Lecture 8, CSE341, Spring 2004 summary

* Functions with free variables (function closures)
* A more careful definition of evaluation in terms of environments

* More on higher-order functions
  * Useful functions for passing to functions like map (e.g.,
  result of add_n)
  * Useful functions for passing as "callbacks" 

* fold
  * even more general than map
  * uses with and without free variables

* combining functions (e.g., compose)