title: What's the meaning of "!", "?", "_", and "." syntax in elixir
body: <p>I need help regarding understanding the following syntaxes in elixir <code>!</code>, <code>?</code>, <code>_</code>, and <code>.</code>. 
  What's those syntaxes role in elixir's function? For example <code>Repo.get!</code>.</p>
  
  <p>I'm not sure whether they were just function name, or has a role. Though I know <code>.</code> is for calling anonymous function. And <code>_</code> for any or variadic?</p>