A “build system” is one of the most important tools in a developer’s toolbox. Roughly, it figures out how to create runnable programs from a bunch of different source files by calling out to the compiler, setting up and executing test suites, and so on. Because you interact with it daily, above all it has to be fast – but it also has to be flexible. Around 2012 we were growing dissatisfied with OMake, then one of OCaml’s standard build systems, and decided to build our own; we called this new sy...