From the book: Introduction to Compiler Design by Torben Mogensen

Exercise 4.1 We extend the language from Sect. 4.2 with boolean operators. We add the following productions to Grammar 4.1: Exp -> not Exp Exp -Exp and Exp When evaluating not e, we first evaluate e to a value u that is checked to be a boolean. If it is, we return v, where - is logical negation. When evaluating ei and e2, we first evaluate ei and e2 to values vi and v2 that are both checked to be Exercise 4.1 We extend the language from Sect. 4.2 with boolean operators. We add the following productions to Grammar 4.1: Exp -> not Exp Exp -Exp and Exp When evaluating not e, we first evaluate e to a value u that is checked to be a boolean. If it is, we return v, where - is logical negation. When evaluating ei and e2, we first evaluate ei and e2 to values vi and v2 that are both checked to be