or this for positional parameters:

 validate_pos( @_, { type => SCALAR }, { type => ARRAYREF, optional => 1 } );
By default, parameters are assumed to be mandatory unless specified as optional.

##</code><code>##

#!/usr/bin/perl

#use strict;
use warnings;
use Params::Validate;

sub func1 {
	validate_pos( @_, { type => SCALAR} );

	print "hi fluffy\n";
}

func1("test");


##</code><code>##

Argument "SCALAR" isn't numeric in subroutine entry at ./a.pl line 8.
Parameter #1 ("test") to main::func1 was a 'scalar', which is not one of the allowed types: 
 at ./a.pl line 8
	main::func1(3) called at ./a.pl line 13