Concise Concrete Syntax

We introduce a notion of ordered context-free grammars (OCFGs) with datatype tags to concisely specify grammars of programming languages. Our work is an extension of syntax definition formalism (SDF) and concrete datatypes that automate scanning, parsing, and syntax tree construction. But OCFGs also capture associativity and precedence at the level of production rules instead of lexical tokens such that a concrete syntax grammar is succinct enough be an abstract syntax definition. By expanding and re-indexing grammar symbols, OCFGs can be translated to grammars for standard lex and yacc such that existing and efficient parsing infrastructures can be reused. We have implemented a Java 5 compiler frontend with OCFGs. The complete grammar for such a realistic language fits comfortably in two pages of this paper, showing the practicality of our formalism.