Define car and cdr for lists

The `Apply` node of multiple output Ops return a list of output. To
allow callers to etuplize this list and later evaluate the expression
tuple back to this list we define the behavior of `car` and `cdr` in
terms of `cons`.

aesara/graph/rewriting/unify.py

@@ -15,7 +15,7 @@
 from typing import Callable, Dict, Optional, Tuple, Union
 
 import numpy as np
-from cons.core import ConsError, _car, _cdr
+from cons.core import ConsError, _car, _cdr, cons
 from etuples import apply, etuple, etuplize
 from etuples.core import ExpressionTuple, etuple
 from etuples.dispatch import etuplize_fn
@@ -73,6 +73,21 @@ def __repr__(self):
         return f"{type(self).__name__}({repr(self.constraint)}, {self.token})"
 
 
+def car_list(x: list):
+    return cons
+
+
+_car.add((list,), car_list)
+
+
+def cdr_list(x: list):
+    x_e = etuple(_car(x), *x, [], evaled_obj=x)
+    return x_e[1:]
+
+
+_cdr.add((list,), cdr_list)
+
+
 class OpExpressionTuple(ExpressionTuple):
     r"""Etuple form for `Op`s.