Pairwise Disjointness Test: Recursive Descent Quiz & Flashcards

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Questions and Answers

Which category of parser produces the parse tree beginning at the root and visits each node before its branches?

Neither top down nor bottom up

Bottom up

Top down (correct)

Both top down and bottom up

Which category of parser produces the parse tree beginning at the leaves and has an order that is the reverse of a rightmost derivation?

Neither top down nor bottom up

Bottom up (correct)

Both top down and bottom up

Top down

Which type of symbols in a grammar are lowercase letters at the beginning of the alphabet and represent small-scale syntactic constructs called lexemes?

Terminals or nonterminals

Strings of terminals

Nonterminal symbols

Terminal symbols (correct)

Which type of symbols in a grammar are uppercase letters at the beginning of the alphabet and represent connotative names or abbreviations of language constructs?

Nonterminal symbols Signup and view all the answers

Which type of symbols in a grammar are uppercase letters at the end of the alphabet and can be either terminals or nonterminals?

Terminals or nonterminals Signup and view all the answers

Which type of symbols in a grammar are lowercase letters at the end of the alphabet and represent sentences of a language?

Strings of terminals Signup and view all the answers

Which type of symbols in a grammar are lowercase Greek letters representing the right-hand sides of grammar rules?

Strings of terminals Signup and view all the answers

Which type of parser must choose the correct A-rule to get the next sentential form in the leftmost derivation, using only the first token produced by A?

Top-down parser Signup and view all the answers

What is the name of the parsing decision problem for top-down parsers?

Parsing problem Signup and view all the answers

Which algorithm is a coded implementation based on BNF description and is a type of top-down parser?

LL algorithm Signup and view all the answers

Which algorithm uses a table-driven implementation of the BNF rules and is a type of top-down parser?

LL algorithm Signup and view all the answers

What is the name of the subprogram for each nonterminal in the grammar, which can parse sentences that can be generated by that nonterminal?

Recursive descent Signup and view all the answers

What is the purpose of the initial process in a recursive-descent parsing when a nonterminal has more than one RHS?

To choose the correct RHS to parse Signup and view all the answers

What is the name of the algorithm that minimizes the number of nonterminals and is ideally suited for being the basis for a recursive-descent parser?

EBNF Signup and view all the answers

Which of the following is true about bottom-up parsing algorithms?

They correspond to a rightmost derivation Signup and view all the answers

What is the time complexity of parsers that work for any unambiguous grammar?

O(n^3) Signup and view all the answers

What is the trade-off when using parsers that work for a subset of all unambiguous grammars?

Generality is traded for efficiency Signup and view all the answers

What is the role of a lexical analyzer in language implementation?

Isolates small-scale parts of a program Signup and view all the answers

Which type of parser is an LL parser?

Recursive-descent parser Signup and view all the answers

What is the parsing problem for bottom-up parsers?

Finding the correct RHS in a right-sentential form to reduce Signup and view all the answers

What is the complexity of bottom-up parsing algorithms in terms of time?

O(n^2) Signup and view all the answers

Which family of parsers is the most common bottom-up parsing approach?

LR parsers Signup and view all the answers

What is the order of time required to parse a string of length n using parsers that work for any unambiguous grammar?

O(n^3) Signup and view all the answers

According to the text, what is the purpose of left recursion in a grammar?

To enable top-down parsing Signup and view all the answers

What is the purpose of the pairwise disjointness test in grammar analysis?

To determine if a grammar can be parsed using a top-down parser Signup and view all the answers

Which of the following is a correct modification to remove left recursion in a grammar?

For each nonterminal A, group the A-rules as A → Aα1 | ... | Aαm | β1 | ... | βn and replace the original A-rules with A → β1A’ | ... | βnA’ and A’ → α1A’ | ... | αmA’ | ε Signup and view all the answers

What is the purpose of bottom-up parsing?

To determine what substring of a right sentential form must be reduced to produce the previous sentential form in the right derivation Signup and view all the answers

What is the purpose of the LL grammar class?

To classify grammars that can be parsed using top-down parsing Signup and view all the answers

What is the purpose of the recursive-descent subprogram for the Java if statement rule?

To parse and validate the syntax of the if statement Signup and view all the answers

What is the purpose of the FIRST set in grammar analysis?

To determine the possible first tokens that can be derived from a given nonterminal Signup and view all the answers

Study Notes

Parser Types

Top-down parsers produce the parse tree beginning at the root and visit each node before its branches.
Bottom-up parsers produce the parse tree beginning at the leaves and have an order that is the reverse of a rightmost derivation.

Grammar Symbols

Terminal symbols are lowercase letters at the beginning of the alphabet and represent small-scale syntactic constructs called lexemes.
Nonterminal symbols are uppercase letters at the beginning of the alphabet and represent connotative names or abbreviations of language constructs.
Start symbols are uppercase letters at the end of the alphabet and can be either terminals or nonterminals.
Sentence symbols are lowercase letters at the end of the alphabet and represent sentences of a language.
Right-hand side (RHS) symbols are lowercase Greek letters representing the right-hand sides of grammar rules.

Parsing Decision Problem

The parsing decision problem for top-down parsers is to choose the correct A-rule to get the next sentential form in the leftmost derivation, using only the first token produced by A.

Top-Down Parsing Algorithms

Recursive-Descent parsing is a coded implementation based on BNF description and is a type of top-down parser.
Table-Driven parsing uses a table-driven implementation of the BNF rules and is a type of top-down parser.
Recursive-Descent subprograms are subprograms for each nonterminal in the grammar, which can parse sentences that can be generated by that nonterminal.

Parsing Process

The initial process in a recursive-descent parsing when a nonterminal has more than one RHS is to minimize the number of nonterminals and is ideally suited for being the basis for a recursive-descent parser.
The purpose of left recursion in a grammar is to remove left recursion.
The pairwise disjointness test in grammar analysis is used to check if a grammar is ambiguous.

Bottom-Up Parsing

Bottom-up parsing algorithms have a time complexity of O(n^3) for any unambiguous grammar.
The trade-off when using parsers that work for a subset of all unambiguous grammars is faster parsing time but limited grammar coverage.
The role of a lexical analyzer in language implementation is to analyze the input string and produce a sequence of tokens.
LL parsers are a type of top-down parser.
The parsing problem for bottom-up parsers is to find the most suitable parse tree for a given input string.
The complexity of bottom-up parsing algorithms is O(n) in terms of time.
The LR parser family is the most common bottom-up parsing approach.

Grammar Analysis

The purpose of the FIRST set in grammar analysis is to compute the set of terminals that can appear as the first symbol of a string generated by a nonterminal.

Parsing Purposes

The purpose of bottom-up parsing is to parse a string of length n in O(n) time.
The purpose of the LL grammar class is to define a grammar that can be parsed using a top-down parser.
The purpose of the recursive-descent subprogram for the Java if statement rule is to parse sentences that can be generated by the Java if statement rule.

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Description

This quiz provides a trace of the lexical and syntax analyzers during a recursive-descent parsing process. Follow along as the analyzers process the expression (sum + 47) / total, providing insight into the next tokens and lexemes encountered. Test your understanding of parsing techniques with this informative quiz.

Recursive-Descent Parsing