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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
Date: Wed, 14 Dec 2016 16:22:10 -0600
Organization: JSA Research & Innovation
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Date: 2016-12-14T16:22:10-06:00
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"Shark8" <onewingedshark@gmail.com> wrote in message 
news:fe2588fe-874d-4826-95a1-02cf5bc4c1e2@googlegroups.com...
On Tuesday, December 13, 2016 at 4:19:32 PM UTC-7, Randy Brukardt wrote:
>> Ada visibility and resolution sadly take all of the fun out
>> of compiler construction. :-)
>
>That's one of the things that I'd like the IR to do; assuming we have
>a DEPENDENCY node (or attribute in the root-node) then it should
>be possible to enforce that property so that your problem of "Tags
>being visible w/o Ada.Tags being WITH'ed". (This is to say, if we
>have the dependencies listed, say as a separate Dependency_Type
>then every entity in the source should have a 'handle' pointing to an
>item in the DEPENDENCY attribute xor to a local construct.)
>
>You could then have a "visibility node" (USE) be a sub-tree that has
> its own handles into the DEPENDENCY attribute and for represents
> the visibility right in the tree-structure.

It's never really about implementing something that gets 95% of 
visibility/resolution right. It's about implementing something that gets 
100% of visibility/resolution right. And that last 5% is always a beast, no 
matter how or where you start. (There are just too many details for anyone 
to get the initial version right.)

The great thing about the ACATS is that it provides a large number of vetted 
tests for Ada, so the expectations are well-defined. Getting a compiler to 
handle all of those tests, however, turns into a slog. Typically, fixing one 
issue in a test or tests just exposes another issue in the tests. It's this 
error fixing slog (plus, of course, customers sending new issues in) that 
takes a lot of the fun out of compiler construction.

                                      Randy.