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Compilers written in Haskell?
by David Banas 28 Jan '20

28 Jan '20

Can anyone provide a list of compilers written in Haskell? Sent from my iPhone

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Need help using a typeclass within an existing API
by Debasish Ghosh 28 Jan '20

28 Jan '20

Hi - (Apologies for the long post) I need some help integrating a typeclass based functionality within an existing API. I am using Control.Monad.Validate for my validation of objects. Here's a simple function based on this .. debit :: forall m. (MonadReader Env m, MonadValidate [Error] m) => Y.Dense "USD" -> Account -> m Account debit amount = updateBalance ((-1) * amount) Now I want to make a change in the API where I would like to fetch the account from some database based on account number. For this I have a typeclass as below .. class (Monad m) => AccountDB m where query :: Text -> m (Maybe Account) .. elided details and I am using persistent - so I have an instance of this class as follows .. -- | Instance of AccountDB for `SqlPersistT` (which is `ReaderT SqlBackend`) instance (MonadIO m) => AccountDB (SqlPersistT m) where query ano = get (AccountKey ano) .. other details elided My question is how can I integrate this typeclass within the above API ? I tried as yet another constraint in the function .. debit :: forall m. (MonadReader Env m, MonadValidate [Error] m, AccountDB m) => Y.Dense "USD" -> Text -> m Account debit amount accNo = do maybeAccount <- query accNo maybe (refuteErr $ InvalidAccountNumber accNo) (updateBalance ((-1) * amount)) maybeAccount This compiles but I don't get the proper instance of the typeclass when I run it - possibly due to the reason that the "m" cannot be the same for AccountDB as the other constraints. And I don't want to hardcode SqlPersistT in the function debit as I would like to be able to run it with other instances of the typeclass as well (example for testing I may like to test against a HashMap). What would be an idiomatic approach to this kind of composition ? Any help will be appreciated. regards. -- Debasish Ghosh http://manning.com/ghosh2 http://manning.com/ghosh Twttr: @debasishg Blog: http://debasishg.blogspot.com Code: http://github.com/debasishg

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Issues requesting permission to publish packages
by Victor Adossi 28 Jan '20

28 Jan '20

Hi Haskell-Cafe, I recently tried to upload a package to hackage and sent an email to hackage-trustees(a)haskell.org to request to be added to the uploaders group. Unfortunately my email was undelivered due to an SPF Failure -- here's what the error emailed to me looks like: > <one-of-the-maintainers(a)personal-email.com> (expanded from > <hackage-trustees(a)haskell.org>): host > host.personal-email.com[xxx.xxx.xxx.xxx] said: 550 5.7.23 > <one-of-the-maintainers(a)personal-email.com>: Recipient address > rejected: Message rejected due to: > SPF fail - not authorized. Please see > http://www.openspf.net/Why?s=mfrom;id=vados@vadosware.io;ip=<IP of > haskell.org server>;r=<UNKNOWN> > (in reply to RCPT TO command) It looks like the SPF settings on my domain forbid the bounce off of hackage-trustees to the individual trustee that was picked. Two points: - This seems like an unintended leaking of information (I have one of the emails of the trustees, via the error message) - How else can I request the ability to become a package uploader? Thanks, Victor

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Munich Haskell Meeting, 2020-01-27 @ 19:30
by Leah Neukirchen 26 Jan '20

26 Jan '20

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, January 27 at Augustiner-Gaststätte Rumpler at 19h30. For details see here: http://muenchen.haskell.bayern/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-jan-2020/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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Problem using Persistent
by Debasish Ghosh 26 Jan '20

26 Jan '20

Hi - I have an entity declaration in persistent as follows: share [mkPersist sqlSettings { mpsGenerateLenses = True, mpsPrefixFields = False }, mkMigrate "migrateAll"] [persistLowerCase| Account accountNo Text accountType AccountType accountHolderName Text accountOpenDate UTCTime default=CURRENT_TIME accountCloseDate UTCTime Maybe default=NULL currentBalance MoneyUSD rateOfInterest Double Primary accountNo deriving Show |] I am getting this compilation error .. • No instance for (Generic (Key Account)) arising from the 'deriving' clause of a data type declaration Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself • When deriving the instance for (aeson-1.4.6.0:Data.Aeson.Types.ToJSON.ToJSON (Key Account)) | 40 | share [mkPersist sqlSettings { mpsGenerateLenses = True, mpsPrefixFields = False }, mkMigrate "migrateAll"] [persistLowerCase| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^... and another exactly similar for FromJSON What exactly is going wrong here ? I am not using json in the above definition. regards. -- Debasish Ghosh http://manning.com/ghosh2 http://manning.com/ghosh Twttr: @debasishg Blog: http://debasishg.blogspot.com Code: http://github.com/debasishg

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[ANN] bz2 library
by Vanessa McHale 25 Jan '20

25 Jan '20

Hi all, I wrote another high-level wrapper around libbz2, https://matrix.hackage.haskell.org/#/package/bz2. It includes low-level bindings (via c2hs) and a bundled copy of bzlib 1.0.8 as well. Cheers, Vanessa McHale

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[ANN] nix-freeze-tree-0.1.0.0 - Freeze a tree using fixed-output derivations
by Jack Kelly 25 Jan '20

25 Jan '20

I have just pushed an initial release of nix-freeze-tree[1] to Hackage. `nix-freeze-tree` is a utility that walks a directory tree, and writes out Nix expressions which rebuild that tree. The generated expressions have two important properties: 1. Each file in the tree is built by a separate fixed-output derivation, and 2. Directories are built by derivations that symlink their contents recursively. If you are using `nix copy` to ship a derivation between nix stores, copying the derivation built by evaluating the output of `nix-freeze-tree` can reuse existing files in the destination store, as fixed-output derivations can be checked against a hash before copying. I use this to speed up deploys to my personal website. Running `nix-freeze-tree` on the output from my site generator and importing the result means that `nix copy` only uploads new files, instead of copying a single giant derivation containing every image on the site. The code is on Sourcehut[2]; bug reports[3] and patches[4] are welcome. The repository also has a Nix helper function for running the tool on your own derivations. Best, -- Jack [1]: https://hackage.haskell.org/package/nix-freeze-tree-0.1.0.0 [2]: https://git.sr.ht/~jack/nix-freeze-tree/ [3]: https://todo.sr.ht/~jack/nix-freeze-tree [4]: https://lists.sr.ht/~jack/nix-freeze-tree-discuss

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[ghc-steering-committee] The GHC Committee welcomes its new members
by Joachim Breitner 24 Jan '20

24 Jan '20

Dear Haskell community, the GHC Steering committee welcomes three new members, Alejandro Serrano Mena, Cale Gibbard and Tom Harding. We are happy to see that there is continued interest in our work, and are looking forward to having fresh insights and energy on the committee. They take the seat of Sandy Maguire, who we thank for this productive work during his tenure. As you might notice, we picked more candidates than we filled slots. This is not because Sandy’s productivity need three people to fill. The idea is that there is no reason to turn away a motivated contributor just to stick to the arbitrary 10 members. Instead, we will aim at “roughly 10”, and probably not call for new members until we have dropped below that number again. On behalf of the committee, Joachim Breitner PS: Alejandro, Cale and Tom, please send me your github handles and subscribe to the mailing list at https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de https://www.joachim-breitner.de/

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Taking over double-conversion on Hackage
by Rinat Stryungis 21 Jan '20

21 Jan '20

Hi everyone, The double-conversion package seems unmaintained. I'd like to take over as maintainer. I have actually forked the repository, added new functionality, tests, and updated the original Google library: https://github.com/haskell-mouse/double-conversion I was advised to consider taking over the maintenance of double-conversion. I tried to contact Bryan O'Sullivan (the maintainer) a few times during the 2 years (!) using all available communication methods (e-mail, LinkedIn). He answered only once and asked me to send an e-mail. I did it but without any effect. I would still prefer not to have this responsibility, but I would also like people to be able to use the new functionality without creating redundant forks.

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a sort of chunk
by PICCA Frederic-Emmanuel 20 Jan '20

20 Jan '20

Hello, I need to write some code in order to do some computations with stack of images coming from hdf5 files. Each computation done per images is quite intensive, so I want to do this on multiple cores of my computer (24 in my case) A stack of images is composed of a list of files. each file contain n images. So I decided to proceed like this: create a data type which represent a chunk of this stack. data Chunk = Chunk { filename :: FilePath , from :: Int , to :: Int } And indeed the full stack is [Chunk] Now since I have n core, I need to split the full stack in equivalent chunk of images. Just for example. at the begining I have this image stack 30476 images [Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00077.nxs" 0 698,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00078.nxs" 0 1104,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00079.nxs" 0 1510,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00080.nxs" 0 1914,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00081.nxs" 0 2318,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00082.nxs" 0 2720,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00083.nxs" 0 2169,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00084.nxs" 0 2445,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00085.nxs" 0 2720,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00086.nxs" 0 490,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00087.nxs" 0 812,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00088.nxs" 0 1133,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00089.nxs" 0 1454,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00090.nxs" 0 1773,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00091.nxs" 0 2090,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00092.nxs" 0 2406,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00093.nxs" 0 2720] so i need to write a function which do something like chunksOf chunksOf :: Int -> [Chunk] -> [[Chunk]] In this case I need to create chunk of 1325 images, so the finla result should be [ [Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00077.nxs" 0 698,Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00078.nxs" 0 627] , [Chunk "/nfs/ruche-sixs/sixs-soleil/com-sixs/2019/Run3/FeSCO_Cu111/sample2_ascan_omega_00078.nxs" 627 1104, ...] ... ] I would like your help in order to give me advices or help me find information whcih can help me implement this chunksOf method. thanks for your help. Frederic

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