Compiler Design Test 3

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Compiler Design Test 3

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Question 1
1 / -0

Consider the following grammar:
S → XYZ
Y.val = X.val
Y.val = S.val
Y.val = Z.val
Above grammar is

A
S-attributed grammar

B
L-attributed grammar

C
Neither S-attributed grammar nor L-attributed grammar

D
Both S-attributed grammar and L-attributed grammar

Solution

Synthesized attributes:
A Synthesized attribute is an attribute of the non-terminal on the left-hand side of a production. Synthesized attributes represent information that is being passed up the parse tree. The attribute can take value only from its children.
S-attributed SDT
If an SDT uses only synthesized attributes, it is called as S-attributed SDT.
Y.val = S.val \\ this violates S-attributed grammar
Inherited attributes:
An attribute of a nonterminal on the right-hand side of a production is called an inherited attribute. The attribute can take value either from its parent or from its siblings.
L-attributed SDT
If an SDT uses both synthesized attributes and inherited attributes with a restriction that inherited attribute can inherit values from left siblings only, it is called as L-attributed SDT.
Therefore every S-attributed definition is L-attributed but vice versa is not true.
Explanation:
Y.val = Z.val \\this violates L-attributed grammar rule
Question 2
1 / -0

Which of the following statement is false?

A
Synthesized attributes can be evaluated by a post-order traversal.

B
Inherited attributes cannot be evaluated by a simple pre-order traversal of the parse-tree.

C
Dependency Graphs are the most general technique used to evaluate syntax directed definitions with both synthesized and inherited attributes.

D
None of the above

Solution

1. True: Synthesized attributes are computed from the values of the attributes of the children nodes. They can be evaluated by a post-order traversal.
2. True: Inherited attributes of the children can depend on both left and right siblings. Inherited attributes that do not depend from right children can be evaluated by a classical pre-order traversal.
3. True: A Dependency Graph shows the inter-dependencies among the attributes of the various nodes of a parse-tree.
Question 3
1 / -0

Consider the grammar with the following translation rules and X as the start symbol.
X -> X₁* Y      {X.value = X₁.value * Y.value}
X -> Y              {X.value = Y.value}
Y -> Y₁- Z       {Y.value = Y₁.value - Z.value}
Y -> Z              {Y.value = Z.value}
Z -> digit          {Z.value = digit.value}
What is the value for the root of the parse tree for the expression: 54 – 5 * 1 * 7 – 4?

A
147-147

B
1474-1471

C
1477-1476

D
1479-1472

Solution

In above grammar – has higher precedence order than *.
Hence, - will be evaluated first.
(54 – 5) * 1 * (7 – 4)
49 * 1 * 3
147
Question 4
1 / -0

Which of the following statement is/are true?
I. Every L-attributed definition is S-attributed
II. Every S-attributed definition is L-attributed
III. Both L-attributed and S-attributed can be used interchangeably

A
Only I

B
Only II

C
Only II and III

D
I, II and III

Solution

Synthesized attributes:
A Synthesized attribute is an attribute of the non-terminal on the left-hand side of a production. Synthesized attributes represent information that is being passed up the parse tree. The attribute can take value only from its children.
S-attributed SDT
If an SDT uses only synthesized attributes, it is called as S-attributed SDT.
Inherited attributes:
An attribute of a nonterminal on the right-hand side of a production is called an inherited attribute. The attribute can take value either from its parent or from its siblings.
L-attributed SDT
If an SDT uses both synthesized attributes and inherited attributes with a restriction that inherited attribute can inherit values from left siblings only, it is called as L-attributed SDT.
Therefore every S-attributed definition is L-attributed but vice versa is not true.
Question 5
1 / -0

Consider the following grammar:
S → pAS | r
A → q
Find the number of reduction steps taken by a bottom-up parser while accepting the string "pqpqpqpqr"?

A
9-9

B
94-91

C
97-96

D
99-92

Solution

Concept:
The class of bottom-up parser follow rightmost derivation in the reverse order.
Explanation:
S → pAS (S → pAS)
S → pApAS (S → pAS)
S → pApApAS (S → pAS)
S → pApApApAS (S → pAS)
S → pApApApAr (S → r)
S → pApApApqr (A → q)
S → pApApqpqr (A → q)
S → pApqpqpqr (A → q)
S → pqpqpqpqr (A → q)
Therefore, the number of reduction steps taken by a bottom-up parser while accepting the string "pqpqpqpqr" is 9.
Question 6
1 / -0

Le the two productions be P → CD and P → AB. Consider the following rules.
Rule 1: P.i = C.i + D.i and C.i = D.i - 1
Rule 2: A.i = P.i * 2 and B.i = A.i + P.i
Each of the five non-terminals P, A, B, C, and D has two attributes: s is a synthesized attribute, and i is an inherited attribute.
Which one of the following is true?

A
Only Rule 1 is L-attributed.

B
Only Rule 2 is L-attributed.

C
Both Rule 1 and Rule 2 are L-attributed.

D
Neither Rule 1 nor Rule 2 is L-attributed.

Solution

Concept:
A rule is said to be L- attributed if it used both synthesized and inherited attributes. But, in the inherited attribute, we can get attribute values from the parent or from the left siblings, but not the right sibling.
Rule 1 is not L- attributed.
Rule 1: P.i = C.i + D.i and C.i = D.i - 1
Explanation:
P.i = C.i + D.i ...{This is synthesized attribute as Parent P is taking values from children C and D}
C.i = D.i - 1 ...{Child C is taking value from right sibling D}
Therefore, this violates the conditions of L- attributed definitions.
Rule 2 is L- attributed
Rule 2: A.i = P.i * 2 and B.i = A.i + P.i
A.i = P.i * 2 ...{This is inherited attributes as Child P is taking values from its parent P}
B.i = A.i + P.i ...{This is inherited attributes child B is taking attribute value from parent P and left sibling Y}
Question 7
1 / -0

Consider the below-given Syntax Directed Translation Scheme
B → aBA print(“^”);
B → a print(“$”);
A → b print(“#”);
What is the output printed by a bottom-up parser, for the input aaaabbb?

A
$^^^^####

B
$#^#^#^#^

C
^#^#^#^#$

D
####^^^^$

Solution

Concept:
Parser
Derivation
LR parsers or Bottom-up Parsers
Rightmost reverse Derivation
LL parsers or Top-down Parsers
Leftmost Derivation
Explanation:
B → aBA print(“^”);
B → aBb   print(“#”);
B → aaBAb   print(“^”);
B → aaBbb print(“#”);
B → aaaBAbb   print(“^”);
B → aaaBbbb print(“#”);
B → aaaaBAbb print(“^”);
B → aaaaBbbb print(“#”);
B → aaaaabbb  print(“$”);
Output: $#^#^#^#^

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Parser	Derivation
LR parsers or Bottom-up Parsers	Rightmost reverse Derivation
LL parsers or Top-down Parsers	Leftmost Derivation

Compiler Design Test 3

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Compiler Design Test 3

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Question 1

S-attributed grammar

L-attributed grammar

Neither S-attributed grammar nor L-attributed grammar

Both S-attributed grammar and L-attributed grammar

Solution

Question 2

Synthesized attributes can be evaluated by a post-order traversal.

Inherited attributes cannot be evaluated by a simple pre-order traversal of the parse-tree.

Dependency Graphs are the most general technique used to evaluate syntax directed definitions with both synthesized and inherited attributes.

None of the above

Solution

Question 3

147-147

1474-1471

1477-1476

1479-1472

Solution

Question 4

Only I

Only II

Only II and III

I, II and III

Solution

Question 5

9-9

94-91

97-96

99-92

Solution

Question 6

Only Rule 1 is L-attributed.

Only Rule 2 is L-attributed.

Both Rule 1 and Rule 2 are L-attributed.

Neither Rule 1 nor Rule 2 is L-attributed.

Solution

Question 7

$^^^^####

$#^#^#^#^

^#^#^#^#$

####^^^^$

Solution

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