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Nice clean code example?
by Han Joosten 01 Jul '17

01 Jul '17

I'd like to showoff some nice Haskell code to a CTO with no experience with FP. I promised to send him a small piece of Haskell so he could get an idea. The code should be easy to read, without obscure looking operators (so sorry, no lens, arrows stuff like that), optionally even do something interesting. Who has the nicest example laying around? (and yes, I need it by yesterday ;-) ) Thanks!

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Re: [Haskell-cafe] Nice clean code example?
by Chris Wong 30 Jun '17

30 Jun '17

How about Hackagebot? https://github.com/lfairy/hircine/blob/master/brigitte/Hackagebot.hs https://github.com/lfairy/hircine/blob/master/brigitte/Utils.hs It involves a lot of concurrency, networking, and data structure manipulation -- all areas Haskell excels in. It avoids using advanced features as well (except maybe pattern synonyms, but those aren't visible in the code that uses them) Here are some numbers: its sibling Cargobot boasts 3+ months continuous uptime, with memory usage never going beyond 12 MB. It has never crashed. I expect Hackagebot to have similar metrics. On Jul 1, 2017 06:34, "Han Joosten" <han.joosten.han(a)gmail.com> wrote: I'd like to showoff some nice Haskell code to a CTO with no experience with FP. I promised to send him a small piece of Haskell so he could get an idea. The code should be easy to read, without obscure looking operators (so sorry, no lens, arrows stuff like that), optionally even do something interesting. Who has the nicest example laying around? (and yes, I need it by yesterday ;-) ) Thanks! _______________________________________________ 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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Dynamically linking frameworks on macOS
by Ryan Trinkle 30 Jun '17

30 Jun '17

Hi everyone, I'm trying to ensure that beginner-level code that uses reflex-dom can be built by simply calling 'ghc myFile.hs', provided that all the necessary libraries are available in ghc-pkg. This works on linux, but on macOS, it's currently necessary for the user to add '-dynamic' to the command line. In particular, without -dynamic, the linker fails to find "_OBJC_CLASS_$_NSURL", which is a symbol in the Foundation system framework. Apple doesn't support (and strongly discourages) statically linked executables[1], so it's not terribly surprising that this doesn't work. Is there anything I can do to avoid the need for -dynamic here? Thanks, Ryan [1] https://developer.apple.com/library/content/qa/qa1118/_index.html

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Domain specific error diagnosis in Haskell, a proposal
by Alejandro Serrano Mena 30 Jun '17

30 Jun '17

Dear Haskellers, Some days ago Jurriaan Hage posted a video of our work on adding custom type error diagnosis to GHC. Here is a GHC proposal for incorporating this support in the mainline compiler: https://github.com/ghc-proposals/ghc-proposals/pull/59 Suggestions, criticisms and ideas are welcome. Alejandro

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Source code location in IO?
by Tom Ellis 30 Jun '17

30 Jun '17

Is it compatible with the semantics of Haskell to have a function sourceLocation :: IO String which when run returns the source file location at which it is used? For example, suppose Main.hs is module Main where main = do putStrLn =<< sourceLocation putStrLn "Hello" putStrLn =<< sourceLocation It would print the following when run Main.hs:4 Hello Main.hs:6 and module Main where main = do let s = sourceLocation putStrLn =<< s putStrLn "Hello" putStrLn =<< s It would print the following when run Main.hs:4 Hello Main.hs:4 If this is not compatible with the semantics of Haskell, why not? I agree that the two programs must have the same denotation, but is there anything that requires them to have the same output when run? Tom

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Problem with pipe/Is there a function that "lifts" functions to Producers?
by Cody Goodman 30 Jun '17

30 Jun '17

Hi all, I have a function from Text -> Text which I want to apply to each line using pipes-text and pipes-group. I'm pretty sure my pipe is not doing what I expect. I'm going back over the pipes tutorial now, but I think I could use some help figuring it out. I have the following (buildable github project: https://github.com/codygman/fixedWidthToDelimited) code: import Data.Monoid import Pipes import qualified Pipes.Text as Text import qualified Pipes.Text.IO as Text import System.IO import Lens.Family import qualified Pipes.Group as Group import qualified Data.Text as T appendAt :: Int -> T.Text -> T.Text -> (T.Text,T.Text) appendAt i appendBS bs = let (first, rest) = T.splitAt i bs in (first <> appendBS <> rest,rest) -- TODO figure out how to test a pipe (I'm sure pipes-text or any other libraries test their pipes) toDelimPipe :: Monad m => [Int] -> Pipe T.Text T.Text m r toDelimPipe offsets = do chunk <- await let text = (fixedWidthLine offsets) chunk if T.null text then (toDelimPipe offsets) else do yield text cat fixedWidthLine :: [Int] -> T.Text -> T.Text fixedWidthLine offsets bs = fst $ go offsets ("" :: T.Text,bs) where go :: [Int] -> (T.Text,T.Text) -> (T.Text,T.Text) go [] x = x go (x:xs) (acc,rest) = let (newAcc,newRest) = T.splitAt x rest in go xs (acc <> (fst $ appendAt x "|" newAcc),newRest) {- got: runEffect $ over Text.lines (Group.maps (>-> toDelimPipe [2,2,2] )) (Text.fromLazy (LT.replicate 2 "x" <> LT.replicate 2 "y" <> LT.replicate 2 "z")) >-> Text.stdout xx|||yyzz Expected: xx|yy|zz| When I use fixedWidthLine alone with the same offsets I get: λ> fixedWidthLine [2,2,2] (T.replicate 2 "x" <> T.replicate 2 "y" <> T.replicate 2 "z") "xx|yy|zz|" I think my pipe is wrong -}

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on the {lambda way}
by marty.alain 29 Jun '17

29 Jun '17

Dear Haskell-Café mailing list, Please excuse me if the Haskell-Café is not the appropriate place to post this question in but, following the advice of M. Simon Peyton Jones, I would like to know if one of you could tell me his opinion about such a work - http://lambdaway.free.fr/lambdaway/data/lambdatalk_20170615.pdf a PDF file directly printed from this wiki page - http://lambdaway.free.fr/lambdaway/?view=oxford introducing an “iconoclastic” approach detailed in long in this workshop - http://lambdaway.free.fr/ transforming a web markup syntax into a small functional programming language that an eleven years old child could understand: - http://lambdaway.free.fr/lambdaway/?view=teaching Best regards Alain Marty engineer architect

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Issue 61 :: Haskell Weekly
by Taylor Fausak 29 Jun '17

29 Jun '17

\ Haskell Weekly \/\/ Issue 61 <https://haskellweekly.news/issues/61.html> Welcome to another issue of Haskell Weekly! Haskell is a purely functional programming language that focuses on robustness, concision, and correctness. This is a weekly summary of what's going on in its community. ## Featured ## - Haxl: Making concurrency unreasonably easy <http://events.techcast.com/bigtechday10/Garmisch-1345/> > Haxl is a big hammer for doing I/O concurrently, testing I/O, and modularity (caching & memoization). - Introduction to Brick <https://samtay.github.io/articles/brick.html> > I'm going to give a short introduction to Brick, a Haskell library for building terminal user interfaces. So far I've used brick to implement Conway's Game of Life and a Tetris clone. I'll explain the basics, walk through an example snake application, and then explain some more complicated scenarios. - Simplexhc: An STG to LLVM compiler <https://pixel-druid.com/blog/announcing-simplexhc/> > STG's lowering to C-- and the decisions taken when implementing it were based in the '90s. That's not to say that the GHC team hasn't done an awesome job keeping it up to date; they have! But, I wonder what a complete rewrite of this lowering would look like. Hence, I'm trying to experiment in this space and see what happens. - Front Row is hiring a senior backend Haskell engineer <https://frontrow.workable.com/j/463B843754> > Come change how 6.5+ million K-12 US students learn Math, Language Arts, Social Studies and more. Use data, advanced type systems, great product design and deep pedagogy to change lives. - Threading responsibly: `forkIO` considered harmful <http://mazzo.li/posts/threads-resources.html> > In this post I want to argue that threads are also a resource, in the sense that they require management after we've created them. A stray thread will consume memory, CPU cycles, and really whatever resource it might need to execute. - The `Has` type class pattern <https://medium.com/@jonathangfischoff/the-has-type-class-pattern-ca12adab70…> > The value in this approach is that I don't have to think about what functions to call to collect the images: it's always `images`. In the prior example, I had to think about the how to collect the images each time, and it took brain power better spent elsewhere. - A tale of two brackets <https://www.fpcomplete.com/blog/2017/06/tale-of-two-brackets> > I hope the primary thing you take away from it is a deeper understanding of how monad transformer stacks interact with operations in the base monad, and how monad-control works in general. - `RecordWildCards` and binary parsing <https://jship.github.io/posts/2017-06-24-record-wildcards-and-binary-parsin…> > `RecordWildCards` is a GHC extension that makes working with Haskell records more convenient. The extension has been blogged about in a few places already, so this post intends to provide a different motivating example: binary parsing. - On naming things: Library design <http://www.parsonsmatt.org/2017/06/23/on_naming_things.html> > I've written a few libraries now and have tried out different naming and exporting conventions. I've developed a bit of a feel for how it is to write and use them, and I'm going to put out my personal preferences and opinions on library design here. - Haskell Bits #6: A guide to mutable references <http://www.kovach.me/posts/2017-06-22-mutable-references.html> > There are quite a few ways to store mutable data in Haskell. Let's talk about some of them! Specifically, we will focus on mutable containers that store a single value that can be modified by one or more threads at any given time. I'm not going to go into a ton of detail here --- I just want to give an overview. - Interfaces and type classes: Number APIs in C# and Haskell <https://mzabani.wordpress.com/2017/06/22/interfaces-and-typeclasses-number-…> > In C# sometimes I sorely miss something like an `INumber<T>` interface with methods add, subtract, multiply, and others. The lack of this means it is cumbersome to write generic code on numbers. ## Package of the week ## This week's package of the week is data-has, a library that provides a simple extensible product system. <https://www.stackage.org/lts-8.20/package/data-has-0.2.1.0> ## In brief ## - Announcing haskus-system 0.7 <http://hsyl20.fr/home/posts/2017-06-29-announcing-haskussystem-07.html> - Defeating evil with data structures <https://mmhaskell.com/blog/2017/6/26/fun-with-data-structures> - stack2nix first public release <https://mailman.science.uu.nl/pipermail/nix-dev/2017-June/024011.html> - Streaming combinators and extracting flat parallelism <https://futhark-lang.org/blog/2017-06-25-futhark-at-pldi.html> - Typing Nix <https://www.tweag.io/posts/2017-05-23-typing-nix.html> - When competing with C, fudge the benchmark <https://medium.com/@n0mad/when-competing-with-c-fudge-the-benchmark-16d3a91…> ## Events ## - Berlin Functional Programming Group's first meeting July 1 <https://www.meetup.com/Berlin-Functional-Programming-Group/events/241040383/> - Haskell.SG's July meetup July 5 <https://www.meetup.com/HASKELL-SG/events/240959693/>

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dsl for atari 2600 vcs?
by Raoul Duke 29 Jun '17

29 Jun '17

Along the lines of atom & ivory & tower, has anyone (I haven't turned up any hits online so I guess not) worked on a dsl in haskell for generating racing-the-beam code? Feels like all the book keeping might be something haskell could do, giving a dsl that is more high level than manual mental cycle counting.

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[ANN] haskus-system 0.7
by Sylvain Henry 29 Jun '17

29 Jun '17

Hi all, I have released haskus-system 0.7. haskus-system <https://github.com/haskus/haskus-system> is a Haskell library for system programming on top of the Linux kernel. You can use it to build systems that only use: * the Linux kernel * the haskus-system library * your code This release features a new build tool that automatically downloads, configures and builds Linux, SysLinux, etc. It can also execute your system within QEMU, build ISO images and even create bootable devices. For instance, to test the Demo example from https://github.com/haskus/haskus-system-examples/ with QEMU, you just have to type: > haskus-system-build test --init Demo The full announce with some screenshots and a video: http://hsyl20.fr/home/posts/2017-06-29-announcing-haskussystem-07.html Cheers, Sylvain

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