Maybe John is attributing more magic to the common free monad patterns than is actually there? Certainly I had stars in my eyes when I first read:

https://people.cs.kuleuven.be/~tom.schrijvers/Research/paper...

> then you'd be able to build something like .NET LINQ on top of Free. But you can't.

You sort of can. You could build an interpreter of Linq commands and then have an executor interpret that. Which I suppose could be argued is making Linq. :)