tidy.source <- function(source = "clipboard", keep.comment = TRUE,
  keep.blank.line = FALSE, begin.comment, end.comment, ...) {
  # parse and deparse the code
  tidy.block = function(block.text) {
      exprs = parse(text = block.text)
      n = length(exprs)
      res = character(n)
      for (i in 1:n) {
        dep = paste(deparse(exprs[i]), collapse = "\n")
        res[i] = substring(dep, 12, nchar(dep) - 1)
      }
      return(res)
  }
  text.lines = readLines(source, warn = FALSE)
  if (keep.comment) {
      # identifier for comments
      identifier = function() paste(sample(LETTERS), collapse = "")
      if (missing(begin.comment))
        begin.comment = identifier()
      if (missing(end.comment))
        end.comment = identifier()
      # remove leading and trailing white spaces
      text.lines = gsub("^[[:space:]]+|[[:space:]]+$", "",
        text.lines)
      # make sure the identifiers are not in the code
      # or the original code might be modified
      while (length(grep(sprintf("%s|%s", begin.comment, end.comment),
        text.lines))) {
        begin.comment = identifier()
        end.comment = identifier()
      }
      head.comment = substring(text.lines, 1, 1) == "#"
      # add identifiers to comment lines to cheat R parser
      if (any(head.comment)) {
        text.lines[head.comment] = gsub("\"", "\'", text.lines[head.comment])
        text.lines[head.comment] = sprintf("%s=\"%s%s\"",
          begin.comment, text.lines[head.comment], end.comment)
      }
      # keep blank lines?
      blank.line = text.lines == ""
      if (any(blank.line) & keep.blank.line)
        text.lines[blank.line] = sprintf("%s=\"%s\"", begin.comment,
          end.comment)
      text.tidy = tidy.block(text.lines)
      # remove the identifiers
      text.tidy = gsub(sprintf("%s = \"|%s\"", begin.comment,
        end.comment), "", text.tidy)
  }
  else {
      text.tidy = tidy.block(text.lines)
  }
  cat(paste(text.tidy, collapse = "\n"), "\n", ...)
  invisible(text.tidy)
}