Load a library, or load then install a library.

gistfile1.el

(defmacro with-library (options &rest body)
  "Try and require a library, if it's not found, install if
requested. If all goes well, then eval body.

    (with-library '((require 'ag)
                    (package-naem 'ag))
        (ag-specific-code))"
  `(let ((symbol (cdr (assoc 'require ,options))))
     (if (or (featurep symbol)
             (require symbol nil t))
         (progn ,@body)
       (save-excursion
         (progn
           (let ((pkg (cdr (assoc 'package-name ,options))))
             (if (not pkg)
                 (progn
                   (switch-to-buffer (get-buffer-create "*with-library errors*"))
                   (insert (format "Failed to load '%s'\n"
                                   (symbol-name symbol))))
               (package-install pkg)
               (message (concat "Installed " (symbol-name pkg)))
               (progn ,@body))))))))