Implementing functional languages on object-oriented virtual machines

Hosting functional languages in object-oriented environments, such as the Java Virtual Machine and Microsoft´s Common Language Infrastructure, so that they inter-operate well with other languages presents a number of problems. In the paper the authors introduce Mondrian, a functional language specifically designed for such environments, and describe the decisions and trade-offs in its design. The paper concentrates on the high-level design decisions made for Mondrian. The authors cover the design of a type system which is part-way between the traditional parametric polymorphism and sum type models of functional languages and the sub-type models used by the virtual machines. Next they discuss how function values and nonstrict evaluation can be provided while supporting easy inter-working with strict object-oriented languages. They briefly comment on the low-level implementation of Mondrian and conclude with a multi-language example using Mondrian and C^#. The work shows that, with appropriate design, it is possible to combine functional and object-oriented programming without losing the unique benefits of each.