type
  NodeKind = enum inner, leaf
  TElement[TKey, TData] = object
    case kind: NodeKind
    of inner:
      key: TKey
      left, right: ref TElement[Tkey, TData]
    of leaf:
      data: ref TData
 
  TTree*[TKey, TData] = distinct TElement[TKey, TData]
 
 
proc find*[TKey, TData](root: TTree[TKey, TData], key: TKey): TData {.raises: [EInvalidKey].} =
    if root.kind != inner:
      raise newException(EInvalidKey, "key does not exist: " & key)
 
    var tmp_element = root
 
    while tmp_element.kind == inner:
      if tmp_element.key < key:
        tmp_element = tmp_element.left
      else:
        tmp_element = tmp_element.right
 
    if tmp_element.key == key:
      return tmp_element.data
    else:
      raise newException(EInvalidKey, "key does not exist: " & key)
 
 

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