S-attributed grammars are a class of attribute grammars characterized by having no inherited attributes, but only synthesized attributes. Inherited attributes, which must be passed down from parent nodes to children nodes of the

abstract syntax tree In computer science, an abstract syntax tree (AST), or just syntax tree, is a tree representation of the abstract syntactic structure of text (often source code) written in a formal language. Each node of the tree denotes a construct occurring ...

during the semantic analysis of the

parsing Parsing, syntax analysis, or syntactic analysis is the process of analyzing a string of symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal grammar. The term ''parsing'' comes from Lati ...

process, are a problem for bottom-up parsing because in bottom-up parsing, the parent nodes of the abstract syntax tree are created ''after'' creation of all of their children. Attribute evaluation in S-attributed grammars can be incorporated conveniently in both

top-down parsing Top-down parsing in computer science is a parsing strategy where one first looks at the highest level of the parse tree and works down the parse tree by using the rewriting rules of a formal grammar. LL parsers are a type of parser that uses a to ...

and bottom-up parsing. Specifications for parser generators in the

Yacc Yacc (Yet Another Compiler-Compiler) is a computer program for the Unix operating system developed by Stephen C. Johnson. It is a Look Ahead Left-to-Right Rightmost Derivation (LALR) parser generator, generating a LALR parser (the part of a comp ...

family can be broadly considered S-attributed grammars. However, these parser generators usually include the capacity to reference global variables and/or fields from within any given grammar rule, meaning that this is not a ''pure'' S-attributed approach. Any S-attributed grammar is also an

L-attributed grammar L-attributed grammars are a special type of attribute grammars. They allow the attributes to be evaluated in one depth-first left-to-right traversal of the abstract syntax tree. As a result, attribute evaluation in L-attributed grammars can be inco ...

See also