code: def eval(self, sample):
      # print("eval sample", sample["obs"].shape)
      # print("eval target", sample["target"].shape)
  
      # start = time.time()
  
      if "ctx_length" in sample:
          ctx_length = sample["ctx_length"]
      else:
          ctx_length = np.array(
              [len(sample["obs"][0])] * len(sample["obs"])
          )
  
      out = self.eval_xmap(
          self.state, sample["obs"], sample["target"], ctx_length
      )
      # print(f"eval dispatched in {time.time() - start:.06}s")
  
      # np.array(out["loss"])
      # print(f"eval done in {time.time() - start:.06}s")
      return out
  
imports: import gc
  import random
  import time
  from functools import partial
  import haiku
  import jax
  import jax.numpy
  import numpy
  import optax
  from jax.experimental.maps import thread_resources
  from jax.experimental.pjit import pjit
  from mesh_transformer.checkpoint import read_ckpt, write_ckpt, write_ckpt_v2, load_ckpt_v2
  from mesh_transformer.layers import EmbeddingShard, TransformerLayerShard, RelativePositionEmbs, ProjectionShard, TransformerLayerShardV2, Projection, EmbeddingShardV2
  from mesh_transformer.util import to_f32, to_bf16, maybe_shard, head_print, global_norm
  from jax.experimental import PartitionSpec
label_desc: Use image node_id 5 for calling the CausalTransformer obj's underlying member method code with example usage: obj.eval(sample) and returns: out