Add '30.nix'

30.nix

@@ -0,0 +1,10 @@
+with import <nixpkgs> { };
+let
+  listOfNumbers = [2 4 6 9 27];
+  myMap = f: l: lib.fold (x: y: [(f x)] ++ y) [] l; 
+in
+rec {
+  #your map should create the same result as the standard map function
+  example = map (x: builtins.div x 2) listOfNumbers; 
+  result = myMap (x: builtins.div x 2) listOfNumbers;
+}