print tree with R

library(magrittr)
library(stringr)
print_dir_f <- function(pathName, layer){
  fileNames <- list.files(pathName)
  isdir <- file.info(fileNames)$isdir
  isdir[is.na(isdir)] <- FALSE
  for (i in seq_along(fileNames))
  {
    if (isdir[i])
    {
      str_c(rep("  ", layer), collapse = "") %>% str_c(fileNames[i], '\n') %>% cat
      str_c(pathName, fileNames[i], sep='/') %>% print_dir_f(layer+1)
    } else
    {
      str_c(rep("  ", layer), collapse = "") %>% str_c(fileNames[i], '\n') %>% cat
    }
  }
}
print_dir_f(".", 0)