In the next chapters we present the design and specification of a family of syntax definition formalisms. The kernel of this family of formalisms is formed by context-free grammars. A number of orthogonal extensions to the kernel is defined. Many of these extensions are defined in terms of the primitives of the kernel by means of normalization functions. This provides a framework for constructing new formalisms by adapting and extending previous ones.
Included in the family are the following extensions of context-free grammars, uniform definition of lexical and context-free syntax, variables, disambiguation by priorities, follow restrictions and reject productions, a rich set of regular expressions defined in terms of context-free productions, character classes, aliases, parameterized modules with hidden imports and renamings. The accumulation of these extensions is the syntax definition formalism SDF.
This chapter provides an introduction to SDF and gives an overview of the design and specification of the family of formalisms.