condition and decondition using traits from #286 without ContextualModel

Project.toml

@@ -5,6 +5,7 @@ version = "0.13.1"
 [deps]
 AbstractMCMC = "80f14c24-f653-4e6a-9b94-39d6b0f70001"
 AbstractPPL = "7a57a42e-76ec-4ea3-a279-07e840d6d9cf"
+BangBang = "198e06fe-97b7-11e9-32a5-e1d131e6ad66"
 Bijectors = "76274a88-744f-5084-9051-94815aaf08c4"
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 Distributions = "31c24e10-a181-5473-b8eb-7969acd0382f"
@@ -15,6 +16,7 @@ ZygoteRules = "700de1a5-db45-46bc-99cf-38207098b444"
 [compat]
 AbstractMCMC = "2, 3.0"
 AbstractPPL = "0.2"
+BangBang = "0.3"
 Bijectors = "0.5.2, 0.6, 0.7, 0.8, 0.9"
 ChainRulesCore = "0.9.7, 0.10"
 Distributions = "0.23.8, 0.24, 0.25"

src/DynamicPPL.jl

@@ -9,6 +9,7 @@ using AbstractMCMC: AbstractMCMC
 using ChainRulesCore: ChainRulesCore
 using MacroTools: MacroTools
 using ZygoteRules: ZygoteRules
+using BangBang: BangBang
 
 using Random: Random
 
@@ -81,6 +82,7 @@ export AbstractVarInfo,
     PriorContext,
     MiniBatchContext,
     PrefixContext,
+    ConditionContext,
     assume,
     dot_assume,
     observe,
@@ -99,6 +101,8 @@ export AbstractVarInfo,
     logprior,
     logjoint,
     pointwise_loglikelihoods,
+    condition,
+    decondition,
     # Convenience macros
     @addlogprob!,
     @submodel

src/compiler.jl

@@ -20,19 +20,66 @@ function isassumption(expr::Union{Symbol,Expr})
 
     return quote
         let $vn = $(varname(expr))
-            # This branch should compile nicely in all cases except for partial missing data
-            # For example, when `expr` is `:(x[i])` and `x isa Vector{Union{Missing, Float64}}`
-            if !$(DynamicPPL.inargnames)($vn, __model__) ||
-               $(DynamicPPL.inmissings)($vn, __model__)
-                true
+            if $(DynamicPPL.contextual_isassumption)(__context__, $vn)
+                # Considered an assumption by `__context__` which means either:
+                # 1. We hit the default implementation, e.g. using `DefaultContext`,
+                #    which in turn means that we haven't considered if it's one of
+                #    the model arguments, hence we need to check this.
+                # 2. We are working with a `ConditionContext` _and_ it's NOT in the model arguments,
+                #    i.e. we're trying to condition one of the latent variables.
+                #    In this case, the below will return `true` since the first branch
+                #    will be hit.
+                # 3. We are working with a `ConditionContext` _and_ it's in the model arguments,
+                #    i.e. we're trying to override the value. This is currently NOT supported.
+                #    TODO: Support by adding context to model, and use `model.args`
+                #    as the default conditioning. Then we no longer need to check `inargnames`
+                #    since it will all be handled by `contextual_isassumption`.
+                if !($(DynamicPPL.inargnames)($vn, __model__)) ||
+                   $(DynamicPPL.inmissings)($vn, __model__)
+                    true
+                else
+                    $(maybe_view(expr)) === missing
+                end
             else
-                # Evaluate the LHS
-                $(maybe_view(expr)) === missing
+                false
             end
         end
     end
 end
 
+"""
+    contextual_isassumption(context, vn)
+
+Return `true` if `vn` is considered an assumption by `context`.
+
+The default implementation for `AbstractContext` always returns `true`.
+"""
+contextual_isassumption(::IsLeaf, context, vn) = true
+function contextual_isassumption(::IsParent, context, vn)
+    return contextual_isassumption(childcontext(context), vn)
+end
+function contextual_isassumption(context::AbstractContext, vn)
+    return contextual_isassumption(NodeTrait(context), context, vn)
+end
+function contextual_isassumption(context::ConditionContext, vn)
+    if hasvalue(context, vn)
+        val = getvalue(context, vn)
+        # TODO: Do we even need the `>: Missing` to help the compiler?
+        if eltype(val) >: Missing && val === missing
+            return true
+        else
+            return false
+        end
+    end
+
+    # We might have nested contexts, e.g. `ContextionContext{.., <:PrefixContext{..., <:ConditionContext}}`
+    # so we defer to `childcontext` if we haven't concluded that anything yet.
+    return contextual_isassumption(childcontext(context), vn)
+end
+function contextual_isassumption(context::PrefixContext, vn)
+    return contextual_isassumption(childcontext(context), prefix(context, vn))
+end
+
 # failsafe: a literal is never an assumption
 isassumption(expr) = :(false)
 
@@ -351,6 +398,11 @@ function generate_tilde(left, right)
                 __varinfo__,
             )
         else
+            # If `vn` is not in `argnames`, we need to make sure that the variable is defined.
+            if !$(DynamicPPL.inargnames)($vn, __model__)
+                $left = $(DynamicPPL.getvalue_nested)(__context__, $vn)
+            end
+
             $(DynamicPPL.tilde_observe!)(
                 __context__,
                 $(DynamicPPL.check_tilde_rhs)($right),
@@ -395,6 +447,11 @@ function generate_dot_tilde(left, right)
                 __varinfo__,
             )
         else
+            # If `vn` is not in `argnames`, we need to make sure that the variable is defined.
+            if !$(DynamicPPL.inargnames)($vn, __model__)
+                $left .= $(DynamicPPL.getvalue_nested)(__context__, $vn)
+            end
+
             $(DynamicPPL.dot_tilde_observe!)(
                 __context__,
                 $(DynamicPPL.check_tilde_rhs)($right),

src/context_implementations.jl

@@ -14,8 +14,17 @@ alg_str(spl::Sampler) = string(nameof(typeof(spl.alg)))
 require_gradient(spl::Sampler) = false
 require_particles(spl::Sampler) = false
 
-_getindex(x, inds::Tuple) = _getindex(view(x, first(inds)...), Base.tail(inds))
+_getindex(x, inds::Tuple) = _getindex(Base.maybeview(x, first(inds)...), Base.tail(inds))
 _getindex(x, inds::Tuple{}) = x
+_getvalue(x, vn::VarName{sym}) where {sym} = _getindex(getproperty(x, sym), vn.indexing)
+function _getvalue(x, vns::AbstractVector{<:VarName{sym}}) where {sym}
+    val = getproperty(x, sym)
+
+    # This should work with both cartesian and linear indexing.
+    return map(vns) do vn
+        _getindex(val, vn)
+    end
+end
 
 # assume
 """
@@ -162,6 +171,8 @@ function tilde_observe(context::SamplingContext, right, left, vi)
 end
 
 # Leaf contexts
+# TODO: Should we maybe not do `args...` here but instead be explicit?
+# Could help avoid stealthy bugs.
 function tilde_observe(context::AbstractContext, args...)
     return tilde_observe(NodeTrait(tilde_observe, context), context, args...)
 end
@@ -177,13 +188,14 @@ tilde_observe(::PriorContext, sampler, right, left, vi) = 0
 function tilde_observe(context::MiniBatchContext, right, left, vi)
     return context.loglike_scalar * tilde_observe(context.context, right, left, vi)
 end
-function tilde_observe(context::MiniBatchContext, right, left, vname, vi)
-    return context.loglike_scalar * tilde_observe(context.context, right, left, vname, vi)
+function tilde_observe(context::MiniBatchContext, sampler, right, left, vi)
+    return context.loglike_scalar *
+           tilde_observe(context.context, sampler, right, left, vname, vi)
 end
 
 # `PrefixContext`
-function tilde_observe(context::PrefixContext, right, left, vname, vi)
-    return tilde_observe(context.context, right, left, prefix(context, vname), vi)
+function tilde_observe(context::PrefixContext, right, left, vi)
+    return tilde_observe(context.context, right, left, vi)
 end
 
 """