Understanding BNF Notation
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Questions and Answers

What are the abstractions being defined in a BNF description called?

  • Terminals
  • Tokens
  • Lexemes
  • Nonterminal symbols (correct)

In a BNF grammar, what are the lexemes and tokens of the rules called?

  • Terminals (correct)
  • Symbols
  • Productions
  • Nonterminals

What is used to describe lists of syntactic elements in programming languages?

  • Iteration
  • Abstraction
  • Derivation
  • Recursion (correct)

When is a rule considered recursive in a BNF grammar?

<p>When its LHS appears in its RHS (C)</p> Signup and view all the answers

What is the sequence of rule applications called in a grammar?

<p>Derivation (B)</p> Signup and view all the answers

What is the name given to the special nonterminal symbol at the beginning of the derivation process?

<p>Start symbol (C)</p> Signup and view all the answers

What is the difference between syntax and semantics in programming languages?

<p>Syntax refers to the form of expressions while semantics refer to the meaning. (D)</p> Signup and view all the answers

Which of the following is an example of a lexeme in a programming language?

<ul> <li>(B)</li> </ul> Signup and view all the answers

What is the function of a token in programming languages?

<p>To represent a category of lexemes (D)</p> Signup and view all the answers

Which grammar class describes the forms of tokens in programming languages?

<p>Regular grammars (D)</p> Signup and view all the answers

What is Backus-Naur Form (BNF) commonly used for in programming language development?

<p>Defining context-free grammars (C)</p> Signup and view all the answers

Why is a metalanguage essential in describing programming language syntax?

<p>To provide an abstract language for describing another language (D)</p> Signup and view all the answers

What is the purpose of using semantic rules in a grammar?

<p>To determine the precedence of operators with the same level of priority (C)</p> Signup and view all the answers

In the given text, what does left recursion specify?

<p>Left associativity (B)</p> Signup and view all the answers

What is the purpose of extended Backus–Naur Form (EBNF)?

<p>To enhance the readability and writability of grammars (B)</p> Signup and view all the answers

How does right recursion differ from left recursion in grammar rules?

<p>Right recursion indicates right associativity (B)</p> Signup and view all the answers

What is a characteristic of a grammar rule that is right recursive?

<p>The LHS appears at the right end of the RHS (A)</p> Signup and view all the answers

Which feature is NOT a part of EBNF extensions?

<p>Introduction of left recursion (D)</p> Signup and view all the answers

Flashcards

BNF

A notation for describing the syntax of programming languages, using abstraction for syntactic structures.

Nonterminal

An abstraction in a BNF grammar, representing a syntactic structure.

Terminal

A concrete element, like a keyword or operator, in a programming language.

Rule/Production

A mapping in BNF, defining how to construct a nonterminal.

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Recursion

A rule where the LHS (left-hand side) appears in the RHS (right-hand side).

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Grammar

A collection of rules that define the syntax of a language.

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Derivation

The process of applying rules to build a sentence.

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Sentential form

Each stage in the derivation process.

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Leftmost Derivation

A derivation where the leftmost nonterminal is always replaced first.

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Rightmost Derivation

A derivation where the rightmost nonterminal is always replaced first.

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Parse Tree

A hierarchical representation that shows the derivation's steps.

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Associativity

A rule to decide which operator has precedence when multiple operators have the same precedence.

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Left Recursion

A rule in which the LHS appears at the beginning of the RHS, specifying left associativity for parsing.

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Right Recursion

A rule where the LHS is on the far right of the RHS, giving right associativity.

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EBNF

Extended BNF, an extension to BNF to improve readability.

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Syntax

The form, structure of a program or language.

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Semantics

The meaning of a program or language structure.

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Language Recognizer

A program that identifies valid sentences of a language.

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Language Generator

A program that can create valid sentences or programs of a language.

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Study Notes

BNF (Backus-Naur Form)

  • A notation for describing syntax, developed by John Backus and Peter Naur in the mid-1950s
  • Uses abstraction for syntactic structures
  • Left-hand side (LHS) - the abstraction being defined
  • Right-hand side (RHS) - the definition of the LHS
  • Rule (or production) - a mixture of tokens, lexemes, and references to other abstractions

Abstractions and Symbols

  • Nonterminal symbols or nonterminals - the abstractions in a BNF description or grammar
  • Terminal symbols or terminals - the lexemes and tokens of the rules

Recursion

  • Used to describe lists of syntactic elements in programming languages
  • A rule is recursive if its LHS appears in its RHS

Grammar

  • A collection of rules that describe the syntax of programming languages
  • Sentences of the language are generated through a sequence of applications of the rules, beginning with the start symbol
  • This sequence of rule applications is called a derivation

Derivation

  • Each of the strings in the derivation is called a sentential form
  • In leftmost derivation, the replaced nonterminal is always the leftmost nonterminal in the sentential form
  • In rightmost derivation, the replaced nonterminal is always the rightmost nonterminal in the sentential form

Parse Tree

  • When an expression includes two operators that have the same precedence, a semantic rule is required to specify which should have precedence
  • The rule is named associativity
  • Left recursion specifies left associativity, while right recursion specifies right associativity

Extended BNF (EBNF)

  • Extended versions of BNF that increase the readability and writability of BNF
  • Three EBNF extensions:
    • Optional parts of an RHS are placed in brackets

Syntax and Semantics

  • Syntax - the form of the expressions, statements, and program units of a programming language
  • Semantics - the meaning of the expressions, statements, and program units of a programming language

Lexemes and Tokens

  • Lexemes - include the numeric literals, operators, and special words of a programming language
  • Token - a category of the lexemes of a language

Language Recognizer and Generator

  • Language recognizer - reads input strings of the language and decides whether the strings belong to the language
  • Language generator - creates sentences of a language

Formal Methods of Describing Syntax

  • Grammar - describes the syntax of programming languages; a collection of rules
  • Noam Chomsky - described four classes of generative devices or grammars that define four classes of language
  • Two of these grammar classes are regular and context-free grammars
  • Regular grammars - describe the forms of the tokens of the programming languages
  • Context-free grammars - describe the syntax of whole programming languages

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Description

Learn about the basics of BNF (Backus-Naur Form) notation, including the definitions of Left-hand side (LHS), Right-hand side (RHS), and Rules. Explore how nonterminal symbols and terminal symbols are used in BNF descriptions. Discover how recursion is applied to describe syntax in BNF.

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