ModuLog : Modular Datalog

This is an implementation of Datalog with an OCaml like module system, including module signatures and higher order modules via functors. The addition of a module system endows Datalog with two previously missing features: code reuse and type abstraction. Modulog was motivated by previous attempts to use the C preprocessor or other text munging to do hacky code reuse in Datalog for points to analysis.

At the moment Modulog has the following features:

• Basic Datalog (no negation, aggregation, etc.)
• An OCaml inspired module system, based on Leroy's modular modules. This is implemented in a core-language generic way, so it could plausibly be reused for
• An bottom-up interpreter that can read input data from CSV files.
• Compilation to C, currently incomplete (doesn't support reading external input yet).

Example:

module type Edges = sig
  type vertex

  pred edge : vertex * vertex
end

module MyEdges = struct
  type vertex = int

  define edge : vertex * vertex
    edge(1, 2)
    edge(2, 3)
    edge(3, 4)
    edge(4, 1)
end

module Path (E : Edges) = struct

  type vertex = E.vertex

  define path : E.vertex * E.vertex
    path(?X,?Y) :- E.edge(?X,?Y)
    path(?X,?Z) :- path(?X,?Y), E.edge(?Y,?Z)

end

module P = Path (MyEdges)

Still to do:

• Finish the C output to be able to read in initial data from CSV files.
• More expressive datatype language.

Related work

• A calculus for the construction of modular prolog programs by Donald T. Sannella and Lincoln A. Wallen, J. Logic Programming, vol 12, issues 1-2, January 1992, pages 147-177.

• QL: Object-oriented Queries on Relational Data by Pavel Avgustinov, Oege de Moor, Michael Peyton Jones, and Max Schäfer, ECOOP 2016: 2:1-2:25. DOI: 10.4230/LIPIcs.ECOOP.2016.2