text: module.exports = read_lines;
  
  var readline = require('readline');
  var fs = require('fs');
  
  function read_lines(filename, on_line, on_close){
  	var files = filename.split(',');
  	if (are_all_files_read(files, on_close)){
  		return;
  	}
  	var f = files[0];
  	files = files.slice(1);
  	read_file(f, on_line, function(){ on_file_complete(files, on_close); });
  }
  
  function on_file_complete(files, on_close){
  	if (are_all_files_read(files)){
  		on_close();
  	} else {
  		files = files.slice(1);
  		read_file(f, on_line, function(){ on_file_complete(files, on_close); });
  	}
  }
  
  function are_all_files_read(files){
  	return files.length == 0;
  }
  
  function read_file(filename, on_line, on_close){
  	var input = fs.createReadStream(filename);
  	var rl_interface = readline.createInterface({
  		input: input
  	});
  	rl_interface.on('line', function(line){
  		if (on_line != null){
  			on_line(line);
  		}
  	});
  	rl_interface.on('close', function(){
  		if (on_close != null){
  			on_close();
  		}
  	});
  }
  
  