#define private public - A Package Riddle, part II (20 Aug 2009)

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---+++ [[DefinePrivatePublic20090820PackageRiddlePart2][A package riddle, part II]] (20 Aug 2009)

<summary>
Yesterday, I <a href="DefinePrivatePublic20090819PackageRiddle">presented some Lisp code</a>
which puzzled me for a little while.
</summary>

To recap, here's the test code again:
<pre>
(defun test()
  (test_dialog))

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

(sd-defdialog 'test_dialog
  :ok-action '(display "test_dialog"))
</pre>

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

<img src="%ATTACHURLPATH%/testdialog.png" alt="testdialog.png"  width="321" height="134" style="float:center;" />
<br clear="all" />

<i>"The function #:TEST_DIALOG is undefined"</i>? 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 <nop>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
[[http://www.flownet.com/gat/packages.pdf][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 <nop>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?

[[DefinePrivatePublic20090822PackageRiddlePart3][To be continued...]]

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r1.2 - 22 Aug 2009 - 09:58 - ClausBrod to top
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