1 files changed, 30 insertions, 8 deletions
diff --git a/coding-exercises/2/78/complex-polar.rkt b/coding-exercises/2/78/complex-polar.rkt
index 725f387..41a81a1 100644
--- a/coding-exercises/2/78/complex-polar.rkt
+++ b/coding-exercises/2/78/complex-polar.rkt
@@ -2,20 +2,42 @@
 (provide install-polar-package)
 (require "../../../shared/data-directed-programming.rkt")
 
-(define (install-polar-package apply-generic put)
+(define (install-polar-package apply-fn put)
+  ;; import methods
+  (define (mul a b)
+    (apply-fn 'mul a b))
+  (define (cos a)
+    (apply-fn 'cos a))
+  (define (sin a)
+    (apply-fn 'sin a))
+  (define (sqr a)
+    (apply-fn 'sqr a))
+  (define (sqrt a)
+    (apply-fn 'sqrt a))
+  (define (atan a b)
+    (apply-fn 'atan a b))
+
+  ;; selectors
   (define (magnitude z)
-    (car z))
-  (define (angle z)
-    (cdr z))
-  (define (make-from-mag-ang r a)
-    (cons r a))
+      (car z)
+    (define (angle z)
+      (cdr z))
+    (define (make-from-mag-ang r a)
+      (cons r a)))
+
+    ;; generic selectors
   (define (real-part z)
-    (apply-generic 'mul (magnitude z) (apply-generic 'cos (angle z))))
+      (mul (magnitude z)
+         (cos (angle z))))
   (define (imag-part z)
-    (apply-generic 'mul (magnitude z) (apply-generic 'sin (angle z))))
+    (mul (magnitude z)
+       (sin (angle z))))
+
+    ;; constructor
   (define (make-from-real-imag x y)
     (cons (sqrt (+ (sqr x) (sqr y)))
           (atan y x)))
+
   ;; register in data-driven package)
   (define (typtag x)
     (attach-tag 'polar x))