What does HackerNews think of project-m36?

You might be interested in Project M36:

https://github.com/agentm/project-m36

Three techniques for sum types in SQL (absorption, separation, and partition):

https://www.parsonsmatt.org/2019/03/19/sum_types_in_sql.html

Also, here is a relational database system with native support for sum types (and also no "NULL" nonsense, which is also not part of pure relational algebra):

https://github.com/agentm/project-m36

Just to say there is "Project:M36 Relational Algebra Engine" [1], which says about itself:

Introduction

Project:M36 implements a relational algebra engine as inspired by the writings of Chris Date.

Description Unlike most database management systems (DBMS), Project:M36 is opinionated software which adheres strictly to the mathematics of the relational algebra. The purpose of this adherence is to prove that software which implements mathematically-sound design principles reaps benefits in the form of code clarity, consistency, performance, and future-proofing.

Project:M36 can be used as an in-process or remote DBMS.

1: https://github.com/agentm/project-m36

Project:M36 is an implementation of the proposed design from the "Out of the Tarpit" paper.

https://github.com/agentm/project-m36

Project M36 is a database that implements a relational model and corresponding query language (TutorialD) based on (among other things) the ideas from Date and Darwen's Third Manifesto. TutorialD solves many of the problems present in SQL, especially around composability.

https://github.com/agentm/project-m36

You might be looking for Project:M36.

https://github.com/agentm/project-m36