Maya: Multiple-Dispatch Syntax Extension in Java

Jason Baker and Wilson C. Hsieh

University of Utah, School of Computing
50 South Central Campus Drive, Room 3190
Salt Lake City, Utah 84112-9205



We have designed and implemented Maya, a version of Java that allows programmers to extend and reinterpret its syntax. Maya generalizes macro systems by treating grammar productions as generic functions, and semantic actions on productions as multimethods on the corresponding generic functions. Programmers can write new generic functions (i.e., grammar productions) and new multimethods (i.e., semantic actions), through which they can extend the grammar of the language and change the semantics of its syntactic constructs, respectively. Maya's multimethods are compile-time metaprograms that transform abstract syntax: they execute at program compile-time, because they are semantic actions executed by the parser. Maya's multimethods can be dispatched on the syntactic structure of the input, as well as the static, source-level types of expressions in the input.

In this paper we describe what Maya can do and how it works. We describe how its novel parsing techniques work and how Maya can statically detect certain kinds of errors, such as code that generates references to free variables. Finally, to demonstrate Maya's expressiveness, we describe how Maya can be used to implement the MultiJava language, which was described by Clifton et al. at OOPSLA 2000.

Appeared in The 2002 Conference on Programming Language Design and Implementation . A previous version of this paper is available as a tech report.

The slides from the ICSE 2002 presentation are also available:

Jason Baker <>
Last modified: Tue Jul 9 13:40:07 MDT 2002