package V;

use Carp;

sub is_array_of_scalar
{
    my $arg = shift;
    if (!defined $arg)
    {
        warn "Undefined value! Expected reference to an array of scala
+rs!";
        return 0
    }
    
    if(ref $arg ne "ARRAY")
    {
        warn "Expected ARRAY reference, found " . ref($arg) . ".";
        return 0;
    }
    
    for my $index(0..$#$arg)
    {
        if(!defined($arg[$index]))
        {
            warn "Undefined value found on position $index.";
            return 0
        }
        if(ref($arg[$index]) ne "")
        {
            warn "Scalar expected, reference found on position $index.
+"; # (1)
            return 0
        }    
    }
    return 1;
}

sub is_array_of_array_of_scalar
{
    my $arg = shift;
    if (!defined $arg)
    {
        warn "Undefined value! Expected reference to an array of scala
+rs!";
        return 0
    }
    
    if(ref $arg ne "ARRAY")
    {
        warn "Expected ARRAY reference, found " . ref($arg) . ".";
        return 0;
    }
    
    for my $index(0..$#$arg)
    {
        if(!is_array_of_scalar($arg[$index]))
        {
            warn "Wrong value(s) in row $index.";
            return 0
        }
    }
    return 1;
}

"true value at the very end";
[download]

And here is the problem: Is it possible to say precisely, i.e. that some wrong value is in row 5, column 3? Above code won't do it. Function is_array_of_scalar doesn't know, which column it is checking. Is the Sub::Contract module proper to perform such checks or rather to do simpler (and not nested) ones only?

Update: $_ corrected in loop, thanks JadeNB