Define rand defaults for AbstractProbabilisticProgram (#79)

This PR adds a 3-arg form of `rand` (suggested by @devmotion in TuringLang/DynamicPPL.jl#466 (comment)) to the interface for `AbstractProbabilisticProgram` and implements the default 1- and 2-arg methods that dispatch to this.

Currently tests fail because this breaks the fallbacks for `GraphPPL.Model`, which expects `rand` to forward to its `rand!` method. I'm not certain how we want to define the interface for this `Model`.

Co-authored-by: Xianda Sun <sunxdt@gmail.com>

Project.toml

@@ -3,7 +3,7 @@ uuid = "7a57a42e-76ec-4ea3-a279-07e840d6d9cf"
 keywords = ["probablistic programming"]
 license = "MIT"
 desc = "Common interfaces for probabilistic programming"
-version = "0.6.2"
+version = "0.6.3"
 
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"

src/abstractprobprog.jl

@@ -1,5 +1,6 @@
 using AbstractMCMC
 using DensityInterface
+using Random
 
 
 """
@@ -60,3 +61,22 @@ m = decondition(condition(m, obs))
 should hold for generative models `m` and arbitrary `obs`.
 """
 function condition end
+
+
+"""
+    rand([rng=Random.default_rng()], [T=NamedTuple], model::AbstractProbabilisticProgram) -> T
+
+Draw a sample from the joint distribution of the model specified by the probabilistic program.
+
+The sample will be returned as format specified by `T`.
+"""
+Base.rand(rng::Random.AbstractRNG, ::Type, model::AbstractProbabilisticProgram)
+function Base.rand(rng::Random.AbstractRNG, model::AbstractProbabilisticProgram)
+    return rand(rng, NamedTuple, model)
+end
+function Base.rand(::Type{T}, model::AbstractProbabilisticProgram) where {T}
+    return rand(Random.default_rng(), T, model)
+end
+function Base.rand(model::AbstractProbabilisticProgram)
+    return rand(Random.default_rng(), NamedTuple, model)
+end

src/graphinfo.jl

@@ -444,9 +444,9 @@ function Random.rand!(m::AbstractPPL.GraphPPL.Model{T}) where T
 end
 
 """
-    rand!(rng::AbstractRNG, m::Model)
+    rand(m::Model)
 
-Draw random samples from the model and mutate the node values. 
+Draw random samples from the model and return the samples as NamedTuple. 
 
 # Examples
 
@@ -470,11 +470,15 @@ julia> rand(m)
 (μ = 1.0, s2 = 1.0907695400401212, y = 0.05821954440386368)
 ```
 """
-function Random.rand(rng::AbstractRNG, sm::Random.SamplerTrivial{Model{Tnames, Tinput, Tvalue, Teval, Tkind}}) where {Tnames, Tinput, Tvalue, Teval, Tkind}
+function Base.rand(rng::AbstractRNG, sm::Random.SamplerTrivial{Model{Tnames, Tinput, Tvalue, Teval, Tkind}}) where {Tnames, Tinput, Tvalue, Teval, Tkind}
     m = deepcopy(sm[])
     get_model_values(rand!(rng, m))
 end
 
+function Base.rand(rng::AbstractRNG, ::Type{NamedTuple}, m::Model)
+    rand(rng, Random.SamplerTrivial(m))
+end
+
 """
     logdensityof(m::Model)
 

test/abstractprobprog.jl

@@ -0,0 +1,37 @@
+using AbstractPPL
+using Random
+using Test
+
+mutable struct RandModel <: AbstractProbabilisticProgram
+    rng
+    T
+end
+
+function Base.rand(rng::Random.AbstractRNG, ::Type{T}, model::RandModel) where {T}
+    model.rng = rng
+    model.T = T
+    return nothing
+end
+
+@testset "AbstractProbabilisticProgram" begin
+    @testset "rand defaults" begin
+        model = RandModel(nothing, nothing)
+        rand(model)
+        @test model.rng == Random.default_rng()
+        @test model.T === NamedTuple
+        rngs = [Random.default_rng(), Random.MersenneTwister(42)]
+        Ts = [NamedTuple, Dict]
+        @testset for T in Ts
+            model = RandModel(nothing, nothing)
+            rand(T, model)
+            @test model.rng == Random.default_rng()
+            @test model.T === T
+        end
+        @testset for rng in rngs
+            model = RandModel(nothing, nothing)
+            rand(rng, model)
+            @test model.rng === rng
+            @test model.T === NamedTuple
+        end
+    end
+end

test/runtests.jl

@@ -13,6 +13,7 @@ using Test
 @testset "AbstractPPL.jl" begin
     include("deprecations.jl")
     include("varname.jl")
+    include("abstractprobprog.jl")
     include("graphinfo/graphinfo.jl")
     @testset "doctests" begin
         DocMeta.setdocmeta!(