[ZPT] TALES: Path expressions?

[Alan Kennedy]

Greetings,

I am looking closely at TALES, and wondering why it 
contains path expressions?

It seems to me that having an Expression Syntax that did 
not contain path expressions would be much simpler to 
implement. The grammar would be much simpler and quicker to 
compile and interpret, for one thing.

Take for example, the expression inside a tal:repeat 
statement, which has two parts: the former part is a loop 
variable name and the latter part is an expression which 
results in a sequence when evaluated.

It seems to me that the latter part could simply be a 
python expression, which could simply be passed to the 
python 'eval()' function.

So dealing with a tal:repeat expression would simply 
involve splitting it in two, using whitespace as a 
delimiter, giving a name and a python expression. 

This would eliminate the need for parsing the TALES 
expression using regular expressions.

The python expression would then be passed to the "eval()" 
function, and evaluated inside a suitable python namespace.

I think (I'm not yet certain :-) the same holds true for 
the expressions used in all TAL commands.

tal:condition  - Either true or false python expression
tal:replace    - Python string expression
tal:content    - Python string expression
tal:attributes - See below
tal:omit-tag   - Either true or false python expression

a tal:attributes expression could be split into a series of 
name/expression pairs separated by ';' (';;' excepted of 
course).

I'm not trying to get TALES changed here. I'm just 
investigating doing my own TAL/TALES/METAL implementation 
suitable for use in Java/Jython servlets.

Why? Because ZPT is way cool, that's why!

Grateful to receive any pointers or opinions.

Cheers,

Alan.



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