April 1st

april1.r

# this will rotate the values of your variables in the global env at each
# garbage collection
local({
  april1st <- function() {
    e <- new.env()
    reg.finalizer(e, function(e) {
      april1st()
      nms <- ls(.GlobalEnv)
      objs <- mget(nms, .GlobalEnv)
      objs <- setNames(objs, c(nms[-1], nms[1]))
      list2env(objs, .GlobalEnv)
    })
    gc() # necessary not to have GC itself interfer with our magic
    invisible(NULL)
  }
  april1st()
})

# this will print a line "I know what you did <user name>" for 0.5 sec, then remove it,
# on each garbage collection
local({
  april1st <- function() {
    e <- new.env()
    reg.finalizer(e, function(e) {
      april1st()
      msg <- sprintf("I know what you did %s", Sys.info()[["user"]])
      n <- nchar(msg) + 1
      message(msg)
      Sys.sleep(0.5)
      cat(strrep("\b", n), strrep(" ", n),"\n")
    })
    gc() # necessary not to have GC itself interfer with our magic
    invisible(NULL)
  }
  april1st()
})