TSa Thomas.Sandlass-at-barco.com |Perl 6| wrote:
sub graph ( &func where {.does: Continuous}, Num $from, Num $to )
{...}
sub square ( Num $x --> Num ) does Continuous { return $x * $x }
graph( &square, -10.0, 10.0 ); # type correct
The odd thing to me is that graph cannot be defined as
sub graph ( Continuous &func, Num $from, Num $to ) {...}
or is that the same? Then how do I get what I want? I think S06 says
that the above means that &func returns a Continuous value as in
sub foo ( Int &func:(Int) --> Int) { return func(17); }
sub double (Int $x --> Int) { return 2 * $x; }
say foo( &double ); # prints 34
In C++, the same problem:
void foo (Continuous (*f)()) // f is a function that takes nothing
and returns Continuous
void foo (Continuous *f) // f is a Continuous
In Perl 6, within a signature
sub foo ( &f:(Int-->Int) )
sub foo ( Continuous &f )
The latter says that &f is of type Continuous, not that the return type
is Continuous. That is what you want, right? The latter would be
sub bar ( &f:(Int -->Continuous) )
A closure parameter block follows the block name. The normal annotation
type before the name works in the usual manner, typing the whole
object. It's not like the C++ syntax at all.
--John
