HaloO,
I'm very puzzled about what is meant by type and class in Perl6.
In the sort ruling
http://groups-beta.google.com/group/perl.perl6.language/msg/1eb1ed4608f5604d
we saw a system of types that allow to nicely dispatch into different version
of &sort. OTOH every class or role name can serve the same purpose.
Built-in value types like Str and Int seem to be auto-coercive instead of
MMD, in particular when playing together with dedicated operators like
binary '+' versus '~'. And how does all this combine with the notion of context?
I guess that basically influences method selection.
Take the following example:
# part 1
class Cyclic[uint $base] is Int
{
multi *postfix:<++> ( Cyclic[uint $base] $i )
returns Cyclic[uint $base]
{
return (($i as uint) + 1) % $base;
}
multi *infix:<+> ( Cyclic[uint $base] $x, Int $y )
returns Cyclic[uint $base]
is symmetric
{
return abs( ($x as uint) + $y ) % $base;
}
...
}
# part 2
sub foo( Int $begin, Int $end )
{
while $begin < $end
{
...
$begin++; # assumes Int axiom: $i + 1 > $i
}
}
#part 3
my Cyclic[8] $cyclic = 3;
foo( $cyclic, 10 ); # never returns?
Does the design intent to catch such "surprises"?
E.g. by giving an error at the line 'class Cyclic[uint $base] is Int'?
But how should the violation of an abstract property of Int be checked
by the compiler?
Can this just be remedied by source code review and human reasoning?
Is there a chance for designers of classes like Int to prevent method
overriding which violates some constraints?
If yes, how are these constraints specified?
my Cyclic[7] enum DayOfWeek <Mon Tue Wed Thu Fri Sat Sun>;
Another thing: does the above definition work together with enums?
my Cyclic[7] enum DayOfWeek <Mon Tue Wed Thu Fri Sat Sun>;
my DayOfWeek $day = Fri;
say "Fri = {$day}, Sat = {$day + 1}, Sun = {$day + 2}, Mon = {$day + 3}";
Does that say "Fri = Fri, Sat = Sat, Sun = Sun, Mon = Mon"?
Regards,
--
TSa (Thomas Sandlaß)
