# New Ticket Created by "brian d foy"
# Please include the string: [perl #130634]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/Ticket/Display.html?id=130634 >
I posted this to Stackoverflow without anyone pointing out the error
of my ways, so I think this is probably a bug.
http://stackoverflow.com/q/41791602/2766176
Imagine a series of complex grammars represented as roles, although
this simple example is enough to show the conflict:
role Alpha {
token alpha { :i <[A..Z]> }
}
role Digit {
token digit { <[0..9]> }
}
role Either
does Alpha
does Digit {
token either { <alpha> | <digit> }
}
grammar Thingy
does Either
does Alpha
{
token TOP { <alpha> <either>* }
}
my $match = Thingy.parse( '1a3' );
dd $match;
This doesn't work because Perl 6 doesn't untangle the relationships to
figure out that the conflict is actually the same thing from the same
source:
Method 'alpha' must be resolved by class Thingy because it exists
in multiple roles
But, reading [S14](https://design.perl6.org/S14.html), I see:
A role may not inherit from a class, but may be composed of other
roles. However, this "crony" composition is not evaluated until
class composition time. This means that if two roles bring in the
same crony, there's no conflict--it's just as if the class pulled
in the crony role itself and the respective roles didn't. A role
may never conflict with itself regardless of its method of
incorporation.
I read that to mean that the roles are applied as late as possible, so
the class `Thingy` would be able to disentangle that `Alpha` is
included in two different parts. I figured this would work something
like creating a list of all of the roles that would make up the final
class, then applying that list only to the final class. That way,
something like `Either` would mix-in only the things it defined and
would rely on the later composition to bring in `Alpha`.
I ran across this when I was trying to implement grammars for various
(IETF) RFCs. Many of them reference the grammars from other RFCs,
which makes it impossible for Perl 6 to resolve inheritance by C3. So,
I figured that roles would disconnect the relationships. Apparently it
doesn't.
