src/include/fst/extensions/pdt/reverse.h

// reverse.h

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Copyright 2005-2010 Google, Inc.
// Author: riley@google.com (Michael Riley)
//
// \file
// Expand a PDT to an FST.

#ifndef FST_EXTENSIONS_PDT_REVERSE_H__
#define FST_EXTENSIONS_PDT_REVERSE_H__

#include <unordered_map>
using std::tr1::unordered_map;
using std::tr1::unordered_multimap;
#include <vector>
using std::vector;

#include <fst/mutable-fst.h>
#include <fst/relabel.h>
#include <fst/reverse.h>

namespace fst {

// Reverses a pushdown transducer (PDT) encoded as an FST.
template<class Arc, class RevArc>
void Reverse(const Fst<Arc> &ifst,
             const vector<pair<typename Arc::Label,
             typename Arc::Label> > &parens,
             MutableFst<RevArc> *ofst) {
  typedef typename Arc::Label Label;

  // Reverses FST
  Reverse(ifst, ofst);

  // Exchanges open and close parenthesis pairs
  vector<pair<Label, Label> > relabel_pairs;
  for (size_t i = 0; i < parens.size(); ++i) {
    relabel_pairs.push_back(make_pair(parens[i].first, parens[i].second));
    relabel_pairs.push_back(make_pair(parens[i].second, parens[i].first));
  }
  Relabel(ofst, relabel_pairs, relabel_pairs);
}

}  // namespace fst

#endif  // FST_EXTENSIONS_PDT_REVERSE_H__