Is there a way to get more information about when Turing is unable to sample from a model?

For example, I tried a simple (univariate) mixture of gaussians model and when I try to sample from it, I get this error:

```
ERROR: ArgumentError: Right-hand side of a ~ must be subtype of Distribution or a vector of Distributions.
```

It would be helpful to know the right-hand side of which “~” is causing the problem. Maybe something in DynamicPPL could give a line number?

Here’s the model:

```
@model mm(y) = begin
N = length(y)
μ1 ~ Normal()
μ2 ~ Normal()
μ3 ~ Normal()
μ ~ [μ1, μ2, μ3]
ps ~ Dirichlet(ones(3))
k = Vector{Int}(undef, N)
for i in 1:N
k[i] ~ Categorical(ps)
y[i] ~ Normal(μ[k[i]])
end
return k
end
```

[fce5fe82] Turing v0.13.0

[31c24e10] Distributions v0.23.2