diff --git a/apps/shared/expression_model_store.cpp b/apps/shared/expression_model_store.cpp
index 431a2c2a8..00289df4e 100644
--- a/apps/shared/expression_model_store.cpp
+++ b/apps/shared/expression_model_store.cpp
@@ -40,7 +40,7 @@ void ExpressionModelStore::tidy() {
   resetMemoizedModelsExceptRecord();
 }
 
-int ExpressionModelStore::numberOfModelsSatisfyingTest(ModelTest test) const {
+int ExpressionModelStore::numberOfModelsSatisfyingTest(ModelTest test, void * context) const {
   int count = 0;
   int index = 0;
   Ion::Storage::Record record;
@@ -49,15 +49,15 @@ int ExpressionModelStore::numberOfModelsSatisfyingTest(ModelTest test) const {
     if (record.isNull()) {
       break;
     }
-    if (test(privateModelForRecord(record))) {
+    if (test(privateModelForRecord(record), context)) {
       count++;
     }
   } while (true);
   return count;
 }
 
-Ion::Storage::Record ExpressionModelStore::recordSatisfyingTestAtIndex(int i, ModelTest test) const {
-  assert(0 <= i && i < numberOfModelsSatisfyingTest(test));
+Ion::Storage::Record ExpressionModelStore::recordSatisfyingTestAtIndex(int i, ModelTest test, void * context) const {
+  assert(0 <= i && i < numberOfModelsSatisfyingTest(test, context));
   int count = 0;
   int index = 0;
   Ion::Storage::Record record;
@@ -67,7 +67,7 @@ Ion::Storage::Record ExpressionModelStore::recordSatisfyingTestAtIndex(int i, Mo
       assert(false);
       break;
     }
-    if (test(privateModelForRecord(record))) {
+    if (test(privateModelForRecord(record), context)) {
       if (i == count) {
         break;
       }
diff --git a/apps/shared/expression_model_store.h b/apps/shared/expression_model_store.h
index 8307136bc..c583b6996 100644
--- a/apps/shared/expression_model_store.h
+++ b/apps/shared/expression_model_store.h
@@ -19,9 +19,13 @@ public:
   // By default, the number of models is not bounded
   virtual int maxNumberOfModels() const { return -1; }
   int numberOfModels() const;
-  int numberOfDefinedModels() const { return numberOfModelsSatisfyingTest(&isModelDefined); }
   Ion::Storage::Record recordAtIndex(int i) const;
-  Ion::Storage::Record definedRecordAtIndex(int i) const { return recordSatisfyingTestAtIndex(i, &isModelDefined); }
+  int numberOfDefinedModels() const {
+    return numberOfModelsSatisfyingTest(&isModelDefined, nullptr);
+  }
+  Ion::Storage::Record definedRecordAtIndex(int i) const {
+    return recordSatisfyingTestAtIndex(i, &isModelDefined, nullptr);
+  }
   ExpiringPointer<ExpressionModelHandle> modelForRecord(Ion::Storage::Record record) const { return ExpiringPointer<ExpressionModelHandle>(privateModelForRecord(record)); }
 
   // Add and Remove
@@ -35,10 +39,10 @@ public:
 protected:
   constexpr static int k_maxNumberOfMemoizedModels = 10;
   int maxNumberOfMemoizedModels() const { return maxNumberOfModels() < 0 ? k_maxNumberOfMemoizedModels : maxNumberOfModels(); }
-  typedef bool (*ModelTest)(ExpressionModelHandle * model);
-  int numberOfModelsSatisfyingTest(ModelTest test) const;
-  Ion::Storage::Record recordSatisfyingTestAtIndex(int i, ModelTest test) const;
-  static bool isModelDefined(ExpressionModelHandle * model) {
+  typedef bool (*ModelTest)(ExpressionModelHandle * model, void * context);
+  int numberOfModelsSatisfyingTest(ModelTest test, void * context) const;
+  Ion::Storage::Record recordSatisfyingTestAtIndex(int i, ModelTest test, void * context) const;
+  static bool isModelDefined(ExpressionModelHandle * model, void * context) {
     return model->isDefined();
   }
   ExpressionModelHandle * privateModelForRecord(Ion::Storage::Record record) const;
diff --git a/apps/shared/function_store.h b/apps/shared/function_store.h
index f4f45266c..2790f6703 100644
--- a/apps/shared/function_store.h
+++ b/apps/shared/function_store.h
@@ -13,13 +13,17 @@ class FunctionStore : public ExpressionModelStore {
 public:
   FunctionStore() : ExpressionModelStore() {}
   uint32_t storeChecksum();
-  int numberOfActiveFunctions() const { return numberOfModelsSatisfyingTest(&isFunctionActive); }
-  Ion::Storage::Record activeRecordAtIndex(int i) const { return recordSatisfyingTestAtIndex(i, &isFunctionActive); }
+  int numberOfActiveFunctions() const {
+    return numberOfModelsSatisfyingTest(&isFunctionActive, nullptr);
+  }
+  Ion::Storage::Record activeRecordAtIndex(int i) const {
+    return recordSatisfyingTestAtIndex(i, &isFunctionActive, nullptr);
+  }
   ExpiringPointer<Function> modelForRecord(Ion::Storage::Record record) const { return ExpiringPointer<Function>(static_cast<Function *>(privateModelForRecord(record))); }
 protected:
-  static bool isFunctionActive(ExpressionModelHandle * model) {
+  static bool isFunctionActive(ExpressionModelHandle * model, void * context) {
     // An active function must be defined
-    return isModelDefined(model) && static_cast<Function *>(model)->isActive();
+    return isModelDefined(model, context) && static_cast<Function *>(model)->isActive();
   }
 };