How to check if a directory exists in elisp?

Question

I've seen how to check if a file exists (file-exists-p), but how to check if a directory exists?

Answer 1

From elisp manual:

-- Function: file-directory-p filename

This function returns ‘t’ if FILENAME is the name of an existing
 directory, ‘nil’ otherwise.

See also its docstring, with a note concerning symlinks:

(file-directory-p FILENAME)

Return t if FILENAME names an existing directory. Symbolic links to directories count as directories. See ‘file-symlink-p’ to distinguish symlinks.

Answer 2

file-directory-p is your friend.

Found using C-u C-h a directory RET and browsing the result.