KU Leuven Haskell Compiler

This repository contains the KU Leuven Haskell Compiler, a simple Haskell compiler featuring type inference with translation to System F. The compiler is constructed at KU Leuven, under the programming languages group of prof Tom Schrijvers, to serve as a basis for implementing and testing new compiler features. This work is based on the following prototype implementation.

Tested with GHC 8.10.2

Implementation

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.
  • Conditions.hs: The implementation of the nonambig condition.

• 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 compiler 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/Test1.hs"

Build an executable

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

cabal build
./dist/build/khc/khc Tests/Test1.hs

TODOs

This is still an early version, so several improvements are planned for the near future:

• Include a System F evaluator, for executing programs.
• Write additional test files.
• Perform kind inference (the compiler currently only performs kind checking).

Adding Tests

Apart from running the test files in directory Tests, you can also create and test your own. Currently, the compiler requires the following syntactic restrictions:

• 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. We currently 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.