I’ve meant to understand Free for quite a while, but it turns out most resources on the subject are either far too complex for me, or just really bad. I’d essentially given up on it until a friend of mine, known to be particularly fond of pithy statements, told me Free is merely the defunctionalisation of Monad in its most uncomfortable configuration. He didn’t add what’s the problem? but it was clearly implied.
What’s really odd though is that after playing with this for a bit, it turned out to be exactly what I needed to hear to get me unstuck.
This talk is my slightly expanded version of that statement.
Note that I will not attempt to justify that programs as values are a good thing here. It’s sort of taken for granted, and if you’re not interested in doing that, then you’re not really interested in Free.