sub calc
{
	## We operate in package main for this subroutine so the local
	## object and row number can be available to the caller's $Sub.

	## The following local vars will be available to $Sub
	## $_r ($main::_r) -- the row number in the entire table
	## $_s ($main::_s) -- the row number in selection or $Recs
	## $_t ($main::_t) -- the table object itself

	package main;			
	use vars qw($_r  $_s  $_t);
	local      ($_r, $_s, $_t);

	$_t							= shift;	
	my ($Sub, $Recs, $Fields)	= @_;

	## These optional params default to current field and current sel

	$Recs						||= $_t->selection();
	$Fields						||= $_t->fieldlist_all();
	
	## Local copy of symbol table.  Didn't seem to help.  Odd.
	## local %main::;	
	
	## We'll build a column of return values from $Sub if needed.
	my $WantVals				= defined(wantarray);
	my $Vals					= $_t->col_empty() if $WantVals;

	## Call col() on each field in list to make sure it exists.
	foreach (@$Fields) {$_t->col($_)};

	foreach $_s (0..$#$Recs)
	{
		$_r = $Recs->[$_s];

		## Bind $FieldName1, $FieldName2, (etc. for each field name in
		## $Fields) point to address of the current value for that
		## field in this record.

		no strict 'refs';
		foreach my $F (@$Fields) {*{$F} = \ $_t->{$F}->[$_r]};

		## Now $Sub may refer to $_r, $_s, $_t, and ${any field name}

		## Call $Sub and capture return values iff caller wants them
		($WantVals ? $Vals->[$_r] = &$Sub() : &$Sub());
	}

	## Return scalar column ref unless return context is undef
	return($WantVals ? $Vals : ());
}