MetamodelX-Protocol.pm6

unit class MetamodelX::Protocol is Metamodel::SubsetHOW is Metamodel::ClassHOW;

method new_type(:$name!) {
    my $type;
    $type := callwith :$name, :refinee(Any), :refinement{ .^methods>>.name.any eq $type.^methods>>.name.all }
    $type
}

method compose(\type) {
    die "A Protocol must have only stub methods!" if type.^methods.grep: not *.yada;
}

Protocol.pm6

my package EXPORTHOW {
    package DECLARE {
        use MetamodelX::Protocol;
        constant protocol = MetamodelX::Protocol;
    }
}

test

MacBook-Pro-de-Fernando:Protocol fernando$ perl6 -Ilib -MProtocol -e '


protocol Bla { method bla { ... } }               

my Bla $a = 42                         


'
Type check failed in assignment to $a; expected Bla but got Int (42)
  in block <unit> at -e line 6

MacBook-Pro-de-Fernando:Protocol fernando$ perl6 -Ilib -MProtocol -e '


protocol Bla { method bla { ... } }

my Bla $a = class { method bla {} }.new


'
MacBook-Pro-de-Fernando:Protocol fernando$ perl6 -Ilib -MProtocol -e '


protocol Bla { method bla { ... }; method ble {} }

my Bla $a = class { method bla {} }.new


'
===SORRY!=== Error while compiling -e
A Protocol must have only stub methods!
at -e:4