[racket] Dynamic Templates?

Did you try using namespace-attach-module to attach 'racket and
'web-server/templates? Something like:

  (define orig-ns (current-namespace))
  (parameterize ([current-namespace (make-base-empty-namespace)])
    (namespace-attach-module orig-ns 'racket)
    (namespace-attach-module orig-ns 'web-server/templates)
    (namespace-require 'racket)
    (eval `(begin
             (require web-server/templates)
             (require ,my-source-path-string)
             (include-template ,my-template-path-string))
          (current-namespace)))

But 7 seconds seems remarkably long (I see a speed up of about 50% for that
function (with the my-source-path-string and my-template-path-string lines
commented out): from 250 to 170 msec).

It may be that your .zo files or something are not up to date. So you may
want to stick a 'raco make' somewhere in there to avoid recompiling your
files every time and just recompile the ones that changed.

Robby




On Mon, Oct 14, 2013 at 1:14 PM, Matthew Butterick
<mb.list.acct at gmail.com>wrote:

> At RacketCon I talked about my Pollen system for making web pages. Though
> I don't use the Racket webserver to provide live generation of web pages, I
> do use it to provide a kind of browser-assisted REPL for development. As I
> edit the project files, I want to reload the URL in the browser and see the
> changes (without restarting the webserver).
>
> Moreover, since it's a development tool, it wants to be maximally dynamic.
> For instance, I might be editing source files containing page content, or
> the design templates (which might also contain Racket code), or supporting
> Racket libraries (e.g., CSS generators).
>
> Jay has suggested that this can be done with eval. And indeed it can.
> Here's the quasicode I use:
>
>   (parameterize ([current-namespace (make-base-empty-namespace)])
>     (namespace-require 'racket)
>     (eval `(begin
>              (require web-server/templates)
>              (require ,my-source-path-string)
>              (include-template ,my-template-path-string))
>           (current-namespace))))
>
> This works great, with one wrinkle: it's the slowest operation in the
> whole system, taking about 7-8 secs to render each page. This is not a
> grave hardship, and certainly faster than restarting the web server. But
> I'd still be curious if I'm overlooking a better approach.
>
> In general, the render time is fairly consistent regardless of what's in
> the page, which suggests to me that most of the expense comes from setting
> up the fresh namespace. I did try making a namespace separately and reusing
> it, but that didn't work (code wouldn't get reloaded). Is there a way to
> "clean" a namespace that's cheaper than setting up a new one?
>
> Another option I considered is starting up another instance of Racket in a
> subprocess, but it would need to be made into a synchronous operation. Long
> drive for a short day at the beach, etc.
>
> It's also possible that I'm running up against the irreducible cost of
> high-quality eval, in which case, I will accept it and move on.
>
>
> Matthew Butterick
>
>
>
>
> On Thu, Jun 6, 2013 at 7:36 PM, Greg Hendershott <
> greghendershott at gmail.com> wrote:
>
>> Great timing! It's been on my short list to make my static blog
>> generator more flexible. From
>> http://docs.racket-lang.org/web-server/templates.html I got the idea
>> that it would be suitable only for static templates, but now I
>> understand that's not the case. Today I made a topic branch using this
>> approach that's working well, which I plan to merge after some testing
>> and polishing.
>>
>> p.s. Maybe it's obvious, but because `include-template` uses
>> `include-at/relative-to/reader`, it won't include a template if you
>> give it a full path. Maybe there's a more-elegant way, but I found it
>> worked to parameterize `current-directory` around the call to `eval`.
>>
>>
>> On Wed, Jun 5, 2013 at 4:45 PM, Jay McCarthy <jay.mccarthy at gmail.com>
>> wrote:
>> > While it is supposed to be pithy, it is also serious.
>> >
>> > When I wrote it, I imagine that people would do something like this:
>> >
>> > #lang racket/base
>> > (require web-server/templates)
>> >
>> > (define (template-content t x)
>> >   (eval #`(let ([x #,x]) (include-template #,t))))
>> >
>> > (template-content "t.txt" 5)
>> > (template-content "t.txt" 6)
>> >
>> > and trust that the template wouldn't include @(system "rm -fr /"). I
>> > think that a simple eval works just fine for when you, the programmer,
>> > want to change the content dynamic (although I'd say it is better to
>> > use the web-server language so you can restart with the same
>> > continuations, etc.)
>> >
>> > Your solution is great for a template that a user provides, although
>> > it has the hole that the template could call @include-template and
>> > maybe find itself and go into a infinite loop, so it's not totally
>> > "secure" unless you use a sandbox.
>> >
>> > Jay
>> >
>> > On Wed, Jun 5, 2013 at 1:53 PM, Joe Gibbs Politz <joe at cs.brown.edu>
>> wrote:
>> >> I'm writing a web server in a #lang that doesn't support macros or
>> >> syntactic abstraction.  I would like to be able to use some sort of
>> >> templating dynamically with bindings given by values, e.g.
>> >>
>> >> template.render("page-with-hole-for-username.html", { username: "Joe"
>> })
>> >>
>> >> The FAQ (
>> http://docs.racket-lang.org/web-server/faq.html#(part._.How_do_.I_use_templates__dynamically__)
>> )
>> >> in the documentation for templates ends with this pithy
>> >> recommendation:
>> >>
>> >> "If you insist on dynamicism, there is always eval."
>> >>
>> >> I assume this isn't intended seriously, and instead to discourage what
>> >> I'm asking about, but I'm unfortunately not seeing another way to
>> >> write my program.  The code at the end of this message seems like the
>> >> best I can do while being relatively safe, but also like a dubious
>> >> inclusion on a web server given the eval.
>> >>
>> >> Is this the best I can hope for?  Is there another collection I should
>> >> be looking into?  Any other recommendations?
>> >>
>> >> Thanks!
>> >> Joe P.
>> >>
>> >>
>> >> #lang racket/base
>> >>
>> >> (require
>> >>   web-server/templates)
>> >>
>> >> (define (render-template filename dict)
>> >>   (define namespace-for-template (make-empty-namespace))
>> >>   (namespace-attach-module (current-namespace) 'web-server/templates
>> >> namespace-for-template)
>> >>   (hash-map dict
>> >>     (lambda (key value)
>> >>       (define name-of-identifier (string->symbol key))
>> >>       (namespace-set-variable-value!
>> >>         name-of-identifier
>> >>         value
>> >>         #f
>> >>         namespace-for-template)))
>> >>   (parameterize [(current-namespace namespace-for-template)]
>> >>     (namespace-require 'web-server/templates))
>> >>   (define to-eval #`(include-template #,(datum->syntax
>> >> #'render-template filename)))
>> >>   (eval to-eval namespace-for-template))
>> >> ____________________
>> >>   Racket Users list:
>> >>   http://lists.racket-lang.org/users
>> >
>> >
>> >
>> > --
>> > Jay McCarthy <jay at cs.byu.edu>
>> > Assistant Professor / Brigham Young University
>> > http://faculty.cs.byu.edu/~jay
>> >
>> > "The glory of God is Intelligence" - D&C 93
>> > ____________________
>> >   Racket Users list:
>> >   http://lists.racket-lang.org/users
>> ____________________
>>   Racket Users list:
>>   http://lists.racket-lang.org/users
>>
>
>
> ____________________
>   Racket Users list:
>   http://lists.racket-lang.org/users
>
>
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