Write an attribute grammar whose BNF basis is that of Example 3.6 inSection 3.4.5 but whose language rules are as follows: Data types cannotbe mixed in expressions, but assignment statements need not have thesame types on both sides of the assignment operator.Example 3.6 is attached EXAMPLE 3.6An Attribute Grammar for Simple Assignment Statements1. Syntax rule: → = Semantic rule: .expected_type ← .actual_type2. Syntax rule: → [2] + [3]Semantic rule: .actual_type ←if ([2].actual_type = int) and([3].actual_type = int)then intelse realend ifPredicate:.actual_type.expected_type3. Syntax rule: → Semantic rule: .actual_type ← .actual_typePredicate:.actual_type.expected_type====4. Syntax rule: → A | B | CSemantic rule: .actual_type ← look-up (.string)The look-up function looks up a given variable name in the symbol table andreturns the variable's type.

Given: The following BNF as the basis: <assign> -> <id> = <expr> <id>…

Answered: EXAMPLE 3.6 An Attribute Grammar for…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

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Write an attribute grammar whose BNF basis is that of Example 3.6 in
Section 3.4.5 but whose language rules are as follows: Data types cannot
be mixed in expressions, but assignment statements need not have the
same types on both sides of the assignment operator.

Example 3.6 is attached

EXAMPLE 3.6
An Attribute Grammar for Simple Assignment Statements
1. Syntax rule: <assign> → <var> = <expr>
Semantic rule: <expr>.expected_type ← <var>.actual_type
2. Syntax rule: <expr> → <var>[2] + <var>[3]
Semantic rule: <expr>.actual_type ←
if (<var>[2].actual_type = int) and
(<var>[3].actual_type = int)
then int
else real
end if
Predicate:
<expr>.actual_type
<expr>.expected_type
3. Syntax rule:
<expr> → <var>
Semantic rule: <expr>.actual_type ← <var>.actual_type
Predicate:
<expr>.actual_type
<expr>.expected_type
==
==
4. Syntax rule: <var> → A | B | C
Semantic rule: <var>.actual_type ← look-up (<var>.string)
The look-up function looks up a given variable name in the symbol table and
returns the variable's type.

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hello ,

I don't understand how the new grammar you provided prevents mixing up the data types in the expressions . I think the answer should be in modifying the IF-Statement ?

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