diff --git a/src/gen_fn_interface.jl b/src/gen_fn_interface.jl
index 40b494a80..9446bcf48 100644
--- a/src/gen_fn_interface.jl
+++ b/src/gen_fn_interface.jl
@@ -61,6 +61,13 @@ When there is no non-addressed randomness, this simplifies to the log probabilit
 """
 function get_score end
 
+"""
+    logpdf(trace)
+
+Synonym for [`get_score`](@ref).
+"""
+logpdf(trace::Trace) = get_score(trace)
+
 """
     gen_fn::GenerativeFunction = get_gen_fn(trace)
 
@@ -394,3 +401,4 @@ export update
 export regenerate
 export accumulate_param_gradients!
 export choice_gradients
+export logpdf
diff --git a/src/modeling_library/modeling_library.jl b/src/modeling_library/modeling_library.jl
index d0797426c..688b81a15 100644
--- a/src/modeling_library/modeling_library.jl
+++ b/src/modeling_library/modeling_library.jl
@@ -73,6 +73,8 @@ include("map/map.jl")
 include("unfold/unfold.jl")
 include("recurse/recurse.jl")
 
+include("override_internal_proposal.jl")
+
 #############################################################
 # abstractions for constructing custom generative functions #
 #############################################################
diff --git a/src/modeling_library/override_internal_proposal.jl b/src/modeling_library/override_internal_proposal.jl
new file mode 100644
index 000000000..6ada20509
--- /dev/null
+++ b/src/modeling_library/override_internal_proposal.jl
@@ -0,0 +1,76 @@
+
+# Generative function combiantor that overrides internal proposal with another
+# generative function
+
+# Not yet implemented:
+# - update
+# - project
+# - choice_gradients
+# - accumulate_param_gradients!
+
+struct ReplaceProposalGFTrace{U} <: Trace
+    model_trace::U
+    gen_fn::GenerativeFunction
+end
+
+get_args(tr::ReplaceProposalGFTrace) = get_args(tr.model_trace)
+get_retval(tr::ReplaceProposalGFTrace) = get_retval(tr.model_trace)
+get_choices(tr::ReplaceProposalGFTrace) = get_choices(tr.model_trace)
+get_score(tr::ReplaceProposalGFTrace) = get_score(tr.model_trace)
+
+struct ReplaceProposalGF{T,U} <: GenerativeFunction{T,ReplaceProposalGFTrace{U}}
+    model::GenerativeFunction{T,U}
+    proposal::GenerativeFunction
+end
+
+get_gen_fn(tr::ReplaceProposalGFTrace) = tr.gen_fn
+
+# gradient ops not implemented yet
+has_argument_grads(f::ReplaceProposalGF) = map(_->false,has_argument_grads(f.model))
+accepts_output_grad(f::ReplaceProposalGF) = false
+
+function project(tr::ReplaceProposalGFTrace, ::EmptySelection)
+    return project(tr.model_trace, EmptySelection())
+end
+
+function simulate(gen_fn::ReplaceProposalGF, args::Tuple)
+    tr = simulate(gen_fn.model, args)
+    return ReplaceProposalGFTrace(tr, gen_fn)
+end
+
+function generate(gen_fn::ReplaceProposalGF, args::Tuple, constraints::ChoiceMap)
+    (proposed_choices, proposal_weight, _) = propose(gen_fn.proposal, (constraints, args...))
+    all_constraints = merge(proposed_choices, constraints)
+    new_tr, model_weight = generate(gen_fn.model, args, all_constraints)
+    @assert isapprox(model_weight, get_score(new_tr))
+    weight = model_weight - proposal_weight
+    return (ReplaceProposalGFTrace(new_tr, gen_fn), weight)
+end
+
+function regenerate(trace::ReplaceProposalGFTrace, args::Tuple, argdiffs::Tuple, selection::Selection)
+    gen_fn = get_gen_fn(trace)
+    prev_args = get_args(trace)
+
+    # u <- create choice map u containing addresses from trace, except for those in selection
+    u = get_selected(get_choices(trace), complement(selection))
+
+    # then, run generate with that u to obtain new-trace t', and weight w = p(t'; x') / q(t; x, u')
+    (new_trace, p_weight) = generate(gen_fn, args, u)
+
+    # then, create choice map u' containing addresses from new-trace, except for those in selection
+    u_backward = get_selected(get_choices(new_trace), complement(selection))
+
+    # then, run generate on custom_q to obtain q(t; x, u')
+    (_, q_weight) = generate(gen_fn.proposal, (u_backward, prev_args...), get_choices(trace)) # NOTE there will be extra choices
+    
+    # then, use get_score(trace) and subtracct it from the weight
+    weight = p_weight + q_weight - get_score(trace)
+
+    return (new_trace, weight, UnknownChange())
+end
+
+function override_internal_proposal(p, q)
+    return ReplaceProposalGF(p, q)
+end
+
+export override_internal_proposal