Question

How do you go about solving this problem?

Suppose I want to write a function that does the following: if the user has library X installed, then use function X-function, otherwise – skip?

What I tried:

(when (symbol-function 'X-function)
  (X-function))

I’m getting a warning for this code – so what is the right way?

Answer 1

How about this:

(when (fboundp 'X-function)
    (X-function))

The docs at http://www.gnu.org/software/emacs/manual/html_node/elisp/Function-Cells.html says about symbol-function

If the symbol’s function cell is void, a void-function error is signaled.

I’m guessing that is what you are seeing. On the other hand, fboundp just returns t or nil depending on whether the function exists.