Toying with declarations of symbols for use with non-standard evaluation.

NamesTest

#' Placeholder function.
#'
#' @export
as_nonstandard <- function()
{
	stop("This is a placeholder function, and should not be called directly.")
}

#' Declare symbols for nonstandard evalution.
#'
#' @param declaration an expression given as \code{symbol <- as_nonstandard()}
#' @export
declare <- function(declaration)
{
	d <- substitute(declaration) 
	p <- parent.frame()
	
	if (!identical(d[[1]], quote(`<-`)))
		stop("Declarations follow the <- syntax.", call. = FALSE)
	
	if (!is.symbol(d[[2]]))
		stop("LHS needs to be a symbol", call. = FALSE)
	
	sym <- as.character(d[[2]])
	
	msg <- sprintf("Symbol '%s' is declared for non-standard use.", sym)

	eval(
		substitute(
			delayedAssign(x, stop(m, call. = FALSE), environment(), environment()),
		list(m = msg, x = sym)), p, p)
}
	
#' test
#' 
#' @export
test <- function() 
{
	declare(Sepal.Length <- as_nonstandard())
	subset(iris, Sepal.Length > 5)
}

#' test2
#' 
#' @export
test2 <- function()
{
	declare(Sepal.Length <- as_nonstandard())
	Sepal.Length
}