Re: Interesting containers problem.

[Shark8 <onewingedshark@gmail.com>]

On Friday, April 17, 2015 at 2:45:07 PM UTC-6, Randy Brukardt wrote:
> "Peter Chapin" wrote in message 
> > On Fri, 17 Apr 2015, Shark8 wrote:
> >
> >> Ok, so let's say we have a type for Identifiers:
> >
> > [snip]
> >
> >> And that's all well and good; however, there is one limitation here that 
> >> is revealed when you need nesting scopes -- there is, apparently, no way 
> >> to define an Element_Type to feed to Indefinite_Ordered_Maps which is an 
> >> instance of Indefinite_Ordered_Maps.Maps or an instance of Variable_Data 
> >> (by way of a variant record; even one which is forward declared).
> >>
> >> What would be the proper way to handle this sort of situation?
> >
> > Perhaps using access types directly? What if the Element_Type of the Map 
> > is an access type that points at an incomplete type, where the completion 
> > follows the instantiation of the Maps generic?
> 
> Bleech. Using access types means that you have to handle the memory 
> management, defeating the #1 value of the containers. Typically, you can use 
> cursors as references between related containers, and I think that is 
> preferable.
> 
> To answer the OPs question, a symbol table for a language like Ada is a 
> multiway tree. That's one reason I pushed for a multiway tree container in 
> Ada, as it seems to be a common data structure. So I'd use a multiway tree 
> as the basic structure. Identifier lookups would use a map (as you noted), 
> and the things that each identifier points at is a list of the symbol table 
> nodes associated with that identifier. So the lookup data is a map of lists 
> of tree cursors. Hiding then is dealt with by checking the relationship of 
> the nodes, or possibly by maintaining a visibility flag in the symbol 
> records.

Ok, I see how a multiway tree maps the structure of nesting scopes... but maybe I'm being obtuse here, because I don't see how to access them because there's no 'key' type. (Maybe a bit of code would help here.)

The way I see it is that the structure we want is essentially a map where an identifier is keyed to one of two things: (a) a variable_data, or (b) another scope-map. -- This would allow/model nesting.