCS format. Submissions should be uploaded to EasyChair (https://easychair.org/conferences/?conf=ocl16) The program committee will review the submissions (minimum 2 reviews per paper, usually 3 reviews) and select papers according to their relevance and interest for discussions that will take place at the workshop. Accepted papers will be published online in a post-conference edition of CEUR (http://www.ceur-ws.org) Important Dates =============== Submission of papers: July 17, 2016 Notification: August 14, 2016 Workshop date: October 2-4, 2016 Organizers ========== Achim D. Brucker, The University of Sheffield, UK Jordi Cabot, ICREA - Open University of Catalonia, Spain Adolfo Sánchez-Barbudo Herrera, University of York, UK Programme Committee (TBC) ========================= Thomas Baar, University of Applied Sciences Berlin, Germany Mira Balaban, Ben-Gurion University of the Negev, Israel Tricia Balfe, Nomos Software, Ireland Domenico Bianculli, University of Luxembourg Dan Chiorean, Babes-Bolyai University, Romania Robert Clariso, Universitat Oberta de Catalunya, Spain Tony Clark, Middlesex University, UK Manuel Clavel, IMDEA Software Institute, Spain Birgit Demuth, Technische Universitat Dresden, Germany Marina Egea, Indra Sistemas S.A., Spain Geri Georg, Colorado State University, USA Martin Gogolla, University of Bremen, Germany Shahar Maoz, Tel Aviv University, Israel Istvan Rath, Budapest University of Technology and Economics, Hungary Bernhard Rumpe, RWTH Aachen, Germany Massimo Tisi, Mines de Nantes, France Frederic Tuong, Univ. Paris-Sud - IRT SystemX - LRI, France Edward Willink, Willink Transformations Ltd., UK Burkhart Wolff, Univ. Paris-Sud - LRI, France Steffen Zschaler, King's College, UK -- Dr. Achim D. Brucker | Senior Lecturer | University of Sheffield https://www.brucker.ch/

1 0

Amazon SES email issues
by David Escobar 04 May '16

04 May '16

Hi everyone, I'm having issues with sending email through Amazon SES. I'm using the *Network.Mail.Mime.SES* package. The error I get is: *email-test-exe: SESException {seStatus = Status {statusCode = 403, statusMessage = "Forbidden"}, seCode = "SignatureDoesNotMatch", seMessage = "The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing method. Consult the service documentation for details.", seRequestId = "8ceb250a-0dd3-11e6-892c-4fb1a14d4732"}* What's confusing is that I'm using the same SES settings in a Rails app as well as a small Rust console program without any issues (it works from the same machine too). The only thing I can think of is that with this Haskell package, I haven't found where to set certain things like the port number (587) and so maybe it's that? Here is a small sample app that illustrates the problem. What am I missing? Thanks. *{-# LANGUAGE OverloadedStrings #-}{-# LANGUAGE QuasiQuotes #-}* *module Main where* *import Data.Function ((&))import GHC.Genericsimport Network.HTTP.Clientimport Network.HTTP.Client.TLSimport Network.Mail.Mimeimport Network.Mail.Mime.SESimport Text.Hamlet (shamlet)import Text.Blaze.Html.Renderer.String (renderHtml)import qualified Data.ByteString.Char8 as C8import qualified Data.Text as Timport qualified Data.Text.Lazy as LTmain :: IO ()main = do manager <- newManager tlsManagerSettings let sesConfig = SES { sesFrom = C8.pack "de(a)somewhere.com <de(a)somewhere.com>", sesTo = [ C8.pack "someone.else(a)somewhereelse.com <someone.else(a)somewhereelse.com>" ], sesAccessKey = "SOMEAWSACCESSKEY", sesSecretKey = "ANEVENLONGERAWSSECRETKEY1234567890", sesRegion = usEast1 } email = Mail { mailFrom = Address (Just "David Escobar") "de(a)somewhere.com <de(a)somewhere.com>", mailTo = [ Address (Just "Someone Else") "someone.else(a)somewhereelse.com <someone.else(a)somewhereelse.com>" ], mailParts = [ [ htmlPart testEmail ] ], mailCc = [], mailBcc = [], mailHeaders = [ ("subject", "Some Test Email"), ("Content-Type", "text/html; charset=ISO-8859-1") ] } renderSendMailSES manager sesConfig emailtestEmail :: LT.TexttestEmail = let rows = [ [ "1", "2", "3" ], [ "4", "5", "6" ]] in renderHtml [shamlet| $doctype 5 <html> <body> <table style="border: 1px solid black; border-collapse: collapse; margin: 25px 0; width: 100%;"> <tr> <th style="background-color: #072a2d; color: white; font-weight: bold; border-right: 1px solid white; padding: 5px 10px; width: 33%;"> Column 1 <th style="background-color: #072a2d; color: white; font-weight: bold; border-right: 1px solid white; padding: 5px 10px; width: 33%;"> Column 2 <th style="background-color: #072a2d; color: white; font-weight: bold; border-right: 1px solid white; padding: 5px 10px; width: 33%;"> Column 3 $forall row <- rows <tr style="background-color: #f8f9ee;"> <td style="border: 1px solid black; padding: 5px 10px; text-align: left; width: 33%;"> #{T.pack $ row !! 0} <td style="border: 1px solid black; padding: 5px 10px; text-align: left; width: 33%;"> #{T.pack $ row !! 1} <td style="border: 1px solid black; padding: 5px 10px; text-align: left; width: 33%;"> #{T.pack $ row !! 2} |] & LT.pack*

6 13

Re: [Haskell-cafe] Bikeshedding request for GHCi's :type
by Richard Eisenberg 03 May '16

03 May '16

I have collected feedback gleaned here, on the ticket, and on reddit and summarized here: https://ghc.haskell.org/trac/ghc/wiki/Design/GHCi/Type#Summaryoffeedbackabo… That summary includes this concrete proposal: 1. Ask for concrete suggestions about names for the new commands. 2. Use these names on my current implementation (which prints out only one specialization) 3. Post a feature request looking for more specializations. I simply don't have time to specify a design or implement an algorithm for printing out multiple specializations. Furthermore, my current implementation meets all specifications proffered for printing out multiple specializations, for all values of "multiple" that equal 1. It is easy to extend later. Separately, there is a groundswell of support for :doc, but that's beyond the scope of my work on this point. (I personally would love :doc, too.) So, what shall we name the two new commands? 1. A new command that specializes a type. (Currently with one specialization, but perhaps more examples in the future.) 2. A new command that preserves specialized type variables so that users of TypeApplications know what type parameters to pass in next. I have suggested :type-def for (1) and :type-spec for (2). I don't strongly like either. :examples and :inst have been suggested for (1). Any other ideas? Thanks! Richard On Apr 26, 2016, at 9:08 AM, Richard Eisenberg <eir(a)cis.upenn.edu> wrote: > Hi devs, > > Over the weekend, I was pondering the Haskell course I will be teaching next year and shuddered at having to teach Foldable at the same time as `length`. So I implemented feature request #10963 (https://ghc.haskell.org/trac/ghc/ticket/10963) which allows for a way for a user to request a specialization of a type. It all works wonderfully, but there is a real user-facing design issue here around the default behavior of :type and whether or not to add new :type-y like commands. I have outlined the situation here: https://ghc.haskell.org/trac/ghc/wiki/Design/GHCi/Type > > I'd love some broad input on this issue. If you've got a stake in how this all works, please skim that wiki page and comment on #10963. > > Thanks! > Richard > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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Re: [Haskell-cafe] Controlling how test data is generated in, QuickCheck 2
by Li-yao Xia 03 May '16

03 May '16

Hi Michael, > What I noticed was the answer suggested that one should write a `newtype`, > wrapping a `[Int]` and making a new `Arbitrary` instance. However, I also > noticed that the answer is from 2012, and `QuickCheck 2` has an `Args` > `datatype` that appears to be able to do what I need. So, can I create a > new `Args` to limit the range of tests, (just want the first 1000 Fibonacci > numbers), and also to limit the number of tests run? If not is the solution > from the above link the approach I would have to take? The module Test.Hspec.QuickCheck has functions to modify the number of tests to be run (modifyMaxSuccess) and the maximum size passed to the generators (modifyMaxSize) (and indeed internally they modify the Args passed to QuickCheck's driver). I believe their purpose is to modify values coming from outside the program, via the command line options --qc-max-success and --qc-max-size. You can certainly set them to constants: modifyMaxSuccess (const 1000) $ prop ... But to specify the domains of your properties from within the program, the approaches mentioned in the answer you linked to are still current. Defining a newtype wrapper with an Arbitrary instance is a somewhat heavyweight solution. Some already exist for common preconditions, for example you can use Positive instead of the first check in modfiz: modfiz :: Positive Int -> Bool modfiz (Positive int) = ... The answer also mentions forAll and standalone generators, which I find to be most straightforward to set the domain of testfib: testfib :: Property testfib = forAll (choose (1, 1000)) $ \n -> ... Li-yao

1 0

Controlling how test data is generated in QuickCheck 2
by Michael Litchard 03 May '16

03 May '16

I have a problem similar to this question < http://stackoverflow.com/questions/9977734/controlling-how-test-data-is-gen…>. Below I will articulate my specifics, the code I am using, and the particular question I have. I have written a fizz-buzz program that uses a Fibonacci sequence as input. I would like to test two things. (1) Does my program emit the correct string given an Int that meets a particular condition. (2) Is my Fibonacci generator generating Fibonacci numbers? The problem I am having is similar to the link above. The range of `Int`s is too large. How do I constrain my tests to say, the first 1000 Fibonacci numbers? Here is code that I think is both adequate and minimal. Please let me know if I need to elaborate. import Data.Numbers.Primes (isPrime) import Test.Hspec (Spec,hspec,describe,it,shouldBe) import Test.Hspec.QuickCheck (prop) qcheck :: Spec qcheck = do describe "QuickCheck test fiz" $ prop "QuickCheck test" $ modfiz describe "QuickCheck test fib" $ prop "QuickCheck test fib" $ testfib modfiz int | int <= 0 = True -- code smell, should never generate number less than or equal to zero. | int == 3 = test3 | int == 5 = test5 | int `mod` 15 == 0 = testMod35 | int `mod` 3 == 0 = testMod3 | int `mod` 5 == 0 = testMod5 | isPrime int == True = testPrime | otherwise = testRest where test3 = Right "Buzz BuzzFizz" == fizzbuzz 3 test5 = Right "Fizz BuzzFizz" == fizzbuzz 5 testMod3 = Right "Buzz " == fizzbuzz int testMod5 = Right "Fizz " == fizzbuzz int testMod35 = Right "Buzz Fizz " == fizzbuzz int testPrime = Right "BuzzFizz" == fizzbuzz int testRest = Right (show int) == fizzbuzz int testfib :: Integer -> Bool testfib n = case (fibb n) of Left _ -> False Right n' -> isFib n' `fibb` takes an `Int` and finds that nth Fibonacci. So `fibb 6` would return `Right 8`. The `Left` value is not relevant to this problem. What I noticed was the answer suggested that one should write a `newtype`, wrapping a `[Int]` and making a new `Arbitrary` instance. However, I also noticed that the answer is from 2012, and `QuickCheck 2` has an `Args` `datatype` that appears to be able to do what I need. So, can I create a new `Args` to limit the range of tests, (just want the first 1000 Fibonacci numbers), and also to limit the number of tests run? If not is the solution from the above link the approach I would have to take? the entire project here <https://github.com/mlitchard/swiftfizz>

1 0

Applications using generalized monads?
by Jan Bracker 02 May '16

02 May '16

Hello, I am currently looking into applications of generalized monads. I am aware of the following generalized monad concepts (and libraries implementing them): * Indexed/Parameterized/Hoare Monads [1] * indexed [8] * simple-sessions [9][4] * monad-param [10][3][6] * Effect Monads [2] * effect-monad [11][5] * monad-param [12][3] * Constrained Monads * rmonad [13] Question 1: Do you know of other libraries that implement generalized monad concepts? Most of the libraries I listed above are in working condition, but still outdated. Question 2: Do you know of (open source) software and applications that use these concepts/libraries to implement something? This mail is a copy of my post on Reddit [7]. I am sorry for reposting it here, but I dod not get a response on that post for almost 2 weeks now. Best, Jan [1]: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.104.3020 [2]: http://dl.acm.org/citation.cfm?doid=2578855.2535846 [3]: http://comonad.com/reader/2007/parameterized-monads-in-haskell/ [4]: http://www.ccs.neu.edu/home/tov/pubs/haskell-session-types/session08.pdf [5]: https://www.cl.cam.ac.uk/~dao29/publ/haskell14-effects.pdf [6]: http://www.researchgate.net/profile/Dominique_Devriese/publication/22128235… [7]: https://www.reddit.com/r/haskellquestions/comments/4fs80x/ [8]: http://hackage.haskell.org/package/indexed [9]: http://hackage.haskell.org/package/simple-sessions [10]: http://hackage.haskell.org/package/monad-param [11]: http://hackage.haskell.org/package/effect-monad [12]: http://hackage.haskell.org/package/monad-param [13]: http://hackage.haskell.org/package/rmonad

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cannot perform arithmetic with GHC.TypeLits?
by Baojun Wang 02 May '16

02 May '16

Hi List, When I try to build below program, the compiler complains Couldn't match type ‘n’ with ‘1 + (n - 1)’ … Why GHC (7.10.3) cannot do type level natural number arithmetic? `` n /= 1 + (n-1)`` at type level? -- | main.hs {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE DeriveGeneric #-} module Main where import qualified Data.ByteString as B import Data.ByteString(ByteString) import Data.Serialize -- require cereal import GHC.TypeLits data Scalar :: Nat -> * -> * where Nil :: Scalar 0 a Cons :: a -> Scalar m a -> Scalar (1+m) a instance (Serialize a) => Serialize (Scalar 0 a) where get = return Nil put _ = return $ mempty instance (Serialize a) => Serialize (Scalar n a) where get = do x <- get :: Get a xs <- get :: Get (Scalar (n-1) a) return $! Cons x xs put (Cons x xs) = do put (x :: a) put xs -- /tmp/vect1/app/Main.hs:31:15: Couldn't match type ‘n’ with ‘1 + (n - 1)’ … ‘n’ is a rigid type variable bound by the instance declaration at /tmp/vect1/app/Main.hs:27:10 Expected type: Scalar n a Actual type: Scalar (1 + (n - 1)) a Relevant bindings include xs :: Scalar (n - 1) a (bound at /tmp/vect1/app/Main.hs:30:5) get :: Get (Scalar n a) (bound at /tmp/vect1/app/Main.hs:28:3) In the second argument of ‘($!)’, namely ‘Cons x xs’ In a stmt of a 'do' block: return $! Cons x xs Compilation failed. - baojun

5 6

Hackage package upload error: Invalid package
by Kostiantyn Rybnikov 02 May '16

02 May '16

Hi! Wanted to upload the 0.8.1 version of hedis, did what I usually did, but getting an error. Running "stack -v upload ." seems to show some tls-related details. ``` ➜ hedis git:(master) stack -v upload . Version 1.0.4.3 x86_64 2016-05-01 15:29:31.034044: [debug] Checking for project config at: /Users/kb/workspace/hedis/stack.yaml @(stack_2rXRdr1j02iFXWAif5re4K:Stack.Config src/Stack/Config.hs:761:9) 2016-05-01 15:29:31.037100: [debug] Loading project config file stack.yaml @(stack_2rXRdr1j02iFXWAif5re4K:Stack.Config src/Stack/Config.hs:779:13) 2016-05-01 15:29:31.110561: [debug] Checking for project config at: /Users/kb/workspace/hedis/stack.yaml @(stack_2rXRdr1j02iFXWAif5re4K:Stack.Config src/Stack/Config.hs:761:9) 2016-05-01 15:29:31.110690: [debug] Loading project config file stack.yaml @(stack_2rXRdr1j02iFXWAif5re4K:Stack.Config src/Stack/Config.hs:779:13) 2016-05-01 15:29:31.111459: [debug] Trying to decode /Users/kb/.stack/build-plan-cache/x86_64-osx/lts-5.3.cache @(stack_2rXRdr1j02iFXWAif5re4K:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:55:5) 2016-05-01 15:29:31.124939: [debug] Success decoding /Users/kb/.stack/build-plan-cache/x86_64-osx/lts-5.3.cache @(stack_2rXRdr1j02iFXWAif5re4K:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:64:13) 2016-05-01 15:29:31.132890: [debug] Trying to decode /Users/kb/.stack/indices/Hackage/00-index.cache @(stack_2rXRdr1j02iFXWAif5re4K:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:55:5) 2016-05-01 15:29:31.421690: [debug] Success decoding /Users/kb/.stack/indices/Hackage/00-index.cache @(stack_2rXRdr1j02iFXWAif5re4K:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:64:13) 2016-05-01 15:29:31.434522: [debug] Run process: ghc --info @(stack_2rXRdr1j02iFXWAif5re4K:System.Process.Read src/System/Process/Read.hs:269:3) 2016-05-01 15:29:31.498337: [debug] Run process: ghc --numeric-version @(stack_2rXRdr1j02iFXWAif5re4K:System.Process.Read src/System/Process/Read.hs:269:3) 2016-05-01 15:29:31.543696: [debug] Run process: ghc-pkg --no-user-package-db field --simple-output Cabal version @(stack_2rXRdr1j02iFXWAif5re4K:System.Process.Read src/System/Process/Read.hs:269:3) 2016-05-01 15:29:31.576011: [debug] Run process: ghc-pkg --no-user-package-db list --global @(stack_2rXRdr1j02iFXWAif5re4K:System.Process.Read src/System/Process/Read.hs:269:3) 2016-05-01 15:29:31.625682: [info] Getting file list for /Users/kb/workspace/hedis/ @(stack_2rXRdr1j02iFXWAif5re4K:Stack.SDist src/Stack/SDist.hs:96:5) 2016-05-01 15:29:31.628599: [debug] Checking resolver: lts-5.3 @(stack_2rXRdr1j02iFXWAif5re4K:Stack.Build.Source src/Stack/Build/Source.hs:164:17) 2016-05-01 15:29:31.628777: [debug] Trying to decode /Users/kb/.stack/build-plan-cache/x86_64-osx/lts-5.3.cache @(stack_2rXRdr1j02iFXWAif5re4K:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:55:5) 2016-05-01 15:29:31.636259: [debug] Success decoding /Users/kb/.stack/build-plan-cache/x86_64-osx/lts-5.3.cache @(stack_2rXRdr1j02iFXWAif5re4K:Data.Binary.VersionTagged src/Data/Binary/VersionTagged.hs:64:13) 2016-05-01 15:29:31.650120: [debug] Run process: ghc-pkg --no-user-package-db list --global @(stack_2rXRdr1j02iFXWAif5re4K:System.Process.Read src/System/Process/Read.hs:269:3) 2016-05-01 15:29:31.679601: [debug] Run process: /Users/kb/.stack/setup-exe-cache/x86_64-osx/setup-Simple-Cabal-1.22.5.0-ghc-7.10.3 --builddir=.stack-work/dist/x86_64-osx/Cabal-1.22.5.0 sdist --list-sources /private/var/folders/7l/3ys9j0lx20j6z69lm6s_9r780000gn/T/stack-sdist56408/source-files-list @(stack_2rXRdr1j02iFXWAif5re4K:System.Process.Read src/System/Process/Read.hs:287:3) 2016-05-01 15:29:31.728919: [info] Building sdist tarball for /Users/kb/workspace/hedis/ @(stack_2rXRdr1j02iFXWAif5re4K:Stack.SDist src/Stack/SDist.hs:98:5) 2016-05-01 15:29:31.756558: [info] Checking package 'hedis' for common mistakes @(stack_2rXRdr1j02iFXWAif5re4K:Stack.SDist src/Stack/SDist.hs:274:5) 2016-05-01 15:29:31.758110: [warn] Package check reported the following warnings: 'ghc-options: -Wall -Werror' makes the package very easy to break with future GHC versions because new GHC versions often add new warnings. Use just 'ghc-options: -Wall' instead. 'ghc-prof-options: -auto-all' is fine during development, but not recommended in a distributed package. @(stack_2rXRdr1j02iFXWAif5re4K:Stack.SDist src/Stack/SDist.hs:285:9) Uploading hedis-0.8.1.tar.gz... TlsExceptionHostPort (HandshakeFailed (Error_Packet_unexpected "Alert [(AlertLevel_Fatal,BadRecordMac)]" " expected: change cipher")) "hackage.haskell.org" 443 ➜ hedis git:(master) stack upload . Getting file list for /Users/kb/workspace/hedis/ Building sdist tarball for /Users/kb/workspace/hedis/ Checking package 'hedis' for common mistakes Package check reported the following warnings: 'ghc-options: -Wall -Werror' makes the package very easy to break with future GHC versions because new GHC versions often add new warnings. Use just 'ghc-options: -Wall' instead. 'ghc-prof-options: -auto-all' is fine during development, but not recommended in a distributed package. Uploading hedis-0.8.1.tar.gz... unhandled status code: 400 Error: Invalid package 'ghc-options: -Wall -Werror' makes the package very easy to break with future GHC versions because new GHC versions often add new warnings. Use just 'ghc-options: -Wall' instead. Upload failed on hedis-0.8.1.tar.gz ``` Hope somebody can take a look. Thank you.

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[TFP'16] call for participation
by Peter Achten 02 May '16

02 May '16

----------------------------- C A L L F O R P A R T I C I P A T I O N ----------------------------- ======== TFP 2016 =========== 17th Symposium on Trends in Functional Programming June 8-10, 2016 University of Maryland, College Park Near Washington, DC http://tfp2016.org/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. TFP 2016 will be the main event of a pair of functional programming events. TFP 2016 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 7nd. == INVITED SPEAKERS == TFP 2016 is pleased to announce keynote talks by the following two invited speakers: * Ronald Garcia, University of British Columbia: "Static and Dynamic Type Checking: A Synopsis" * Steve Zdancewic, University of Pennsylvania: "Type- and Example-Driven Program Synthesis" == HISTORY == The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in * Edinburgh (Scotland) in 2003; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * Soesterberg (The Netherlands) in 2014; * and Inria Sophia-Antipolis (France) in 2015. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2016 program chair, David Van Horn. == BEST PAPER AWARDS == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == SPONSORS == TFP is financially supported by CyberPoint, Galois, Trail of Bits, and the University of Maryland Computer Science Department. == PAPER SUBMISSIONS == Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which ALL authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. We use EasyChair for the refereeing process. Papers must be submitted at: https://easychair.org/conferences/?conf=tfp2016 Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site: http://www.springer.com/computer/lncs?SGWID=0-164-6-793341-0 == IMPORTANT DATES == Submission of draft papers: April 25, 2016 Notification: May 2, 2016 Registration: May 13, 2016 TFP Symposium: June 8-10, 2016 Student papers feedback: June 14, 2016 Submission for formal review: July 14, 2016 Notification of acceptance: September 14, 2016 Camera ready paper: October 14, 2016 == PROGRAM COMMITTEE == Amal Ahmed Northeastern University (US) Nada Amin École Polytechnique Fédérale de Lausanne (CH) Kenichi Asai Ochanomizu University (JP) Małgorzata Biernacka University of Wroclaw (PL) Laura Castro University of A Coruña (ES) Ravi Chugh University of Chicago (US) Silvia Ghilezan University of Novi Sad (SR) Clemens Grelck University of Amsterdam (NL) John Hughes Chalmers University of Technology (SE) Suresh Jagannathan Purdue University (US) Pieter Koopman Radboud University Nijmegen (NL) Geoffrey Mainland Drexel University (US) Chris Martens University of California, Santa Cruz (US) Jay McCarthy University of Massachusetts, Lowell (US) Heather Miller École Polytechnique Fédérale de Lausanne (CH) Manuel Serrano INRIA, Sophia-Antipolis (FR) Scott Smith Johns Hopkins University (US) Éric Tanter University of Chile (CL) David Van Horn (Chair) University of Maryland (US) Niki Vazou University of California, San Diego (US) Stephanie Weirich University of Pennsylvania (US)

1 0

Transforming graphs with loops with Hoopl
by Anakreontas 01 May '16

01 May '16

I am trying to implement a program transformation with Hoopl. The transformation replaces a particular statement with variable declarations provided that the variables have not been previously declared. A map keeps track of declared variables where the map keys store variable names. The transformation works only for programs without loops. In the program below, it should replace line 2 rec #3 INxt B37H00G with 1 Global Field B37H00G 2 Global Array B37HO3R 3 rec #3 INxt B37H00G but it doesn't. === Example graph == 0 goto L4 1 L4: 2 rec #3 INxt B37H00G 3 while #3 goto L5 goto L2 4 L5: 5 Global Field VSTF01a 6 goto L4 7 L2: I think the reason it fails is because there are two paths leading to L4, one from the program start (line 0) and a second when the loop repeats from line 6. In the first case the transformation produces the substitution graph since the two variables are not in the map. In the analysis of the second path however, the variables are in the name space so the rewrite function returns Nothing. In the end, the second transformation result is preserved (i.e. Nothing) and the graph is not transformed. Do I understand correctly why the transformation fails for loops? How would you suggest to solve this problem? Regards

2 1

Call for Contributions - Haskell Communities and Activities Report, May 2016 edition (30th edition)
by Mihai Maruseac 01 May '16

01 May '16

Dear all, It's that time of the year again (https://ro-che.info/ccc/16) :) We would like to collect contributions for the 30th edition of the ============================================================ Haskell Communities & Activities Report http://www.haskell.org/haskellwiki/Haskell_Communities_and_Activities_Report Submission deadline: 30 April 2016 ============================================================ The short story follows: * If you are working on _any_ project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is small, unfinished or used only by yourself or you think it is not important enough, please reconsider and submit an entry anyway! * The submission file can be in _any_ format you like. Although the final report uses LaTeX, if it is easier for you to submit a Markdown file, text file, Doc file or anything else, please do so. We'll be happy to do the translation and get a new entry in the HCAR :) * If you are interested in an existing project related to Haskell that has not previously been mentioned in the HCAR, please tell me or contact a project leader to get them to submit an entry. We have received feedback in the past that some projects were missing from the edition, but, sadly, that was too late at the time, but those projects will be contacted for this edition. * Feel free to pass on this call for contribution to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the previous edition --- you will find interesting projects described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Mihai FAQ: Q: What format should I write in? A: The recommeneded format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/05-2016/template.tex There is also a LaTeX style file at http://haskell.org/communities/06-2016/hcar.sty that you can use to preview your entry. If you modify an old entry that you have written for an earlier edition of the report, you should soon receive your old entry as a template (provided we have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. _However_, if you don't want/have time to format the entry for LaTeX, you can submit it in any other format possible and we will be happy to convert it for the final report. Q: Can I include Haskell code? A: Yes. Please use lhs2tex syntax (http://www.andres-loeh.de/lhs2tex/) The report is compiled in mode polycode.fmt. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg or .png format, then, PNG being preferred for simplicity. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or "historic" overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep up entries. There is no minimum length of an entry! The report aims for being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports about distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also simply ask us. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. You can use HCAR to ask for more contributors to your project, it is a good way to gain visibility and traction. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell us that there are no changes. The old entry will typically be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them. Q: Will I get confirmation if I send an entry? How do I know whether my email has even reached its destination, and not ended up in a spam folder? A: Prior to publication of the final report, we will send a draft to all contributors, for possible corrections. So if you do not hear from us within two weeks after the deadline, it is safer to send another mail and check whether your first one was received. -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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[ANN] Pre-announcing ZuriHac 2016
by Alexander Bernauer 29 Apr '16

29 Apr '16

Hello fellow Haskellers, it's my pleasure to announce that this year's ZuriHac, the Zurich Haskell hackathon, will happen from July 22nd to 24th. The registration will open this Saturday at 12pm (UTC+2). More information will follow. Greetings, Alex on behalf of the orga team

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[ANN] Darcs 2.12.0 release
by Guillaume Hoffmann 29 Apr '16

29 Apr '16

Hi all, The Darcs team is pleased to announce the release of Darcs 2.12.0. # Downloading # One way of installing Darcs 2.12.0 is with stack: $ stack install darcs-2.12.0 Or first install the Haskell Platform (http://www.haskell.org/platform) and install Darcs with cabal-install: $ cabal update $ cabal install darcs-2.12.0 You can also download the tarball from http://darcs.net/releases/darcs-2.12.0.tar.gz and build it by hand. The 2.12 branch is also available as a darcs repository from http://darcs.net/releases/branch-2.12 # What's new since Darcs 2.10.3 # ## New features ## * `darcs show dependencies`: export patch dependency graph as dot file (Ale Gadea) ## User Interface ## * improvements in `darcs record` output with irrelevant files (Ben Franksen) * `darcs log -v --machine-readable`: show internal representation of patches (including explicit dependencies). Remove patch viewing via the "darcs annotate" command. (Guillaume Hoffmann) * `whatsnew -s` (and `status`) show conflicting files (Guillaume Hoffmann) * honor "quiet" flag in command outputs (Ben Franksen) * a single `show patch-index` command (Guillaume Hoffmann) * remove deprecated aliases of show (Guillaume Hoffmann) * remove hack to enable arbitrary protocols via env variables (Guillaume Hoffmann) ## Performance ## * handle file moves natively when importing from git (Owen Stephens) ## Developer-related ## * require GHC 7.6 (base > 4.6) and support GHC 8 (Ganesh Sittampalam) * switch to sandi from dataenc (Daniil Frumin) * refactoring to prepare stash (Ganesh Sittampalam) * change argument order of type witness RL (Ben Franksen) * Darcs.Repository / repository cloning refactoring (Ben Franksen) * use of async when cloning with packs (Ben Franksen) * SSH code refactoring (Ben Franksen) * Patch and RealPatch renamed to RepoPatchV1 and RepoPatchV2 (Guillaume Hoffmann) * merged hashed-storage into libdarcs and hashed-storage tests into darcs-test (Guillaume Hoffmann) * reorganize Darcs.Repository.* modules (Guillaume Hoffmann) ## Issues resolved in Darcs 2.12 ## * issue1807: clarify help of PAGER, DARCS_PAGER (Guillaume Hoffmann) * issue2258: improve patch index error message with suggestion (Guillaume Hoffmann) * issue2269: push hijack test to suspend time (Eric Kow) * issue2276: Keep track of patch hijack decisions (Eric Kow) * issue2138: report conflicting files in whatsnew -s (Guillaume Hoffmann) * issue2393: remove whatsnew functionality from annotate (Guillaume Hoffmann) * issue2400: use async package to keep track of unpack threads (Ben Franksen) * issue2459: fall back to writing the file if createLink fails (Ben Franksen) * issue2479: root dir most not be among the sources of a move (Ben Franksen) * issue2481: expose API for 'darcs diff' command (Ganesh Sittampalam) * issue2486: obliterate --not-in-remote -q should be more quiet (Ben Franksen) * issue2489: dequote filepaths while importing from git (Guillaume Hoffmann) * issue2494: output of darcs record with file arguments (Ben Franksen) Thanks! Guillaume

1 0

[ANNOUNCE] GHC 8.0.1 release candidate 4 available
by Ben Gamari 29 Apr '16

29 Apr '16

Hello Haskellers, The GHC team is happy to announce the availability of fourth release candidate of the Glasgow Haskell Compiler's 8.0.1 release. Source and binary distributions can be found at, http://downloads.haskell.org/~ghc/8.0.1-rc4/ This is the last of four candidates leading up to the 8.0.1 release, addressing nearly all of the known issues of the previous candidates. These include, * A type-checker panic triggered by use of Typeable on a kind-polymorphic type constructor (#11334) * A type-checker explosion where -XTypeInType would gobble up massive amounts of memory when used in a data instance (#11407) * A variety of other typechecker issues (#11811, #11797, #11813, #11814) * A build issue seen on OS X (#11828) * Template Haskell can now produce instances with OVERLAPP{ING,ABLE,ED} pragmas * Autoconf has improved version checks for libdw (#11820) * Typeable and hs-boot files now interact nicely (#11824) * The build system now checks for the broken Apple `nm` utility (#11823, #11744) * Various issues involving unexpected laziness resulting in exception handlers not being invoked (#11555) * GHC now fails more gracefully when used with an older cabal-install release (#11558) * TypeInType now has proper documentation in the users guide (#11614) * The story surrounding type `RuntimeRep`s (formerly known as `Levity`) is now far better developed, closing several doors to unsafe behavior that TypeInType previously opened (#11473, #11723) * A long-standing bug in the constant-folding rules for `mod` for the `Word` type has been resolved (#11702) * Various issues introduced by OverloadedRecordFields have been fixed (#11662, #11401) * A regression in the typechecker resulting in the rejection of code in the `free` and `microlens` packages has been fixed (#11608) * A bug in the LLVM code generator which caused some programs to emit unbuildable LLVM IR has been fixed (#11649) * A bug where pattern synonyms defined in terms of a pattern match on a record would be rejected if the fields weren't written in the same order as they were defined has been resolved (#11633) * A bug in the runtime system's treatment of weak references which could result in segmentation faults in some cases has been fixed (#11108) * a variety of optimizations improving compiler performance have been merged * and many others Mac OS X users should be aware that the recent XCode 7.3 release ships with a broken `nm` utility which breaks the GHC build (#11744, #11823). The build system will check for this condition and request that the tree is configured to use the `nm-classic` utility if found. OS X users running XCode 7.3 are encouraged to open a ticket with Apple so that this issue may be fixed in future XCode releases. If no major issues pop up we expect that this will be the last release candidate before the final release, which we hope to push out in the coming weeks. Thanks to everyone who has contributed code, testing, builds, and bug reports thusfar! Cheers and happy testing, - Ben

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Fw: Bikeshedding request for GHCi's :type
by Takenobu Tani 28 Apr '16

28 Apr '16

Dear cafe, I'm forwarding mail from ghc-devs ML [1]. I think `:type` command is very important for beginners and middle users. Please feedback your opinion to them ;) [1]: https://mail.haskell.org/pipermail/ghc-devs/2016-April/011933.html > 2016-04-26 22:08 GMT+09:00 Richard Eisenberg <eir(a)cis.upenn.edu>: > Hi devs, > > Over the weekend, I was pondering the Haskell course I will be teaching next year and shuddered at having to teach Foldable at the same time as `length`. So I implemented feature request #10963 ( https://ghc.haskell.org/trac/ghc/ticket/10963) which allows for a way for a user to request a specialization of a type. It all works wonderfully, but there is a real user-facing design issue here around the default behavior of :type and whether or not to add new :type-y like commands. I have outlined the situation here: https://ghc.haskell.org/trac/ghc/wiki/Design/GHCi/Type > > I'd love some broad input on this issue. If you've got a stake in how this all works, please skim that wiki page and comment on #10963. > > Thanks! > Richard Cheers, Takenobu

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Re: [Haskell-cafe] Fw: Bikeshedding request for GHCi's :type
by Anton Felix Lorenzen 28 Apr '16

28 Apr '16

As a middle user, I often depend on `:type` when learning a library. I don't have strong preferences over one proposal or the other, but I would like to add, that there should always be `:type` in its current form (renamed or not). I wouldn't like getting lots of for me irrelevant information, like examples, when I only want a one-line type signature. That said, I like the general idea, although I don't know, whether a beginner would like having to learn the type signatures again, when getting to a more advanced level. - Anton Lorenzen

1 0

ANN: Haskell Prime 2020 committee has formed
by Herbert Valerio Riedel 28 Apr '16

28 Apr '16

Dear Haskell Community! Some time ago I asked for nominations to reboot the Haskell Prime process[1], and now I'm pleased to finally announce the formation of the new Haskell Language 2020 Committee! The goal of the Haskell Language committee together with the Core Libraries Committee is to work towards a new Haskell 2020 Language Report. I'd like to remind everyone that the Haskell Prime Process[4] relies on *everyone* in the community to help by contributing proposals which the committee will then evaluate and if suitable help formalise for inclusion. Everyone interested in participating is also invited to join the haskell-prime mailing list. Four years (or rather ~3.5 years) from now may seem like a long time. However, given the magnitude of the task at hand, to discuss, formalise, and implement proposed extensions (taking into account the recently enacted three-release-policy[3]) to the Haskell Report, the process shouldn't be rushed. Consequently, this may even turn out to be a tight schedule after all. However, it's not excluded there may be an interim revision of the Haskell Report before 2020. Based on this schedule, GHC 8.8 (likely to be released early 2020) would be the first GHC release to feature Haskell 2020 compliance. Prior GHC releases may be able to provide varying degree of conformance to drafts of the upcoming Haskell 2020 Report. The Haskell Language 2020 committee starts out with 20 members which contribute a diversified skill-set. These initial members also represent the Haskell community from the perspective of practitioners, implementers, educators, and researchers. - Andres Löh - Antonio Nikishaev - Austin Seipp - Carlos Camarao de Figueiredo - Carter Schonwald - David Luposchainsky - Henk-Jan van Tuyl - Henrik Nilsson - Herbert Valerio Riedel - Iavor Diatchki - John Wiegley - José Manuel Calderón Trilla - Jurriaan Hage - Lennart Augustsson - M Farkas-Dyck - Mario Blažević - Nicolas Wu - Richard Eisenberg - Vitaly Bragilevsky - Wren Romano The Haskell 2020 committee is a language committee; it will focus its efforts on specifying the Haskell language itself. Responsibility for the libraries laid out in the Report is left to the Core Libraries Committee (CLC)[5]. Incidentally, the CLC still has an available seat[2]; if you would like to contribute to the Haskell 2020 Core Libraries you are encouraged to apply for this opening. As this is a general announcement broadcasted to multiple mailing lists, a separate email discussing the next steps of the new committee will be sent to the haskell-prime mailing list shortly. [1]: https://mail.haskell.org/pipermail/haskell-prime/2015-September/003936.html [2]: https://mail.haskell.org/pipermail/libraries/2015-November/026497.html [3]: https://prime.haskell.org/wiki/Libraries/3-Release-Policy [4]: https://prime.haskell.org/wiki/Process [5]: https://prime.haskell.org/wiki/Libraries -- hvr

1 0

Sending email
by David Escobar 28 Apr '16

28 Apr '16

Hi everyone, I'm trying to use the *Network.Mail.SMTP* library to send email: *{-# LANGUAGE OverloadedStrings #-}* *module Main where* *import Control.Exception* *import qualified Data.Text as T* *import qualified Data.Text.Lazy as LT* *import Network.Mail.SMTP* *main :: IO ()* *main = do* * sendEmail (“Person sender”, “sender@somewhere.com <sender(a)somewhere.com>”)* * [(“Person recipient“, “recipient@somewhere.com <recipient(a)somewhere.com>”)]* * "Test email"* * "Some message goes here."* *sendEmail :: (T.Text, T.Text) -> [(T.Text, T.Text)] -> T.Text -> T.Text -> IO ()* *sendEmail (fromName, fromEmail) toAddresses subject' body' = do* * let toNameAddrs = map (\(toName, toEmail) -> Address (Just toName) toEmail) toAddresses* * msg = simpleMail (Address (Just fromName) fromEmail)* * toNameAddrs* * []* * []* * subject'* * [ plainTextPart $ LT.fromStrict body' ]* * result <- try $ sendMailWithLogin' "smtp.gmail.com <http://smtp.gmail.com>"* * 465 -- SSL port* * “sender_login”* * “sender_password”* * msg :: IO (Either SomeException ())* * case result of* * Left e -> putStrLn $ "Exception caught: " ++ (displayException e)* * Right _ -> putStrLn "Sent email successfully."* The program compiles, but when I run it, I get: *Exception caught: <socket: 49>: Data.ByteString.hGetLine: end of file* I tried using the TLS port of 587, but then I just get an authentication failure. Am I using the wrong library or is it just the wrong configuration. Thanks.

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Summer of Haskell - Now Accepting Applications!
by Gershom B 27 Apr '16

27 Apr '16

(Note: I am posting this on behalf of Edward Kmett who has spotty availability at the moment) We've posted an official Summer of Haskell website: https://summer.haskell.org/ It contains the full timeline for the program this summer, and most importantly, a form for submitting student applications, also linked here: https://docs.google.com/forms/d/1JLIa58u7AcWN31bH_LcCBujN9uzAwfd3HxrT32qz9_… The student application period ends next Friday, May 6. Last year we had a very successful project brainstorming thread. This led to our largest and most successful Summer of Code, ever. There is a thread on reddit now devoted to the purpose of further brainstorming for this year: https://www.reddit.com/r/haskell/comments/4gh1tu/summer_of_haskell_now_acce… If you have a proposal that you think a student could make a good dent in over the course of a summer, especially one with broad impact on the community, please feel free to discuss it there. If you are a potential student, please feel free to skim the proposals for ideas, or put forth ones of your own! If you are a potential mentor, please feel free to comment on proposals that interest you, put forth ideas looking for students and express your interest, to help us pair up potential students with potential mentors. Ultimately, the project proposals that are submitted get written by students, but if we can give a good sense of direction for what the community wants out of the summer, we can improve the quality of proposals, and we can recruit good mentors to work with good students on good projects. Resources: We have a wiki on https://ghc.haskell.org/trac/summer-of-code/ It is, of course, a Wiki, so if you see something out of order, take a whack at fixing it. We have an active #haskell-gsoc channel on irc.freenode.net that we run throughout the summer. Potential mentors and students alike are welcome. We have a Trac full of suggested Google Summer of Code proposals both current and from years past, but it could use a whole lot of eyeballs and an infusion of fresh ideas: https://ghc.haskell.org/trac/summer-of-code/report/1 Many of our best proposals in years have come from lists of project suggestions that others have blogged about. Many of our best students decided to join the summer of code based on these posts. The Trac isn't the only source of information on interesting projects, and I'd encourage folks to continue posting their ideas. If you or your employer would be interested in helping to fund additional students, please feel free to reach out to me. Thank you, -Edward Kmett

2 2

Hackage package index download failure
by Sean Leather 27 Apr '16

27 Apr '16

I'm unable to download the package index file used by cabal: $ cabal update Downloading the latest package list from hackage.haskell.org cabal: Failed to download http://hackage.haskell.org/packages/archive/00-index.tar.gz : ErrorMisc "Error HTTP code: 502" A few hours ago the error was a 503. Anybody know what's going on? Regards, Sean

2 1

Interactive ASCII graphics
by Jeffrey Brown 27 Apr '16

27 Apr '16

Gary Fixler recently gave a talk, to the Santa Monica Haskell Users Group at Brainium, in which he creates an interactive explorer for (among other images) the Mandelbrot set, using nothing but text. No complex libraries for graphics or reactivity are involved -- the only foreign import statements are to Data.Monoid, Data.Function, Data.Complex, and System.IO. The code is here: https://github.com/gfixler/continou This gif demonstrates it: http://www.garyfixler.com/2016-04-18-012037_3840x1024_scrot.gif The video is here: https://vimeo.com/163287967/99e0595942 -- Jeffrey Benjamin Brown

2 1

When using Cereal, what is the right way to write `get` for multi-constructor type?
by Magicloud Magiclouds 27 Apr '16

27 Apr '16

Hi, Say I have code already like: data STH = A | B | C instance Serialize STH where put A = putWord8 1 put B = putWord8 66 put C = putWord8 111 Then what is the better way to do `get`? Is following the only one? get = do i <- getWord8 case i of 1 -> return A 66 -> return B 111 -> return C Thanks.

4 5

Dropping support for NHC98 and old GHC from containers
by David Feuer 26 Apr '16

26 Apr '16

The containers package currently includes CPP and Cabal directives intended to support NHC98 and versions of GHC before 7.0. However, our TravisCI script tests only GHC versions 7.0 and above. It is therefore likely that the compatibility code is bit-rotted to some extent. Wren Romano and I are strongly inclined to immediately remove all code intended to support NHC98 or pre-7.0 GHC. If anyone uses any such implementations with the current version of containers, please speak now or forever hold your peace. Thanks, David Feuer

4 3

Cabal extensions tracking
by David Feuer 26 Apr '16

26 Apr '16

It's possible to enable extensions using an "extensions" field in a Cabal file, in which case Cabal will be able to report what language extensions the package requires. Unfortunately, this can be confusing, since the extensions in effect do not appear at the top of each affected module. Is there any way to get Cabal to report required extensions *based on LANGUAGE pragmas*? David

1 0

Re: [Haskell-cafe] (no subject)
by Tom Ellis 25 Apr '16

25 Apr '16

On Sun, Apr 24, 2016 at 08:07:40PM +0000, haskell-cafe-bounces(a)haskell.org wrote: > >From int-e(a)gmx.de Sun Apr 24 21:13:18 2016 > Date: Sun, 24 Apr 2016 21:13:18 +0200 > From: Bertram Felgenhauer <bertram.felgenhauer(a)googlemail.com> > To: haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] Is it possible to make lazy combinators for IO? > Message-ID: <20160424191319.GA32509@24f89f8c-e6a1-4e75-85ee-bb8a3743bb9f> > References: <CAMgWh9t4MbzbbdvnU8zz6Lm-p9Gtf2UO-%2BGaW%3DofPsNLmt4aCA(a)mail.gmail.com> > <CAErCyQ-J%2BiYo2tXVs9S4VtGtuurFaNp%3DzsrY_58%3D7EeL7q0HVQ(a)mail.gmail.com> > <CAMgWh9s3%2BksQOh52oU%3DazKcdLDyuFy2sYKPbz30xaXnTkLK9cw(a)mail.gmail.com> > <CAErCyQ8OVMF0fMDuxLpuvHimCt7RBijjzp1wEBMxRFyyyCXZVg(a)mail.gmail.com> > <CAMgWh9vsxijoCuNrMxeAZmVxML%2BA8iNUwpTy9Es1BF0z_%2BpryQ(a)mail.gmail.com> > <CAMgWh9tV_aq2%3DNkKZ79QZX6Xn6V953RwWoFqTeUMDggF0%3DZZ%2Bg(a)mail.gmail.com> > <CAErCyQ_zUqn53x1%3Dg3RKDjQc3%2BGXfXkj1VvaTxo8ONPeTfym0A(a)mail.gmail.com> > <CAMgWh9s%3D0bAsjGEgGwSr8bPL6vDqNL8yyY%3DG%2BqANoz35G0NKuw(a)mail.gmail.com> > MIME-Version: 1.0 > Content-Type: text/plain; charset=us-ascii > Content-Disposition: inline > In-Reply-To: <CAMgWh9s%3D0bAsjGEgGwSr8bPL6vDqNL8yyY%3DG%2BqANoz35G0NKuw(a)mail.gmail.com> > User-Agent: Mutt/1.5.24 (2015-08-30) > Status: RO > Content-Length: 1283 > Lines: 37 > > David Feuer wrote: > > What I'm looking for is more limited than lazy IO or unsafeInterleaveIO, > > but it seems quite possible that there's no way to get just what I'm > > looking for with the IO type proper using GHC's implementation of IO. Lazy > > IO allows evaluation to drive action. When a thunk is forced, it may > > trigger I/O (spooky action at a distance). What I'm talking about is > > separating what actions are performed from what values are calculated from > > them. Here's a partial concept which won't actually compile because of the > > lazy pattern matches: > > > > data MyIO a = forall b . MyIO (b -> a) (IO b) > > instance Functor MyIO where > > fmap f ~(MyIO t m) = MyIO (f . t) m > > instance Applicative MyIO where > > pure a = MyIO (const a) (pure ()) > > MyIO t1 m1 <*> ~(MyIO t2 m2) = > > MyIO (\(r1, r2) -> t1 r1 (t2 r2)) ((,) <$> m1 <*> m2) > > instance Monad MyIO where > > ??? > > instance MonadFix MyIO where > > ??? > > I believe that using this interface `unsafeInterleaveIO` could be > implemented as follows, making it just as powerful as lazy IO: > > data Box a = Box a > > unsafeInterleaveMyIO :: MyIO a -> MyIO a > unsafeInterleaveMyIO act = do > act' <- Box `fmap` act > return $ case act' of Box !r -> r > > Have I missed anything? Since MyIO and its associate functions don't contain any unsafe primitives it seems highly unlikely you can implement unsafeInterleaveIO with them! In fact I can't see how MyIO is any different to IO. All you can do with the function field is fmap it over the IO action field. Tom

3 5

Munich Haskell Meeting, 2016-04-28 @ 19:30
by Christian Neukirchen 25 Apr '16

25 Apr '16

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, April 28 at Cafe Puck at 19h30. For details see here: http://chneukirchen.github.io/haskell-munich.de/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-apr-2016/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

1 0

(no subject)
by None 24 Apr '16

24 Apr '16

>From int-e(a)gmx.de Sun Apr 24 21:13:18 2016 Date: Sun, 24 Apr 2016 21:13:18 +0200 From: Bertram Felgenhauer <bertram.felgenhauer(a)googlemail.com> To: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] Is it possible to make lazy combinators for IO? Message-ID: <20160424191319.GA32509@24f89f8c-e6a1-4e75-85ee-bb8a3743bb9f> References: <CAMgWh9t4MbzbbdvnU8zz6Lm-p9Gtf2UO-%2BGaW%3DofPsNLmt4aCA(a)mail.gmail.com> <CAErCyQ-J%2BiYo2tXVs9S4VtGtuurFaNp%3DzsrY_58%3D7EeL7q0HVQ(a)mail.gmail.com> <CAMgWh9s3%2BksQOh52oU%3DazKcdLDyuFy2sYKPbz30xaXnTkLK9cw(a)mail.gmail.com> <CAErCyQ8OVMF0fMDuxLpuvHimCt7RBijjzp1wEBMxRFyyyCXZVg(a)mail.gmail.com> <CAMgWh9vsxijoCuNrMxeAZmVxML%2BA8iNUwpTy9Es1BF0z_%2BpryQ(a)mail.gmail.com> <CAMgWh9tV_aq2%3DNkKZ79QZX6Xn6V953RwWoFqTeUMDggF0%3DZZ%2Bg(a)mail.gmail.com> <CAErCyQ_zUqn53x1%3Dg3RKDjQc3%2BGXfXkj1VvaTxo8ONPeTfym0A(a)mail.gmail.com> <CAMgWh9s%3D0bAsjGEgGwSr8bPL6vDqNL8yyY%3DG%2BqANoz35G0NKuw(a)mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <CAMgWh9s%3D0bAsjGEgGwSr8bPL6vDqNL8yyY%3DG%2BqANoz35G0NKuw(a)mail.gmail.com> User-Agent: Mutt/1.5.24 (2015-08-30) Status: RO Content-Length: 1283 Lines: 37 David Feuer wrote: > What I'm looking for is more limited than lazy IO or unsafeInterleaveIO, > but it seems quite possible that there's no way to get just what I'm > looking for with the IO type proper using GHC's implementation of IO. Lazy > IO allows evaluation to drive action. When a thunk is forced, it may > trigger I/O (spooky action at a distance). What I'm talking about is > separating what actions are performed from what values are calculated from > them. Here's a partial concept which won't actually compile because of the > lazy pattern matches: > > data MyIO a = forall b . MyIO (b -> a) (IO b) > instance Functor MyIO where > fmap f ~(MyIO t m) = MyIO (f . t) m > instance Applicative MyIO where > pure a = MyIO (const a) (pure ()) > MyIO t1 m1 <*> ~(MyIO t2 m2) = > MyIO (\(r1, r2) -> t1 r1 (t2 r2)) ((,) <$> m1 <*> m2) > instance Monad MyIO where > ??? > instance MonadFix MyIO where > ??? I believe that using this interface `unsafeInterleaveIO` could be implemented as follows, making it just as powerful as lazy IO: data Box a = Box a unsafeInterleaveMyIO :: MyIO a -> MyIO a unsafeInterleaveMyIO act = do act' <- Box `fmap` act return $ case act' of Box !r -> r Have I missed anything? Cheers, Bertram

1 0

Should webassembly be a target for GHC?
by Dimitri DeFigueiredo 24 Apr '16

24 Apr '16

I'm interested in webassembly's recent momentum https://hacks.mozilla.org/2016/03/a-webassembly-milestone/ Is this a way we could get a foot in the web? I'm curious, just putting the thought out there. Cheers, Dimitri

7 7

Automatically Deriving Numeric Type Class Instances
by Jake 23 Apr '16

23 Apr '16

Is it possible to automatically derive instances of Numeric type classes like Num, Fractional, Real, Floating, etc? I currently have two datatypes, Pair and Triple, that are defined like this: data Pair a = Pair a a data Triple a = Triple a a a I wrote these pretty trivial instances for Num and Floating: instance Num a => Num (Pair a) where (+) = liftA2 (+) (*) = liftA2 (*) abs = liftA abs negate = liftA negate signum = liftA signum fromInteger = pure . fromInteger instance Fractional a => Fractional (Pair a) where (/) = liftA2 (/) recip = liftA recip fromRational = pure . fromRational and practically identical instances for Triple as well. Is there anyway to have GHC derive these instances and the other numeric type classes? Thanks, Jake

3 3

Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 152, Issue 27
by Julian Leviston 23 Apr '16

23 Apr '16

There were quite a few responses to you so far, but no one seemed to mention that what you actually asked for are called anamorphisms. https://en.wikipedia.org/wiki/Anamorphism <https://en.wikipedia.org/wiki/Anamorphism> They’re not a *class* per se (as in… they’re not a typeclass), but rather they’re a kind of higher-order function which we call unfold (the kind-of “opposite" action to a fold). Here’s a nice little thing I found which is quite helpful as an explanation: https://gist.github.com/CMCDragonkai/b586ee9ecce297ceeeb3 and Data.List has unfoldr: http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-List.html#v:unfol… <http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-List.html#v:unfol…> If you google around for either "anamorphism Haskell” or “unfold Haskell” you’ll find some nice explanatory resources. Hope that helps! Julian http://www.happylearnjavascripttutorial.com/ <http://www.happylearnjavascripttutorial.com/> - begin programming with JavaScript today using our awesome new method! http://www.happylearnhaskelltutorial.com/ <http://www.happylearnhaskelltutorial.com/> - begin programming with Haskell today using our awesome new method! > On 23 Apr 2016, at 10:00 PM, haskell-cafe-request(a)haskell.org wrote: > > Hi. I'm more in the shallow end of the Haskell pool right now, so > forgive me if this is really basic... In Haskell, what is the class for > things that can provide an infinite sequence? I mean, things that > produce a value as well as function for producing the next value? > Clearly RandomGen does this, but what is the next level of abstraction > above RandomGen (i.e., RandomGen minus the randomness aspect).

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wxhaskell: Play sound not working on OSX?
by Tilmann 23 Apr '16

23 Apr '16

Is it possible that play . sound might not work on OSX or I'm I doing something wrong? This advice from around 2006 is all I could find: "Did you build wxWidgets with configuring --enable-sound build option?" Is this still valid? If so, how do I do that? Tilmann |import Graphics.UI.WX main :: IO () main = start $ do f <- frame [] p <- panel f [] set f [layout := minsize(Size 100 100) $ widget p] play (sound "alarm.wav") | Using OSX 10.9.5, GHC 7.10.2, WX 0.92.2.0 http://stackoverflow.com/questions/36809989/play-sound-with-wxhaskell-not-w…

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[ANN] Aivika: A parallel distributed discrete event simulation library
by David Sorokin 23 Apr '16

23 Apr '16

Hi Cafe! I’m glad to announce the first add-on module [3] of Aivika simulation library that allows creating and running parallel distributed discrete event simulations. It is destined for clusters and supercomputers, although it works on a stand-alone notebook too. My module implements an optimistic strategy that implies transparent rollbacks. It is mainly inspired by ideas of the Time Warp algorithm, which first publication is dated early 80s. Please note that this is the first version. It is mainly experimental, but it already shows good results. For example, when using the reproducible random number generators on different nodes, I always get the same simulation results. Furthermore, for testing purposes, I rewrote one of my examples with discrete processes and the shared resource so that it uses too much messages just to see how it works. The add-on module allows doing everything that the generalized version [2] of Aivika can do in a part related to the discrete event simulation. Moreover, the parallel nodes can communicate to each other sending and receiving asynchronous messages, but these messages have the send and receive times. If the node receives the past message, a transparent rollback occurs so that the node can process the received message. When rolling the computation back, the node sends so called anti-messages to cancel the invalidated messages that came from the node. It allows us to have a predictable distributed simulation satisfying the time constraints and causality. There are different customization parameters that allow tuning the library. For example, by default the library waits 5 seconds to consider the local time of the node defined. Therefore, when running test models, you can see a small delay, which is necessary for finishing the synchronization between the nodes and so called time server. Unfortunately, there is a lack of documentation. But the main idea is as follows. The generalized version [2] is almost the same as the core library [1] which already has a documentation. The represented add-on [3] just allows using the generalized version for creating and running parallel distributed discrete event simulations within the specified computation. Best regards, David Sorokin, Yoshkar-Ola, Russia [1] http://hackage.haskell.org/package/aivika [2] http://hackage.haskell.org/package/aivika-transformers [3] http://hackage.haskell.org/package/aivika-distributed

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Generators? Iterators?
by Christopher Howard 23 Apr '16

23 Apr '16

Hi. I'm more in the shallow end of the Haskell pool right now, so forgive me if this is really basic... In Haskell, what is the class for things that can provide an infinite sequence? I mean, things that produce a value as well as function for producing the next value? Clearly RandomGen does this, but what is the next level of abstraction above RandomGen (i.e., RandomGen minus the randomness aspect). -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

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Documenting extensions
by Doug McIlroy 23 Apr '16

23 Apr '16

I'd like to believe the Haskell report is a bible. I learned H98 using the Prelude as a source of examples and Hugs as a testbed. That was a comfortable and rewarding combination. Later I discovered that by default GHC rejected almost all my report-conforming (H98 and H2010) code. Ironically, its website at the time asserted, "Haskell is a standard language." In fact, far from reflecting biblical authority, the de facto Haskell discussed in this cafe comes in some 2^99 flavors -- enough to use a different language for every run of the compiler for the life of the universe. Witness: ghc --supported-languages | grep -v '^No[A-Z]' | wc -l (99 is the answer for GHC 7.8.4. In fact not all combinations of -X options are legal, but you get the point.) Unfortunately there is no coherent discussion of all those Haskells. The extensions section of the GHC User Guide gives no formal syntax, often teaches semantics only by example, and is replete with sales pitches, partial analogies, inconsistent terminology, and (helpful) appeals to outside sources. Definitely not a bible. I understand that many GHC extensions are probationary. Nevertheless, in the interest of facilitating their full and correct use, I would plead that a report-grade description accompany each language feature incorporated in official releases. This seems like a small amount of effort beyond the hard work of conception and implementation. Are there cogent reasons for doing otherwise? Doug

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Haskell in Leipzig 2016: Call for Papers
by Joachim Breitner 22 Apr '16

22 Apr '16

Haskell in Leipzig September 14-15, 2016 HTKW Leipzig, Germany http://hal2016.haskell.org/ == About HaL == The workshop series “Haskell in Leipzig”, now in its 11th year, brings together Haskell developers, Haskell researchers, Haskell enthusiasts and Haskell beginners to listen to talks, take part in tutorials, and join in interesting conversations. Everything related to Haskell is on topic, whether it is about current research, practical applications, interesting ideas off the beaten track, education, or art, and topics may extend to functional programming in general and its connections to other programming paradigms as well. This year, HaL is colocated with two related conferences, * the Workshop on Functional and (Constraint) Logic Programming (WFLP) and * the Workshop on (Constraint) Logic Programming (WLP), to form the Leipzig Week of Declarative Programming (L-DEC): http://nfa.imn.htwk-leipzig.de/LDEC2016/ In order to accommodate and welcome a more international audience, this year’s HaL will be held in English. == Submissions == Contributions can take the form of * talks (about 30 minutes), * tutorials (about 90 minutes), * demonstrations, artistic performances, or other extraordinary things. Please submit an abstract that describes the content and form of your presentation, the intended audience, and required previous knowledge. We recommend a length of 2 pages, so that the PC and the audience get a good idea of your submission, but this is not a hard requirement. You can submit your abstract, as an PDF document, at https://easychair.org/conferences/?conf=hal2016 until Friday, July 1, 2016. You will be notified by July 15, 2016. == Program committee == * Andreas Abel, Chalmers and Gothenburg University, Sweden * Heinrich Apfelmus, Leipzig, Germany * Joachim Breitner, Karlsruhe Institute of Technology, Germany (Chair) * Matthias Fischmann, Zerobuzz, Germany * Petra Hofstedt, BTU Cottbus-Senftenberg, Germany * Wolfgang Jeltsch, Institute of Cybernetics at Tallinn University of Technology, Estonia * Andres Löh, Well-Typed LLP, Germany * Alejandro Serrano Mena, Universiteit Utrecht, Netherlands * Neil Mitchell, Standard Chartered Bank, UK * Katie Ots, Facebook, UK * Peter Stadler, University of Leipzig, Germany * Henning Thielemann, Freelancer, Germany * Niki Vazou, University of California, San Diego, USA If you have any questions, please don’t hesitate to contact Joachim Breitner <breitner(a)kit.edu>. -- Dipl.-Math. Dipl.-Inform. Joachim Breitner Wissenschaftlicher Mitarbeiter http://pp.ipd.kit.edu/~breitner

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I have a question about Haskell
by Eunsu Kim 22 Apr '16

22 Apr '16

Hi i have a problem in my code! here is my code: here is error message: in very bottom function (polyEvaluate), why is not working “result <- map (\(a,b) -> a+b) powers” ??? in Prelude, it is working Thanks!

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I've wanted a Haskell shirt for awhile
by Stegosaurus Armatus 21 Apr '16

21 Apr '16

Does anyone know where I can get one? Failing that, I made one to celebrate today. https://teespring.com/haskell-stay-lifted Disclaimer: I don't intend to be spammy, but I totally understand and respect if some people don't like this. I was just happy and wanted to share. Please don't hate.

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Generics changes in GHC 8 break containers
by David Feuer 21 Apr '16

21 Apr '16

containers does not currently build with GHC 8 because of changes to Generics. I only have a shallow understanding of GHC.Generics. Could someone give me a hand figuring out what I need to change? Thanks, David Feuer

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ANN: New Haskell.org committee members
by John Wiegley 21 Apr '16

21 Apr '16

The Haskell.org committee has selected its new member following the March self-nomination period. The new (returning) member is: * Gershom Bazerman Thank you to everyone who submitted a self-nomination. Note that if you have self-nominated in the past, but not been picked, please self-nominate again in the future. -- John Wiegley GPG fingerprint = 4710 CF98 AF9B 327B B80F http://newartisans.com 60E1 46C4 BD1A 7AC1 4BA2

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