R编程功能没有（）(R programming function without ())

 所以，我有以下非常简单的map.r文件。 
 
 我正在尝试让用户在交互模式下键入“click”，然后使用该功能。 
 
 由于它是一个函数，用户必须键入“click（）”我如何才能使它们只需要单词（没有括号），然后让该函数对img做一些事情。 
 
 所以用户输入： 
 
 
 
 mydist（ “image.pnm”） 
 
 
 点击 
 
 
 //然后单击函数会执行它应该执行的操作 
 
mydist <- function(mapfile) {

    img <- read.pnm(mapfile)

    plot(img)
}

click <- function() {

    //Prompt user to click on img
}

So, I Have the following very simple map.r file.
 
I'm trying to have the user type "click" in interactive mode and then have the function .
 
Since it's a function, the user has to type "click()" how can I make it so that they only have to the word (w/o parentheses), and then have that function do something with the img.
 
So the user types:
 
 
 
mydist("image.pnm")
 
 
click
 
 
//And then the function click does what it's supposed to
 
mydist <- function(mapfile) {

    img <- read.pnm(mapfile)

    plot(img)
}

click <- function() {

    //Prompt user to click on img
}

原文：https://stackoverflow.com/questions/8130469