Proceedings of the 26th International Symposium on Principles and Practice of Declarative Programming

The proceedings contain 19 papers. The topics discussed include: a simple view of multiparty session types; on the preciseness of subtyping in session types: 10 years later; higher-order unification for free!: reusing the meta-language unification for the object language; declarative macro-programming of collective systems with aggregate computing: an experience report; hierarchical higher-order port-graphs: a rewriting-based modelling language; on the almost-sure termination of binary sessions; formal verification of executable matrix inversion via adjoint matrix and gaussian elimination; grammar-based pattern matching and type checking for difference data structures; evidence tampering and chain of custody in layered attestations; and towards effective ASP-based stream reasoning: facilitate the reasoning over patterns of events.