Update net/ricketyspace/sicp/one/thirtyseven.scm.

1 files changed, 18 insertions, 7 deletions

diff --git a/net/ricketyspace/sicp/one/thirtyseven.scm b/net/ricketyspace/sicp/one/thirtyseven.scm
index 09081d4..ad257c7 100644
--- a/net/ricketyspace/sicp/one/thirtyseven.scm
+++ b/net/ricketyspace/sicp/one/thirtyseven.scm
@@ -3,20 +3,31 @@
 ;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
 
 (define-module (net ricketyspace sicp one thirtyseven)
-  #:export (cont-frac-iter))
+  #:export (cont-frac-iter
+            cont-frac-rec))
 
-(define (cont-frac-iter n d k)
-  (define (do-iter n d i)
+(define (cont-frac-rec n d k)
+  (define (do-rec n d i)
     (cond ((< i k) (/ (n i)
-                      (+ (d i) (do-iter n d (1+ i)))))
+                      (+ (d i) (do-rec n d (1+ i)))))
           (else (/ (n i) (d i)))))
-  (do-iter n d 1))
+  (do-rec n d 1))
+
+(define (cont-frac-iter n d k)
+  (define (do-iter n d i acc)
+    (cond ((= i 0) acc)
+          (else (do-iter n d (1- i) (/ (n i) (+ (d i) acc))))))
+  (do-iter n d k 0))
 
 ;;; Guile REPL
 ;;;
 ;;; scheme@(guile-user)> ,use (net ricketyspace sicp one thirtyseven)
+;;; scheme@(guile-user)> (cont-frac-rec (lambda (i) 1.0) (lambda (i) 1.0) 10)
+;;; $7 = 0.6179775280898876
 ;;; scheme@(guile-user)> (cont-frac-iter (lambda (i) 1.0) (lambda (i) 1.0) 10)
-;;; $16 = 0.6179775280898876
+;;; $8 = 0.6179775280898876
+;;; scheme@(guile-user)> (cont-frac-rec (lambda (i) 1.0) (lambda (i) 1.0) 11)
+;;; $9 = 0.6180555555555556
 ;;; scheme@(guile-user)> (cont-frac-iter (lambda (i) 1.0) (lambda (i) 1.0) 11)
-;;; $17 = 0.6180555555555556
+;;; $10 = 0.6180555555555556