Add interface functions for InferenceAlgorithm

Author: penelopeysm

src/mcmc/algorithm.jl

@@ -11,4 +11,46 @@ this wrapping occurs automatically.
 """
 abstract type InferenceAlgorithm end
 
+# TODO(penelopeysm): remove
 DynamicPPL.default_chain_type(sampler::Sampler{<:InferenceAlgorithm}) = MCMCChains.Chains
+
+"""
+    update_sample_kwargs(spl::AbstractSampler, N::Integer, kwargs)
+    update_sample_kwargs(spl::InferenceAlgorithm, N::Integer, kwargs)
+Some InferenceAlgorithm implementations carry additional information about
+the keyword arguments that should be passed to `AbstractMCMC.sample`. This
+function provides a hook for them to update the default keyword arguments.
+The default implementation is for no changes to be made to `kwargs`.
+"""
+function update_sample_kwargs(spl::Sampler{<:InferenceAlgorithm}, N::Integer, kwargs)
+    return update_sample_kwargs(spl.alg, N, kwargs)
+end
+update_sample_kwargs(::AbstractSampler, N::Integer, kwargs) = kwargs
+update_sample_kwargs(::InferenceAlgorithm, N::Integer, kwargs) = kwargs
+
+"""
+    get_adtype(spl::AbstractSampler)
+    get_adtype(spl::InferenceAlgorithm)
+Return the automatic differentiation (AD) backend to use for the sampler.
+This is needed for constructing a LogDensityFunction.
+By default, returns nothing, i.e. the LogDensityFunction that is constructed
+will not know how to calculate its gradients.
+If the sampler or algorithm requires gradient information, then this function
+must return an `ADTypes.AbstractADType`.
+"""
+get_adtype(::AbstractSampler) = nothing
+get_adtype(::InferenceAlgorithm) = nothing
+get_adtype(spl::Sampler{<:InferenceAlgorithm}) = get_adtype(spl.alg)
+
+"""
+    requires_unconstrained_space(sampler::AbstractSampler)
+    requires_unconstrained_space(sampler::InferenceAlgorithm)
+Return `true` if the sampler / algorithm requires unconstrained space, and
+`false` otherwise. This is used to determine whether the initial VarInfo
+should be linked. Defaults to true.
+"""
+requires_unconstrained_space(::AbstractSampler) = true
+requires_unconstrained_space(::InferenceAlgorithm) = true
+function requires_unconstrained_space(spl::Sampler{<:InferenceAlgorithm})
+    return requires_unconstrained_space(spl.alg)
+end