The Mk I Build System

The Mark One build system is probably not a build system at all: it's just a script you run which produces whatever output files you need. Maybe it does some manual out of date checks but it possibly just blurts out all the generate calls regardless.

#!/bin/fish
# an example of a Mk1 build system
pandoc -t gfm README.md -f html -o README.html

This is just a script. It has no abstract knowledge of out of date, dependencies, parallel execution and the like. You have to specifically tell it how to do literally everything.