October 2017 - Haskell-Cafe

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

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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

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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

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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

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ANN: hledger 1.4
by Simon Michael 01 Oct '17

01 Oct '17

Aloha! I'm pleased to announce hledger 1.4. Thank you release contributors: Nicholas Niro, Hans-Peter Deifel, Jakub Zárybnický, Felix Yan, Mark Hansen, Christian G. Warden, Nissar Chababy and Peter Simons. Also, if I haven't already mentioned it: this year hledger turns 10! Here's the first commit, from January 27 2007: https://github.com/simonmichael/hledger/commit/85864b41 We have come a way, but there is much yet to look forward to. Onward and upward! The next major release is scheduled for 2017/12/31. What is hledger ? ----------------- hledger (http://hledger.org) is an evolving, dependable, robust, cross-platform program for tracking money, time, or any other commodity, using double-entry accounting and a simple plain text file format. It is a haskell reimplementation of Ledger and the plain text accounting concept, providing command-line, curses and web interfaces. hledger aims to be a pleasant and practical tool for personal, business or institutional finance and time tracking. What's new ? ------------ The full release notes are at http://hledger.org/release-notes#hledger-1.4 . Some highlights: - Easy install script: we have a new installation method for the hledger tools, intended to dodge common pitfalls and just-work more often. Building on the stack team's install script, this bash script is cross platform, uses cabal or stack, installs stack and GHC if needed, and installs the latest release of all major hledger packages. See http://hledger.org/download for details. - More batteries included: most experimental addon commands formerly shipped in bin/ are now built in and work out of the box. - New commands: balancesheetequity (a balance sheet including equity), tags (list tags in use), import (detects new transactions in multiple input files and adds them to the main journal, particularly useful with CSV downloads). - Balance reports can be sorted by amount - makes those high expenses easy to spot. - CLI conveniences: @ARGSFILE is expanded to the set of args/flags in ARGSFILE. depth:2 or --depth=2 can be written as -2. - Help improvements: reorganized docs page, a more useful commands list, a smarter help command, --help and -h are the same again (by popular demand), Getting started --------------- See http://hledger.org/download for all install methods. To get the latest hledger release, you may need to build it yourself using stack or cabal. But don't worry, this is.. getting quite painless. The new hledger installer requires only bash and will install everything you need in one step: the hledger tools in $HOME/.local/bin/, and (if required) stack and GHC in $HOME/.stack/. Run it like so: $ curl -sSLO http://hledger.org/hledger-install.sh $ less hledger-install.sh # review script, for the security conscious $ bash hledger-install.sh # install the latest hledger tools Ensure $HOME/.local/bin is in your $PATH. Now try some commands: $ hledger -h # quick help $ hledger help # list built-in manuals $ hledger add # record some transactions $ hledger # list available commands Now perhaps work through the tutorial at http://hledger.org/step-by-step.html Or review the fine documents, presentations etc. at http://hledger.org and http://plaintextaccounting.org Or say hello and ask questions in the #hledger IRC channel on Freenode: http://irc.hledger.org If you have been finding hledger useful, I invite you to become a sponsor or contributor to make it stronger. Donate using one of the funding links on the home page, give feedback, report bugs, send pull requests, write about it, or help in some other way. Thanks for your support! I hope to meet you online. -Simon

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