Tag Archives: Termination

Anton Setzer argued in his letter to the Agda mailing list that we should go back to a category theoretical view of codata, and Dan Doel soon successfully experimented the ideas.

It would be nice to if we could write the program and prove its termination separately. Adam Megacz published an interesting paper: A Coinductive Monad for Prop-Bounded Recursion. As a practice, I tried to port his code to Agda.

Given a relation < that has been shown to be well-founded, we know that a recursively defined function is terminating if its arguments becomes “smaller” with respect to < at each recursive call. We can encode such well-founded recursion in Agda’s style of structural recusion.

After seeing our code, Nils Anders Danielsson suggested two improvements. Firstly, to wrap the bound in the seed. Secondly, to define unfoldT↓ using well-founded recursion.

I hope to come up with a variation of unfoldr which, given a proof of well-foundedness, somehow passes the termination check.