fix extsampler

Author: penelopeysm

usage/external-samplers/index.qmd

@@ -37,8 +37,8 @@ end
 Now we sample the model to generate some observations, which we can then condition on.
 
 ```{julia}
-(; x) = rand(funnel() | (θ=0,))
-model = funnel() | (; x);
+vnt = rand(funnel() | (θ=0,))
+model = funnel() | (; x=vnt[@varname(x)]);
 ```
 
 Users can use any sampler algorithm to sample this model if it follows the `AbstractMCMC` API.
@@ -146,4 +146,4 @@ In general, we recommend that the `AbstractMCMC` interface is implemented direct
 However, any DynamicPPL- or Turing-specific functionality is best implemented in a `MySamplerTuringExt` extension.
 
 [^1]: Xu et al., [AdvancedHMC.jl: A robust, modular and efficient implementation of advanced HMC algorithms](http://proceedings.mlr.press/v118/xu20a/xu20a.pdf), 2019
-[^2]: Zhang et al., [Pathfinder: Parallel quasi-Newton variational inference](https://arxiv.org/abs/2108.03782), 2021
+[^2]: Zhang et al., [Pathfinder: Parallel quasi-Newton variational inference](https://arxiv.org/abs/2108.03782), 2021