YakYak: Parsing with Logical Side Constraints

Niels Damgaard, Nils Klarlund, and Michael I. Schwartzbach


Programming language syntax is often described by means of a context-free grammar, which is restricted by constraints programmed into the ac tion code associated with productions. Without such code, the grammar would explode in size if it were to describe the same language.

We present the tool YakYak, which extends Yacc with first-order logic for specifying constraints that are regular tree languages. Concise formulas about the parse tree replace explicit programming, and they are turned into canonical attribute grammars through tree automata calculations. YakYak is implemented as a preprocessor for Yacc, in which the transitions of the calculated tree automata are merged into the action code. We provide both practical experience and theoretical evidence that the YakYak approach results in fast and concisely specified parsers.