Syntax Analysis and Parsing Questions and Answers

Q: State whether the following is true or false.A parser can detect that a variable has been used before its declaration.

Correct answer: FalseUse before declaration depends on what has appeared elsewhere in the program, which no context free grammar can express - the grammar constrains the shape of the token stream, not the relationship between distant parts of it. The check belongs to semantic analysis and is made against the symbol table.

71.

A parser that builds no tree at all but calls semantic actions directly is

A.restricted to grammars with no recursion whatsoever
B.using a bottom-up method rather than a top-down one
C.performing syntax directed translation during the parse
D.necessarily unable to detect any syntax errors present

Answer: C

Correct answer: performing syntax directed translation during the parse

Building no tree and calling the semantic actions as each production is recognised is exactly syntax directed translation, and it is what a one-pass compiler does. It is available to both top-down and bottom-up parsers, and it detects syntax errors as readily as any other - what it gives up is the ability to make a second pass over the structure.

Discuss in Forum

72.

The advantage of building an explicit tree over acting during the parse is

A.the parser becomes faster because no actions are executed
B.syntax errors are detected earlier in the compilation
C.the grammar may then be ambiguous without causing trouble
D.later phases may traverse the structure more than once

Answer: D

Optimisation and analysis often need several traversals in different orders. An explicit tree makes those possible, at the cost of the memory to hold it. Optimising compilers therefore build a tree while simple translators often do not.

Discuss in Forum

73.

State whether the following is true or false.
A parser can detect that a variable has been used before its declaration.

A.False
B.True only at large scales
C.False only at small scales
D.True

Answer: A

Correct answer: False

Use before declaration depends on what has appeared elsewhere in the program, which no context free grammar can express - the grammar constrains the shape of the token stream, not the relationship between distant parts of it. The check belongs to semantic analysis and is made against the symbol table.

Discuss in Forum

74.

The grammar symbol epsilon in a production denotes

A.a terminal symbol that the scanner will never produce at all
B.the empty string, so the nonterminal may derive nothing
C.an error condition detected during the parse
D.the end of the input token stream being parsed

Answer: B

Epsilon productions let a construct be optional. They complicate parsing, since the parser must consult FOLLOW to decide when to apply them rather than looking only at FIRST. Removing them is possible but usually multiplies the number of productions.

Discuss in Forum

75.

Removing all epsilon productions from a grammar

A.always makes the grammar ambiguous as a side effect
B.reduces the number of productions in every case
C.is possible without changing the language, except for the empty string
D.is quite impossible for any grammar containing recursion of any kind

Answer: C

Standard constructions eliminate epsilon productions, usually at the cost of many more productions. The empty string itself must be handled separately if the language contains it. The construction is theoretical groundwork rather than a step compilers perform.

Discuss in Forum

76.

A grammar in Chomsky normal form has every production of the form

A.a nonterminal going to any string of terminals only
B.a single terminal going to a string of nonterminals
C.a nonterminal going to exactly three symbols in all cases
D.a nonterminal going to two nonterminals or to one terminal

Answer: D

The restricted shape is what makes the CYK parsing algorithm work. It is a theoretical convenience rather than something compiler writers impose on real language grammars. Converting a real grammar to this form would obscure it beyond recognition.

Discuss in Forum

77.

The CYK algorithm parses any context free grammar in time

A.proportional to the cube of the input length
B.proportional to the input length alone
C.proportional to the square of the input length
D.exponential in the length of the input string

Answer: A

The cubic bound covers every context free grammar, including ambiguous ones. Compilers use linear methods instead by restricting the grammars they accept. A cubic algorithm on a large source file would make compilation unacceptably slow.

Discuss in Forum

78.

Deterministic parsing methods are preferred in compilers because

A.they detect semantic as well as syntactic errors
B.they parse in time linear in the length of the input
C.they can handle every context free grammar without restriction
D.they require no lookahead token to make their decisions

Answer: B

Linear time matters when compiling large programs. The price is that the grammar must fall in a restricted class, which language designers accommodate deliberately. Language syntax is shaped in part by what parsers can handle efficiently.

Discuss in Forum

79.

Generalised LR parsing differs from ordinary LR parsing in that it

A.abandons the stack in favour of a purely recursive method
B.operates on characters rather than on tokens from a scanner
C.explores several parses in parallel where conflicts arise
D.requires the grammar to be unambiguous before it can run

Answer: C

GLR forks the parse at a conflict and discards branches that fail. It handles ambiguous grammars at the cost of losing the linear time guarantee. Natural language processing uses the method far more often than compilers do.

Discuss in Forum

80.

Parser combinators build a parser by

A.generating a table from a grammar specification file
B.converting the grammar into a deterministic finite automaton
C.translating productions into an intermediate representation
D.composing small parsing functions using higher order operators

Answer: D

Correct answer: composing small parsing functions using higher order operators

A parser combinator is a function that consumes input and returns a result, and larger parsers are built by combining smaller ones with operators for sequence, choice and repetition. The grammar is thereby expressed directly in the host language, with no separate specification file and no generation step.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Syntax Analysis and Parsing Questions and Answers || Syntax Analysis and Parsing MCQ Questions and Answers || Syntax Analysis and Parsing GK Questions and Answers || Syntax Analysis and Parsing GK MCQ Questions || Syntax Analysis and Parsing Multiple Choice Questions and Answers || Syntax Analysis and Parsing GK || GK on Syntax Analysis and Parsing || Compiler Design Questions and Answers || Compiler Design MCQ Questions and Answers || Compiler Design GK Questions and Answers || GK on Compiler Design

Syntax Analysis and Parsing Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications