Sketch of VarNamedTuple

src/DynamicPPL.jl

@@ -183,6 +183,8 @@ include("contexts/conditionfix.jl")  # Must come after contexts/prefix.jl
 include("model.jl")
 include("sampler.jl")
 include("varname.jl")
+include("varnamedtuple.jl")
+using .VarNamedTuples: VarNamedTuple
 include("distribution_wrappers.jl")
 include("submodel.jl")
 include("varnamedvector.jl")

src/varinfo.jl

@@ -154,6 +154,7 @@ const NTVarInfo = VarInfo{<:NamedTuple}
 const VarInfoOrThreadSafeVarInfo{Tmeta} = Union{
     VarInfo{Tmeta},ThreadSafeVarInfo{<:VarInfo{Tmeta}}
 }
+const TupleVarInfo = VarInfo{<:VarNamedTuple}
 
 function Base.:(==)(vi1::VarInfo, vi2::VarInfo)
     return (vi1.metadata == vi2.metadata && vi1.accs == vi2.accs)
@@ -356,6 +357,28 @@ function typed_vector_varinfo(
     return typed_vector_varinfo(Random.default_rng(), model, init_strategy)
 end
 
+function make_leaf_metadata((r, dist), optic)
+    md = Metadata()
+    vn = VarName{:_}(optic)
+    push!(md, vn, r, dist)
+    return md
+end
+
+function tuple_varinfo()
+    metadata = VarNamedTuple((;), make_leaf_metadata)
+    return VarInfo(metadata, copy(default_accumulators()))
+end
+function tuple_varinfo(
+    rng::Random.AbstractRNG,
+    model::Model,
+    init_strategy::AbstractInitStrategy=InitFromPrior(),
+)
+    return last(init!!(rng, model, tuple_varinfo(), init_strategy))
+end
+function tuple_varinfo(model::Model, init_strategy::AbstractInitStrategy=InitFromPrior())
+    return tuple_varinfo(Random.default_rng(), model, init_strategy)
+end
+
 """
     vector_length(varinfo::VarInfo)
 
@@ -639,6 +662,9 @@ Return the metadata in `vi` that belongs to `vn`.
 """
 getmetadata(vi::VarInfo, vn::VarName) = vi.metadata
 getmetadata(vi::NTVarInfo, vn::VarName) = getfield(vi.metadata, getsym(vn))
+function getmetadata(vi::TupleVarInfo, vn::VarName)
+    return getindex(vi.metadata, remove_trailing_index(vn))
+end
 
 """
     getidx(vi::VarInfo, vn::VarName)
@@ -744,6 +770,10 @@ end
 Return the distribution from which `vn` was sampled in `vi`.
 """
 getdist(vi::VarInfo, vn::VarName) = getdist(getmetadata(vi, vn), vn)
+function getdist(vi::TupleVarInfo, vn::VarName)
+    main_vn, optic = split_trailing_index(vn)
+    return getdist(getindex(vi.metadata, main_vn), VarName{:_}(optic))
+end
 getdist(md::Metadata, vn::VarName) = md.dists[getidx(md, vn)]
 # TODO(mhauru) Remove this once the old Gibbs sampler stuff is gone.
 function getdist(::VarNamedVector, ::VarName)
@@ -782,6 +812,10 @@ Set the value(s) of `vn` in the metadata of `vi` to `val`.
 The values may or may not be transformed to Euclidean space.
 """
 setval!(vi::VarInfo, val, vn::VarName) = setval!(getmetadata(vi, vn), val, vn)
+function setval!(vi::TupleVarInfo, val, vn::VarName)
+    main_vn, optic = split_trailing_index(vn)
+    return setval!(getindex(vi.metadata, main_vn), VarName{:_}(optic))
+end
 function setval!(md::Metadata, val::AbstractVector, vn::VarName)
     return md.vals[getrange(md, vn)] = val
 end
@@ -1579,6 +1613,7 @@ function Base.haskey(vi::NTVarInfo, vn::VarName)
     end
     return any(md_haskey)
 end
+Base.haskey(vi::TupleVarInfo, vn::VarName) = haskey(vi.metadata, vn)
 
 function Base.show(io::IO, ::MIME"text/plain", vi::UntypedVarInfo)
     lines = Tuple{String,Any}[
@@ -1673,6 +1708,25 @@ function BangBang.push!!(vi::VarInfo, vn::VarName, r, dist::Distribution)
     return vi
 end
 
+function BangBang.push!!(vi::TupleVarInfo, vn::VarName, r, dist::Distribution)
+    @assert ~(haskey(vi, vn)) "[push!!] attempt to add an existing variable $(getsym(vn)) ($(vn)) to TupleVarInfo with dist=$dist"
+    return VarInfo(setindex!!(vi.metadata, (r, dist), vn), vi.accs)
+end
+
+# TODO(mhauru) Implement properly
+function is_transformed(vi::TupleVarInfo, vn::VarName)
+    return false
+end
+
+function getindex(vi::TupleVarInfo, vn::VarName)
+    main_vn, optic = split_trailing_index(vn)
+    return getindex(getindex(vi.metadata, main_vn), VarName{:_}(optic))
+end
+function getindex_internal(vi::TupleVarInfo, vn::VarName)
+    main_vn, optic = split_trailing_index(vn)
+    return getindex_internal(getindex(vi.metadata, main_vn), VarName{:_}(optic))
+end
+
 function Base.push!(vi::UntypedVectorVarInfo, vn::VarName, val, args...)
     push!(getmetadata(vi, vn), vn, val, args...)
     return vi

src/varname.jl

@@ -41,3 +41,24 @@ Possibly existing indices of `varname` are neglected.
 ) where {s,missings,_F,_a,_T}
     return s in missings
 end
+
+function remove_trailing_index(vn::VarName{sym,Optic}) where {sym,Optic}
+    return if Optic === typeof(identity)
+        vn
+    elseif Optic isa IndexLens
+        VarName{sym}()
+    else
+        prefix(remove_trailing_index(unprefix(vn, sym)), sym)
+    end
+end
+
+function split_trailing_index(vn::VarName{sym,Optic}) where {sym,Optic}
+    return if Optic === typeof(identity)
+        (vn, identity)
+    elseif Optic isa IndexLens
+        (VarName{sym}(), Optic.index)
+    else
+        (prefix, index) = split_trailing_index(unprefix(vn, sym))
+        (prefix(prefix, sym), index)
+    end
+end