print $_,$/ for ronge(qw( 3.0 4.0 0.1 ));

sub ronge {
  my( $lll, $rrr, $iii ) = @_;
  my @rrr = $lll;
  while( $lll <= $rrr ){
     $lll += $iii;
     push @rrr, sprintf '%.1f', $lll;
  }
  return @rrr;
}
__END__
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0