invert the sequences (if needed) before anything else

theano/sandbox/scan_module/scan_utils.py

@@ -189,12 +189,30 @@ def canonical_arguments(sequences,
     inputs = []
     for input in to_list(sequences):
         if not isinstance(u, dict):
-            inputs.append(tensor.as_tensor_variable(input))
+            nw_input = tensor.as_tensor_variable(input)
+            if go_backwards:
+                nw_input = nw_input[::-1]
+            if n_steps is not None:
+                nw_input = tensor.switch(n_steps < 0, nw_input[::-1],
+                                         nw_input)
+            inputs.append(tensor.as_tensor_variable(nw_input))
         elif input.get('taps', True) is None:
-            inputs.append(tensor.as_tensor_variable(input['input']))
+            nw_input = tensor.as_tensor_variable(input['input'])
+            if go_backwards:
+                nw_input = nw_input[::-1]
+            if n_steps is not None:
+                nw_input = tensor.switch(n_steps < 0, nw_input[::-1],
+                                         nw_input)
+            inputs.append(nw_input)
         elif input.get('taps', None):
             mintap = numpy.min(input['taps'])
             maxtap = numpy.max(input['taps'])
+            orig_input = tensor.as_tensor_variable(input['input'])
+            if go_backwards:
+                orig_input = orig_input[::-1]
+            if n_steps is not None:
+                orig_input = tensor.switch(n_steps < 0, orig_input[::-1],
+                                         org_input)
             for k in input['taps']:
                 # We cut the sequence such that seq[i] to correspond to
                 # seq[i-k]
@@ -202,7 +220,7 @@ def canonical_arguments(sequences,
                     offset = abs(maxtap)
                 else:
                     offset = 0
-                nw_input = tensor.as_tensor_variable(input['input'])
+                nw_input = orig_input
                 if maxtap == mintap and maxtap != 0:
                     nw_input = nw_input[:abs(maxtap)]
                 elif maxtap - k != 0:
@@ -210,8 +228,6 @@ def canonical_arguments(sequences,
                                               -(maxtap - k)]
                 else:
                     nw_input = nw_input[offset + k - mintap:]
-                if go_backwards:
-                    nw_input = nw_input[::-1]
                 inputs.append(nw_input)
         else:
             raise ValueError('Provided sequence makes no sense', str(input))