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.

1) Syntax rule: → =
2) Syntax rule: → [2] + [3]
Predicate: [2].actual_type == [3].actual_type
3) Syntax rule: →
4) Syntax rule: → A | B | C
Semantic rule: .actual_type ← lookup(.string)