1 files changed, 20 insertions, 0 deletions

diff --git a/subprojects/store-query/src/main/java/tools/refinery/store/query/term/StatelessAggregator.java b/subprojects/store-query/src/main/java/tools/refinery/store/query/term/StatelessAggregator.java
new file mode 100644
index 00000000..74dbd335
--- /dev/null
+++ b/subprojects/store-query/src/main/java/tools/refinery/store/query/term/StatelessAggregator.java
@@ -0,0 +1,20 @@
+package tools.refinery.store.query.term;
+
+import java.util.stream.Stream;
+
+public interface StatelessAggregator<R, T> extends Aggregator<R, T> {
+        R add(R current, T value);
+
+        R remove(R current, T value);
+
+        @Override
+        default R aggregateStream(Stream<T> stream) {
+                var accumulator = getEmptyResult();
+                var iterator = stream.iterator();
+                while (iterator.hasNext()) {
+                        var value = iterator.next();
+                        accumulator = add(accumulator, value);
+                }
+                return accumulator;
+        }
+}