Walter D?rwald wrote:
> Paul Moore wrote:
>
> > Guido van Rossum <guido@python.org> writes:
> >
> >
> >>I'm now wondering if there aren't really only two interesting cases,
> >>none of which require saving the thunk and calling it later:
> >>
> >>- synchronized-like, where the block should connect to its environment
> >>
> >>- property-like, where the block should introduce a new scope, and the
> >> caller should be able to inspect or control that scope's namespace
> >
> >
> > I certainly haven't seen any use cases other than these two. In fact,
> > pretty much all of the cases I am aware of are synchronised-like,
> > which I've been referring to as acquire/release. The only
> > property-like cases I'm aware of are properties themselves.
>
> A use case I can think of is some kind of XML DOM API (Ruby does
> something like that with it's cgi module, where node content is
> created inside a block).
>
> With the current Python you can have something like that:
>
> node = html.table(
> html.tr(
> html.th("foo"),
> html.td("bar")
> ),
> html.tr(
> html.th("spam"),
> html.td("eggs")
> ),
> border=0,
> cellpadding=3
> )
>
> i.e. element classes that use * and ** arguments in their constructor
> to collect content and attribute nodes.
>
> The problem with this approach is, that the attributes are maximally
> separated from their element and that control structures (like if) are
> not possible inside the constructor.
>
> With blocks ifs and fors could look like this:
>
> node = html.table(border=0, cellpadding=0):
> html.tr():
> html.th(): "foo"
> html.td(): "bar"
> if cond:
> html.tr():
> html.th(): "spam"
> html.td(): "eggs"
> for i in xrange(10):
> html.tr():
> html.th(): i
> html.td(): i*i
you probably missed my other posting where i actually went
one step further and implemented this via <...> syntax.
Actually i tried *exactly* the syntax you propose here first but
i think it's *hopelessly* ambigous with the Python grammar.
You simple have no way to know which construct you are in
until you read the ':'. Until then you could be in a
normal expression. The 'class', 'def', 'if', 'while' etc.
keywords disambiguate this right at the beginning.
Without a much deeper parser look-ahead this can't
be done, i am afraid.
holger
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