Syntax Directed Translation
Syntax Directed Translation
- The Principle of Syntax Directed Translation states that the meaning of an input sentence is related to its syntactic structure, i.e., to its Parse-Tree.
- By Syntax Directed Translations we indicate those formalisms for specifying translations for programming language constructs guided by context-free grammars.
- We associate attributes to the grammar symbols representing the language constructs.
- Values for attributes are computed by semantic rules associated with grammar productions.
- In the semantic rule, attribute is VAL and an attribute may hold anything like a string, a number, a memory location and a complex record.
Syntax Directed Translation
- Evaluation of Semantic Rules may:
- Generate code ,
- Insert information into the symbol table ,
- Perform semantic check ,
- Issue error messages.
- There are two notations for attaching semantic rules:
- Syntax Directed Definitions - High-level specification hiding many implementation details (also called Attribute Grammars).
- Translation Schemes - More implementation oriented: Indicate the order in which semantic rules are to be evaluated.
Notations for Semantic Rules
Example
| Production | 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 → (F) | F.val := F.val |
| F → num | F.val := num.lexval |
E.val is one of the attributes of E.
num.lexval is the attribute returned by the lexical analyzer.