diff --git a/serket/_src/nn/convolution.py b/serket/_src/nn/convolution.py
index 0dd674d..49b5a8b 100644
--- a/serket/_src/nn/convolution.py
+++ b/serket/_src/nn/convolution.py
@@ -29,14 +29,12 @@
 
 from serket import TreeClass
 from serket._src.nn.initialization import resolve_init
-from serket._src.utils.convert import canonicalize
-from serket._src.utils.dispatch import single_dispatch
-from serket._src.utils.lazy import maybe_lazy_call, maybe_lazy_init
-from serket._src.utils.padding import (
+from serket._src.utils.convert import (
     calculate_transpose_padding,
     canonicalize,
     delayed_canonicalize_padding,
 )
+from serket._src.utils.dispatch import single_dispatch
 from serket._src.utils.lazy import maybe_lazy_call, maybe_lazy_init
 from serket._src.utils.typing import (
     DilationType,
diff --git a/serket/_src/nn/linear.py b/serket/_src/nn/linear.py
index c352a88..815ff91 100644
--- a/serket/_src/nn/linear.py
+++ b/serket/_src/nn/linear.py
@@ -15,7 +15,7 @@
 from __future__ import annotations
 
 import functools as ft
-from typing import Sequence
+from typing import Any, Sequence
 
 import jax
 import jax.numpy as jnp
@@ -35,11 +35,12 @@
 from serket._src.utils.validate import validate_pos_int
 
 
+@ft.lru_cache(maxsize=None)
 def generate_einsum_pattern(
     lhs_ndim: int,
     rhs_ndim: int,
-    in_axis: Sequence[int],
-    out_axis: Sequence[int],
+    in_axis: tuple[int, ...],
+    out_axis: tuple[int, ...],
 ) -> tuple[str, str, str]:
     # helper function to generate the einsum pattern for linear layer
     # with flexible input and output axes
@@ -90,8 +91,9 @@ def _(
     in_axis: Sequence[int] = (-1,),
     out_axis: Sequence[int] = (-1,),
 ) -> jax.Array:
-    pattern = generate_einsum_pattern(input.ndim, weight.ndim, in_axis, out_axis)
-    result = jnp.einsum(pattern, input, weight)
+    in_axis, out_axis = tuple(in_axis), tuple(out_axis)
+    lhs, rhs, out = generate_einsum_pattern(input.ndim, weight.ndim, in_axis, out_axis)
+    result = jnp.einsum(f"{lhs},{rhs}->{out}", input, weight)
 
     if bias is None:
         return result
diff --git a/tests/test_rnn.py b/tests/test_rnn.py
index 4817fb9..b888008 100644
--- a/tests/test_rnn.py
+++ b/tests/test_rnn.py
@@ -11,6 +11,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from __future__ import annotations
 
 import os