Question

Consider the following grammar and the semantic actions to support the inherited type declaration attributes. Let $X_1,X_2,X_3,X_4,X_5\text{and}{X}_6$ be the place holders for the non-terminals D, T, L or $L_1$ in the following table:

Production rule	Semantic action
$D\to TL$	$X_1.type=X_2.type$
$T\to int$	T.type = int
$T\to Float$	T.type = float
$L\to L_1.id$	$X_3.type=X_4.type\text{add Type (id.entry,}{X}_5.type)$
$L\to id$	add Type (id. entry, $X_6$. type)

Which one of the following are the appropriate choices for $X_1,X_2,X_3\text{and}{X}_4?$

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

Answer 1

The correct option is B $X_1=L,X_2=T,X_3=L_1,X_4=L$

SDT for inserting type information in the symbol table
$D\to TL$ {L. idtype = T.stype}
$T\to int$ {T. stype = int}
$T\to$ float {T. stype = float}
$L\to L_1,id$ {$L_1.$ itype = L.itype}
addtype(id.entry, L.itype)
$L\to id$ addtype (id.entry, L.itype)

Replace these attribute information in the given SDT.

So option (a) is the correct answer.