Exercise 1.4. 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:

`(define (a-plus-abs-b a b) ((if (> b 0) + -) a b))`

This procedure applies an operator to `a`

and `b`

. That operator is the compound expression `(if (> b 0) + -)`

. If `b`

is greater than 0, the operator evaluates to `+`

. If not, it evaluates to `-`

.

The overall effect is to return `a`

plus the absolute value of `b`

.