Associative Definition of Programming Languages1

Associative Language Descriptions are a recent grammar model, theoretically less powerful than Context Free grammars, but adequate for describing the syntax of programming languages. ALD do not use nonterminal symbols, but rely on permissible contexts for specifying valid syntax trees. In order to assess ALD adequacy, we analyze the descriptional complexity of structurally equivalent CF and ALD grammars, finding comparable measures. The compression obtained using CF copy rules is matched by context inheritance in ALD. The family of hierarchical parentheses languages, an abstract paradigm of HTML, and of expressions with operator precedences is studied. A complete ALD grammar of Pascal testifies of the practicality of the ALD approach.