[tbnl-devel] Re: [Lispweb] tbnl: what package?

[Edi Weitz]

On Fri, 10 Feb 2006 08:52:20 -0700 (MST), Jim Prewett <download at hpc.unm.edu> wrote:

> I think you're missing the point Edi :)

I don't... :)

> Here is a simple example that I think gets to the heart of the
> problem: I'm certainly not claiming that this isn't a problem with
> my understanding, however :)
>
> When you visit /foo, the webpage returned displays this text:
> "package: #<The COMMON-LISP-USER package>"
>
> What I'm not understanding is *why* that is what is displayed.  I
> would have hoped for "package: #<MYPACKAGE package>".
>
> (defpackage :mypackage)
> (in-package :mypackage)
>
> (defun some-func ()
>   (cl-who:with-html-output-to-string (*standard-output* nil :prologue nil 
> :indent nil)
>     (:HTML 
>      (:HEAD 
>       (:TITLE "foo"))
>      (:BODY
>       (cl-who:str
>        (CL-WHO:ESCAPE-STRING 
>         (format () "package: ~A" *package*)))))))
>      
> (setq tbnl:*dispatch-table*
>       (list (tbnl:create-prefix-dispatcher 
>              "/foo"
>              #'some-func)))

Why should it display #<MYPACKAGE package>?  *PACKAGE* is a runtime
concept, it's not a literal constant that's hard-coded into the
function when you compile it:

  CL-USER 1 > (defpackage :foo (:use :cl))
  #<PACKAGE FOO>

  CL-USER 2 > (in-package :foo)
  #<PACKAGE FOO>

  FOO 3 > (defun foo () *package*)
  FOO

  FOO 4 > (foo)
  #<PACKAGE FOO>

  FOO 5 > (in-package :cl-user)
  #<PACKAGE COMMON-LISP-USER>

  CL-USER 6 > (foo::foo)
  #<PACKAGE COMMON-LISP-USER>

The package you see in your example depends on how (from where) you
started TBNL and how (from where) the thread that handles the request
is invoked.  The ANSI standard doesn't specify the package newly
created threads start in (because it doesn't mention MP) but your
Lisp's documentation will probably tell you.  I think it's not unusual
(and makes sense) to just re-bind *PACKAGE* to *PACKAGE*.

So, the important part is missing in your example above: When and how
did you invoke TBNL:START-TBNL?  I bet you did that from CL-USER and
you will see a different result if you start it from MYPACKAGE.

If you're doing something with packages at runtime you should always
re-bind *PACKAGE* - or in the case of INTERN you should use its second
argument.

Cheers,
Edi.