                  else:
                      self.unshift()
              elif (self.length - self._b_i) >= 1 and self.stack_depth() == 0:
                  self.push()
              else:
                  break
  
      cdef void add_arc(self, int head, int child, int label) nogil:
          if self.has_head(child):
              self.del_arc(self.H(child), child)
 
</s> remove         while self.buffer_length() == 0 or self.stack_depth() == 0:
 </s> add         while self.buffer_length() == 0 \
        or self.stack_depth() == 0 \
        or Lexeme.c_check_flag(self.S_(0).lex, IS_SPACE): </s> remove         # Don't allow spaces to be the first word of a sentence
        elif Lexeme.c_check_flag(st.B_(0).lex, IS_SPACE):
            return False
 </s> add  </s> remove @pytest.mark.xfail
 </s> add  </s> remove     doc.from_array([HEAD], numpy.asarray([[1, 0, -1, -2, -1, -1, -5,
                                           4, 3, 2, 1, 0, 2, 1, -3, 1, 1, -3, -7]],
                                 dtype='int32').T)
 </s> add 
            elif Lexeme.c_check_flag(self.S_(0).lex, IS_SPACE):
                self.add_arc(self.B(0), self.S(0), 0)
                self.pop()
                  else:
                      self.unshift()
              elif (self.length - self._b_i) >= 1 and self.stack_depth() == 0:
                  self.push()
            elif Lexeme.c_check_flag(self.S_(0).lex, IS_SPACE):
                self.add_arc(self.B(0), self.S(0), 0)
                self.pop()
              else:
                  break
  
      cdef void add_arc(self, int head, int child, int label) nogil:
          if self.has_head(child):
              self.del_arc(self.H(child), child)
keep keep keep add keep keep keep keep keep keep
 * Unwind limit to sentence boundary detection that prevents it from inserting boundaries on whitespace. Replace it with a check for whitespace in StateClass.fast_forward, so that whitespace is LeftArced when it's on the stack. This should prevent the previous problem of whitespace-only sentences. Should fix Issue #184, but may cause further problems. Needs testing. 
spacy/syntax/stateclass.pyx