Typeclasses such as Bifunctor are often expressed in terms of whether they are covariant or contravariant. While these terms may appear intimidating to the unfamiliar, they are a precise language for discussing these concepts, and once explained are relatively easy to understand. Furthermore, the related topics of positive and negative position can greatly simplify how […]
The content below is still correct, but has been absorbed into the more comprehensive safe exception handling tutorial document instead. I recommend reading that, which provides more information and more up-to-date library references. Over the years, I’ve written a number of different documents, tutorials, comments, and libraries on how to do proper exception handling in […]
In our last blog post we showed you the new docker init executable pid1. What if we wanted to use our shiny new pid1 binary on a CentOS Docker image but we compiled it on Ubuntu? The answer is that it wouldn’t likely work. All Linux flavors package things up a little differently and with […]
As we’ve discussed on this blog before, FP Complete has been running a Hackage mirror for quite a few years now. In addition to a straight S3-based mirror of raw Hackage content, we’ve also been running some Git repos providing the same content in an arguably more accessible format (all-cabal-files, all-cabal-hashes, and all-cabal-metadata). In the […]
This is part 2 of a three part series. If you haven’t seen it already, I’d recommend starting with the first part, which covers communication protocols and streaming of data. This second part will cover network communication and some basic concurrency in Haskell. Simple HTTP client We saw previously how to send and receive binary […]
Working with data in Haskell In data mining or general exploration, it’s common to need to easily access data efficiently and without ceremony. Typically, a programming language will be designed for this case specifically, like R, or a library will be written for it, like Python with the pandas library. Implementing this in Haskell, we […]
The other day I threw together a quick program to solve an annoyance some people on our team were expressing. We sometimes do our development on remote machines, but would still like to use local file editors. There are plenty of solutions for this (SSHFS, inotify+rsync), but none of us ever found a prebaked solution […]
We have set up a new public Jenkins CI server for use with our open source projects. This server currently runs the Stack integration tests, and deploys to ci.haskell-lang.org and ci.stackage.org every time a commit is pushed to the master branch of their respective repositories. In the future, we also intend to set up Jenkins […]
This blog post is an initial announcement of a new package, safe-exceptions (and Github repo). This is a follow up to a number of comments I made in last week’s blog post. To quote the README: Safe, consistent, and easy exception handling Runtime exceptions – as exposed in base by the Control.Exception module – have […]
For a change of pace, I wanted to cover a simple topic: asynchronous exceptions, and how they interact with Software Transactional Memory and MVars, as well as the GHC runtime system’s deadlock detection. As fate would have it, the topics in question occurred twice in the past month, once in a bug report against the […]