text: define(function(require){
      "use restrict";
      return function line(option){
          var option = option || {},
              x = option.x || [],
              y = option.y || [];
  
          var line = function() {
              if(x.length && y.length) {
                  var path = ["M", x[0], y[0]];
                  for(var i = 1, l=x.length; i<l; i++){
                      path.push("L");
                      path.push(x[i]);
                      path.push(y[i]);
                  }
                  return path.join(" ");
              } else {
                  throw new Error("x or y undefined.")
              }
          }
  
          line.x = function(d) {
              x = x.concat(d);
              return line;
          }
  
          line.y = function(d) {
              y = y.concat(d);
              return line;
          }
  
          return line;
      };
  });
  