Haskell Weekly


Issue 255 2021-03-18

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Welcome to another issue of Haskell Weekly! Haskell is a safe, purely functional programming language with a fast, concurrent runtime. This is a weekly summary of what’s going on in its community.



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In brief

  • Async Control Flow by Matt Parsons

    This post is an investigation of persistent issue #1199 where an asynchronous exception caused a database connnection to be improperly returned to the pool.

  • The bottom of the Haskell Pyramid by Gil Mizrahi

    I’ve decided to make a more modest list of things one should be familiar with to be productive with Haskell, the bottom of The Haskell Pyramid if you will, hoping it will help to focus learners of the language that might get loss in the vast amount of information.

  • Chat Wisely by Haskell Weekly Podcast

    Special guests Michael Litchard and Brian Hurt talk with us about their new social networking site Chat Wisely. We hear about their experience using Haskell not only on the backend but also on the frontend through GHCJS.

  • Free book for subscribers by Julie Moronuki

    As our latest Joy of Haskell monograph, Sockets and Pipes, is nearing completion, we have released the coupon that enables all Typeclasses members to download the book for free.

  • Functional Programming Leaders with Doug Beardsley by Compositional

    This episode’s guest is Doug Beardsley, also known as mightybyte, director of engineering at Kadena, a blockchain company that uses Haskell in production.

  • Haskell Knowledge Map by Kowainik

    Haskell has a lot of topics, and we arranged them by difficulty and timeline to help with your learning journey.

  • Haskenthetical update: user-defined macros by Phil Hazelden

    A while back I wrote about Haskenthetical, a language that I’m implementing for fun. I’m still working on it, at least from time to time.

  • Haskellings Beta! by Monday Morning Haskell

    This program is meant to be an interactive tutorial for learning the Haskell language. If you’ve never written a line of Haskell in your life, this program is designed to help you take those first steps!

  • Hyperfunctions by Donnacha Oisín Kidney

    Check out this type: newtype a -&> b = Hyp { invoke :: (b -&> a) -> b }. This a hyperfunction, and I think it’s one of the weirdest and most interesting newtypes you can write in Haskell.

  • Reddit Haskell Stats by Dan Fithian

    Having posted a lot of blog entries to the Haskell Subreddit lately with mixed results, I wrote a script to gather all /r/haskell posts for the last year and visualize them.

  • Through the Looking Class: Contravariant Functors and Applicatives by Siddharth Bhat

    In this blog post, we will learn about Contravariant and Divisible which provide duals for Data.Functor and Data.Applicative respectively.

  • Tricks for Compilers in Haskell by Vanessa McHale

    By making the abstract syntax tree polymorphic in the annotation type, we get type safety at all phases.

Show & tell

  • recover-rtti by Edsko de Vries

    The main function in this package is classify, which looks at the GHC heap to recover type information about arbitrary values.

  • relude version 1.0 by Dmitrii Kovanikov

    Reexport libs entirely, GHC 9, official standard

  • singletons version 3.0 by Ryan Scott

    I’m happy to announce the 3.0 release of the singletons library, as well as the debut of its companion libraries, singletons-th and singletons-base.

Call for participation