[racket] Dynamic Templates?

On Mon, Oct 14, 2013 at 6:20 PM, Matthew Butterick
<mb.list.acct at gmail.com>wrote:

> I reviewed the docs about the module registry<http://docs.racket-lang.org/reference/syntax-model.html?q=module%20registry#%28tech._module._registry%29>,
> but just so I understand the principle behind this technique —
>
> When you call (namespace-attach-module orig-ns 'module-name), what you're
> saying to the new namespace is "if you need module-name, use the one that's
> already been imported into orig-ns". Is this right?
>
>
Right.


> And if so, do I improve performance by adding another (namespace-attach-module
> ...) declaration for each module that will never need to be reloaded in the
> eval namespace?
>
>
Right.


> BTW I tried your suggestion on the quasicode, and it was indeed faster.
> However, when I moved it back into the real code, there was no improvement
> — in fact, the real code became slower. Running the real code through
> profile suggests that most of the time is being spent traversing the
> imports (which is consistent with my observation that the complexity of the
> page itself doesn't count for much). So whatever I can do to avoid
> re-importing modules will probably be the winning technique.
>
>
Which module's imports, do you know?

Robby


> Thanks.
>
>
> On Mon, Oct 14, 2013 at 11:22 AM, Robby Findler <
> robby at eecs.northwestern.edu> wrote:
>
>> 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:
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>>>>
>>>
>>>
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>>
>
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