use IO::File;

sub process_each_file_line
{
  my( $filename, $preprocess_cb, $process_cb ) = @_;
  my $fh = IO::File->new( "< $filename" ) 
    or die "open $filename for reading: $!";
  while ( <$fh> )
  {
    $process_cb->( $preprocess_cb->() );
  }
}

sub process
{
  my( $filename, @indexes ) = @_;
  my @result;
  process_each_file_line(
    $filename,
    sub { (split)[ @indexes ] },
    sub { local $" = ','; push @result, "test : @_\n"; }
  );
  return @result;
}

# call the function:
print process( "my.dat", qw( 3 0 4 5 6 7 ) );