Syntax Directed Definition (SDD) || Types of Attributes || Types of SDDs || Compiler Design

Summary

In this video, the concept of Syntax-Directed Definitions (SDD), also known as Syntax-Directed Translation (SDT), is explained within the context of compiler design. The discussion covers the role of parsers, attributes of non-terminals and terminals, and how syntax trees are refined using semantic rules. Key topics include synthesized and inherited attributes, the process of improving parse strings, and different categories of SDTs, such as S-attributed and L-attributed. By exploring these concepts, the video offers a comprehensive understanding of how compilers evaluate and translate expressions using syntax-directed methods.

Takeaways

• 😀 Syntax Directed Definition (SDD) is a concept in compiler design related to the translation of syntactical rules into an executable form.
• 😀 In a compiler, the output of parsers is a parse tree, which is later improved using Syntax Directed Translation (SDT) or Syntax Directed Definition (SDD).
• 😀 Non-terminals in a grammar can have attributes, whereas terminals only have lexical values and no attributes.
• 😀 Attributes in non-terminals can be synthesized or inherited, and these attributes are used for evaluating expressions during parsing.
• 😀 Synthesized attributes are associated with non-terminals on the left-hand side of productions, while inherited attributes are associated with non-terminals on the right-hand side.
• 😀 A terminal symbol can be evaluated based on its lexical value (ID's LexVal), while non-terminals are evaluated based on their children's values.
• 😀 Semantic rules are used in conjunction with productions to define how attributes are evaluated for non-terminals, and they are key to the translation process.
• 😀 Syntax Directed Translations (SDTs) can be categorized into S-attributed and L-attributed, based on whether synthesized or inherited attributes are used.
• 😀 S-attributed SDTs use synthesized attributes and typically follow a bottom-up parsing method.
• 😀 L-attributed SDTs use inherited attributes with constraints, particularly relying on the left sibling for the evaluation of attributes.
• 😀 The final output of an SDT is an improved parse tree that includes semantic evaluations for each non-terminal, based on its attributes and the production rules.

Q & A

What is the primary topic of the video script?

The primary topic of the video script is Syntax Directed Definitions (SDD) in compiler design, focusing on attributes, semantic rules, and their application in parsing.

What are terminals and non-terminals in the context of Syntax Directed Definitions?

Terminals are symbols that cannot be expanded further and are typically the leaf nodes in a parse tree, while non-terminals are symbols that can be expanded until they reach the leaf nodes.

What is the difference between synthesized and inherited attributes?

Synthesized attributes are associated with non-terminals on the left-hand side (LHS) of a production, and their values are derived from the children of the non-terminal. Inherited attributes are associated with non-terminals on the right-hand side (RHS) of a production, and their values depend on their parent or sibling nodes.

What are the two types of attributes discussed in the video?

The two types of attributes discussed are synthesized attributes and inherited attributes.

How are semantic rules applied to productions in Syntax Directed Definitions?

Semantic rules are applied to the productions to evaluate the values of non-terminals. These rules are defined for each production and are used to calculate the expression or output based on the values of attributes.

What are the two categories of Syntax Directed Translations (SDT)?

The two categories of Syntax Directed Translations (SDT) are S-attributed SDTs and L-attributed SDTs.

What is an example of an S-attributed SDT?

An example of an S-attributed SDT is when synthesized attributes are used, and bottom-up parsing is applied to evaluate the expression. For instance, in a production 'A → B C', the value of A depends on the values of B and C.

How do inherited attributes work in an L-attributed SDT?

In an L-attributed SDT, inherited attributes are passed from the parent node to the non-terminals on the right-hand side of a production. The value of a non-terminal depends on its parent or left sibling, with some constraints applied, such as the value of a non-terminal only depending on its left sibling.

What is the role of attributes in Syntax Directed Definitions?

Attributes play the role of storing properties or values associated with non-terminals in a syntax tree. They are used in conjunction with semantic rules to evaluate expressions, ensuring the correct output from the parser.

How are productions and semantic rules related in Syntax Directed Definitions?

In Syntax Directed Definitions, productions define the syntactic structure of the language, while semantic rules provide the evaluation logic for calculating the attribute values of non-terminals based on the production. Together, they enable the translation of source code into an output representation.