The paper is freely available in the ACM Digital Library: https://dl.acm.org/authorize?N46678.
Alternatively, you can download the preprint from https://github.com/snowleopard/alga-paper/releases.
Talks:
- Haskell eXchange 2017 (longer and more recent): slides, video.
- Haskell Symposium 2017: slides, video.
The paper presents a minimalistic and elegant approach to working with graphs in Haskell. It is built on a rigorous mathematical foundation --- an algebra of graphs --- that allows us to apply equational reasoning for proving the correctness of graph transformation algorithms. Algebraic graphs let us avoid partial functions typically caused by 'malformed graphs' that contain an edge referring to a non-existent vertex. This helps to liberate APIs of existing graph libraries from partial functions.
The algebra of graphs can represent directed, undirected, reflexive and transitive graphs, as well as hypergraphs, by appropriately choosing the set of underlying axioms. The flexibility of the approach is demonstrated by developing a library for constructing and transforming polymorphic graphs.
See https://github.com/snowleopard/alga for the source code and links to blog posts.
There are also draft implementations in Scala and Agda, see https://github.com/algebraic-graphs.