Parsing Questions

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61.

Which one of the following is true at any valid state in shift-reduce parsing?

A

At the bottom we find the prefixes

B

None of the mentioned

C

Stack contains only viable prefixes

D

Stack consists of viable prefixes

Correct Answer: C

The prefixes on the stack of a shift-reduce parser are called viable prefixes.

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62.

In the context of abstract-syntax-tree and control-flow-graph. Which one of the following is true?

A

In both AST and CFG if node N2 be the successor of node N1

B

For any input program, neither AST nor CFG will contain a cycle

C

The max number of successors of a node in an AST and a CFG depends on the input program

D

None of the mentioned

Correct Answer: C

Successors depends on input .

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63.

Match the following.

   List-I                  List-II
A. Lexical analysis       1. Graph coloring
B. Parsing                2. DFA minimization
C. Register allocation    3. Post-order traversal
D. Expression evaluation  4. Production tree

 

A

A

B

A

C

A

D

A

Correct Answer: C

The entire column an items matches the Column B items in a certain way.

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64.

Which of the following pairs is the most powerful?

A

SLR, LALR

B

Canonical LR ,LALR

C

SLR canonical LR

D

LALR canonical LR

Correct Answer: C

parser algorithm is simple.

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65.

Consider the following grammar G.

 S ? F ? H
  F ? p ? c
  H ? d ? c

Which one is true?S1: All strings generated by G can be parsed with help of LL (1).
S2: All strings generated by G can be parsed with help of LR (1).

A

Only S1

B

Only S2

C

Both S1 & S2

D

None of the mentioned

Correct Answer: D

There is ambiguity as the string can be derived in 2 possible ways. First Leftmost Derivation S ? F F ? c Second Leftmost Derivation S ? H H ? c.

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66.

What is the maximum number of reduce moves that can be taken by a bottom-up parser for a grammar with no epsilon- and unit-production to parse a string with n tokens?

A

n/2

B

n-1

C

2n-1

D

2^n

Correct Answer: B

The moves are n-1.

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67.

Consider the following two sets of LR (1) items of an LR (1) grammar.

X -> c.X, c/d
   X -> .cX, c/d
   X -> .d, c/d
   X -> c.X, $
   X -> .cX, $
   X -> .d, $

Which one is false?

1. Cannot be merged since look ahead

A

1 only

B

2 only

C

1 and 4 only

D

1, 2, 3 and 4 only

Correct Answer: D

All these are valid reasons.

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68.

Which of these is also known as look-head LR parser?

A

SLR

B

LR

C

LLR

D

None of the mentioned

Correct Answer: C

LLR is the look ahead parser.

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69.

What is the similarity between LR, LALR and SLR?

A

Use same algorithm, but different parsing table

B

Same parsing table, but different algorithm

C

Their Parsing tables and algorithm are similar but uses top down approach

D

Both Parsing tables and algorithm are different

Correct Answer: A

The common grounds of these 3 parser is the algorithm but parsing table is different.

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70.

An LR-parser can detect a syntactic error as soon as __________

A

The parsing starts

B

It is possible to do so a left-to-right scan of the input

C

It is possible to do so a right-to-left scan of the input

D

Parsing ends

Correct Answer: B

Error is found when it the input string is scanned.

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