[Zope] organizational questions

[Jim Fulton]

Paul Everitt wrote:
> 
> Martin Dougiamas wrote:
> > The funny thing is that
> >
> >   <!--#var "myapp.myfunction"-->
> >
> > correctly returns all the raw content of the DTML document,
> > so it *can* find it OK.
> >
> > Any ideas?
> 
> The quotes switch DTML into "expr" (expression) mode.  Outside of
> expressions, DTML is limited to very safe operations.  Getting
> attributes (the dot) is an operation that requires the security
> machinery to get involved, to make sure that you have permission.

Dot notation and expressions have nothing to do with security.

The difference is really about language.

  <!--#var foo-->

is a short-hand for 

  <!--#var name="foo"-->

while:

  <!--#var "foo"--> 

is a short-hand for:

  <!--#var expr="foo"-->

The argument to the name attribute is a DTML name, where
there is no restrictions on characters in the name 
and no special interpretation has been given to any
characters.  Further, when a name is looked up, and
the value is a document template or a callable object that
requires no arguments, it is called.

The argument for the expr attribute is a Python
expression.  The semantics for this value are defined
by the Python language and any special objects, like '_'.
In Python, objects are not called unless you supply
the call operator.  If you have a function, foo, the
expression "foo" returns the function, not the result
of calling the function.
 
> I agree that this inconsistency

I don't agree that this is an inconsistency.

An expression attribute always takes a Python
expression with Python expression semantics. 
A name attribute always takes a DTML name, with
DTML name lookup semantics.

> is confusing,

The confusomg part is that:

  <!--#var "foo"-->

looks so much like:

  <!--#var foo-->

Perhaps this shorthand notation (which was added
by popular demand) should be discouraged.

> as are things like
> sequence-item outside an expression and sequence_item inside an
> expression. 

"sequence_item" is not a special spelling for "sequence-item".

When used as a name, you say:

  <!--#var sequence-item-->

This is consistent with rules for DTML names.
The dash was used in this (and similar names)
to avoid conflicts with other names.

In expressions, you say:

  <!--#var "_['sequence-item']-->

Because "sequence-item" is not a legal Python name, 
we have to quote the name and do an explicit lookup from
the namespace object, '_'.  This seems very consistent to me.

> Perhaps if we do a major overhaul of DTML (e.g. changing it
> to an XML-ish syntax) we'll look for ways to make it more consistent.

I don't expect adding an XML-compliant format to DTML to cause
a major overhaul.  XML *is* far more explicit that current DTML
(and HTML) formats, so confusing short-hands will not be an option.
You will *have* to name the attributes explicitly.  Of course, 
people will still have to know the semantics for the various
attributes.

Jim

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