Hmm, yeah, sounds like an interesting use case.

You might not even need Type::Params. The Tuple type from Types::Standard might be sufficient. Something like:

use Types::Standard -types;

my $row_type  = Tuple[ Str, Str, Int, Bool, Optional[Num] ];
my $row_check = $row_type->compiled_check;

while (my $row = $csv->get_line($fh)) {
   $row_check->($row) or die $row_type->get_message($row);
}
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If you've got Type::Tiny::XS installed, and your row specification is simple enough, you might even find that $row_type was able to generate $row_check as an xsub. (Off the top of my head, I don't think the one in the example is, as I don't think Optional is implemented in XS yet.)

If you end up with something cool, I would love to see and maybe incorporate it or something like it into the documentation.