net: Add (net ricketyspace sicp one fortysix).

* net/ricketyspace/sicp/one/fortysix.scm: New file.

1 files changed, 26 insertions, 0 deletions

diff --git a/net/ricketyspace/sicp/one/fortysix.scm b/net/ricketyspace/sicp/one/fortysix.scm
new file mode 100644
index 0000000..b97945d
--- /dev/null
+++ b/net/ricketyspace/sicp/one/fortysix.scm
@@ -0,0 +1,26 @@
+;;;; Under Creative Commons Attribution-ShareAlike 4.0
+;;;; International. See
+;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
+;;;;
+
+(define-module (net ricketyspace sicp one fortysix)
+  #:export (fixed-point fp-sqrt))
+
+(define (iterative-improve good-enough? improve)
+  (define (try guess)
+    (let ((next (improve guess)))
+      (if (good-enough? guess next)
+          next
+          (try next))))
+  try)
+
+(define (fixed-point f guess)
+  (define tolerance 0.00001)
+  (define (close-enough? v1 v2)
+    (< (abs (- v1 v2)) tolerance))
+  ((iterative-improve close-enough? f) guess))
+
+(define (fp-sqrt x)
+  (define (average x y) (/ (+ x y) 2.0))
+  (fixed-point (lambda (y) (average y (/ x y)))
+               1.0))