Executable Grammars in Newspeak

We describe the design and implementation of a parser combinator library in Newspeak, a new language in the Smalltalk family. Parsers written using our library are remarkably similar to BNF; they are almost entirely free of solution-space (i.e., programming language) artifacts. Our system allows the grammar to be specified as a separate class or mixin, independent of tools that rely upon it such as parsers, syntax colorizers etc. Thus, our grammars serve as a shared executable specification for a variety of language processing tools. This motivates our use of the term executable grammar. We discuss the language features that enable these pleasing results, and, in contrast, the challenge our library poses for static type systems.