title: See which S3 generic methods are available in environment
body: <p>Sorry if missing something obvious here... Is there any way to see in advance which S3 generic methods currently exist in the current environment (say <code>&lt;environment: R_GlobalEnv&gt;</code>. A list of all current generic methods in base <code>R</code> would do fine but I can't seem to find one.</p>
  
  <p>The reason I'm asking is I'm defining some <code>methods</code> for a <code>class</code> and some of them will already be generic S3 methods so I'd like to know in advance without having to check each one manually. </p>
  
  <p>For example:</p>
  
  <pre><code>isGeneric("mean")
  &gt;TRUE
  
  isGeneric("quantile")
  &gt;FALSE
  </code></pre>
  
  <p>At the moment the closest I've come is:</p>
  
  <pre><code>ls(,all.names=TRUE)[sapply(ls(, all.names=TRUE), FUN=isGeneric)]
  </code></pre>
  
  <p>Which works if I already have a method defined (but doesn't give other potential generic methods) and gives the following error when I give it as a first command in a new <code>R</code> session:</p>
  
  <pre><code>  invalid subscript type 'list'
  </code></pre>