code: function doVisit(lo, hi, compare, visit, node) {
    var l = compare(lo, node.key)
    var h = compare(hi, node.key)
    var v
    if(l <= 0) {
      if(node.left) {
        v = doVisit(lo, hi, compare, visit, node.left)
        if(v) { return v }
      }
      if(h > 0) {
        v = visit(node.key, node.value)
        if(v) { return v }
      }
    }
    if(h > 0 && node.right) {
      return doVisit(lo, hi, compare, visit, node.right)
    }
  }
docs: Visit all nodes within a range