title: Making YACC output an AST (token tree)
body: <p>Is it possible to make YACC (or I'm my case MPPG) output an Abstract Syntax Tree (AST).</p>
  
  <p>All the stuff I'm reading suggests its simple to make YACC do this, but I'm struggling to see how you know when to move up a node in the tree as your building it.</p>