April 2019 - Haskell-Cafe

CDelta and Haskell
by Tysha Moore 25 Apr '19

25 Apr '19

Haskell Developers, We at Pyrofex Corporation are working on an exciting new project called CDelta (cdelta.io <http://cdelta.io/>), a transaction based blockchain that will compete with Visa and Venmo. This blockchain is written in Haskell and we are looking for build a team of Haskell developers here in Utah to bring this project to fruition. Our job description is below. We would LOVE to hear from you. Cryptocurrency Software Engineer Are you ready to work for a company of engineers, managed by engineers, and focused on engineers and the work they can do? Your opportunity to work with a brilliant team that’s developing world-changing technology is here—seize it! At Pyrofex, we do things differently: we hire great engineers, give them the tools to do great things, and expect them to do so. We are invested in each team member's growth and foster a workplace that celebrates accomplishments and hard work by focusing on our engineers and what they need in order to be successful. Pyrofex is hiring. Show us your best work. About Us Pyrofex Corporation is changing the blockchain game and quickly growing a world-class team to do it. As one of Utah Valley’s first cryptocurrency startups, founded in 2016 by ex-Googlers Mike Stay and Nash Foster, Pyrofex is busy creating next-generation blockchain platforms that are simple, secure, and always reliable. We take pride in our work. We set high expectations for everyone, from our founders to each team member, and as a result we deliver extraordinary products and services. At Pyrofex, we hire for strength, not for lack of weakness. We hire for capability and talent, not specific knowledge of a tool or language. We hire people who have a passion for quality and innovation. Each team member achieves great things in an environment supporting both independence and collaboration. About You You collaborate well with others to design and architect our complex systems. You take the amorphous sets of needs and use cases and distill these into written designs and specifications. You demonstrate a fastidious attention to detail, knowledge of your programming tools, and the ability to regularly produce working, correct code. You are interested in building high-performance, high-bandwidth networks, and solving interesting problems. Pyrofex hires engineers at all levels of experience—from current students to engineers with decades of experience. Our engineers have worked on compilers, system software, distributed data storage, service and reliability, and JavaScript language security features through their careers. The path each of us has taken to get here is unique and we suspect the same will be true of our best employees. We are most interested in hiring strong programmers with experience working with large datasets and peer-to-peer networking. We desire to hear from candidates with experience with functional programming (Scala, Clojure, F#, SCheme, Haskell) and encryption technology. Our most successful candidates also have a background in computer science, but if you think this job is for you, we'll take a look. About the Job Developers on our team design, implement, test, deploy, and manage a variety of systems and products using technologies like Haskell, GNU/Linux, and C/C++. The engineers on this team will design, implement, test, deploy, and manage a large-scale global software system using Linux and the JVM. Pyrofex builds cryptocurrency systems and large-scale distributed and decentralized applications. If this sounds good to you, then e-mail us at jobs(a)pyrofex.net <mailto:jobs@pyrofex.net> with the subject line, “AWW MAN! I CAN”T WAIT!!!” and your resume or linkedin profile. We would also enjoy a cover letter telling us about your work ethic and your favorite project. If you can send us examples of your code, that would be most excellent. Tysha Moore Talent Acquisition Specialist Pyrofex Corporation

1 0

Why are && and || right-associative?
by Richard Eisenberg 24 Apr '19

24 Apr '19

Hi café, Why are && and || in the Prelude right-associative? This contradicts my expectation and the way these work in other languages. That said, I can't think of any harm in it. This came up from a question asked by a student, and I have no idea why the design is this way. Thanks, Richard

16 29

[ANNOUNCE] GHC 8.6.5 is now available
by Ben Gamari 24 Apr '19

24 Apr '19

Hello everyone, The GHC team is proud to announce the release of GHC 8.6.5. The source distribution, binary distributions, and documentation are available at https://downloads.haskell.org/~ghc/8.6.5 Release notes are also available [1]. This release fixes a handful of issues with 8.6.4: - Binary distributions once again ship with Haddock documentation including syntax highlighted source of core libraries (#16445) - A build system issue where use of GCC with `-flto` broke `configure` was fixed (#16440) - An bug affecting Windows platforms wherein XMM register values could be mangled when entering STG has been fixed (#16514) - Several Windows packaging issues resulting from the recent CI rework. (#16408, #16398, #16516) Do note that due to linking issues (see #15934) profiling will be rather unreliable on Windows. This will be fixed in 8.8.1. As always, if anything looks amiss do let us know. Happy compiling! Cheers, - Ben [1] http://downloads.haskell.org/~ghc/8.6.5/docs/html/users_guide/8.6.5-notes.h…

1 0

Munich Haskell Meeting, 2019-04-25 @ 19:30
by Leah Neukirchen 23 Apr '19

23 Apr '19

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Thursday, April 25 at Cafe Puck 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-apr-2019/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> http://leahneukirchen.org/

1 0

Problem on exception and laziness
by Magicloud Magiclouds 23 Apr '19

23 Apr '19

Hi, I am aware that laziness sometimes may cause exception handling in unexpected ways. Recently I have such a problem that I cannot figure out how to fix (simply). I have a function `watch` that parse the content of /proc/. And I use `catch` to wrap `readFile` call, since the data in /proc/ could be gone any time. ```Haskell wrap2Maybe :: IO a -> IO (Maybe a) wrap2Maybe f = catch ((<$>) Just $! f) (\(_ :: IOException) -> return Nothing) watch args = do mStat <- wrap2Maybe (readFile ("/proc/" </> fp </> "stat")) >>= return . flip (>>=) parseStat print mStat watch args ``` But occasionally, my tool exits with message: GoM: /proc/1484/stat: hGetContents: does not exist (No such process) Since above code is the only `readFile` call which leads to hGetContents, I could not figure out what else should I do to catch the error. -- 竹密岂妨流水过山高哪阻野云飞

2 3

how do I intercalate for Data.Text.Lazy.Builder
by Javran Cheng 22 Apr '19

22 Apr '19

Hi Cafe, Just a quick question, the title says it all: how do I intercalate for the Builder? Given what it does, it makes sense that things like `intercalate` should be out of the box, yet I feel the export list of Builder is very limited. -- Javran (Fang) Cheng

2 2

When does ICFP open registration?
by Alexey Raga 22 Apr '19

22 Apr '19

Hello, For bureaucracy reasons, it may be a time in our company to start sorting out ICFP trips/tickets. Does anyone have any information about when the registration may be opening? I couldn't find anything on their website, and I couldn't find any contact details on that website either, so asking here just in case if anyone knows :) Best Regards, Alexey Raga

3 2

Re: [Haskell-cafe] Is there already a lib to parse a line of string with a pattern and generate key-value map or a record?
by Olaf Klinke 19 Apr '19

19 Apr '19

You could emulate this with some custom parser combinators on top of any monadic parser combinator library such as attoparsec or megaparsec. keyed :: (Ord key, Functor parser) => key -> parser a -> parser (Map key a) keyed key = fmap (singleton key) Then, assuming 'char' and 'digitChar' exists in the parser library, you may write integer = some digitChar logline = fmap mconcat $ sequence [ keyed "year" (integer <* char '/'), keyed "month" (integer <* char '/'), keyed "day" (integer <* char ' '), -- etc. ] Olaf

2 2

-fdefer-type-errors
by Bill Hallahan 18 Apr '19

18 Apr '19

Hi, I'm trying to use the -fdefer-type-error flag, discussed in an ICFP paper from 2012: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.366.841&rep=rep1&t… <http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.366.841&rep=rep1&t…> On page 2, the paper has an example, showing that fdefer-type-errors will allow a the first element to be extracted fro a tuple, even if the second element does not correctly typecheck: ghci> let foo = (True, ’a’ && False) Warning: Couldn’t match ‘Bool’ with ‘Char’ ghci> :type foo (Bool, Bool) ghci> fst foo True However, with GHC 8.2.2, I get an error when trying to do this: GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help Prelude> let foo = (True, 'a' && False) <interactive>:1:18: warning: [-Wdeferred-type-errors] • Couldn't match expected type ‘Bool’ with actual type ‘Char’ • In the first argument of ‘(&&)’, namely ‘'a'’ In the expression: 'a' && False In the expression: (True, 'a' && False) Prelude> :type foo foo :: (Bool, Bool) Prelude> fst foo *** Exception: <interactive>:1:18: error: • Couldn't match expected type ‘Bool’ with actual type ‘Char’ • In the first argument of ‘(&&)’, namely ‘'a'’ In the expression: 'a' && False In the expression: (True, 'a' && False) (deferred type error) Does anyone know the reason for the change in the behavior? Is there any way to get back to the old behavior, i.e. allow the first element of the tuple to still be extracted? Ideally, I would like to get the errors given by defer-type-errors to be as fine-grained/close-to-the-source as possible. Thanks, Bill Hallahan

4 4

Is there already a lib to parse a line of string with a pattern and generate key-value map or a record?
by Magicloud Magiclouds 18 Apr '19

18 Apr '19

Hi, I saw this function in some web tools, pretty useful when parsing log or so. So I wonder if Haskell has similar libs already. Sample: Input line: "2019/04/17 17:27 User magicloud runs command ls." Pattern: "${year}/${month}/${day} ${hour}:${minute} User ${username} runs command ${command}." Output: toList [ ("year", "2019"), ("month", "04") , etc ] -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

5 8