Eiffel like reports for Design by Contract contracts

[Richard (Rikki) Andrew Cattermole]

Some notes:

1. The ``Identifier :`` syntax is used for labels within a statement list.

2. The feature in question you are asking about is assertion clauses. D 
does not have this. 
https://www.eiffel.org/doc/solutions/Design_by_Contract_and_Assertions 
https://www.eiffel.org/doc/eiffel/Eiffel_programming_language_syntax#Assertions

3. Eiffel requires assertion clauses in the in condition (with the tag), 
but not in the out contract.

4. Instead of introducing new syntax specific to this task, I would 
suggest introduce having UDA's on statements. ``@AssertClause("more than 
zero") { ... }``

5. We support the class inheritance behavior of contracts. Right now 
this is butting heads against our exception handling behavior and is 
preventing us from making certain changes (that are not necessarily better).

6. The current behavior of contracts, when they get compiled in and 
executed isn't what is expected currently. This needs fixing.

7. Its unlikely the behavior of interfaces wrt. method behavior (such as 
no default body) is going to align with what you expect. Again, I want 
to resolve this but it isn't on my short term list.

If you come up with a concrete set of changes, then you would post it on 
the ideas forum as a starting point.

Classes in general are on my list of things that need work, but my 
attention is elsewhere and that lot of work is waiting on other work 
done by other people to both start and finish. Specifically related to 
TypeInfo removal.