Syntax Analysis and Parsing Questions and Answers

Q: Which of the following is a Parser generating tool ?

The parser generating tool is yacc.yacc (Yet Another Compiler-Compiler) takes a grammar specification with actions and generates an LALR parser in C. It is usually used together with lex.lex generates lexical analysers (scanners), not parsers. vi is a text editor and ls is the Unix command that lists directory contents.

Q: The grammar S \(\rightarrow\) aSa/bS/d is :

The grammar is both LL(1) and LR(1).The three alternatives of S begin with different terminals: FIRST(aSa) = {a}, FIRST(bS) = {b}, FIRST(d) = {d}. These sets are disjoint and no alternative derives the empty string, so a parser can always choose the production from one token of lookahead. The grammar is LL(1).Every LL(1) grammar is also LR(1), since an LR(1) parser has at least as much information when it decides. So the grammar is both, which rules out the three options that deny one of the two.

Q: If A is a top-down parser and B is a bottom-up parser, which of the following statements is false ?

The false statement is A uses canonical reduction to check the syntactic errors.A top-down parser starts from the start symbol and expands non-terminals to generate a derivation of the input (a leftmost derivation), so statement A is true.Canonical reduction belongs to bottom-up parsing: a bottom-up parser reduces the input string step by step to the start symbol, tracing a rightmost derivation in reverse, which is the canonical reduction sequence. So B's two statements are true and the one assigning canonical reduction to the top-down parser is false.

91.

Which of the following is a Parser generating tool ?

A.vi
B.ls
C.lex
D.yacc

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: D

The parser generating tool is yacc.

yacc (Yet Another Compiler-Compiler) takes a grammar specification with actions and generates an LALR parser in C. It is usually used together with lex.

lex generates lexical analysers (scanners), not parsers. vi is a text editor and ls is the Unix command that lists directory contents.

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92.

The syntax of expression in a language can be characterised by :

(i) a table giving associativity and precedence
(ii) a grammar for expression
(iii) expression are always to be written in infix notation
(iv) use of terminal per precedence level

A.(i) and (ii)
B.(ii) and (iii)
C.(iii) and (iv)
D.(i), (ii) and (iii)

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: A

The syntax of expressions can be characterised by (i) and (ii), so the answer is (i) and (ii).

One way is a table listing each operator's precedence and associativity; the other is a grammar for expressions, where precedence is built into the structure of the productions. Both fix how an expression such as a - b * c is grouped.

Statement (iii) is false: expressions can be written in prefix or postfix notation as well as infix. Statement (iv) is also wrong as worded: an expression grammar uses one nonterminal per precedence level, not one terminal. Options containing (iii) or (iv) are therefore wrong.

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93.

The grammar S \(\rightarrow\) aSa/bS/d is :

A.LL(1) but not LR(1)
B.Neither LL(1) nor LR(1)
C.LR(1) but not LL(1)
D.Both LL(1) and LR(1)

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: D

The grammar is both LL(1) and LR(1).

The three alternatives of S begin with different terminals: FIRST(aSa) = {a}, FIRST(bS) = {b}, FIRST(d) = {d}. These sets are disjoint and no alternative derives the empty string, so a parser can always choose the production from one token of lookahead. The grammar is LL(1).

Every LL(1) grammar is also LR(1), since an LR(1) parser has at least as much information when it decides. So the grammar is both, which rules out the three options that deny one of the two.

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94.

If A is a top-down parser and B is a bottom-up parser, which of the following statements is false ?

A.A generates the string to be parsed, beginning with the start symbol of the grammar
B.B reduces the input string to the start symbol of the grammar
C.A uses canonical reduction to check the syntactic errors
D.B uses canonical reduction to reach the start symbol

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

The false statement is A uses canonical reduction to check the syntactic errors.

A top-down parser starts from the start symbol and expands non-terminals to generate a derivation of the input (a leftmost derivation), so statement A is true.

Canonical reduction belongs to bottom-up parsing: a bottom-up parser reduces the input string step by step to the start symbol, tracing a rightmost derivation in reverse, which is the canonical reduction sequence. So B's two statements are true and the one assigning canonical reduction to the top-down parser is false.

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