L-Attribute class of Syntax Directed Definition (SDD) is called L-Attributed definitions.
The idea behind this class is that, between the attributes associated with a production body, dependency-graph edges can go from left to right, but not from right to left hence L-attribute.
L-Attribute 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 SDD. As a result, attribute evaluation in L-attributed grammars can be incorporated conveniently in top-down parsing.
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.
In L-attributed SDTs, a non-terminal can get values from its parent, child, and sibling nodes.
Example:
Let following production
S –>ABC
- S can take values from A, B, and C (synthesized).
- A can take values from S only.
- B can take values from S and A.
- C can get values from S, A, and B.
- No non-terminal can get values from the sibling to its right.
Attributes in L-attributed SDTs are evaluated by depth-first and left-to-right parsing manner.
