[html-template-devel] Re: question regarding HTML-TEMPLATE

[Edi Weitz]

Hi Jan!

On Fri, 09 Jul 2004 23:57:42 -0700, Jan Rychter <jan at rychter.com> wrote:

> First of all, I'd like to thank you for the excellent libraries that
> you make available. I particularly appreciate how carefully finished
> and documented they are.

Thanks, you're welcome.

> I would like to ask you a question regarding HTML-template --
> somehow I cannot get to work the way I would like to. I am puzzled
> as to what I'm doing wrong: I have read and reread the
> documentation, and tried a number of things.
>
> The problem I have is that my templates print on the standard output
> (in the REPL) instead of being captured into strings. The absolutely
> narrowed-down example is:
>
> (with-output-to-string (*standard-output*) 
>   (with-input-from-string (s "test <!-- TMPL_VAR a --> one") 
>      (html-template:fill-and-print-template s '(:a "1"))))
>
> This prints "test 1 one" in my REPL and returns an empty string.

This happens because FILL-AND-PRINT-TEMPLATE rebinds *STANDARD-OUTPUT*
to the value of *DEFAULT-TEMPLATE-OUTPUT* which is *STANDARD-OUTPUT*
(the original one!) by default.

I admit that this is an unfortunate design decision which happened
mainly because I was too lazy to type. I might chance this in a future
release.

In other words: All statements like

  (write-string string)

in CREATE-SIMPLE-PRINTER in 'template.lisp' should rather be

  (write-string string *default-template-output*)

instead. That way I wouldn't need the

  (let ((*standard-output* stream))

rebinding in 'api.lisp'.

> Adding a :stream *standard-output* argument to
> fill-and-print-template helps in this case. However, it doesn't help
> at all if I call this code from TBNL. In that case, everything still
> ends up in the standard output of my REPL, instead of on the web
> page.
>
> I'm sorry for bothering you with such a trivial problem. Perhaps you
> could add a simple usage example together with TBNL to the
> documentation of one of the packages?

All of these should work:

  (with-output-to-string (*default-template-output*)
    (with-input-from-string (s "test <!-- TMPL_VAR a --> one") 
       (html-template:fill-and-print-template s '(:a "1"))))

  (with-output-to-string (out) 
    (with-input-from-string (s "test <!-- TMPL_VAR a --> one") 
       (html-template:fill-and-print-template s '(:a "1") :stream out)))

  (with-output-to-string (out)
    (let ((*default-template-output* out))
      (with-input-from-string (s "test <!-- TMPL_VAR a --> one") 
         (html-template:fill-and-print-template s '(:a "1")))))

This is also documented here:

  <http://weitz.de/html-template/#default-template-output>

Let me know if this works for you or if you still have problems.

Cheers,
Edi.

PS: I'm sending a copy to the mailing list. Please use the list for
    bug reports and questions. Thanks.