This is a project I'm working on while I'm at the Recurse Center. The idea is to implement a stripped-down version of a Datomic-style database: immutable facts, queried with Datalog, with separation of reads and writes.
You will need a recent nightly version of Rust to compile the project.
cargo run
This starts a repl where you can add facts and query the database. Adding a fact looks like this:
add (0 name "Logan")
(0 name "Logan") is a fact in entity, attribute, value form. To see
all the facts currently in the database, you can type dump.
Queries look like this:
find ?entity where (?entity name "Logan")
There can be any number of clauses after the where, e.g.:
find ?name where (?person name "Bob) (?person parent ?child) (?child name ?name)
Symbols starting with a question mark are free logic variables, and the query is executed by trying to unify the variables in all the clauses. So the above query is asking, "What is the name of the child of the person named "Bob"?
Currently there is no type checking of attributes, and values can only be strings or references to other entities, but I hope to extend the query language soon to support more primitive types and more sophisticated relationships.
Help is most welcome! Let me know if you're interested.