Recently, bidirectional long short-term memory networks (bi-LSTM) (Graves and Schmidhuber, 2005; Hochreiter and Schmidhuber, 1997) have been used for language modelling<cite> (Ling et al., 2015)</cite> , POS tagging<cite> (Ling et al., 2015</cite>;<cite> Wang et al., 2015)</cite> , transition-based dependency parsing (Ballesteros et al., 2015; Kiperwasser and Goldberg, 2016) , fine-grained sentiment analysis (Liu et al., 2015) , syntactic chunking (Huang et al., 2015) , and semantic role labeling (Zhou and Xu, 2015) .