complex-msg.rkt

#lang racket

(require "numerical.rkt")
(provide make-from-real-imag make-from-mag-ang real-part imag-part magnitude angle)

(define (make-from-real-imag x y)
  (define (dispatch op)
    (cond ((eq? op 'real-part) x)
          ((eq? op 'imag-part) y)
          ((eq? op 'magnitude)
           (sqrt (+ (square x) (square y))))
          ((eq? op 'angle) (atan y x))
          (else (error "Unknown op - MAKE-FROM-REAL-IMAG" op))))
  dispatch)

(define (make-from-mag-ang r a)
  (define (dispatch op)
    (cond ((eq? op 'magnitude) r)
          ((eq? op 'angle) a)
          ((eq? op 'real-part)
           (* r (cos a)))
          ((eq? op 'imag-part)
           (* r (sin a)))
          (else (error "Unknown op - MAKE-FROM-MAG-ANG" op))))
  dispatch)

(define (apply-generic op arg) (arg op))

(define (real-part z) (apply-generic 'real-part z))
(define (imag-part z) (apply-generic 'imag-part z))
(define (magnitude z) (apply-generic 'magnitude z))
(define (angle z) (apply-generic 'angle z))