net: Add (net ricketyspace sicp one thirtythree).

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

1 files changed, 68 insertions, 0 deletions

diff --git a/net/ricketyspace/sicp/one/thirtythree.scm b/net/ricketyspace/sicp/one/thirtythree.scm
new file mode 100644
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+++ b/net/ricketyspace/sicp/one/thirtythree.scm
@@ -0,0 +1,68 @@
+;;;; Under Creative Commons Attribution-ShareAlike 4.0
+;;;; International. See
+;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.
+
+;;;  ___________________
+;;; < fuck abstraction. >
+;;;  -------------------
+;;;   \                 __
+;;;    \               (oo)
+;;;     \              (  )
+;;;      \             /--\
+;;;        __         / \  \
+;;;       UooU\.'@@@@@@`.\  )
+;;;       \__/(@@@@@@@@@@) /
+;;;            (@@@@@@@@)((
+;;;            `YY~~~~YY' \\
+;;;            ||    ||   >>
+
+(define-module (net ricketyspace sicp one thirtythree)
+  #:use-module (net ricketyspace sicp one twentyeight)
+  #:export (filtered-accumulate sum-odd sum-prime-sqrs))
+
+(define (filtered-accumulate combiner null-value term a next b filter)
+  (cond ((> a b) null-value)
+        ((not (filter a))
+         (combiner null-value
+                   (filtered-accumulate combiner null-value
+                                        term (next a) next b
+                                        filter)))
+        (else
+         (combiner (term a)
+                   (filtered-accumulate combiner null-value
+                                        term (next a) next b
+                                        filter)))))
+
+(define (sum-odd n)
+  (let ((null-value 0)
+        (term (lambda (x) x))
+        (next (lambda (x) (1+ x))))
+    (filtered-accumulate + null-value term 0 next n odd?)))
+
+(define (sum-prime-sqrs a b)
+  "Return sum of prime squares between A and B.
+
+A and B must be an integer greater than zero."
+  (let ((null-value 0)
+        (term (lambda (x) (* x x)))
+        (next (lambda (x) (1+ x))))
+    (filtered-accumulate + null-value term a next b prime?)))
+
+
+;;; Guile REPL
+;;; scheme@(guile-user)> ,use (net ricketyspace sicp one thirtythree)
+;;; scheme@(guile-user)> (sum-odd 1)
+;;; $9 = 1
+;;; scheme@(guile-user)> (sum-odd 5)
+;;; $10 = 9
+;;; scheme@(guile-user)> (sum-odd 10)
+;;; $13 = 25
+;;; scheme@(guile-user)> (sum-prime-sqrs 1 5)
+;;; $10 = 39
+;;; scheme@(guile-user)> (+ 1 4 9 25)
+;;; $11 = 39
+;;; scheme@(guile-user)> (sum-prime-sqrs 1 10)
+;;; $12 = 88
+;;; scheme@(guile-user)> (+ 1 4 9 25 49)
+;;; $13 = 88
+