Sometimes we have an AST node and sometimes we have a raw value

lib/chervil/ast/identifier.rb

       if value.nil?
         ::Chervil::Error.new("unbound variable #{@name}")
       else
-        value.evaluate(env)
+        if value.respond_to?(:evaluate)
+          value.evaluate(env)
+        else
+          value
+        end
       end
     end
   end