GATE CSE 2019 | Question: 36

Question

Consider the following grammar and the semantic actions to support the inherited type declaration attributes. Let $X_1, X_2, X_3, X_4, X_5$, and $X_6$ be the placeholders for the non-terminals $D, T, L$ or $L_1$ in the following table:

$$\begin{array}{|l|l|} \hline  \text{Production rule} & \text{Semantic action} \\ \hline D \rightarrow T L & X_1.\text{type} = X_2.\text{type} \\ \hline T \rightarrow \text{int} & T.\text{type} = \text{int} \\ \hline T \rightarrow \text{float} & T.\text{type} = \text{float} \\ \hline
L \rightarrow L_1, id & X_3.\text{type}= X_4.\text{type}  \\ 
&\text{addType}(id. \text{entry}, X_5.\text{type})\\ \hline
L \rightarrow id & \text{addType}(id. \text{entry}, X_6.\text{type}) \\ \hline \end{array}$$

Which one of the following are appropriate choices for $X_1, X_2, X_3$ and $X_4$?

• A. $X_1=L, \: X_2=T, \: X_3=L_1, \: X_4 = L$
• B. $X_1=T, \: X_2=L, \: X_3=L_1, \: X_4 = T$
• C. $X_1=L, \: X_2=L, \: X_3=L_1, \: X_4 = T$
• D. $X_1=T, \: X_2=L, \: X_3=T, \: X_4 = L_1$

Comments

same question gate-cse-1992-question-11a

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https://youtu.be/VC4wpru1yRE?si=rmGbgWpVv47X01s9&t=6899

 

Answer 1

Let's analyze the production rules and semantic actions to determine the appropriate choices for X1, X2, X3, and X4.

Production Rule: D -> TL

Semantic Action: X1.type = X2.type

This action indicates that the type of the declaration D is inherited from the type of T. So, X1 should be D and X2 should be T.

Production Rule: T -> int or T -> float

Semantic Action: T.type = int or T.type = float

These rules directly assign a type to the terminal T.

Production Rule: L -> L1 id or L -> id

Semantic Action: X3.type = X4.type and addType(id.entry, X5.type)

In the first production, L is composed of L1 and id. The type of L is inherited from the type of L1. So, X3 should be L and X4 should be L1.

In the second production, L directly consists of id. The type of id is inherited from the type of L. So, X6 should be L.

Based on the above analysis, the correct choices for X1, X2, X3, and X4 are:

X1 = D, X2 = T, X3 = L, X4 = L1

Therefore, the correct answer is A.

Answer 2

Slide Number 13 [ As it is Given]  :https://cse.iitkgp.ac.in/~bivasm/notes/SDD.pdf

Answer 3

look 1 translation D->TL where X1.type = X2.type

as above metions it support inherited type declaration ,

so in translation x1 take value either from left sibling or parent

now x2 has only 2 option x2 = T or D

we have option x2 = T  so choose it

Answer 4

According to how the attributes need to be inherited option A seems correct 

Answer 5

First lets understand what the given grammar is ,
D → T L
T → int
T → float
L → L1 , id
L → id
This grammar generates an example like
int a
int a, b, c
float x, y
Here T gives the type and L is for identifiers.
From the information it is inherited attribute and from the table we can see T decides type of L .

Therefore  X1 = L & X2 = T 
Similarly we can say L1 inherits L type.

X3 = L1 & X4 = L.
Answer is A.