sicp/two: Add thirtythree.scm.

1 files changed, 45 insertions, 0 deletions

diff --git a/net/ricketyspace/sicp/two/thirtythree.scm b/net/ricketyspace/sicp/two/thirtythree.scm
new file mode 100644
index 0000000..c97f5d0
--- /dev/null
+++ b/net/ricketyspace/sicp/two/thirtythree.scm
@@ -0,0 +1,45 @@
+;;;; License: CC0-1.0
+
+(define-module (net ricketyspace sicp two thirtythree)
+  #:export (sicp-map
+            sicp-append
+            sicp-length))
+
+
+(define (accumulate op initial sequence)
+  (if (null? sequence)
+      initial
+      (op (car sequence)
+          (accumulate op initial (cdr sequence)))))
+
+
+(define (sicp-map p sequence)
+  (accumulate (λ (x y)
+                (cons (p x) y))
+              '() sequence))
+
+
+(define (sicp-append seq1 seq2)
+  (accumulate cons seq2 seq1))
+
+
+(define (sicp-length sequence)
+  (accumulate (λ (x y)
+                (+ 1 y))
+              0
+              sequence))
+
+;;; Guile REPL
+;;;
+;;;
+;;; scheme@(guile-user)> ,use (net ricketyspace sicp two thirtythree)
+;;;
+;;; scheme@(guile-user)> (sicp-map (λ (x) (expt 2 x)) '(1 2 3 4 5 6 7 8 9 10))
+;;; $5 = (2 4 8 16 32 64 128 256 512 1024)
+;;; 
+;;; scheme@(guile-user)> (sicp-append '(1 2 3 4 5 6 7 8 9 10) '(11 12 13 14 15 16))
+;;; $7 = (1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16)
+;;; 
+;;; scheme@(guile-user)> (sicp-length '(40 41 42 43 44 45 46 47 48 49))
+;;; $11 = 10
+;;;