Added context mutator function

Signed-off-by: ama2369 <ama2369@columbia.edu>

Author: ama2369

functions-gql/src/lib.rs

@@ -41,6 +41,7 @@ pub fn register_default_gql_functions(registry: &FunctionRegistry) {
     register_list_functions(registry);
     register_metadata_functions(registry);
     register_drasi_functions(registry);
+    register_context_mutators(registry);
     register_aggregation_functions(registry);
     register_temporal_instant_functions(registry);
     register_temporal_duration_functions(registry);
@@ -93,6 +94,13 @@ fn register_drasi_functions(registry: &FunctionRegistry) {
     registry.register_function("drasi.stdevp", Function::Scalar(Arc::new(DrasiStdevP {})));
 }
 
+fn register_context_mutators(registry: &FunctionRegistry) {
+    registry.register_function(
+        "retainHistory",
+        Function::ContextMutator(Arc::new(RetainHistory {})),
+    );
+}
+
 fn register_aggregation_functions(registry: &FunctionRegistry) {
     registry.register_function("sum", Function::Aggregating(Arc::new(Sum {})));
     registry.register_function("avg", Function::Aggregating(Arc::new(Avg {})));