Observe that our model of evaluation allows for combinations whose operators are compound expressions. Use this observation to describe the behavior of the following procedure:

In the body of a-plus-abs-b a b, the expression (if (> b 0) + -) evaluates to an arithmetic operation (either + or -, depending on the sign of b’s actual argument). The interpreter obtains a primitive procedure that it applies to the arguments replacing the formal parameters `a and b.