Distributed Agreement on Random Order – Fun with Lamport Timestamps

If we succeed in this task, we will have succeeded in building what easily qualifies as one of the world most wasteful way to random shuffle. We now have a stupid task to do, and a perfect architecture to do it. We just miss the perfect language for the task...   It is quite astonishing... Continue Reading →

How small programming faults led to overflowing an entire system

It is 10 in the morning. Approaching at 2 o'clock, a feature demo. We are supposed to show some of last developments on one of the newest micro-service of the platform. The code worked nice before. We did not touch the implementation of the service since the last tests. There is no reason why it... Continue Reading →

Continuation passing style Free Monads and direct style Free Monads

Generalized Algebraic Data Types gives us the power to develop type-safe Free Monads, without having to rely on continuation passing style when using simple Algebraic Data Types. The resulting Abstract Syntax Tree acts as easy to understand specifications for the interpreters of the language it defines.   In today's post, we will revisit the first... Continue Reading →

Answering r/haskell: How to unit test code that uses polymorphic interfaces?

This short post is an answer to the following question asked on r/haskell. The original question is about how to test code that lives in a Monad class with polymorphic functions. I highly encourage you to read the post. Its different answers are full of technical gems which we are not going to explore here... Continue Reading →

C++ Design Tip: Objects should not point back to an object that owns them

In today's post, we will be advising against storing back-pointers in objects. This is something that we can find in our code, and which unfortunately leads to bugs, decreased performance, code that is harder to reason about and cannot be used in generic algorithms such as the STL ones. We will first describe these numerous... Continue Reading →

Free Monads: from the basics to the implementation of composable and effectful stream processing

In the previous post, we introduced IdrisPipes, a library for composable and effectful production, transformation and consumption of streams of data in Idris. We talked about the motivations behind this library, its API and its model, and some of the features it offers. In this post, we will embark in a journey from the basics... Continue Reading →

IdrisPipes: a library for composable and effectful stream processing in Idris

We will continue our series on post on Idris, by implementing a pipe library for Idris, inspired by the great Haskell pipes and Haskell conduit libraries. The goal is to provide Idris with a library for composable and effectful production, transformation and consumption of streams of data. In short, IdrisPipes is an Idris package that... Continue Reading →

Monoids: what they are, why they are useful, and what they teach us about software

Monoids are a pretty interesting concept in software development. Monoids are everywhere. Monoids are simple yet powerful. And Monoids have a lot to teach us about software, in particular about composition and building powerful abstraction. This post will take you through a small tour of what Monoids are and are for. We will first define... Continue Reading →

A follow up of the study of 4 Money class designs: why not having currencies as type parameters?

In the previous post, we went through a comparative study of 4 different designs for a Money class that represents an amount of money. To do so, the Money class groups an amount with a currency (its unit) and implements a safe arithmetic which takes into account the currencies. This article received a quite positive... Continue Reading →

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