On Nov 17, 2009, at 2:57 AM, David Schmitt wrote:
Markus Roberts wrote:
It'd be great if you could abolish the parse-order dependency
altogether. As long as all variable/value reference chains form a
directed acylcic graph, they could be evaluated after finishing the
parse, regardless of order.
Could you elaborate on this?
The best I can think of is to do something like store a reference
to a variable and a scope during compilation, and then only deref
them when we're converting the catalog at the last minute.
That's basically it; the more general form is to use the futures (aka
promises) mentioned earlier in this thread. Instead of stashing a
(variable,scope) reference you create a placeholder object which
either
holds a value or the tree to evaluate to get that value.
After parsing is done (and the full forest is known) you fulfill all
futures that contain values, than iteratively fulfill all futures
which
only depend on fulfilled values. If it's a DAG, you're set. If
there
are loops, you'll be left with unfulfillable nodes and it's an error.
Yes. You make it sound so easy :-) I'm worried because this also
affects
function evaluation including include() and template(), both of which
might alter the manifest significantly, including autoloading new
stuff.
Not saying it can't be done, just that it is really a sweeping change
through many parts of the language.
I think this is somewhat of a concern, but I really do think that the
vast majority of cases will just work correctly more easily.
As Markus has mentioned earlier, I think very people are intentionally
using the existing buggy behaviour, so I don't really think it'll be a
problem.
--
I don't deserve this award, but I have arthritis and I don't deserve
that either. -- Jack Benny
-
Luke Kanies | http://reductivelabs.com | http://madstop.com
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