'Score the accuracy of the chunker against the gold standard.
Remove the chunking the gold standard text, rechunk it using
the chunker, and return a ``ChunkScore`` object
reflecting the performance of this chunk peraser.
:type gold: list(Tree)
:param gold: The list of chunked sentences to score the chunker on.
:rtype: ChunkScore'

def evaluate(self, gold):

    chunkscore = ChunkScore()
    for correct in gold:
        chunkscore.score(correct, self.parse(correct.leaves()))
    return chunkscore
