Maxi Wuttke’s Master’s Thesis

Advisor: Deepak Garg


In this thesis, we study coeffect-based and effect-based refinement type systems for verification and complexity analysis of pure functional recursive programs. These type systems are relatively complete, which roughly means that they can be fine-tuned either for expressiveness or for tractability.

We consider two approaches: using coeffects and using effects. For the first approach, we generalise and simplify previous work by introducing a system that targets a call-by-push-value (CBPV) version of the programming language PCF, which supports higher-order recursive functions. We derive soundness and relative completeness for the new system. From this, these properties also follow for the old systems. In the effect-based approach, we also target CBPV.

For both approaches, we explain how the systems can be extended with features of modern programming language like polymorphism. One of the key properties of these systems is that they are compositional, which enables modular verification. We (informally) discuss efficient, sound and complete type inference algorithms that exploit this fact. Finally, we (informally) compare and combine both approaches, and we formalise a sound and relatively complete coeffect-based system from prior work in the proof assistant Coq.


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