Metamodel-Aware Textual Concrete Syntax Specification

Metamodeling is raising more and more interest in the field of language engineering. While this approach is now well understood for the definition of abstract syntaxes, the formal definition of concrete syntaxes is still a challenge. Concrete syntaxes are traditionally expressed with rules, conforming to EBNF-like grammars, which can be processed by compiler compilers to generate parsers. Unfortunately, these generated parsers produce concrete syntax trees, leaving a gap with the abstract syntax defined by metamodels. This gap is usually filled by time consuming ad-hoc hand-coding. In this paper we propose a new kind of specification for concrete syntaxes that takes advantage of metamodels to generate tools (such as parsers or text generators) which directly manipulate abstract syntax trees. The principle is to map abstract syntaxes to concrete syntaxes via EBNF-like rules that explain how to render an abstract concept into a given concrete syntax, and how to trigger other rules to handle the properties of the concepts. The major difference with EBNF is that rules may have sub-rules, which can be automatically triggered based on the inheritance hierarchy of the abstract syntax concepts.