add last_n function to prelude

assets/prelude.ld

@@ -854,6 +854,12 @@ fn slice_n {
 	(str as :string, start as :number, n as :number) -> slice (str, start, add (start, n))
 }
 
+fn last_n {
+	"Returns a list or string containing the last n elements of a list or string."
+	(xs as :list, n as :number) -> slice_n (xs, sub (count (xs), n), n)
+	(str as :string, n as :number) -> slice_n (str, sub (count (str), n), n)
+}
+
 fn butlast {
 	"Returns a list, omitting the last element."
 	(xs as :list) -> slice (xs, 0, dec (count (xs)))
@@ -1609,6 +1615,7 @@ fn key_down? {
 	keys_down
 	keyword?
 	last
+	last_n
 	left!
 	link!
 	list