this paper is a discussion of the expressive power of various languages, but efficiency is always a concern, especially with constructs that must examine large collections. It should therefore be pointed out that the expression of a loop in terms of mapping functions, function closures and recursive function-calling does not mean inefficiency. It is well-known how to compile "tail-recursive" functions into highly efficient iteration [Steele78], and high quality Lisp systems have been "open-coding" mapping functions for at least 20 years.