1 (define (make-from-real-imag x y)
2   (define (dispatch op)
3     (cond ((eq? op 'real-part) x)
4 	  ((eq? op 'imag-part) y)
5 	  ((eq? op 'magnitude)
6 	   (sqrt (+ (square x) (square y))))
7 	  ((eq? op 'angle) (atan y x))
8 	  (else (error "Unknown op -- MAKE-FROM-REAL-IMAG" op))))
9   dispatch)