Haskell Weekly


Issue 74 2017-09-28

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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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  • Beautiful aggregations with Haskell

    Aggregating data is a common, tedious task. In imperative languages we often end up with a rat’s nest of mutable variables, nested loops and other awful constructs. In functional languages a naive implementation also results in spaghetti and usually less than ideal performance.

  • Immutability and unboxing in array programming

    Well written code based on unboxed arrays and using the discussed pattern to create arrays by initializing a mutable version, which is subsequently frozen, can achieve performance comparable to low-level C code.

  • apecs tutorial: Making games fast

    The reason for this tutorial is not that you need to know all of this in order to use apecs. For simple 2D games, apecs won’t be a bottleneck. Once you start worrying about 3D and render times however, that’s when you might need apecs to be fast, and this is how you do that.

  • Type-driven strictness

    How can we know when to be lazy or strict? We can use Dhall’s type system to guide whether or not we keep the accumulator strict. We already have access to the type of the accumulator for our loop, so we can define a function that tells us if our accumulator type is compact or not.

  • What does Free buy us?

    To tame that complexity, we factored the “what to do next” back out into a new data type, this time called Free instead of List. Free and List are similar; and we can use Free to write List and other interesting data structures.

  • Free monad considered harmful

    Of course the title is a click bait and I do not mean to be so categorical. Free monads do have their uses, but in most cases I’d think twice before committing to that style of programming because it’s somewhat tedious and inefficient.

  • Working with the DOM

    We’ll be building up pieces of a todo-list application along the way. It is probably becoming a cliche by now, but it is familiar to a lot of people and will give me something concrete to use while demonstrating some of the cooler things that reflex provides as the series progresses.

  • Well-typed printfs cannot go wrong

    The aim of this post is to show another way of achieving the same result, with tools that are available in PureScript — a strongly-typed functional language, with no dependent types.

  • Debugging C with Haskell’s Divisible

    This article: Introduces the Delta Debugging technique; Implements a general-purpose delta-debugging tool; Uses Haskell’s FFI to control a C chess engine; Locates an error introduced into the chess engine.

  • Simula: A 3D window manager for Linux

    Mission: Facilitate a Linux future for VR & AR Desktop. In the short-run, this means allowing people to run 2D Linux apps with current generation headsets. In the long-run, this means allowing people to run Linux in standalone AR & VR HMDs.


  • Code Haskell. Build great things. (ad)

    We’re Wrinkl, a well-funded startup working closely with Obsidian Systems to build a powerful new communications platform. We use Haskell on both the backend and the frontend (using GHCJS and Reflex). And we’re looking to hire Haskell developers, preferably in the Philly area or willing to relocate to Philly. Women and minorities strongly encouraged to apply.

In brief

Package of the week

This week’s package of the week is tree-diff, a library for diffing expression trees. It also provides a way to diff arbitrary data types using Generic helpers.

Call for participation


Unfortunately we don’t know of any Haskell events. Do you know of an event that Haskell users would enjoy? Let us know about it by emailing info@haskellweekly.news!