xo-reader: prefer xo::bp spelling to xo::ref::brw

xo-reader/src/reader/envframe.cpp

@@ -20,6 +20,20 @@ namespace xo {
             return nullptr;
         }
 
+        void
+        envframe::upsert(bp<Variable> target) {
+            for (auto & var : this->argl_) {
+                if (var->name() == target->name()) {
+                    /* replace existing variable -- may change type */
+                    var = target.promote();
+                    return;
+                }
+            }
+
+            /* here: target not already present in this frame, append it */
+            this->argl_.push_back(target.promote());
+        }
+
         void
         envframe::print(std::ostream & os) const {
             os << "<envframe"