title: Lookahead with postfix language
body: <p>Let's say I have a postfix language like</p>
  
  <pre><code>3 2 result +      // equivalent to result = 3 + 2
  result 1 result + // equivalent to ++result
  </code></pre>
  
  <p>how should I implement a lookahead for a recursive descent parser (I'm doing this in C++)?</p>
  
  <p>I'm unsure on how to design such a parsing algorithm since I can't deduce the type of instruction from just the first token</p>