July 2017 - Haskell-Cafe

Call for Participation: ICFP 2017
by Lindsey Kuper 18 Jul '17

18 Jul '17

[ Early registration ends 4 August. ] ===================================================================== Call for Participation ICFP 2017 22nd ACM SIGPLAN International Conference on Functional Programming and affiliated events September 3 - September 9, 2017 Oxford, UK http://icfp17.sigplan.org/ ===================================================================== ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. A full week dedicated to functional programming: ICFP, 2 co-hosted conferences, 1 co-hosted symposium, workshops, tutorials, programming contest results, student research competition, and mentoring workshop * Overview and affiliated events: http://icfp17.sigplan.org/home * Program: http://icfp17.sigplan.org/program/program-icfp-2017 * Accepted papers: http://icfp17.sigplan.org/track/icfp-2017-papers * Registration is available via: https://regmaster4.com/2017conf/ICFP17/register.php Early registration is due 4 August, 2016. * Programming contest, 4-7 August, 2016: http://2017.icfpcontest.org * Student Research Competition: http://icfp17.sigplan.org/track/icfp-2017-Student-Research-Competition * Follow @icfp_conference on twitter for the latest news: http://twitter.com/icfp_conference There are several events affiliated with ICFP: Sunday, September 3 Workshop on Higher-order Programming with Effects Workshop on Type-Driven Development Scheme and Functional Programming Workshop Programming Languages Mentoring Workshop ICFP Tutorials Monday, September 4 – Wednesday, September 6 ICFP FSCD - Days 1-3 Thursday, September 7 Haskell Symposium – Day 1 ML Family Workshop Workshop on Functional High-Performance Computing Commercial Users of Functional Programming – Day 1 FSCD - Day 4 Friday, September 8 Haskell Symposium – Day 2 OCaml Workshop Erlang Workshop Commercial Users of Functional Programming – Day 2 Saturday, September 9 Commercial Users of Functional Programming – Day 3 Haskell Implementors Workshop Functional Art, Music, Modeling and Design Conference Organizers: General Chair: Jeremy Gibbons (University of Oxford, UK) Program Chair: Mark Jones (Portland State University, USA) Artifact Evaluation Co-Chair: Matthew Flatt (University of Utah, USA) Artifact Evaluation Co-Chair: Ryan R. Newton (Indiana University, USA) Industrial Relations Chair: Ryan Trinkle (Obsidian Systems LLC, USA) PLMW Co-Chair: Neelakantan R. Krishnawami (University of Cambridge, UK) PLMW Co-Chair: Dan Licata (Wesleyan University, USA) PLMW Co-Chair: Brigitte Pientka (McGill University, Canada) Programming Contest Organiser: Sam Lindley (University of Edinburgh, UK) Publicity and Web Chair: Lindsey Kuper (Intel Labs, USA) Student Research Competition Chair: Ilya Sergey (University College London, UK) Student Volunteer Co-Captain: Yosuke Fukuda (Kyoto University, Japan) Student Volunteer Co-Captain: Yuki Nishida (Kyoto University, Japan) Student Volunteer Co-Captain: Jakub Zalewski (University of Edinburgh, UK) Video Chair: Jose Calderon (Galois, Inc., USA) Workshops Co-Chair: Andres Löh (Well-Typed LLP, UK) Workshops Co-Chair: David Christiansen (Indiana University, USA) Sponsors and industrial partners: Platinum partners Ahrefs Jane Street Capital Gold partners Bloomberg X Silver partners Galois Oracle Bronze partners Obsidian Systems Portland State University Well-Typed

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Is there something new in GHCi?
by Francisco Vieira de Souza 18 Jul '17

18 Jul '17

I´m using GHCi for Windows and I found sometrhing new. Mainly, there is no way for using GHC tooI for making a executable program. I had been doing all that is written in the page of Haskell and the same thing. I think that is something wrong in this new way of installation of GHC. Someone can help me in this case? Thanks in advance! Vieira -- "Embora ninguém possa voltar atrás e fazer um novo começo, qualquer um pode começar agora e fazer um novo fim". (Chico Xavier)

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Fwd: Memoization in Type Calculation
by Dmitry Olshansky 17 Jul '17

17 Jul '17

Rahul, thanks! It is really simple! 2017-07-17 21:33 GMT+03:00 Rahul Muttineni <rahulmutt(a)gmail.com>: > Hi Dmitry, > > You can effectively think of the type-level language of Haskell as a > strict functional language with almost no syntactic sugar, and recursion is > the *only* way of getting the behaviour of a loop. The best you can do to > improve the performance of that type family is to write it in > tail-recursive form using a helper function and which will make the type > family reduction look more linear vs a tree like it is now and make it > easier for the type checker to quickly spit out the result. > > type family Fib (n::Nat) :: Nat where > Fib n = GoFib 0 1 n > > type family GoFib (a :: Nat) (b :: Nat) (n :: Nat) where > GoFib a _ 0 = a > GoFib a b n = GoFib b (a + b) (n - 1) > > Hope that helps, > Rahul > > On Mon, Jul 17, 2017 at 11:19 AM, Dmitry Olshansky <olshanskydr(a)gmail.com> > wrote: > >> Hello, cafe! >> >> I wonder is there some possibility to get Memoization in Type Calculation >> (e.g. in closed Type Families)? >> >> Can we make something more efficient for famous Fib function then >> >> type family Fib (n::Nat) :: Nat where >> Fib 1 = 1 >> Fib 2 = 1 >> Fib n = Fib (n-1) + Fib (n-2) >> >> This Fib has obviously exponential calculation time and we need some >> memoization. >> >> If it is impossible right now, maybe there is a ticket for this? It seems >> to me very important things, no? >> >> Probably in this case we can write TypeChecker Plugin, but it looks like >> the common problem. >> >> Best regards, >> Dmitry >> >> >> >> >> _______________________________________________ >> 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. >> > > > > -- > Rahul Muttineni >

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Memoization in Type Calculation
by Dmitry Olshansky 17 Jul '17

17 Jul '17

Hello, cafe! I wonder is there some possibility to get Memoization in Type Calculation (e.g. in closed Type Families)? Can we make something more efficient for famous Fib function then type family Fib (n::Nat) :: Nat where Fib 1 = 1 Fib 2 = 1 Fib n = Fib (n-1) + Fib (n-2) This Fib has obviously exponential calculation time and we need some memoization. If it is impossible right now, maybe there is a ticket for this? It seems to me very important things, no? Probably in this case we can write TypeChecker Plugin, but it looks like the common problem. Best regards, Dmitry

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[Hiring] NStack is hiring Haskellers in London (onsite / remote)
by Mandeep Gill 17 Jul '17

17 Jul '17

NStack (www.nstack.com / www.github.com/nstack/nstack) lets data scientists and analysts to do sophisticated data work in the cloud without a team of engineers. To accomplish this, we’re a building a platform for composable, data-driven microservices, using a mixture of Haskell and Linux systems tech (including Kubernetes, systemd, and local IPC) with some typed DSLs, systems code, and distributed systems thrown in - think Bash-piping for distributed, containerised microservices. Our aim is to bring many of the ideas from functional programming, such as typed APIs and composition to the analytics space. We have an early demo of the product available, see www.github.com/nstack/nstack to get started and https://demo.nstack.com (very early demo, built using GHCJS - see [1]), and are currently in trials with several enterprises. We’re looking for talented programmers experienced using typed functional languages with preferably some Linux/Unix systems knowledge. It’s a challenging role, working on hard problems, and offers the chance to work with a top technical team and shape a company and product from an early stage. NStack is funded by top-tier investors from the West Coast, the founders are both technical and ex-YC / academia, and our team is lucky enough to include world-class talent for the problem we're solving. Salaries are competitive and include generous stock options. We're generally hiring onsite, however several of us work across Europe and we welcome remote applications within suitable timezones. Unfortunately we can not sponsor work visas. We're a team of 10, including 5 full-time Haskellers, and are looking at a range of positions and experience levels - whether you’ve just left uni or been hacking for 20 years, so if you’re interested please get in touch. Any questions please email direct or take a look at https://angellist.com/nstack/jobs Cheers, Mandeep [1] log in using `user-id` = `be56de22d8444786ae3231953b2cf4b1` and `secret-key` = `8d245132f0a9402d9284cf2e0a280391`

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intero-neovim: Bring the joy of Intero to your Neovim!
by Matt 17 Jul '17

17 Jul '17

Hi everyone, I would like to invite you to try out my intero-neovim[1] plugin for giving Neovim IDE-like features. It's a port of the excellent intero plugin for emacs, and does many of the same things: type at point, go to definition, loading specific stack targets, etc. It has recently been significantly refactored and a ton of bugs have been fixed thanks to contributions by Reuben D'Netto and Jake Zimmerman. It's been working great for me on my work projects (stack-based with about a dozen packages) as well as one-off files and smaller projects. I would appreciate any and all feedback on features or bugs :D https://github.com/parsonsmatt/intero-neovim Thanks, Matt Parsons

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Haskell IDE Engine progress report for July 2017
by Alan & Kim Zimmerman 17 Jul '17

17 Jul '17

This report is also available online at [1] Haskell IDE Engine progress report for July 2017. <https://github.com/haskell/haskell-ide-engine/blob/master/docs/Report-2017-…>What is Haskell IDE Engine? Not an IDE. It is a common point for people in the Haskell community to pool their efforts with respect to tooling. For tool writers, provide tools as a HIE plugin, so it can be available on supported IDEs For IDE developers, integrate to HIE, and all the Haskell tools supported as plugins become available For users, it means the overall Haskell experience should improve. Currently, we are targeting the Language Server Protocol as the channel via which we talk to IDEs and editors. This would allow much broader IDE support. <https://github.com/haskell/haskell-ide-engine/blob/master/docs/Report-2017-…>Important developments Zubin Duggal started work on a Summer of Haskell project to improve the LSP support in HIE and implement more of the protocol. Large portions of the HIE codebase have been refactored and rearchitectured with LSP support in mind. Plugins for brittany and hoogle have been implemented. A new plugin request and dispatcher system has been implemented, along with a new architecture for the loading and caching of TypecheckedModules from source, which are used to drive many queries and features like type information, document symbols, document highlights and go to definition. Technical details regarding these changes are described in Architecture <https://github.com/haskell/haskell-ide-engine/blob/master/docs/Architecture…> . As of July 2017, HIE supports a large portion of the LSP. For the complete feature list, check the README <https://github.com/haskell/haskell-ide-engine/blob/master/README.md>. <https://github.com/haskell/haskell-ide-engine/blob/master/docs/Report-2017-…>Current project focus HIE (with vscode support via a plugin) is ready for an alpha release. Currently, the focus is on bug fixing and hooking up already existing features in HIE to LSP, like Hoogle queries and HaRe refactorings, and also providing additional features via LSP Code Actions and Code Lenses If you have experience writing Typescript or developing Visual Studio Code extensions, your help is needed to improve the vscode hie extension. <https://github.com/haskell/haskell-ide-engine/blob/master/docs/Report-2017-…>Contributors active in June and July Alan Zimmerman, Zubin Duggal, Lennart Spitzner <https://github.com/haskell/haskell-ide-engine/blob/master/docs/Report-2017-…> Contributing Haskell IDE Engine needs volunteers like any other open source project. For more information see: https://github.com/haskell/haskell-ide-engine Also drop by our IRC channel: #haskell-ide-engine at irc.freenode.net. Thanks! Zubin and Alan [1] https://github.com/haskell/haskell-ide-engine/blob/master/docs/Report-2017-…

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Wrapping Turtle ls function to work with 0 or 1 arguments (polyvariadic)
by Cody Goodman 16 Jul '17

16 Jul '17

I'm trying to get ls to work in ghci like it does in bash using variadiac arguments in Haskell. I'm stuck at the moment so I thought I'd send this to #haskell-cafe for some help. I'm not quite sure how to proceed. See the main function for what I want the end result to look like. Here is the code: {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE OverloadedStrings #-} -- | An example module. module Example (main) where import qualified Turtle as Turtle import Control.Foldl import Control.Monad.IO.Class lsDirEx :: MonadIO io => io [Turtle.FilePath] lsDirEx = do Turtle.fold (Turtle.ls "/home") list class PrintAllType t where -- use PrintAllType from https://rosettacode.org/wiki/Variadic_function#Haskell process :: [Turtle.FilePath] -> t -- instance MonadIO io => PrintAllType (io [Turtle.FilePath]) where instance PrintAllType (IO [Turtle.FilePath]) where process [] = do -- ls received no args print current directory Turtle.pwd >>= \fp -> Turtle.fold (Turtle.ls fp) list process (filePath:[]) = do -- ls recieved one filePath liftIO $ Turtle.fold (Turtle.ls filePath) list process _ = error "multiple arguments not currently supported" -- instance (Show a, PrintAllType r) => PrintAllType (a -> r) where -- process args = \a -> process (args ++ [fmt a]) -- where fmt thing = _ $ Turtle.format Turtle.w thing ls :: (PrintAllType t) => t ls = process [] -- | An example function. main :: IO () main = do ls -- lists current directory ls ("/home" :: String) -- lists /home directory Thanks, Cody

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Re: [Haskell-cafe] parallelism and state
by dominic＠steinitz.org 16 Jul '17

16 Jul '17

Excellent news! How did you test it? One way would be to make it callable by C and then use testu01 but perhaps you have already done this or similar? See here for a bit more detail: https://idontgetoutmuch.wordpress.com/2017/01/14/calling-haskell-from-c/ <https://idontgetoutmuch.wordpress.com/2017/01/14/calling-haskell-from-c/>. Testing the split function might need thinking about though. > I recently made a SplitMix implentation: > http://hackage.haskell.org/package/splitmix <http://hackage.haskell.org/package/splitmix> > > When generating `Word64`s it's noticeable faster than `tf-random` (and > `mwc-random` and obviously `random). I didn't benchmark `Double` > generation, as `tf-random` own `Random` class doesn't support it [1], > and using `random`'s class would be very unfair. > > I haven't announced it (well, mentioned on Twitter), but please give it > a try! > > - Oleg Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Feedback on use of State monad
by Atrudyjane 15 Jul '17

15 Jul '17

Hello Everyone, In the HPFFP book, there's a homework problem where you're supposed to refactor a recursive function that rolls dice to return the number of rolls it takes to reach or exceed an input sum and the list of die that occurred. As practice, decided to take the solution and implement it using the State monad: -- Refactor rollsCountLoggged to use State -- limit sum count StdGen [Die] type RollsState = (Int, Int, Int, StdGen, [Die]) -- count [Die] type RollsValue = (Int, [Die]) runRolls :: State RollsState RollsValue runRolls = do (l, s, c, sg, xs) <- get if (s >= l) then return (c, reverse xs) else do let (d, ng) = randomR (1, 6) sg put (l, s + d, c + 1, ng, intToDie d : xs) runRolls rollsCountState :: Int -> IO () rollsCountState n = print $ evalState (runRolls) (n, 0, 0, mkStdGen 0, []) I'm wondering if that 'do' block under the else is a not so great stylistic choice. If the 'let' and 'put' is moved above the 'if', then that's just an unnecessary call at the end. Or is it just the nature of running inside a monad? Thank You, Andrea Sent with [ProtonMail](https://protonmail.com) Secure Email.

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