Q. Consider the following grammar and the semantic actions to support the inherited type declaration attributes. Let ๐1, ๐2, ๐3, ๐4, ๐5, and ๐6 be the placeholders for the non- terminals D, T, L or L1 in the following table:
| Production rule | Semantic action |
| D โ T L | ๐1.type = ๐2.type |
| T โ int | T.type = int |
| T โ float | T.type = float |
| L โ L1 , id | ๐3.type = ๐4.type addType(id.entry, ๐5.type) |
| L โ id | addType(id.entry, ๐6.type) |
Which one of the following are the appropriate choices for ๐1, ๐2, ๐3 and ๐4?
| (A) ๐1 = ๐ฟ , ๐2 = ๐, ๐3 = ๐ฟ1, ๐4 = ๐ฟ | (B) ๐1 = ๐ , ๐2 = ๐ฟ, ๐3 = ๐ฟ1, ๐4 = ๐ |
| (C) ๐1 = ๐ฟ , ๐2 = ๐ฟ, ๐3 = ๐ฟ1, ๐4 = ๐ | (D) ๐1 = ๐ , ๐2 = ๐ฟ, ๐3 = ๐, ๐4 = ๐ฟ1 |
Solution:
The correct answer is X1ย = L, X2ย = T, X3ย = L1, X4ย = L
According to Inherited attribute definition, an attribute is inherited if the attribute value of a parse-tree node is determined from attribute values of its parent and siblings.
So, semantic rules should be as following below:
D โ TL {L.idtype = T.stype}
T โ int {T.stype = int}
T โ float {T.stype = float}
L โ L1, id {L1.itype = L.itype}
addtype(id.entry, L.itype)
L โ id addtype(id.entry, L.itype)
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