[ZPT] v2 of Path Prefixes in CVS

[Evan Simpson]

I've just checked in a major revamp of evan-pathprefix-branch, which 
adds some tests (that all pass!), and the ability to define prefixes 
other than the builtins.

After a private conversation with Shane, I've settled on the following 
syntax for defining prefixes:

tal:define="prefix {name} {pexpr}"

That is, I've added a 'prefix' scope qualifier, similar to the existing 
'local' and 'global'.  Unlike 'local' and 'global', 'prefix' causes 
tal:define to operate on the prefix namespace, and to use a restricted 
set of prefix expression types rather than the normal range of TALES 
expression types.  This means that only two expression types are 
currently available:

tal:define="prefix i builtin:item"
tal:define="prefix n ext:PageTemplates.NumericConversions"

The 'builtin' type allows you to define aliases for builtin prefix 
types, while 'ext' provides access to additional types defined by 
trusted filesystem code.  The second example defines 'n' as the sample 
prefix defined in Products/PageTemplates/ExtSample.py.

In the future, I'd like to allow Path Expressions as a prefix expression 
type, with the purpose of supporting libraries of simple functions 
within ZODB Folders, like so:

<div tal:define="prefix my here/zptlib"
      tal:replace="foo/bar/my:complexscript">

...which would be roughly equivalent to 
"python:here.zptlib.complexscript(foo.bar)".  For now, I'm going to wait 
for reactions to the current implementation.

Cheers,

Evan @ 4-am