Functional programming has a reputation for being notoriously hard to understand. In this post, we examine its basic principles, abstractions, and building blocks. Hopefully, after reading this, you will be able to decide for yourself whether you really want to embark on a trip into this wonderland.

The notion of software design may imply a multitude of various aspects. For example, it may be concerned with the quality of user experience or subtle intricacies of project management. If you are asking yourself more mundane questions, such as: “How should I assign responsibilities to these classes?” or “How to implement API of the service layer?” this post is for you. We begin with well-known basic concepts that you may have encountered elsewhere, but not suspected that they are all parts of a larger picture, and finish with rarely-read graduate-level literature. Maybe in the end, you will find your own answer to the question - how to design software systems?

Despite that there are gigabytes of writings on this topic, ranging from the recipes for managing a bunch of markdown files on GitHub to the manuals for setting up a local MediaWiki server, I will describe the solution that works for me.

Command interfaces - an integral part of life in the 1980s - gain a new breath with the advent of Enso Launcher and iShell Extension. Although graphical user interfaces have opened a new world in the computer industry, in certain domains text commands still offer advantages in usability and accessibility. With the tools mentioned above, you can create powerful commands that will free you from routine GUI interactions.

org-protocol offers a nice possibility to capture URLs along with some selected text from many web-browsers into Emacs org-mode. But most of the tools you can find out there allow a little control over the process - usually, it is only possible to put just plain text into some hard-coded org file. Below we develop an iShell Extension command which allows to capture org-formatted text under any headline in one of the several user-specified org files. If you are interested only in iShell or only in Org (or only in Windows), you may still skim through the code to find out how things work.

It sometimes happens that you need to read gigabyte-long files on the client side of a web application, and placing them as a whole into memory is not an option. Of course, there is File.slice, but things get complicated when you have to read, for example, an UTF-8-encoded text file. You need to do some byte juggling, and ES6 async generators allow to perform this in a pretty elegant way.