Add additional checks to the validation function

theano/scan_module/scan_op.py

@@ -209,6 +209,48 @@ class Scan(PureOp):
                                     "type '%s' and '%s' respectively." %
                                     (self.name, type_input, type_output))
 
+        # If scan has the flag 'gpu' set to false (meaning that is shouldn't
+        # use the CUDA gpu backend ), ensure that is has no input and no
+        # output with type CudaNdarrayType
+        from theano.sandbox.cuda import CudaNdarrayType
+        if not self.info.get("gpu", False):
+            for inp in self.inputs:
+                if isinstance(inp.type, CudaNdarrayType):
+                    raise TypeError("Inconsistency in the inner graph of "
+                                    "scan '%s' : one of the inputs to the "
+                                    "inner graph is of type CudaNdarray but "
+                                    "the attributes of the scan op indicate "
+                                    "that it shouldn't be the case")
+
+            for out in self.outputs:
+                if isinstance(out.type, CudaNdarrayType):
+                    raise TypeError("Inconsistency in the inner graph of "
+                                    "scan '%s' : one of the outputs to the "
+                                    "inner graph is of type CudaNdarray but "
+                                    "the attributes of the scan op indicate "
+                                    "that it shouldn't be the case")
+
+        # If scan has the flag 'gpua' set to false (meaning that is shouldn't
+        # use the gpuarray gpu backend ), ensure that is has no input and no
+        # output with type GpuArrayType
+        from theano.sandbox.gpuarray import GpuArrayType
+        if not self.info.get("gpua", False):
+            for inp in self.inputs:
+                if isinstance(inp.type, GpuArrayType):
+                    raise TypeError("Inconsistency in the inner graph of "
+                                    "scan '%s' : one of the inputs to the "
+                                    "inner graph is of type GpuArrayType but "
+                                    "the attributes of the scan op indicate "
+                                    "that it shouldn't be the case")
+
+            for out in self.outputs:
+                if isinstance(inp.type, GpuArrayType):
+                    raise TypeError("Inconsistency in the inner graph of "
+                                    "scan '%s' : one of the outputs to the "
+                                    "inner graph is of type GpuArrayType but "
+                                    "the attributes of the scan op indicate "
+                                    "that it shouldn't be the case")
+
     def __setstate__(self, d):
         self.__dict__.update(d)
         self.validate_inner_graph()