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-rw-r--r--net/ricketyspace/sicp/one/fortyfour.scm37
1 files changed, 37 insertions, 0 deletions
diff --git a/net/ricketyspace/sicp/one/fortyfour.scm b/net/ricketyspace/sicp/one/fortyfour.scm
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+;;;; Under Creative Commons Attribution-ShareAlike 4.0
+;;;; International. See
+;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
+;;;;
+
+(define-module (net ricketyspace sicp one fortyfour)
+ #:export (smooth))
+
+(define (avg-3 x y z)
+ (/ (+ x y z) 3.0))
+
+(define dx 0.00001)
+
+(define (smooth f)
+ (lambda (x) (avg-3 (f (- x dx))
+ (f x)
+ (f (+ x dx)))))
+
+;;; GNU Guile REPL
+;;;
+;;; scheme@(guile-user)> ,use (net ricketyspace sicp one fortythree)
+;;; scheme@(guile-user)> ,use (net ricketyspace sicp one fortyfour)
+;;; scheme@(guile-user)> (sqrt 27)
+;;; $2 = 5.196152422706632
+;;; scheme@(guile-user)> ((smooth sqrt) 27)
+;;; $3 = 5.1961524227065725
+;;; scheme@(guile-user)> ((smooth (smooth sqrt)) 27)
+;;; $4 = 5.196152422706514
+;;; scheme@(guile-user)> ((smooth (smooth (smooth sqrt))) 27)
+;;; $5 = 5.196152422706454
+;;; scheme@(guile-user)> (((repeated smooth 1) sqrt) 27)
+;;; $6 = 5.1961524227065725
+;;; scheme@(guile-user)> (((repeated smooth 2) sqrt) 27)
+;;; $7 = 5.196152422706514
+;;; scheme@(guile-user)> (((repeated smooth 3) sqrt) 27)
+;;; $8 = 5.196152422706454
+;;;