use Types::Standard qw( Int );

if ( not Int->check($var) ) {
   die "It's supposed to be an integer!\n";
}

##</code><code>##

use Types::Standard qw( Int );

Int->assert_valid($var);

##</code><code>##

use Types::Standard qw( Object Num );
sub transfer_money {
   my $from_account = Object->assert_return( shift );
   my $to_account   = Object->assert_return( shift );
   my $amount       = Num->assert_return( shift );
   
   ...;
}

##</code><code>##

use feature qw( state );  # enable the `state` feature from Perl 5.10+
use Types::Standard qw( Object Num );
use Type::Params qw( compile );
sub transfer_money {
   state $check = compile( Object, Object, Num );
   my ($from_account, $to_account, $amount) = $check->(@_);
   
   ...;
}

##</code><code>##

perl -MTypes::Standard=-all -le'print Int->inline_check(q($val))'