#! /usr/bin/env python
# -*- coding: utf-8 -*-
# vim:fenc=utf-8
#
# Copyright © 2017 lafrite <lafrite@Poivre>
#
# Distributed under terms of the MIT license.

"""
Evaluating a binary tree
"""

from .operator import OPERATORS

class ComputeError(Exception):
    pass

def compute(node, left_v, right_v):
    """ 
    Computing a node 

    :example:

    >>> compute("+", 1, 2)
    3
    >>> compute("-", None, 2)
    -2
    >>> compute("-", 1, 2)
    Traceback (most recent call last):
        ...
    mapytex.calculus.core.evaluate.ComputeError: left_v need to be None for operator with arity 1
    """
    op = OPERATORS[node]
    lv = left_v
    rv = right_v
    if op['arity'] == 1:
        if lv is None:
            return op["operate"](rv)()
        else:
            raise ComputeError("left_v need to be None for operator with arity 1")
    else:
        try:
            return op["operate"](lv)(rv)
        except NotImplemented:
            return op["roperate"](rv)(lv)




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