In order to describe structure, attribute grammars adopt
context-free grammars as their basic skeletons. Context-free
grammars use syntax rules to define the syntax of the language.
Each rule explains the structure of a composite construction
(i.e., a non-terminal symbol) in terms of simpler composite
construction, as well as in terms of primitive construction (i.e.,
terminal symbols). For instance, the rule exp → exp + term in
Figure 1a states that “an expression may be a simpler
expression, followed by the + operator, and followed by a