1 files changed, 22 insertions, 0 deletions
diff --git a/vespajlib/src/main/java/com/yahoo/tensor/functions/ScalarFunction.java b/vespajlib/src/main/java/com/yahoo/tensor/functions/ScalarFunction.java
new file mode 100644
index 00000000000..c6a244b64df
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+++ b/vespajlib/src/main/java/com/yahoo/tensor/functions/ScalarFunction.java
@@ -0,0 +1,22 @@
+// Copyright 2019 Oath Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.tensor.functions;
+
+import com.yahoo.tensor.evaluation.EvaluationContext;
+
+import java.util.function.Function;
+
+/**
+ * A function which returns a scalar
+ *
+ * @author bratseth
+ */
+public interface ScalarFunction extends Function<EvaluationContext<?>, Double> {
+
+    @Override
+    Double apply(EvaluationContext<?> context);
+
+    default String toString(ToStringContext context) {
+        return toString();
+    }
+
+}