Blocks from strings

Nevin Pratt nevin at
Thu Jan 1 19:04:22 UTC 2004

Avi Bryant wrote:

> <snip>
> Although I'm very interested in macros and how or why they might be 
> integrated with Smalltalk, I've lost the thread of how this relates 
> back to the original posting.  Nevin, can you tell us what you were 
> actually trying to do by converting strings into blocks, so that I can 
> try to understand if macros would help?
> Avi
Yes, but it will take me a bit to explain it.  It is in conjunction with 
Seaside and search engine spiders.

First, if you remember a thread on the Seaside list from back in March 
2003, titled "[Seaside] anchors behaving like buttons?", you'll remember 
that I have code that allows the web user to invoke an arbitrary method 
on a component.  For example...

...will invoke the #viewcart method of the 'index' component, which 
would then take them to the shopping cart.

This scheme allows me to email somebody a URL that will allow them to 
enter the Seaside app at a relatively arbitrary point/page.  Once they 
enter the app, though, it is thereafter tracked like any normal Seaside 
app, and thereafter has the normal Seaside URL's.

How the above scheme works is that I actually only have one component 
(the "index", or home page component), but it has an instance variable 
that can have different components assigned to it to control the actual 
contents of the current webpage being displayed.  The "index" component 
I also refer to as the "top" component.

I also have a subclass of WASession (which I call BBSession), that 
provides a method for accessing the "top" component (via #topComponent).

Thus far, I have the interesting situation where I can now call any 
arbitrary method of the top component from anywhere in the app.  For 
example, suppose the app is on a page where the user clicks a button 
which invokes a method of that page, and within that method I have "self 
session topComponent viewCart".  The result is that they can click the 
button and have the shopping cart shown to them.  Yes, I know there are 
many other alternate ways to accomplish this same thing, but bear with me...

Next, I have added "WARenderer>>imageWithSource: srcUrl action: 
actionBlock ", per an earlier message of yours a few months ago.  I have 
also added "WARenderer>>imageWithSource: srcUrl link: aLink" per your 
earlier message.  I commonly have code like this:

   html imageWithSource: aShoppingCartJPEGLink
           action: [self session topComponent viewcart]

(of course, the "viewcart" message in the block above might be some 
other method that the top component understands-- I am just using 
#viewcart as an example).

Now, the idea is, if the WARenderer knows it is *not* servicing a 
spider, I want it to invoke #imageWithSource:action:, as shown above.  
But if it is servicing a spider, I want it to automatically do this instead:

   html imageWithSource: aShoppingCartJPEGLink
            link: ""

This approach results in spiders automatically seeing a static site with 
static URL's, and everybody else seeing a normal Seaside app.  A way to 
do that would be to create a method somewhat like this:

   html imageWithSource: aShoppingCartJPEGLink
            method: #viewcart

...and then let the #imageWithSource:method: code either construct a 
static URL or a block, and then it calls one of the earlier two methods.

Then my code would always use #imageWithSource:method:.  All spiders 
would then automatically see what looks to the spider like a static site 
with normal URL's, and everybody else would automatically see a normal 
Seaside site.  Well, almost...

To finish the job of spiders seeing static pages, I have a page cache 
similar to what Cees did with Janus.  So, for example, if my Seaside app 
sees this URL coming in:

and if the requester is a spider, it checks the page cache for the 
#viewcart page, and if it is present, it feeds it back to the spider.  
If it is not present, it generates it, caches it, and feeds it to the 

But for everybody else, it is just a normal Seaside app.

Janus comes pretty close to this identical thing, too.


Nevin Pratt
Bountiful Baby
(801) 992-3137

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