1 ]=> (define (a-plus-abs-b a b)
  ((if (> b 0) + -) a b))

;Value: a-plus-abs-b

1 ]=> (a-plus-abs-b 3 4)

;Value: 7

1 ]=> (a-plus-abs-b 3 -4)

;Value: 7

The expression (if (> b 0) + -) evaluates to an operator which is applied to a and b.