The cost-effective construction of functionally correct software systems remains an unmet challenge for Computer Science. Although industrial best practices for software construction (such as testing, code reviews, automatic bug finding) have low cost, they cannot provide strong guarantees about correctness. Classical verification methods, on the other hand, are not cost-effective. Recently, the research community has been exploring the idea of dependent types, which extend the expressive power of programming languages to support verification. These rich types allow the programmer to express non-trivial invariant properties of her data and code as a part of her program. That way, verification is incremental, localized and at source-language level.
This multi-institution collaborative project is for the design and implementation of a programming language with dependent types, called Trellys. Technically, Trellys is call-by-value functional programming language with full-spectrum dependency. Overall, the project combines numerous fragmented research results into a coherent language design, by building a robust open-source implementation. The design draws on diverse solutions to the technical problems that arise from extending traditional programming languages accommodate dependent types: type and effect inference, language interoperability, compilation, and concurrency.
