What is the meaning of the dollar sign "$" in R function()? : <p>Through learning <code>R</code>, I just came across the following code explained <a href="https://cran.r-project.org/doc/manuals/R-intro.html#Scope" rel="noreferrer">here</a>. </p>

<pre><code>open.account &lt;- function(total) {
  list(
    deposit = function(amount) {
      if(amount &lt;= 0)
        stop("Deposits must be positive!\n")
      total &lt;&lt;- total + amount
      cat(amount, "deposited.  Your balance is", total, "\n\n")
    },
    withdraw = function(amount) {
      if(amount &gt; total)
        stop("You don't have that much money!\n")
      total &lt;&lt;- total - amount
      cat(amount, "withdrawn.  Your balance is", total, "\n\n")
    },
    balance = function() {
      cat("Your balance is", total, "\n\n")
    }
  )
}

ross &lt;- open.account(100)
robert &lt;- open.account(200)

ross$withdraw(30)
ross$balance()
robert$balance()

ross$deposit(50)
ross$balance()
ross$withdraw(500)
</code></pre>

<p>What is the most of my interest about this code, learning the use of <code>"$"</code> dollar sign which refer to an specific <code>internal function</code> in  <code>open.account()</code> function. I mean this part :</p>

<pre><code>    ross$withdraw(30)
    ross$balance()
    robert$balance()

    ross$deposit(50)
    ross$balance()
    ross$withdraw(500)
</code></pre>

<p><strong>Questions:</strong> <br></p>

<p>1-  What is the meaning of the dollar sign <code>"$"</code> in <code>R</code> <code>function()</code> ? <br> 
2-  How to <strong>identify</strong> its attributes in functions, specially for the functions that you adopting from other (<em>i.e.</em> you did not write it)?<br> 
I used the following script </p>

<pre><code>&gt; grep("$", open.account())
[1] 1 2 3
</code></pre>

<p>but it is not useful I want to find a way to extract the name(s) of internal functions that can be refer by "$" without just by calling and searching the written code as  <code>&gt; open.account()</code> . <br>
  For instance in case of <code>open.account()</code> I'd like to see something like this:</p>

<pre><code>$deposit
$withdraw
$balance
</code></pre>

<p>3- Is there any reference that I can read more about it? <br>
tnx!</p>
