Prof. Dr. Jan Christiansen

We show how various Haskell language features that are related to ambient effects can be modeled in Coq. For this purpose we build on previous work that demonstrates how to reason about existing Haskell programs by translating them into monadic Coq programs. A model of Haskell programs in Coq that is polymorphic over an arbitrary monad results in non-strictly positive types when transforming recursive data types likes lists. Such non-strictly positive types are not accepted by Coq’s termination checker. Therefore, instead of a model that is generic over any monad, the approach we build on uses a specific monad instance, namely the free monad in combination with containers, to model various kinds of effects. This model allows effect-generic proofs.

One Monad to Prove Them All is a modern fairy tale about curiosity and perseverance, two important properties of a successful PhD student. We follow the PhD student Mona on her adventure of proving properties about Haskell programs in the proof assistant Coq. On the one hand, as a PhD student in computer science Mona observes an increasing demand for correct software products. In particular, because of the large amount of existing software, verifying existing software products becomes more important. Verifying programs in the functional programming language Haskell is no exception. On the other hand, Mona is delighted to see that communities in the area of theorem proving are becoming popular. Thus, Mona sets out to learn more about the interactive theorem prover Coq and verifying Haskell programs in Coq.