jaspervdj - Haskell Puzzles
Some Haskell Puzzles from ZuriHac 2023 Published on June 19, 2023 under the tag haskell At ZuriHac 2023, I worked on some Haskell Puzzles together with Alex, Francesco, Jussi and Patrick. You are given some Haskell tokens and a goal term, and you need to rearrange the tokens into an expression that produces the goal. Here a simple warmup exercise just to get an idea of how it works:
jaspervdj - Lazy Sort: Counting Comparisons
How good is Haskell's lazy sort actually? Published on September 17, 2020 under the tag haskell Haskell’s laziness allows you to do many cool things. I’ve talked about searching an infinite graph before. Another commonly mentioned example is finding the smallest N items in a list. Because programmers are lazy as well, this is often defined as: This happens regardless of the language of choice if w
jaspervdj - Visual Arrow Syntax
Finally, better Arrow syntax, completely free of hacks Published on March 12, 2020 under the tag haskell Not to be taken seriously. Haskell is great building at DSLs – which are perhaps the ultimate form of slacking off at work. Rather than actually doing the work your manager tells you to, you can build DSLs to delegate this back to your manager so you can focus on finally writing up that GHC pro
jaspervdj - Dependent Types in Haskell: Binomial Heaps 101
Who put binary numbers in my type system? Published on September 4, 2018 under the tag haskell Haskell eXchange Update: I gave a talk about this blogpost at the Haskell eXchange 2018 on the 11th of October 2018. You can watch the video here. Note that you will need to create an account in on the skillsmatter website in order to watch the recording. Introduction This post makes a bit of a departure
jaspervdj - Haskell Design Patterns: The Handle Pattern
A neat and simple way to build services in Haskell Published on March 8, 2018 under the tag haskell Introduction I’d like to talk about a design pattern in Haskell that I’ve been calling the Handle pattern. This is far from novel – I’ve mentioned this before and the idea is definitely not mine. As far as I know, in fact, it has been around since basically forever1. Since it is ridiculously close t
jaspervdj - Package takeover: indents
A Parsec package to deal with indentation Published on December 22, 2016 under the tag haskell 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, and it has inspired new generations of general purpose parsing libraries. Parsec makes it really easy to
jaspervdj - On Ad-hoc Datatypes
Use ad-hoc datatypes liberally to improve code readability Published on May 11, 2016 under the tag haskell 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 used enough. Most libraries and code I see use “heavier” datatypes: canonical and very well-tho
jaspervdj - Tries and elegant Scope Checking
A less frequently discussed part of DSL design Published on October 30, 2015 under the tag haskell 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 focussed on Ludwig, a DSL used to program Fugue, the ideas around scope checking are broadly applicab
jaspervdj - The Prio Applicative
An interesting Applicative which lets us prioritize computations Published on May 26, 2015 under the tag haskell 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 Monad). Applicative does not require access to previously computed results, which helps i
jaspervdj - Can we write a Monoidal Either?
About the problems with clashing Applicative and Monad Published on May 19, 2015 under the tag haskell {-# LANGUAGE GeneralizedNewtypeDeriving #-} import Control.Applicative (Applicative (..)) import Data.Monoid (Monoid, (<>)) Introduction For the last month or, I have been working as a contractor for Luminal. I am helping them implement Fugue, and more specifically Ludwig – a compiler a for stati
jaspervdj - Practical testing in Haskell
Testing the LRU Cache from the last post as an example Published on March 13, 2015 under the tag 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 on how I would test or benchmark such a module. For the sake of brevity, I will constrain myse
jaspervdj - Writing an LRU Cache in Haskell
Using psqueues to write simple but fast code Published on February 24, 2015 under the tag 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 idea). The reason for this is mostly that having a one-size-fits all cache is really hard, and people of
jaspervdj - Image Processing with Comonads
A simple real-world example showing an image-processing Comonad Published on November 27, 2014 under the tag haskell 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 mention the canonical example of evaluating cellular automata. Because many image
jaspervdj - Profiteur: a visualiser for Haskell GHC .prof files
A nicer way to browse big profile files Published on February 25, 2014 under the tag haskell 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, at Erudify, we have a huge amount of Haskell code – and at this point .prof files can become very unwieldy
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jaspervdj - Partial application using flip
jaspervdj - Dynamic Graphs
jaspervdj - Video: Getting things done in Haskell
jaspervdj - An informal guide to better compiler errors
jaspervdj - Lazy I/O and graphs: Winterfell to King's Landing
jaspervdj - Haskell Design Patterns: .Extended Modules