Add '18.nix'

18.nix

@@ -0,0 +1,15 @@
+let
+  x = { a="bananas"; b= "pineapples"; };
+  y = { a="kakis"; c ="grapes";};
+  z = { a="raspberrys"; c= "oranges"; };
+
+  func = {a, b, c ? "another secret ingredient"}: "A drink of: " + 
+    a + ", " + b + " and " + c;
+in
+rec {
+  ex00=func ( x );  
+  # hit 'run', you need the output to solve this!
+  ex01=func (y // x);  
+  ex02=func (x // { c="lychees";});
+  ex03=func (z // x // z);
+}