[ZPT] RFC: TALES adapters and TAL/Tales variable namespaces

[Evan Simpson]

Jim Fulton wrote:
> I've posted two proposals:
> 
>   http://dev.zope.org/Zope3/TALESPathExpressionAdapters
> 
> Proposes a mechanism for easily using adapters in TALES expressions.

I'm not at all clear on how the proposed mechanism is superior to the 
implementation of path segment prefixes that exists in Zope 2.  This 
differs from the namespace proposal that you cite, in that the object 
named on the left of the colon is not a namespace or adapter.  It is 
simply a registered name that is associated with code that interprets 
the text to the right of the colon.  This allows constuctions such as 
"a/sequence/index:2" (a.sequence[2]), "a/bag/var:x/call:" (a.bag[x]()), 
and "an/object/adapt:foo.bar" (foo.bar(an.object)).

>   http://dev.zope.org/Zope3/ZPTVariableNamespaces
> 
> proposes a mechanism for qualifying names defined in TAL and used in
> TALES expressions.

This would of course conflict with prefixes as currently defined, and 
seems weakly motivated.  I can imagine getting a similar effect with a 
more consistent syntax by allowing tal:define="x/y foo" when x supports 
an ITALESNamespace interface.  The path "x/y/z" then does exactly what 
the user would expect.  A namespace "x" can be created without any new 
TAL syntax by providing a built-in constructor, as in tal:define="x 
namespace", that creates an empty dictionary-like object with support 
with ITALESNamespace.

Cheers,

Evan @ 4-am