text: ### Add to history() and avoid repeatedly appending suffix.
  addhistory <- function(read)
  {
    tmp <- as.character(read)
    suffix <- paste0(" # ", getval(prompt))
    if (!grepl(x = tmp, pattern = paste0(suffix, "$"), perl = TRUE))
      tmp <- paste0(tmp, suffix)
    
    if (isWindows() && isRStudio())
    {
      ### This adds history to native R but is insufficient for Rtudio IDE.
      # .rs.registerReplaceHook("timestamp", "utils", function(original, ...)
      # {
      #   invisible(.Call("rs_timestamp", "bb"))
      # })
      # timestamp()
    }
    else
      utils::timestamp(stamp = tmp, prefix = "", suffix = "", quiet = TRUE)
    
    invisible()
  }
  