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Profiteur: a visualiser for Haskell GHC .prof files
Introduction GHC comes with some amazing tools to do profiling of Haskell programs. In .prof files, you can see exactly in which function most time is spent and where most allocation is done. However,...
View ArticleGeneralizing function composition
TL;DR In this blogpost I present a proof-of-concept operator $.$, which allows you to replace: foo x0 x1 x2 ... xN = bar $ qux x0 x1 x2 ... xN by: foo = bar $.$ qux Introduction This is a literate...
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Image Processing with Comonads
Introduction A Comonad is a structure from category theory dual to Monad. Comonads are well-suited for image processing – Pretty much everyone on the internet Whenever Comonads come up, people usually...
View ArticleHaskell Design Patterns: .Extended Modules
Introduction For a long time, I have wanted to write a series of blogposts about Design Patterns in Haskell. This never really worked out. It is hard to write about Design Patterns. First off, I have...
View ArticleWriting an LRU Cache in Haskell
Introduction In-memory caches form an important optimisation for modern applications. This is one area where people often tend to write their own implementation (though usually based on an existing...
View ArticlePractical testing in Haskell
Introduction There has been a theme of “Practical Haskell” in the last few blogposts I published, and when I published the last one, on how to write an LRU Cache, someone asked me if I could elaborate...
View ArticleCan we write a Monoidal Either?
> {-# LANGUAGE GeneralizedNewtypeDeriving #-} > import Control.Applicative (Applicative (..)) > import Data.Monoid (Monoid, (<>)) > newtype Expr = Expr String > instance Show Expr...
View ArticleThe Prio Applicative
Introduction When writing some code recently, I came across a very interesting Applicative Functor. I wanted to write about it for two reasons: It really shows the power of Applicative (compared to...
View ArticleErasing "expected" messages in Parsec
Introduction Parsec is an industrial-strength parser library. I think one of its main advantages is that it allows you generate really good error messages. However, this sometimes requires some...
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Tries and elegant Scope Checking
Introduction This blogpost is mostly based upon a part of the talk I recently gave at the Haskell eXchange. I discussed scope checking – also referred to as scope analysis or renaming. While the talk...
View ArticleHaskell: mistakes I made
A week or two ago, I gave a talk at the Zurich Haskell Meetup about Haskell mistakes I have made in the past, and how you can fix them. The slides can be found here, and you can watch the talk below,...
View ArticleOn Ad-hoc Datatypes
In Haskell, it is extremely easy for the programmer to add a quick datatype. It does not have to take more than a few lines. This is useful to add auxiliary, ad-hoc datatypes. I don’t think this is...
View ArticleCryptographic Hashes and Cyclic Dependencies
I recently wrote a blog entry on the Fugue blog, about the problems that arise when you want to compute cryptographic hashes of resources that can have dependency cycles. You can read it here. Thanks...
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Patat and Myanmar travels
Presentations in the terminal At work, I frequently need to give (internal) presentations and demos using video conferencing. I prefer to do these quick-and-dirty presentations in the terminal for a...
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Package takeover: indents
Parsers are one of Haskell’s indisputable strengths. The most well-known library is probably Parsec. This parser combinator library has been around since at least 2001, but is still widely used today,...
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Lazy I/O and graphs: Winterfell to King's Landing
Introduction This post is about Haskell, and lazy I/O in particular. It is a bit longer than usual, so I will start with a high-level overview of what you can expect: We talk about how we can represent...
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WebSockets 0.11
Introduction Today, I released version 0.11 of the Haskell websockets library. Minor changes include: Support for IPv6 in the built-in server, client and tests (thanks to agentm). Faster masking...
View ArticleAn informal guide to better compiler errors
Earlier this month I gave a talk at the HaskellX Bytes meetup on how to improve compiler errors. Haskell is very commonly used to implement DSLs. When you implement one of these DSLs, the focus is...
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ZuriHac plays
Introduction This is a small write-up of a fun Haskell project that Andras Slemmer, Francesco Mazzoli and I worked on during ZuriHac 2017. I work with Haskell professionally, and it can be hard to...
View ArticleVideo: Getting things done in Haskell
Someone alerted me that the video of my talk at the Skills Matter Haskell eXchange 2017 is now available. You can watch it on their website. The slides can be found here. It’s a talk aimed towards...
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