L-attributed grammar

L-attributed grammars are a special type of attribute grammars.¹ 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 incorporated conveniently in top-down parsing.

A syntax-directed definition is L-attributed if each inherited attribute of ${\displaystyle X_{j}}$ on the right side of ${\displaystyle A\rightarrow X_{1},X_{2},\dots ,X_{n}}$ depends only on

1. the attributes of the symbols ${\displaystyle X_{1},X_{2},\dots ,X_{j-1}}$
2. the inherited attributes of ${\displaystyle A}$ (but not its synthesized attributes)

Every S-attributed syntax-directed definition is also L-attributed.

Implementing L-attributed definitions in Bottom-Up parsers requires rewriting L-attributed definitions into translation schemes.

Many programming languages are L-attributed. Special types of compilers, the narrow compilers, are based on some form of L-attributed grammar. These are a strict superset of S-attributed grammars. Used for code synthesis.

Either "inherited attributes" or "synthesized attributes" associated with the occurrence of symbol ${\displaystyle X_{1},X_{2},\dots ,X_{n}}$.