title: How to get the values from nodes in tree-sitter?
body: <p>If I have a simple grammar in tree-sitter:</p>
  <pre><code>rules: {
      expr: $ =&gt; choice(
          /[0-9]+/,
          prec.right(seq($.expr, /[+-]/, $.expr)),
      )
  }
  </code></pre>
  <p>And an input:</p>
  <pre><code>3+4
  </code></pre>
  <p>I get the followng CST:</p>
  <pre><code>(start [0, 0] - [0, 3]
    (expr [0, 0] - [0, 3]
      (expr [0, 0] - [0, 1])
      (expr [0, 2] - [0, 3])))
  </code></pre>
  <p>So my question is, how do I get the values, i.e. what was parsed, from these nodes/leafes. I somehow have to evaluate the tree. I'm certainly sure there is way, because I can also do syntax-highlighting with tree-sitter, for what I need the values (I guess). But I read the documentation and couldn't find any note, how to do it.</p>