Solve Problem 4.

1 files changed, 23 insertions, 0 deletions

diff --git a/problem-4.scm b/problem-4.scm
new file mode 100644
index 0000000..3622b5e
--- /dev/null
+++ b/problem-4.scm
@@ -0,0 +1,23 @@
+(use-modules (srfi srfi-1)
+             (srfi srfi-42))
+
+(define (products min max)
+  (list-ec (:range x min max) (:range y min max) (* x y)))
+
+(define (palindrome? x)
+  (define (test s)
+    (cond ((or (string-null? s)
+               (= (string-length s) 1))
+           #t)
+          ((equal? (string-ref s 0)
+                   (string-ref s (1- (string-length s))))
+           (test (substring s 1 (1- (string-length s)))))
+          (else
+           #f)))
+  (let ((s (number->string x)))
+    (test s)))
+
+(define (palindrome-products min max)
+  (filter palindrome? (products min max)))
+
+(reduce max 0 (palindrome-products 100 1000))