The Body of the insert-buffer Function

The body of the insert-buffer function has two major parts: an or expression and a let expression. The purpose of the or expression is to ensure that the argument buffer is bound to a buffer and not just the name of a buffer. The body of the let expression contains the code which copies the other buffer into the current buffer.

In outline, the two expressions fit into the insert-buffer function like this:

(defun insert-buffer (buffer)
  "documentation..."
  (interactive "*bInsert buffer: ")
  (or ...
      ...

  (let (varlist)
      body-of-let... )

To understand how the or expression ensures that the argument buffer is bound to a buffer and not to the name of a buffer, it is first necessary to understand the or function.

Before doing this, let me rewrite this part of the function using if so that you can see what is done in a manner that will be familiar.