[R] Prevent Printing Function's Environment

[Martin Maechler]

>>>>> Abs Spurdle 
>>>>>     on Tue, 14 Aug 2018 15:16:08 +1200 writes:

    > Hi All

    > When you print a function constructed within a function, R
    > prints it's environment.  For example:

     > > myfunction = function ()
     > + {   f = function () NULL
     > +     attributes (f) = list (class="myfunction", myattribute=1)
     > +     f
     > + }

     > > myfunction.f = myfunction ()

     > > myfunction.f
     > function ()
     > NULL
     > <environment: 0x03fcbc30>
     > attr(,"class")
     > [1] "myfunction"
     > attr(,"myattribute")
     > [1] 1

     > One way to prevent this is to set the function's environment to the global
     > environment.
     > But I was wondering if there's a way to stop R from printing the
     > environment without changing the environment?

Probably, not the way you want, but if you need it e.g., for
didactical reasons, here's a way that may be didactically
relevant in it self:

  > ls.str
  function (pos = -1, name, envir, all.names = FALSE, pattern, 
      mode = "any") 
  {
      if (missing(envir)) 
	  envir <- as.environment(pos)
      nms <- ls(name, envir = envir, all.names = all.names, pattern = pattern)
      r <- unlist(lapply(nms, function(n) exists(n, envir = envir, 
	  mode = mode, inherits = FALSE)))
      structure(nms[r], envir = envir, mode = mode, class = "ls_str")
  }
  <bytecode: 0xb222858>
  <environment: namespace:utils>

so, I want to suppress the last two lines that are printed.
That's a piece of cake if you know  capture.output() :

  > P2 <- function(.) writeLines(head(capture.output(.), -2))
  > P2(ls.str)
  function (pos = -1, name, envir, all.names = FALSE, pattern, 
      mode = "any") 
  {
      if (missing(envir)) 
	  envir <- as.environment(pos)
      nms <- ls(name, envir = envir, all.names = all.names, pattern = pattern)
      r <- unlist(lapply(nms, function(n) exists(n, envir = envir, 
	  mode = mode, inherits = FALSE)))
      structure(nms[r], envir = envir, mode = mode, class = "ls_str")
  }
  >