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-rw-r--r--net/ricketyspace/sicp/one/fortysix.scm26
1 files changed, 26 insertions, 0 deletions
diff --git a/net/ricketyspace/sicp/one/fortysix.scm b/net/ricketyspace/sicp/one/fortysix.scm
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--- /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))