No need to be ashamed of the eval, it's a standard technique in happy programs (who said "programs that generate other programs are the happiest programs of all"?).

For a simple case like ascending/descending you can just generate the coderef at once:

sub sortmaker {
  my $order = shift;
  my $sub = $order ? sub { $a <=> $b } : sub {$b <=> $a};
  return $sub;
}
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but if you need to build the subroutine then eval is the way to go. I would write it a little more verbosely though:

sub sortmaker {
  my $order = shift;
  my $clause = $order ? '$a <=> $b' : '$b <=> $a';
  my $sub= eval "sub { $clause}";  # create the coderef
  return $sub;                                # explicitely return it
}
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