- Haskell-Cafe - Haskell.org

Call for a maintainer of protocol-buffers
by Kostiantyn Rybnikov 22 Jun '18

22 Jun '18

Hey everyone, I'm looking for a person who would become the major maintainer of the protocol-buffers package. Details here: https://github.com/k-bx/protocol-buffers/issues/64 Please comment on the issue or send me an email if you'd like to apply. Thank you

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dfinity-radix-tree: A Merkleized key–value data store.
by Enzo 21 Jun '18

21 Jun '18

I am pleased to announce the first release of dfinity-radix-tree: A Merkleized key–value data store. The library provides a simple and easy to use data integrity layer for LevelDB. For more information, please see: [1] https://github.com/dfinity-lab/hs-radix-tree [2] https://hackage.haskell.org/package/dfinity-radix-tree Warm regards, Enzo Haussecker DFINITY Stiftung *We're hiring Haskell developers in Palo Alto and Zürich. Apply now:* [3] https://dfinity.org/openings

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Timeouts inside a ConduitParser
by Luke Lau 21 Jun '18

21 Jun '18

I have a ConduitParser <https://hackage.haskell.org/package/conduit-parse-0.2.1.0/docs/Data-Conduit…> (a Sink with some parsing state) with a version of satisfy that can time out: satisfy :: MonadIO m => (a -> Bool) -> ConduitParser a m a satisfy pred = do tId <- liftIO myThreadId timeoutThread <- liftIO $ forkIO $ do threadDelay 1000000 throwTo tId TimeoutException x <- await liftIO $ killThread timeoutThread if pred x then return x else empty However I would rather not deal with the risks involved with handling concurrency myself and use a system library like System.Timeout: satisfy :: MonadIO m => (a -> Bool) -> ConduitParser a m a satisfy pred = do x <- timeout 1000000 await if pred x then return x else empty This doesn’t work though since I need to be able to both lift and unlift await from IO, and ConduitParser lies on top of ConduitT, which is one of the types of monads that UnliftIO cannot be an instance of <https://github.com/fpco/unliftio#limitations>. Are there any better approaches to this? <https://github.com/fpco/unliftio#limitations> <https://github.com/fpco/unliftio#limitations> <https://github.com/fpco/unliftio#limitations>

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Re: [Haskell-cafe] How to use Reader?
by Hilco Wijbenga 21 Jun '18

21 Jun '18

Ah, quite simple. Thanks! On Tue, Jun 19, 2018 at 9:39 PM, Matt <parsonsmatt(a)gmail.com> wrote: > showText text = do > a <- showA > return ("[" `append` text `append` a `append` "]") > > > Matt Parsons > > On Tue, Jun 19, 2018 at 10:35 PM, Hilco Wijbenga <hilco.wijbenga(a)gmail.com> > wrote: >> >> Hi all, >> >> I think I'm pretty close but not quite there yet. Let's say I have the >> following: >> >> {-# LANGUAGE OverloadedStrings #-} >> >> module Main where >> >> import Prelude (IO) >> import Data.Text (Text, append) >> import Data.Text.IO (putStrLn) >> >> main :: IO () >> main = >> putStrLn (showText "Hello World!" config) >> where >> config :: Config >> config = Config (A "Boo") >> >> data A = A Text >> >> data Config = Config { a :: A } >> >> showText :: Text -> Config -> Text >> showText text config = >> "[" `append` text `append` (showA config) `append` "]" >> >> showA :: Config -> Text >> showA config = >> "'" `append` text `append` "'" >> where >> A text = a config >> >> Now I want to use Reader. This is as close as I can get: >> >> {-# LANGUAGE OverloadedStrings #-} >> >> module Main where >> >> import Prelude (IO, return, ($)) >> import Data.Text (Text, append) >> import Data.Text.IO (putStrLn) >> import Control.Monad.Reader (Reader, asks, runReader) >> >> main :: IO () >> main = >> putStrLn (runReader (showText "Hello World!") config) >> where >> config :: Config >> config = Config (A "Boo") >> >> data A = A Text >> >> data Config = Config { a :: A } >> >> showText :: Text -> Reader Config Text >> showText text = >> return $ >> "[" `append` text `append` showA `append` "]" >> >> showA :: Reader Config Text >> showA = do >> A text <- asks a >> return $ >> "'" `append` text `append` "'" >> >> This is almost correct, except for the showA invocation in showText. >> It wants a Text but it's getting a Reader Config Text. What is the >> magic to make this work? >> >> Cheers, >> Hilco >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> Only members subscribed via the mailman list are allowed to post. > >

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Looking for simple C statements parser for Parsec, MegaParsec or Happy
by Bulat Ziganshin 20 Jun '18

20 Jun '18

Hello all, I develop a preprocessor transpiling subset of C statements into gcc _asm statements. For this project, I will be happy to reuse existing C statements parser written with any popular Haskell technology, or just start with some simple C subset parser in order to avoid redoing existing work. Unfortunately, so far I found grammars just for everything but C. And while I can start with Parsec grammars for Java/Go, it seems that MegaParsec now is better choice? I can quickly develop grammar for small C subset, but ready-to-use grammar for larger C subset will allow me to completely skip the development of C statement parser and focus on the meat of project - asm code generation. Eventually, it may turn into LLVM pass transpiling parts of C++ code, but for quick prototype, I prefer Haskell, especially if I can find ready-to-use parser. PS: It was the first time I ever asked at SO, but it turned out to be offtopic there: https://stackoverflow.com/questions/50949118/simple-c-grammar-for-haskell-p… -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Re: [Haskell-cafe] GHCi: how to load another file than .ghci ?
by Artem Pelenitsyn 20 Jun '18

20 Jun '18

It worked for me on a dummy project, but I may miss something. Maybe, it is `stack ghci` you want to use, not `stack exec ghci`. But I wasn't able to convince stack to catch `-ghci-script` for some reason. My best bet was: stack ghci --ghci-options="-ghci-script ~/my-ghci" PS You probably want to reply not just to me but to the whole mailing-list, so that people know that your problem hasn't been resolved. -- Best, Artem On Wed, 20 Jun 2018 at 16:08 PY <aquagnu(a)gmail.com> wrote: > strange, because result is different (I got a lot of errors about not > found modules, etc). > > 20.06.2018 16:21, Artem Pelenitsyn пишет: > > Hello Paul, > > You can supply arguments for commands run by stack like this: stack exec > CMD -- ARGS > In your case the argument you're interested in is -ghci-script. So the > answer is > > stack exec ghci -- -ghci-script path/to/somefile.txt > > -- > Best wishes, Artem > > > On Wed, 20 Jun 2018 at 14:44 PY <aquagnu(a)gmail.com> wrote: > >> Hello, Cafe! If I have typical .ghci file, but it's called somefile.txt, >> how to call "stack exec ghci" to load and exec this "somefile.txt" (as >> it does with ".ghci" usual)? >> >> >> === >> >> Best regards, Paul >> >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> Only members subscribed via the mailman list are allowed to post. > > >

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GHCi: how to load another file than .ghci ?
by PY 20 Jun '18

20 Jun '18

Hello, Cafe! If I have typical .ghci file, but it's called somefile.txt, how to call "stack exec ghci" to load and exec this "somefile.txt" (as it does with ".ghci" usual)? === Best regards, Paul

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Re: [Haskell-cafe] Memory leak in infinite recursion
by Dr.Koster 20 Jun '18

20 Jun '18

In general infinite monadic recursion will leak, since the tail position is always >> or >>= instead of your own recursive function, but under certain situations, e.g. IO without arguments, the compiler will figure there's no need to push new stack frame. But anyway it's better to checkout yourself rather relying on some weak assumptions. 发自我的iPhone ------------------ Original ------------------ From: Никита Фуфаев <kitttoran(a)gmail.com> Date: Wed,Jun 20,2018 2:37 AM To: haskell-cafe <haskell-cafe(a)haskell.org> Subject: Re: [Haskell-cafe] Memory leak in infinite recursion Hello everyone In C you can't implement main loop with recursion like void mainLoop() { doSomething(); mainLoop(); } because without optimisations stack will overflow. In haskell it's common to write mainLoop = doSomething >> mainLoop, and it doesn't leak memory because of haskell's evaluation model. Does memory leak or argument stack overflow happen in this case? mainLoop = doSomething >> mainLoop >> exit ExitSuccess What about this case? mainLoopModeA = do doSomething when condition mainLoopModeB mainLoopModeA mainLoopModeB = do doSomethingElse when anotherCondition mainLoopModeA mainLoopModeB or this case? mainLoopModeA = do doSomething if condition then mainLoopModeB else mainLoopModeA mainLoopModeB = do doSomethingElse if anotherCondition then mainLoopModeA else mainLoopModeB -- Nikita Fufaev

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How to define CPP macro definition with stack?
by PY 20 Jun '18

20 Jun '18

Hello all, I'm using conditional compilation: #ifdef BLAH blahBlah #endif And I want to define BLAH, but not in *.hs file. For example, with `stack` option or as environment variable... How can I do it? For example, `stack -DBLAH=1 build` or something else. I tried stack build --flag='*:BLAH' - no effect. Also I tried stack build --flag=my-library:BLAH and get error that my-library package does not define flag BLAH. So, it's total secret for me how to make such thing (like we can do with gcc, make, etc) :-) === Best regards, Paul

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How to use Reader?
by Hilco Wijbenga 20 Jun '18

20 Jun '18

Hi all, I think I'm pretty close but not quite there yet. Let's say I have the following: {-# LANGUAGE OverloadedStrings #-} module Main where import Prelude (IO) import Data.Text (Text, append) import Data.Text.IO (putStrLn) main :: IO () main = putStrLn (showText "Hello World!" config) where config :: Config config = Config (A "Boo") data A = A Text data Config = Config { a :: A } showText :: Text -> Config -> Text showText text config = "[" `append` text `append` (showA config) `append` "]" showA :: Config -> Text showA config = "'" `append` text `append` "'" where A text = a config Now I want to use Reader. This is as close as I can get: {-# LANGUAGE OverloadedStrings #-} module Main where import Prelude (IO, return, ($)) import Data.Text (Text, append) import Data.Text.IO (putStrLn) import Control.Monad.Reader (Reader, asks, runReader) main :: IO () main = putStrLn (runReader (showText "Hello World!") config) where config :: Config config = Config (A "Boo") data A = A Text data Config = Config { a :: A } showText :: Text -> Reader Config Text showText text = return $ "[" `append` text `append` showA `append` "]" showA :: Reader Config Text showA = do A text <- asks a return $ "'" `append` text `append` "'" This is almost correct, except for the showA invocation in showText. It wants a Text but it's getting a Reader Config Text. What is the magic to make this work? Cheers, Hilco

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