tisp

commit ab055d71ddf82410dc2209d96701b21decf39a69
parent 15021c575138e4842d8fd41764bd99b5699b2caa
Author: Ed van Bruggen <edvb@uw.edu>
Date:   Sat, 27 Jul 2019 17:26:58 -0700

Add nth function to get numbered elemented of list

Diffstat:
tibs/lib.tsp
 | 
8
++++++++

1 file changed, 8 insertions(+), 0 deletions(-)
diff --git a/tibs/lib.tsp b/tibs/lib.tsp
@@ -82,10 +82,18 @@
 (define first car)
 (define rest cdr)
 (define (list . lst) lst)
+
 (define (last lst)
   (cond
     ((cdr lst) (last (cdr lst)))
     (else (car lst))))
+
+(define (nth i l)
+  (when (pair? l)
+    (if (<= i 0)
+      (car l)
+      (nth (- i 1) (cdr l)))))
+
 (define (apply fn args)
   (eval (cons fn args)))
 (define (map fn lst)