diff --git a/fastNLP/api/api.py b/fastNLP/api/api.py
index 9c20c2a6..996d0b17 100644
--- a/fastNLP/api/api.py
+++ b/fastNLP/api/api.py
@@ -14,3 +14,8 @@ class API:
         _dict = torch.load(name)
         self.pipeline = _dict['pipeline']
         self.model = _dict['model']
+
+    def save(self, path):
+        _dict = {'pipeline': self.pipeline,
+                 'model': self.model}
+        torch.save(_dict, path)
diff --git a/fastNLP/api/parser.py b/fastNLP/api/parser.py
new file mode 100644
index 00000000..67bcca4f
--- /dev/null
+++ b/fastNLP/api/parser.py
@@ -0,0 +1,36 @@
+from fastNLP.api.api import API
+from fastNLP.core.dataset import DataSet
+from fastNLP.core.predictor import Predictor
+from fastNLP.api.pipeline import Pipeline
+from fastNLP.api.processor import *
+from fastNLP.models.biaffine_parser import BiaffineParser
+
+
+class DependencyParser(API):
+    def __init__(self):
+        super(DependencyParser, self).__init__()
+
+    def predict(self, data):
+        self.load('xxx')
+
+        dataset = DataSet()
+        dataset = self.pipeline.process(dataset)
+
+        pred = Predictor()
+        res = pred.predict(self.model, dataset)
+
+        return res
+
+    def build(self):
+        pipe = Pipeline()
+
+        # build pipeline
+        word_seq = 'word_seq'
+        pos_seq = 'pos_seq'
+        pipe.add_processor(Num2TagProcessor('<NUM>', 'raw_sentence', word_seq))
+        pipe.add_processor(IndexerProcessor(word_vocab, word_seq, word_seq+'_idx'))
+        pipe.add_processor(IndexerProcessor(pos_vocab, pos_seq, pos_seq+'_idx'))
+
+        # load model parameters
+        self.model = BiaffineParser()
+        self.pipeline = pipe
diff --git a/fastNLP/api/pipeline.py b/fastNLP/api/pipeline.py
index 0edceb19..83aef66e 100644
--- a/fastNLP/api/pipeline.py
+++ b/fastNLP/api/pipeline.py
@@ -19,4 +19,7 @@ class Pipeline:
         return dataset
 
     def __call__(self, *args, **kwargs):
-        return self.process(*args, **kwargs)
\ No newline at end of file
+        return self.process(*args, **kwargs)
+
+    def __getitem__(self, item):
+        return self.pipeline[item]
diff --git a/fastNLP/api/pos_tagger.py b/fastNLP/api/pos_tagger.py
index fbd689c1..2157231e 100644
--- a/fastNLP/api/pos_tagger.py
+++ b/fastNLP/api/pos_tagger.py
@@ -5,9 +5,10 @@ import numpy as np
 from fastNLP.core.dataset import DataSet
 from fastNLP.loader.model_loader import ModelLoader
 from fastNLP.core.predictor import Predictor
+from fastNLP.api.api import API
 
 
-class POS_tagger:
+class POS_tagger(API):
     def __init__(self):
         pass
 
diff --git a/fastNLP/api/processor.py b/fastNLP/api/processor.py
index 3f8cc057..d21c1050 100644
--- a/fastNLP/api/processor.py
+++ b/fastNLP/api/processor.py
@@ -2,6 +2,8 @@
 from fastNLP.core.dataset import DataSet
 from fastNLP.core.vocabulary import Vocabulary
 
+import re
+
 class Processor:
     def __init__(self, field_name, new_added_field_name):
         self.field_name = field_name
@@ -64,6 +66,7 @@ class FullSpaceToHalfSpaceProcessor(Processor):
         if self.change_space:
             FHs += FH_SPACE
         self.convert_map = {k: v for k, v in FHs}
+
     def process(self, dataset):
         assert isinstance(dataset, DataSet), "Only Dataset class is allowed, not {}.".format(type(dataset))
         for ins in dataset:
@@ -77,6 +80,37 @@ class FullSpaceToHalfSpaceProcessor(Processor):
         return dataset
 
 
+class MapFieldProcessor(Processor):
+    def __init__(self, func, field_name, new_added_field_name=None):
+        super(MapFieldProcessor, self).__init__(field_name, new_added_field_name)
+        self.func = func
+
+    def process(self, dataset):
+        for ins in dataset:
+            s = ins[self.field_name]
+            new_s = self.func(s)
+            ins[self.new_added_field_name] = new_s
+        return  dataset
+
+
+class Num2TagProcessor(Processor):
+    def __init__(self, tag, field_name, new_added_field_name=None):
+        super(Num2TagProcessor, self).__init__(field_name, new_added_field_name)
+        self.tag = tag
+        self.pattern = r'[-+]?([0-9]+[.]?[0-9]*)+[/eE]?[-+]?([0-9]+[.]?[0-9]*)'
+
+    def process(self, dataset):
+        for ins in dataset:
+            s = ins[self.field_name]
+            new_s = [None] * len(s)
+            for i, w in enumerate(s):
+                if re.search(self.pattern, w) is not None:
+                    w = self.tag
+                new_s[i] = w
+            ins[self.new_added_field_name] = new_s
+        return dataset
+
+
 class IndexerProcessor(Processor):
     def __init__(self, vocab, field_name, new_added_field_name, delete_old_field=False):
 
diff --git a/fastNLP/core/dataset.py b/fastNLP/core/dataset.py
index e3162356..82b55818 100644
--- a/fastNLP/core/dataset.py
+++ b/fastNLP/core/dataset.py
@@ -86,6 +86,8 @@ class DataSet(object):
         return self.field_arrays[name]
 
     def __len__(self):
+        if len(self.field_arrays) == 0:
+            return 0
         field = iter(self.field_arrays.values()).__next__()
         return len(field)
 
diff --git a/fastNLP/modules/decoder/CRF.py b/fastNLP/modules/decoder/CRF.py
index cd68d35d..11cde48a 100644
--- a/fastNLP/modules/decoder/CRF.py
+++ b/fastNLP/modules/decoder/CRF.py
@@ -89,7 +89,7 @@ class ConditionalRandomField(nn.Module):
         score = score.sum(0) + emit_score[-1]
         if self.include_start_end_trans:
             st_scores = self.start_scores.view(1, -1).repeat(batch_size, 1)[batch_idx, tags[0]]
-            last_idx = masks.long().sum(0)
+            last_idx = mask.long().sum(0)
             ed_scores = self.end_scores.view(1, -1).repeat(batch_size, 1)[batch_idx, tags[last_idx, batch_idx]]
             score += st_scores + ed_scores
         # return [B,]
diff --git a/reproduction/Biaffine_parser/run.py b/reproduction/Biaffine_parser/run.py
index 45668066..209e45cb 100644
--- a/reproduction/Biaffine_parser/run.py
+++ b/reproduction/Biaffine_parser/run.py
@@ -352,7 +352,7 @@ if __name__ == "__main__":
     elif args.mode == 'test':
         test(args.path)
     elif args.mode == 'infer':
-        infer()
+        pass
     else:
         print('no mode specified for model!')
         parser.print_help()