- Haskell-Cafe - Haskell.org

Job opportunity at Scrive
by Jonathan Jouty 05 Oct '17

05 Oct '17

Hey! We have a "full stack" Haskell position that just opened up: https://stackoverflow.com/jobs/156727/haskell-full-stack-developer-scrive Please apply directly on Stack Overflow. I'll be at Haskell eXchange in London next week if you want to meet, otherwise send an email. Cheers. -- Jonathan Jouty *Lead Developer* at *Scrive* www.scrive.com

2 1

Re: [Haskell-cafe] Cabal hell (8.2.1,/Haskell Package/MacOS X)
by Stuart A. Kurtz 05 Oct '17

05 Oct '17

Dear Imants, > Is it possible that some ghc version is installed with /usr prefix, and another with /usr/local > ? > > If yes - try uninstalling the older versions. > You may need to clean up the obsolete library folders. Joy! Which is to say, after several unsuccessful attempts involving progressively more draconian deletion strategies, ending with % uninstall-hs all --remove and reinstalling the Core Platform from the installer, which finally worked. Many thanks! Peace, Stu

1 0

Functional Languages Beat Procedural/Object-Oriented
by Gregory Guthrie 05 Oct '17

05 Oct '17

Functional Languages Beat Procedural/Object-Oriented Application Development Trends David Ramel October 3, 2017 Researchers at the University of Virginia and the University of California, Davis say they have completed a study evaluating the impact of programming languages on software quality, and found functional languages are superior to procedural/object-oriented languages in some respects. The team analyzed more than 700 GitHub projects containing about 63 million lines of source code. The researchers note empirically assessing software quality is complex, shaped by numerous interacting variables. "By triangulating findings from different methods, and controlling for confounding effects such as team size, project size, and project history, we report that language design does have a significant, but modest effect on software quality," the team says. Among their findings is that disallowing type confusion seems to offer an improvement over permitting it, while static typing is somewhat better than dynamic in functional languages. The team also found functional languages are associated with fewer defects than procedural/scripting languages, and that managed memory usage is better than unmanaged. The research was published in the October edition of Communications of the ACM. https://orange.hosting.lsoft.com/trk/click?ref=znwrbbrs9_6-17370x31326fx040… ---------------------------------------------------------------

2 1

Haskell in Leipzig 2017: 2nd call for participation
by Wolfgang Jeltsch 04 Oct '17

04 Oct '17

Event: Haskell in Leipzig 2017 Time: October 26–28, 2017 Place: HTWK Leipzig, Germany Homepage: https://hal2017.softbase.org/ About ===== Haskell is a modern functional programming language that allows rapid development of robust and correct software. It is renowned for its expressive type system, its unique approaches to concurrency and parallelism, and its excellent refactoring capabilities. Haskell is both the playing field of cutting-edge programming language research and a reliable base for commercial software development. The workshop series Haskell in Leipzig (HaL), now in its 12th year, brings together Haskell developers, Haskell researchers, Haskell enthusiasts, and Haskell beginners to listen to talks, take part in tutorials, join in interesting conversations, and hack together. To support the latter, HaL will include a one-day hackathon this year. The workshop will have a focus on functional reactive programming (FRP) this time, while continuing to be open to all aspects of Haskell. As in the previous year, the workshop will be in English. Invited Speaker =============== * Ivan Perez, University of Nottingham, UK Invited Performer ================= * Lennart Melzer, Robert-Schumann-Hochschule Düsseldorf, Germany Registration ============ Registration information is available on the web page of the local organizers at http://nfa.imn.htwk-leipzig.de/HAL2017/. Program Committee ================= * Edward Amsden, Plow Technologies, USA * Heinrich Apfelmus, Germany * Jurriaan Hage, Utrecht University, The Netherlands * Petra Hofstedt, BTU Cottbus-Senftenberg, Germany * Wolfgang Jeltsch, Tallinn University of Technology, Estonia (chair) * Andres Löh, Well-Typed LLP, Germany * Keiko Nakata, SAP SE, Germany * Henrik Nilsson, University of Nottingham, UK * Ertuğrul Söylemez, Intelego GmbH, Germany * Henning Thielemann, Germany * Niki Vazou, University of Maryland, USA * Johannes Waldmann, HTWK Leipzig, Germany Questions ========= If you have any questions, please do not hesitate to contact Wolfgang Jeltsch at wolfgang-it(a)jeltsch.info.

1 0

Loading a csv file with ~200 columns into Haskell Record
by Guru Devanla 04 Oct '17

04 Oct '17

Hello All, I am in the process of replicating some code in Python in Haskell. In Python, I load a couple of csv files, each file having more than 100 columns into a Pandas' data frame. Panda's data-frame, in short is a tabular structure which lets me performs on bunch of joins, and filter out data. I generated different shapes of reports using these operations. Of course, I would love some type checking to help me with these merge, join operations as I create different reports. I am not looking to replicate the Pandas data-frame functionality in Haskell. First thing I want to do is reach out to the 'record' data structure. Here are some ideas I have: 1. I need to declare all these 100+ columns into multiple record structures. 2. Some of the columns can have NULL/NaN values. Therefore, some of the attributes of the record structure would be 'MayBe' values. Now, I could drop some columns during load and cut down the number of attributes i created per record structure. 3. Create a dictionary of each record structure which will help me index into into them.' I would like some feedback on the first 2 points. Seems like there is a lot of boiler plate code I have to generate for creating 100s of record attributes. Is this the only sane way to do this? What other patterns should I consider while solving such a problem. Also, I do not want to add too many dependencies into the project, but open to suggestions. Any input/advice on this would be very helpful. Thank you for the time! Guru

7 14

Catch-all considered harmful?
by Vilem-Benjamin Liepelt 03 Oct '17

03 Oct '17

Catch-all considered harmful? ============================= I have been thinking about a potential source of bugs from catch-all pattern matches on sum types and would like to know your thoughts. Motivation ---------- Totality is usually a desirable property of a function and the catch-all can conveniently buy us totality. But at what price? I have been indoctrinated that rigour goes above convenience (think along the lines of: "Once we indulge in the impurities of I/O, there is no redemption.") I would like to evaluate the trade-offs between convenience for the programmer and a potential source of bugs. My questions to the community— 1. Are there real world examples of bugs caused by catch-alls? 2. Do you think that a language extension that disallows catch-alls (and annotations to opt back in at pattern match sites or type declaration) could be useful for certain code bases? 3. If this is a potential problem, then can you think of any better solutions a compiler could provide (i.e. that don't rely on an IDE / structured editing) other than disallowing catch-alls? Feel free to chip in with your 2p (or 2¢), but please only if you have any concrete experience (or compelling theoretical evidence). Example ------- Consider the sum type: data Answer = No | Yes and the function: foo : Answer -> String foo Yes = "Woo-hoo!" foo _ = "Bother." Say we need to extend our sum type: data Answer = No | Perhaps | Yes However, we forget to handle the new case appropriately in `foo`. The compiler is happy, but at runtime `foo Perhaps` would evaluate to `"Bother."`—with potentially catastrophic consequences. (Please imagine this happening in a large codebase with several contributors, no single one of whom knows the entire codebase.)

3 4

CfP: Dutch FP-day 2018
by Arjen 03 Oct '17

03 Oct '17

Dear all, The next Dutch Functional Programming day will take place on Friday 5th of January 2018, at the Walter Bos Complex of the Dutch Tax Service at the John F. Kennedylaan 8, Apeldoorn. This is the first call for presentations, and we apologize if you received multiple copies. If you would like to give a presentation, please send an e-mail to a.van.weelden(a)belastingdienst.nl with a title, abstract, name of the speaker and expected duration of the talk. We'll try our best to make a proper program out of it with various subjects related to functional programming. Please note that to the nature of the location, registration in advance is required. As well as matching identification (passport, driver's license, or similar) before entering the venue! Photography and/or setting up a local WiFi network is explicitly not allowed. A dinner (pizza's) and drinks will be provided free of charge at the end of the day at the same location. Given that registration is mandatory this time, we'll assume that you stay around for this unless you specify otherwise. More information about registering for attendance and a website with information about the schedule and location will follow soon(ish). Feel free to invite other people who might take an interest. Best regards and looking forward to seeing you, Betsy Pepels and Arjen van Weelden

1 0

Re: [Haskell-cafe] Loading a csv file with ~200 columns into Haskell Record
by dominic＠steinitz.org 03 Oct '17

03 Oct '17

I don’t know if this helps but here’s something I created in 5 minutes yesterday. Once you have the data you can convert to e.g. frames with all the help that types can give. I once used frames on a file with 10,000 columns and it worked (probably I shouldn’t have done this). Also an option is in Chris Done’s blog: https://www.fpcomplete.com/blog/2016/09/data-haskell PS My script below will fail if I have missing data but then I can use something better than read. > {-# OPTIONS_GHC -Wall #-} > > import qualified Data.Vector as V > import qualified Data.ByteString.Lazy as BL > import qualified Data.ByteString.Lazy.Char8 as BLC > import Data.Csv > import Data.List > import Plots > import Diagrams.Prelude > import Diagrams.Backend.Rasterific > > main :: IO () > main = do > evalsCsv <- BLC.readFile "/Users/dom/.local/share/simwork/data/Models/Lorenz.csv" > let records :: Either String (V.Vector (V.Vector BL.ByteString)) > records = decode NoHeader $ BLC.unlines $ BLC.lines evalsCsv > case records of > Left err -> putStrLn err > Right evals -> do > let hdrs :: V.Vector String > hdrs = V.map BLC.unpack $ V.head evals > let zss :: [[Double]] > zss = map (map read) $ map (map BLC.unpack) $ > transpose $ V.toList $ V.map V.toList $ V.drop 1 evals > renderRasterific "diagrams/lorenz.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!0) (zss!!1)) > renderRasterific "diagrams/lorenz1.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!0) (zss!!2)) > renderRasterific "diagrams/lorenz2.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!0) (zss!!3)) > renderRasterific "diagrams/lorenz3.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!1) (zss!!2)) > renderRasterific "diagrams/lorenz4.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!1) (zss!!3)) > renderRasterific "diagrams/lorenz5.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!2) (zss!!3)) > > jSaxis :: [Double] -> [Double] -> Axis B V2 Double > jSaxis ts xs = r2Axis &~ do > linePlot' $ zip ts xs Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

1 0

EduHaskell
by erwig 02 Oct '17

02 Oct '17

Dear Haskell aficionados, We will be using Haskell in an introductory course to computer science for college freshmen. From my past experience in using Haskell for students, the biggest hurdle and source of frustration is the type checker, or more precisely, the error messages generated. I see three major kinds of errors that get in the way of a smoother programming experience: * Errors resulting from overloading * Errors due to undefined type class instances (specifically, Eq and Show) * Errors in the context of parametric polymorphism While these problems are not unsurmountable, having to talk about these errors is a distraction from the major goal of explaining basics of (functional) programming. It would be great to have a Haskell compiler that offers the following features (and maybe others): * Type classes and overloading could be turned off * Eq and Show (and maybe Ord) instances would be automatically defined for any data type definition (when type classes are enabled) My questions are: (1) Does there exist a good solution to this problem already? Should one use Helium? I haven't checked lately, but it used to avoid type classes. This might have the disadvantage of having to switch to GHC in case one wants to use overloading. (I have used Helium in the past, and while I admire the effort, I am not sure it's the best option.) Are there versions of the Prelude available that accomplish some of this? (2) Are there other Haskellers out there who also want a simpler, more educationally suited version of GHCi? (3) If the answer to (1) is NO and to (2) is YES, is there any interest in forming a group for creating something like "EduHaskell"? I'd be grateful for any comments or suggestions! Thanks, Martin

7 7

hs-bibutils 6.2 candidate package
by Václav Haisman 02 Oct '17

02 Oct '17

Hi. I have created a candidate package for hs-bibutils 6.2. This synchronizes the hs-bibutils with Bibutils which it wraps. The candidate is at https://hackage.haskell.org/package/hs-bibutils-6.2/candidate. Please check it out and test it if you are interested. -- VH

1 0