net: Add (net rickteyspace sicp two twentyseven).

1 files changed, 30 insertions, 0 deletions

diff --git a/net/ricketyspace/sicp/two/twentyseven.scm b/net/ricketyspace/sicp/two/twentyseven.scm
new file mode 100644
index 0000000..eea04bd
--- /dev/null
+++ b/net/ricketyspace/sicp/two/twentyseven.scm
@@ -0,0 +1,30 @@
+;;;; License: CC0-1.0
+
+(define-module (net ricketyspace sicp two twentyseven)
+  #:export (sicp-deep-reverse))
+
+(define (sicp-append list1 list2)
+  (if (null? list1)
+      list2
+      (cons (car list1) (sicp-append (cdr list1) list2))))
+
+(define (sicp-deep-reverse items)
+  (cond ((null? items) '())
+        ((pair? (car items))
+         (sicp-append (sicp-deep-reverse (cdr items))
+                      (list (sicp-deep-reverse (car items)))))
+        (else
+         (sicp-append (sicp-deep-reverse (cdr items))
+                      (list (car items))))))
+
+;;; Guile REPL
+
+;;; scheme@(guile-user)> ,use (net ricketyspace sicp two twentyseven)
+;;; scheme@(guile-user)> (sicp-deep-reverse '((1 2 3) (4 5 6)))
+;;; $27 = ((6 5 4) (3 2 1))
+;;; scheme@(guile-user)> (sicp-deep-reverse '(1 (4 5 6)))
+;;; $28 = ((6 5 4) 1)
+;;; scheme@(guile-user)> (sicp-deep-reverse '(1 (6)))
+;;; $29 = ((6) 1)
+;;; scheme@(guile-user)> (sicp-deep-reverse '(1 2 3 4 5 6))
+;;; $30 = (6 5 4 3 2 1)