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Quantified Class Constraints

This repository provides a prototype implementation of type inference with translation to System F of Quantified Class Constraints, as presented in the paper ``Quantified Class Constraints'' by Gert-Jan Bottu, Georgios Karachalias, Tom Schrijvers, Bruno C. d. S. Oliveira and Philip Wadler.

Tested with GHC 8.4.3

Contents

The implementation is split over three directories: Frontend, Backend and Utils. The most important modules are the following:

  • Frontend

    • HsTypes.hs: Source language abstract syntax.
    • HsParser.hs: A simple parser.
    • HsRenamer.hs: The renamer.
    • HsTypeChecker.hs: The type inference algorithm with translation to System F, as explained in the paper.
    • Conditions.hs: The implementation of the nonambig condition, as explained in the paper.

  • Backend

    • FcTypes.hs: The abstract syntax of System F with datatypes and recursive let bindings.
    • FcTypeChecker.hs: A System F type checker.

Building & Running

You can try out the prototype in two ways: build it as a cabal package and try the generated executable file or load it in GHCi.

Try it in GHCi

The easiest way to try out the prototype in examples is by loading it in GHCi. For example:

:load Main.hs
runTest "Tests/Test2.hs"

Build an executable

Since the implementation is also a cabal package you can also build an executable instead:

cabal build
./dist/build/quantcs/quantcs Tests/Test2.hs

Adding Tests

Apart from running the test files in directory Tests, you can also create and test your own. Currently, the prototype requires the syntactic restrictions explained in the paper. Additionally, we require the following:

  • Type parameters of datatypes and type classes should be explicitly annotated with their kind.
  • Type variables in instance heads should be annotated with their kind.
  • Universally quantified variables should also be annotated with their kind at their binding site.

The above are illustrated in the existing tests in directory Tests. Since this is a proof-of-concept implementation, we do not perform kind inference, hence the above requirements (the implementation still performs kind checking though).

If you have any inquiries concerning the implementation please do not hesitate to contact us.