1 files changed, 42 insertions, 0 deletions
diff --git a/semestr-2/racket/l9z16/solution.rkt b/semestr-2/racket/l9z16/solution.rkt
new file mode 100644
index 0000000..0af169d
--- /dev/null
+++ b/semestr-2/racket/l9z16/solution.rkt
@@ -0,0 +1,42 @@
+#lang racket
+
+(provide lcons lnull lnull? lcar lcdr)
+
+
+(define (lcons x f) (mcons x f))
+
+(define lnull null)
+
+(define lnull? null?)
+
+(define (lcar xs) (mcar xs))
+
+(define (lcdr xs) 
+  (let ([x (mcdr xs)])
+    (cond [(not (mpair? x)) (set-mcdr! xs (x))]))
+  (mcdr xs))
+
+(define (from n)
+  (lcons n (lambda () (from (+ n 1)))))
+
+(define nats
+  (from 0))
+
+(define (lnth n xs)
+  (cond [(= n 0) (lcar xs)]
+        [else (lnth (- n 1) (lcdr xs))]))
+
+(define (lfilter p xs)
+  (cond [(lnull? xs) lnull]
+        [(p (lcar xs))
+         (lcons (lcar xs) (lambda () (lfilter p (lcdr xs))))]
+        [else (lfilter p (lcdr xs))]))
+
+(define (prime? n)
+  (define (factors i)
+    (cond [(>= i n) (list n)]
+          [(= (modulo n i) 0) (cons i (factors (+ i 1)))]
+          [else (factors (+ i 1))]))
+  (= (length (factors 1)) 2))
+
+(define primes (lfilter prime? (from 2)))
+\ No newline at end of file