function with dot(.) and comma(,) put together

Question

map_wc <- function(.,lines)                                              
{                                                                        

  lines_lst = unlist(strsplit(lines,"\r\n",fixed=TRUE))                  
  l_cnt<-1;
  keys_l<-c()
  data_l<-c()
  for (line in lines_lst)
  { 
    words = unlist(strsplit(line,";",fixed=TRUE))

    if (length(words) != 5){
      next
    }
  }  

Anyone using Rhadoop might be familiar with the code above. Can someone please explain to me the reason why ".," i.e dot(.) and (,) in the first line function are placed side-by-side. Please when answering note that am new to R.