Fix unassigned variables

Author: penelopeysm

src/compiler.jl

@@ -463,6 +463,11 @@ function generate_tilde_literal(left, right)
     end
 end
 
+assign_or_set!!(lhs::Symbol, rhs) = AbstractPPL.drop_escape(:($lhs = $rhs))
+function assign_or_set!!(lhs::Expr, rhs)
+    return AbstractPPL.drop_escape(:($BangBang.@set!! $lhs = $rhs))
+end
+
 """
     generate_tilde(left, right)
 
@@ -476,9 +481,6 @@ function generate_tilde(left, right)
     # if the LHS represents an observation
     @gensym vn isassumption value dist supplied_val
 
-    fixed_expr = :($BangBang.@set!! $left = $(DynamicPPL.getfixed_nested)(
-        __model__.context, $(DynamicPPL.prefix)(__model__.context, $vn)
-    ))
     return quote
         $dist = $right
         $vn = $(DynamicPPL.resolve_varnames)($(make_varname_expression(left)), $dist)
@@ -488,7 +490,12 @@ function generate_tilde(left, right)
             # use Accessors.@set to safely set it.
             # We need overwrite=true to make sure that the parent value `x` is overwritten
             # after this statement.
-            $(AbstractPPL.drop_escape(fixed_expr))
+            $(assign_or_set!!(
+                left,
+                :($(DynamicPPL.getfixed_nested)(
+                    __model__.context, $(DynamicPPL.prefix)(__model__.context, $vn)
+                )),
+            ))
         elseif $isassumption
             $(generate_tilde_assume(left, dist, vn))
         else
@@ -515,6 +522,7 @@ function generate_tilde(left, right)
                 $vn,
                 __varinfo__,
             )
+            $(assign_or_set!!(left, value))
             $value
         end
     end