tentatively seems to be working.

src/bin.rs

@@ -1,5 +1,6 @@
 extern crate nom;
 
+use crate::renderer::CompareContextElement;
 use crate::renderer::IntoBoxedContextElement;
 use parser::Filter;
 use renderer::compile_template;
@@ -11,6 +12,7 @@ use renderer::RenderError;
 use renderer::Renderable;
 use renderer::WalkError;
 use renderer::Walkable;
+use std::any::Any;
 use std::env;
 use std::fs;
 use std::io::{self, Read};
@@ -144,3 +146,16 @@ impl IntoBoxedContextElement for serde_json::Value {
         Box::new(self.clone())
     }
 }
+
+impl CompareContextElement for serde_json::Value {
+    fn to_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn equals(&self, other: &dyn ContextElement) -> bool {
+        other
+            .to_any()
+            .downcast_ref::<Self>()
+            .map_or(false, |a| self == a)
+    }
+}