On 09/14/2011 12:06 AM, Rainer Schuetze wrote:
On 14.09.2011 00:04, Walter Bright wrote:
Don, just so you know, I've been thinking for a while about
transitioning from doing the semantic pass in order to doing it
completely "on demand". In other words, try to semantic a
declaration. In the process, any declarations it depends on are
semantic'd if not already, recursively.
I've been trying something similar for Visual D in its yet to
integrate semantic analysis for intellisense. Still, static if and
mixins get in the way of complete "on demand" handling. When a symbol
is searched in a scope (e.g. a module, class, struct), some
preparational work has to be done before the member list can be searched:
1. all "simple" non-scoping members are expanded (version/debug
conditions, attributed declaration blocks). the branch inserted to the
scopes' member list is also searched for "simple" non-scoping members
(this step could also be done non-lazily, but doing it lazily slightly
changes the interaction of version statements and conditionals with
"static if" conditionals - good or bad, I don't know)
2. "complex" non-scoping members are expanded in lexical order (static
if, mixins). When inserting the expanded branch into the scopes member
list, the expansion restarts at 1.
This works out better than the current dmd implementation, e.g. when
forward referencing symbols in a mixin. There are still situations
that depend on interpretation order, but that is to be expected when
"static if" is used.
Every time I've puzzled over the problem, the solution I've gravitated
to is to have the symbol table logic result be tri-state: symbol-found,
no-symbol, unknown/incomplete (for when a lookup includes an unprocessed
scope). From there, you greedily evaluate all symbol that you can and
proceed with whatever processing can be done, bailing when an
"incomplete" results is found and keeping a list of where to come back
and try again later. The only question then is how to handle the case
where you dead lock. I suspect that if you make that illegal, a lot of
legacy code will break. I'm going to guess we will want to have a small
set of well thought out deadlock escape rules.
It might be good to define the lookup mechanism, so it would be
possible to determine whether a failing forward reference is beyond
expected behaviour rather than a compiler-implementation detail.
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