add sublist

list.rkt

@@ -84,4 +84,12 @@
 (provide values->list)
 (define-syntax (values->list stx)
   (syntax-case stx ()
-    [(_ values-expr) #'(call-with-values (λ () values-expr) list)]))
+    [(_ values-expr) #'(call-with-values (λ () values-expr) list)]))
+
+
+(define+provide/contract (sublist xs i j)
+  (list? (and/c integer? (not/c negative?)) (and/c integer? (not/c negative?)) . -> . list?)
+  (cond
+    [(> j (length xs)) (error 'sublist (format "ending index ~a exceeds length of list" j))]
+    [(>= j i) (take (drop xs i) (- j i))]
+    [else (error 'sublist (format "starting index ~a is larger than ending index ~a" i j))]))

tests.rkt

@@ -156,3 +156,8 @@
 (check-equal? (slicef-at (range 5) odd? #t) '((1 2) (3 4)))
 (check-equal? (slicef-at (range 5) procedure?) '((0 1 2 3 4)))
 (check-exn exn:fail:contract? (λ() (slicef-at (range 5) 3)))
+
+
+(check-equal? (sublist (range 5) 0 0) '())
+(check-equal? (sublist (range 5) 0 1) '(0))
+(check-equal? (sublist (range 5) 0 5) '(0 1 2 3 4))