Extending a given language with new dedicated features is a general and quite
used approach to make the programming language more adapted to problems. Being
closer to the application, this leads to less programming flaws and easier
maintenance. But of course one would still like to perform program analysis on
these kinds of extended languages, in particular type checking and inference.
In this case one has to make the typing of the extended features compatible
with the ones in the starting language.
The Tom programming language is a typical example of such a situation as it
consists of an extension of Java that adds pattern matching, more particularly
associative pattern matching, and reduction strategies.
This paper presents a type system with subtyping for Tom, that is compatible
with Java's type system, and that performs both type checking and type
inference. We propose an algorithm that checks if all patterns of a Tom program
are well-typed. In addition, we propose an algorithm based on equality and
subtyping constraints that infers types of variables occurring in a pattern.
Both algorithms are exemplified and the proposed type system is showed to be
sound and complete
