Syntax-Directed Translation (SDT): Integrating Semantics into Compiler Design
Learn about syntax-directed translation (SDT), a compiler design technique that combines grammar rules with semantic actions. This guide explains how SDT integrates translation into the parsing process, using attributes and semantic rules to efficiently translate source code.
Syntax-Directed Translation
What is Syntax-Directed Translation?
Syntax-directed translation (SDT) is a method used in compiler design to perform translations by combining a formal grammar (describing the language's syntax) with semantic rules (actions or code that manipulate the program's data). This approach integrates the translation process directly into the grammar rules themselves, specifying exactly what actions should be performed at each stage of parsing. This makes it easier to understand and manage the translation process.
Attributes in SDTs
In SDT, each non-terminal symbol in the grammar can have one or more associated attributes. Attributes hold values that are computed and manipulated by semantic rules. These rules are associated with the grammar’s production rules and dictate how the values of attributes are evaluated and updated. A common attribute is `VAL`, which might contain various data types.
The Translation Process in SDT
As the parser analyzes the code according to the grammar rules, the associated semantic rules are executed. These rules determine how to translate language constructs and compute the values of the attributes. This tightly coupled approach makes translation more efficient compared to other methods. The actions are specified directly within the production rules of the grammar itself. This ensures that they are performed at the correct time, enhancing efficiency and making it easier to understand and manage the translation process.
Example SDTS
Here’s an example SDT for evaluating arithmetic expressions. The semantic rules calculate the value of the expression using the values from the sub-expressions.
| Production Rule | Semantic Rule |
|---|---|
E → E + T |
E.val := E.val + T.val |
E → T |
E.val := T.val |
T → T * F |
T.val := T.val * F.val |
T → F |
T.val := F.val |
F → (E) |
F.val := E.val |
F → num |
F.val := num.lexval |
E.val, T.val, and F.val represent attribute values. num.lexval is the value of a numeric token obtained from the lexical analyzer.