use strict;
use warnings;
use Type::Tiny;

my $Is_A_Duck = "Type::Tiny"->new(
   name       => "DuckCheck",
   constraint => sub { $_->{speech} eq "QUACK" and $_->{walk} eq "WADD
+LE" },
   message    => sub { "$_->{name} is not a duck!" },
);

my @candidates = (
          {name=>"Daffy",  speech=> "QUACK",   walk=> "WADDLE"},
      {name=>"Daisy",  speech=> "QUACK",   walk=> "WADDLE"},
      {name=>"Donald", speech=> "Bizarre", walk=> "WADDLE"},
      {name=>"Platypus",speech=>"QUACK",   walk=> "SHUFFLE"},
      );

for my $c (@candidates){
  
  if (my $msg= $Is_A_Duck->validate($c)){
     print "$_\n" for @{ $Is_A_Duck->validate_explain($c, $c->{name}) 
+};
  }else{
     print "$c->{name} is a Duck!\n";
  }
}
print "Exiting...\n";
[download]

>perl typetest.pl
Daffy is a Duck!
Daisy is a Duck!
Donald is not a duck! (in Donald)
"DuckCheck" is defined as: sub { $_->{'walk'} eq 'WADDLE' if $_->{'spe
+ech'} eq 'QUACK'; }
Platypus is not a duck! (in Platypus)
"DuckCheck" is defined as: sub { $_->{'walk'} eq 'WADDLE' if $_->{'spe
+ech'} eq 'QUACK'; }
Exiting...
[download]