See the header in the source file for details. It's very easy to use:

(require 'memoize)

(memoize 'my-function)

The macro defmemoize is also provided to directly create memoized functions:

(defmemoize my-expensive-function (n)
  (if (zerop n)
      1
    (* n (my-expensive-function (1- n)))))

Some functions are run over buffer contents, and need to be cached only so long as the buffer contents do not change. For these use-cases, we have the function memoize-by-buffer-contents as well as the defmemoize-by-buffer-contents macro.

To restore the original definition of a memoized function symbol (not a lambda or closure), use memoize-restore:

(memoize 'my-function)
(memoize-restore 'my-function)