20. Write an attribute grammar whose base BNF is that of Example 3.2 andwhose type rules are the same as for the assignment statement exampleof Section 3.4.5.>>>> please note that. the assignment statement example of section 3.4.5 is exercise 3.6 -attached- EXAMPLE 3.2A Grammar for Simple Assignment Statements → → A | B | C → + | *=| ( )| 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_type4. 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.

Syntax rule: <assign> → <var> = <expr> Syntax rule: <var> → A | B | C…

Answered: 0. Write an attribute grammar whose…

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

Problem 1PE

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20. Write an attribute grammar whose base BNF is that of Example 3.2 and
whose type rules are the same as for the assignment statement example
of Section 3.4.5.
>>>> please note that. the assignment statement example of section 3.4.5 is exercise 3.6 -attached-

EXAMPLE 3.2
A Grammar for Simple Assignment Statements
<expr>
<assign> →<id>
<id> → A | B | C
<expr> →<id> + <expr>
| <id> *
<expr>
=
| ( <expr>)
| <id>

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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