         case .concrete(let h, _):
             return h
         case .symbolic(_, _, _):
-            assert(false, "TODO: to be send out in a separate PR.")
+            fatalError("TODO: to be send out in a separate PR.")
             // return op.materialized(index: index)
         }
     }

        case TF_VARIANT: return "variant"
        case TF_UINT32: return "uint32"
        case TF_UINT64: return "uint64"
        default: assert(false, "Unhandled type: \(cDataType)")
        }
    }
}

    func updateAttribute<In: TensorGroup, Out: TensorGroup>(
        _ name: String, _ value: (In) -> Out) {
        // TODO:
        fatalError("Unimplemented [TFFunction] attribute.")
    }

    func execute() {}
