SYNTAX DIRECTED TRANSLATION 11 CS 30011 Types of

Types of Attributes There are two types of attributes for nonterminals : • Synthesized

Types of Attributes • Inherited Attributes : For a non-terminal X at a parse-tree

Example : T -> FT’ T’ -> *FT’ T’ -> ɛ F -> id

Let val be the synthesized attribute of F and T. Let inh be the

The Symantic Rules corresponding to each production is : T -> FT’ T’. inh

Annotated Parse Tree after applying the semantic rules: T. val = 4*5 T T.

S-attributed SDD A syntax-directed definition (SDD) that involves only synthesized attributes is called S-attributed

S-attributed SDD Evaluation of S-attributed Parse Trees: When an SDD is S-attributed , its

L-attributed SDD In a L-attributed SDD each attribute must be either synthesised or inherited

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SYNTAX DIRECTED TRANSLATION 11 CS 30011

Types of Attributes There are two types of attributes for nonterminals : • Synthesized Attributes : For a non-terminal X at a parse-tree node T , the synthesized attribute is defined only in terms of attribute values at the children of T.

Types of Attributes • Inherited Attributes : For a non-terminal X at a parse-tree node T , the synthesized attribute is defined only in terms of attribute values at the T’s parent , T itself and T’s siblings.

Example : T -> FT’ T’ -> *FT’ T’ -> ɛ F -> id T T’ T F ɛ id PARSE TREE F * id

Let val be the synthesized attribute of F and T. Let inh be the inherited attribute of T’ and let syn be the synthesized attribute of T’. Let lexval be the synthesized attribute of id , which is an integer value returned by the lexical analyzer. Let the input string be 4 * 5

The Symantic Rules corresponding to each production is : T -> FT’ T’. inh = F. val T. val = T’. syn T’-> *FT’’ T’’. inh = T’. inh * F. val T’. syn = T’’. syn T’-> ɛ T’. syn = T’. inh F-> val F. val = id. lexval

Annotated Parse Tree after applying the semantic rules: T. val = 4*5 T T. inh = 4*5 T. syn = 4*5 T’ T’ F F F. val = 4 id id. lexval = 4 * F. val = 5 ɛ id id. lexval = 5

S-attributed SDD A syntax-directed definition (SDD) that involves only synthesized attributes is called S-attributed SDD. In an S-attributed SDD, each rule computes an attribute for the nonterminal at the head of a production from attributes taken from the body of the production.

S-attributed SDD Evaluation of S-attributed Parse Trees: When an SDD is S-attributed , its attributes can be evaluated in any bottom up order of the nodes of the parse tree. The attributes can be evaluated by performing a post-order traversal of the parse tree and evaluating the attributes at a node N when the traversal leaves N for the last time.

L-attributed SDD In a L-attributed SDD each attribute must be either synthesised or inherited but there are some conditions: For a production A->X 1 X 2 X 3…. Xn The rule associated with this production used for computing an inherited attribute Xi. a may use: a)Inherited attributes associated with the head. b)Either inherited or synthesized attributes associated with the occurrences of symbols X 1, X 2, . . . , Xi-1 located to the left of Xi. c) Inherited or synthesized attributes associated with this occurrence of Xi itself, but only in such a way that there are no cycles in a dependency graph formed by the attributes of this Xi.