Live Programming

Jun 23, 2021

Every developer knows the pain of the inner development loop. Make code changes, rebuild, run tests, redeploy, and examine the differences. All developers do this - from frontend web developers to backend cloud infrastructure engineers. Engineers hate repetitive tasks and try to automate everything, so it's only natural that they would try to automate this loop as well.

I call it live programming, but it goes by many names: hot reloading, hot swapping, interactive programming. It's the process of automating and optimizing the build and deploy pipeline for developers to see the changes they make in code instantly. Three forces enable the live programming paradigm:

Moore's Law. We have more powerful computers that can compile code quicker.

Standardized tooling. Docker is a standard build and runtime target that enables us to automate build and deploy pipelines.

The rise of interpreted languages. Python and JavaScript provide a large userbase for live programming tools.

Live programming tools need three components.

  1. File-watcher. The value proposition of the tool is that the inner development loop no longer becomes a manual process, so there need to be events that trigger different stages. File changes are a logical entry point.
  2. Packager. Before, it wasn't easy to find a universal packager. That means that the previous generation of tools was language-specific - one for JavaScript, another for Ruby, another for Python, etc.
  3. Runtime. Not only was packaging language-specific, but runtime was as well. Static websites could get away with generic webservers, but other use cases needed language-specific servers that knew how to hot-reload classes and functions. Docker also changed this, providing a wrapper around language runtimes.

Here are some examples of live programming tools.

  • skaffold. I'm biased because I created the tool. But skaffold uses Kubernetes as a developer platform, automating compiling software, building docker images, and deploying to Kubernetes in a tight, iterative loop. The magic of skaffold is that it is the only tool that is genuinely full-stack. The code syncs to the running instance for interpreted or static code  (JavaScript, Python, CSS, etc.). For compiled code, rebuild and redeploy. And for configuration changes, a redeploy.
  • Gunicorn/Flask/Django. Live programming for python web developers.
  • webpack. The packager and development server for JavaScript and TypeScript. It also works for Ruby on Rails. While many other live programming tools evolved from runtimes, webpack evolved from packaging.
  • Pluto.jl. A notebook-like tool for Julia programmers that automatically updates all affected cells when a function or variable is changed.
  • Observable. A live programming environment for JavaScript, primarily focusing on visualizations and data analysis (from the creator of d3.js).
  • Excel. The original live programming environment. As cells change, Excel recalculates dependent cells. Developers and users can see each computation at intermediate steps.