Re: Syntax for specifying role parameters

[TSa (Thomas Sandlaß)]

HaloO Ingo,
you wrote:
I wondered if it would be useful/good/nice if the syntax for 
specifying role parameters would be the same as the standard 
subroutine signature syntax (minus the colon, which 
separates the parameters which do account to the long name 
of the role from the ones which don't). 
Hmm, first you exclude the colon, then you use it the example??
I for my part hope that roles are---among other things---parametric
types. This means that in the brackets one should find type variables,
value variables and possibly recursive constraints. E.g.
role Ordered[::Type does Ordered[Type]]
{
   multi method infix:{'<='} ( T $x, T $y ) returns bit
   {
     ...
   }
   multi method infix:{'>'} ( T $x, T $y ) returns bit
   {
      return not $x <= $y;
   }
}
class Num does Ordered[Num] { ... }
class Str does Ordered[Str] { ... }
expresses that instances of these classes can be only ordered amongst
themselfs and their subtypes. E.g. with
class Int is Num {...}
the following is allowed:
my Int $i = 3;
my Num $n = 3.14;
if $i < $n {...}
but
my Str $s = "foo";
if $s < $n {...} # type error
This type error can be alleviated with implementing
class Scalar does Ordered[Num|Str] {...}
Actually the class might be needed only as namespace containing
the implementation of &infix:{'<='}:(Num|Str,Num|Str: --> bit).
OTOH it could implement caching of conversion results or some such.
--
$TSa =:= all( none( @Larry ), one( @p6l ))