A package riddle, part II (20 Aug 2009)

Yesterday, I presented some Lisp code which puzzled me for a little while.

To recap, here's the test code again:

(defun test()
  (test_dialog))

(in-package :clausbrod.de)
(use-package :oli)

(sd-defdialog 'test_dialog
  :ok-action '(display "test_dialog"))

Here is what happens if you save this code into a file, then load the file into CoCreate Modeling and call the (test) function:

"The function #:TEST_DIALOG is undefined"? Let's review the code so that you can understand why I found this behavior surprising.

First, you'll notice that the function test is defined in the default Lisp package. After its definition, we switch into a different package (clausbrod.de), in which we then define a CoCreate Modeling dialog called test_dialog.

The (test) function attempts to call that dialog. If you've had any exposure with other implementations of Lisp before, I'm sure you will say: "Well, of course the system will complain that TEST_DIALOG is undefined! After all, you define it in package clausbrod.de, but call it from the default package (where test is defined). This is trivial! Go read The Complete Idiot's Guide to Common Lisp Packages instead of wasting our time!"

To which I'd reply that sd-defdialog, for practical reasons I may go into in a future blog post, actually makes dialogs visible in CoCreate Modeling's default package. And since the function test is defined in the default package, it should therefore have access to a symbol called test_dialog, and there shouldn't be any error messages, right?

To be continued...

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