Issue 281 2021-09-16
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.
I’m excited to announce Evoke, a GHC plugin that automatically derives type class instances without using generics or Template Haskell.
Deferred Derivation by Matt Parsons
Freeing a module from Template Haskell speeds up our build tremendously - not because Template Haskell is slow (it’s very fast) but because compiling at all is slow. The best way to speed something up is to spend 0 time doing it — don’t do it at all!
GHC rewrite rules by Jonathan Dowland
The Glasgow Haskell Compiler (GHC) has support for user-supplied rewrite rules, which applied during one of the compiler optimisation stages. I spent some time today looking at these more closely.
Our Call for Papers is currently open and we want to hear your proposals! (Especially if you’re new to Haskell or a first-time speaker!)
Haskell series part 4 by Pierre Guillemot
This is the fourth article of a series on the functional language Haskell for beginners. In this article we are going to cover tuples and pattern matching.
JSON Vulnerability in Haskell’s Aeson library by Tom Sydney Kerckhove
This blogpost describes a DoS vulnerability in Haskell’s
aesonpackage. We have followed appropriate procedure for responsible disclosure but the problem was not fixed, so now we are releasing this to the public in the hope that it may still be fixed after all.
Optics are monoids by Gabriella Gonzalez
This post documents my favorite
lenstrick of all time. Also, this trick works for any optics package based on van Laarhoven lenses, like
Reader for Free by Patrick Brisbin
This may be obvious or well-known to some, but I discovered the other day that you can make a
MonadReader envinstance for any
MonadState env mtrivially. This makes total sense conceptually, since
Readerwith the extra ability to modify.
Reflecting on the Shake Build System by Neil Mitchell
As a medium-sized build system, Shake has some good bits and some bad bits.
What is an appropriate type for smart contracts? by Ari Fordsham
Before I answer the main question, I’m going to try to define a bit more precisely what it would mean to write code in Haskell or Idris and compile it to run on an Ethereum-like blockchain.
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Cayley Representation of… Monads? by Konrad Kleczkowski
The moral of this story is that sometimes operation of “original” monoid can be not effective enough, so we can switch to the Cayley representation that is more preformant.
Competitive programming in Haskell: Kadane’s algorithm by Brent Yorgey
We are presented with a linear sequence of cells, each colored either red or blue, and we are supposed to find the (contiguous) segment of cells with the maximal absolute difference between the number of red and blue.
Core Libraries Committee Elections by Emily Pillmore
Dear Haskell Community, The Core Libraries Committee is seeking new members!
Effect is a phantom by Xy Daylily
All effect systems introduce an unavoidable heavy performance penalty, even so with
mtlif you aren’t careful enough about specialization. But here, hot take: you probably don’t need an effect system at all.
Evoking Instances by Haskell Weekly Podcast
Taylor Fausak talks with Cameron Gera about Evoke, Taylor’s latest GHC plugin for deriving instances without generics or Template Haskell.
From the three staple higher-order functions —
Haskell Implementors’ Workshop 2021 by Well-Typed
We enjoyed taking part in the Haskell Implementors’ Workshop (HIW 2021) this year, as part of ICFP 2021. Many thanks to the program chair, Ningning Xie, and the other organisers!
Haskellings Demo Video! by Monday Morning Haskell
If you’ve been following my Twitch stream, you know I’ve been continuing to work quite a bit on the Haskellings automated tutorial. This week I’m releasing a short YouTube video demonstrating how to get started with this program and use it!
Leibniz coercion by Oleg Grenrus
Recently Ryan Scott wrote an article about Leibniz (and Martin-Löf) equality. Interestingly we can do the same thing for coercions (which are representational equalities).
Show & tell
Cabal version 220.127.116.11 by Emily Pillmore
The Cabal team is excited to announce the release of both
Haskell Language Server version 1.4.0 by Javier Neira
After a month of vacation a new HLS release has arrived.