1 files changed, 37 insertions, 0 deletions
diff --git a/net/ricketyspace/sicp/one/fortyfour.scm b/net/ricketyspace/sicp/one/fortyfour.scm
new file mode 100644
index 0000000..b7079f8
--- /dev/null
+++ b/net/ricketyspace/sicp/one/fortyfour.scm
@@ -0,0 +1,37 @@
+;;;; 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
+;;;