Focused-modules

An implementation of a type system for ML-style modules proposed by [Crary 2020] in Standard ML. [Crary 2020] solves the avoidance problem, a problem related to abstract types and scoping, by ideas from focused logic.

Getting started

You need a Standard ML compiler (MLKit or MLton) and cmtool. Make sure that mlkit (or mlton), cmlex and cmyacc are in your $PATH.

$ git clone --recursive https://github.com/elpinal/focused-modules
$ cd focused-modules

Build with MLKit

$ make
$ ./focused-modules-mlkit

Build with MLton

$ make mlton
$ ./focused-modules-mlton

Syntax

The syntax is what is described in the paper, extended with let-binding for ordinary modules.

• Supports n-ary lambda abstraction at term, type and module level.
• Supports shorthand M for 'a/M when 'a does not occur free in the scope.
• Supports non-dependent versions of functions and products.
• Supports boolean and integer literals.

References

A focused solution to the avoidance problem

Karl Crary.
Journal of Functional Programming, 30, e24, 2020.
http://www.cs.cmu.edu/~crary/papers/2020/exsig.pdf

Extensional equivalence and singleton types

Christopher A. Stone and Robert Harper.
ACM Transactions on Computational Logic 7(4), 676–722, 2006.
http://www.cs.cmu.edu/~rwh/papers/singletons/tocl.pdf