Serialize scalar functions with context

12 files changed, 135 insertions, 64 deletions

diff --git a/config-model/src/test/derived/tensor/rank-profiles.cfg b/config-model/src/test/derived/tensor/rank-profiles.cfg
index d28746bd520..617901130a6 100644
--- a/config-model/src/test/derived/tensor/rank-profiles.cfg
+++ b/config-model/src/test/derived/tensor/rank-profiles.cfg
@@ -93,3 +93,20 @@ rankprofile[].fef.property[].name "vespa.type.attribute.f4"
 rankprofile[].fef.property[].value "tensor(x[10],y[20])"
 rankprofile[].fef.property[].name "vespa.type.attribute.f5"
 rankprofile[].fef.property[].value "tensor<float>(x[10])"
+rankprofile[].name "profile6"
+rankprofile[].fef.property[].name "rankingExpression(joinedtensors).rankingScript"
+rankprofile[].fef.property[].value "tensor(i[10])(i) * attribute(f4)"
+rankprofile[].fef.property[].name "rankingExpression(joinedtensors).type"
+rankprofile[].fef.property[].value "tensor(i[10],x[10],y[20])"
+rankprofile[].fef.property[].name "vespa.rank.firstphase"
+rankprofile[].fef.property[].value "rankingExpression(firstphase)"
+rankprofile[].fef.property[].name "rankingExpression(firstphase).rankingScript"
+rankprofile[].fef.property[].value "reduce(tensor<float>(d0[1],x[2]):{{d0:0,x:0}:attribute(f6),{d0:0,x:1}:reduce(rankingExpression(joinedtensors), sum)}, sum)"
+rankprofile[].fef.property[].name "vespa.type.attribute.f2"
+rankprofile[].fef.property[].value "tensor<float>(x[2],y[1])"
+rankprofile[].fef.property[].name "vespa.type.attribute.f3"
+rankprofile[].fef.property[].value "tensor(x{})"
+rankprofile[].fef.property[].name "vespa.type.attribute.f4"
+rankprofile[].fef.property[].value "tensor(x[10],y[20])"
+rankprofile[].fef.property[].name "vespa.type.attribute.f5"
+rankprofile[].fef.property[].value "tensor<float>(x[10])"
diff --git a/config-model/src/test/derived/tensor/tensor.sd b/config-model/src/test/derived/tensor/tensor.sd
index fa139d1e769..13727d1ec49 100644
--- a/config-model/src/test/derived/tensor/tensor.sd
+++ b/config-model/src/test/derived/tensor/tensor.sd
@@ -66,4 +66,16 @@ search tensor {
 
   }
 
+  rank-profile profile6 {
+
+    first-phase {
+      expression: sum(tensor<float>(d0[1],x[2]):[[attribute(f6), sum(joinedtensors())]])
+    }
+
+    function joinedtensors() {
+        expression: tensor(i[10])(i) * attribute(f4)
+    }
+
+  }
+
 }
diff --git a/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/Const.java b/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/Const.java
index fc895b07d53..01fd7ee55bd 100644
--- a/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/Const.java
+++ b/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/Const.java
@@ -9,9 +9,6 @@ import com.yahoo.searchlib.rankingexpression.rule.ConstantNode;
 import com.yahoo.searchlib.rankingexpression.rule.ExpressionNode;
 import com.yahoo.searchlib.rankingexpression.rule.ReferenceNode;
 import com.yahoo.searchlib.rankingexpression.rule.TensorFunctionNode;
-import com.yahoo.tensor.TensorType;
-import com.yahoo.tensor.evaluation.VariableTensor;
-import com.yahoo.tensor.functions.Rename;
 import com.yahoo.tensor.functions.TensorFunction;
 
 import java.util.List;
@@ -53,7 +50,7 @@ public class Const extends IntermediateOperation {
         } else {
             expressionNode = new ReferenceNode(Reference.simple("constant", vespaName()));
         }
-        return new TensorFunctionNode.TensorFunctionExpressionNode(expressionNode);
+        return new TensorFunctionNode.ExpressionTensorFunction(expressionNode);
     }
 
     /** Constant names are prefixed by "modelName_" to avoid name conflicts between models */
diff --git a/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/IntermediateOperation.java b/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/IntermediateOperation.java
index 26b376cce1c..87a3f1a8e66 100644
--- a/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/IntermediateOperation.java
+++ b/model-integration/src/main/java/ai/vespa/rankingexpression/importer/operations/IntermediateOperation.java
@@ -3,7 +3,6 @@
 package ai.vespa.rankingexpression.importer.operations;
 
 import ai.vespa.rankingexpression.importer.DimensionRenamer;
-import ai.vespa.rankingexpression.importer.IntermediateGraph;
 import ai.vespa.rankingexpression.importer.OrderedTensorType;
 import com.yahoo.searchlib.rankingexpression.Reference;
 import com.yahoo.searchlib.rankingexpression.evaluation.Value;
@@ -74,7 +73,7 @@ public abstract class IntermediateOperation {
         if (function == null) {
             if (isConstant()) {
                 ExpressionNode constant = new ReferenceNode(Reference.simple("constant", vespaName()));
-                function = new TensorFunctionNode.TensorFunctionExpressionNode(constant);
+                function = new TensorFunctionNode.ExpressionTensorFunction(constant);
             } else if (outputs.size() > 1) {
                 rankingExpressionFunction = lazyGetFunction();
                 function = new VariableTensor(rankingExpressionFunctionName(), type.type());
diff --git a/searchlib/abi-spec.json b/searchlib/abi-spec.json
index 1258601a2d1..8d7bf4f9f14 100644
--- a/searchlib/abi-spec.json
+++ b/searchlib/abi-spec.json
@@ -1580,7 +1580,7 @@
     ],
     "fields": []
   },
-  "com.yahoo.searchlib.rankingexpression.rule.TensorFunctionNode$TensorFunctionExpressionNode": {
+  "com.yahoo.searchlib.rankingexpression.rule.TensorFunctionNode$ExpressionTensorFunction": {
     "superClass": "com.yahoo.tensor.functions.PrimitiveTensorFunction",
     "interfaces": [],
     "attributes": [
@@ -1612,7 +1612,7 @@
       "public java.lang.StringBuilder toString(java.lang.StringBuilder, com.yahoo.searchlib.rankingexpression.rule.SerializationContext, java.util.Deque, com.yahoo.searchlib.rankingexpression.rule.CompositeNode)",
       "public com.yahoo.tensor.TensorType type(com.yahoo.tensor.evaluation.TypeContext)",
       "public com.yahoo.searchlib.rankingexpression.evaluation.Value evaluate(com.yahoo.searchlib.rankingexpression.evaluation.Context)",
-      "public static com.yahoo.searchlib.rankingexpression.rule.TensorFunctionNode$TensorFunctionExpressionNode wrap(com.yahoo.searchlib.rankingexpression.rule.ExpressionNode)",
+      "public static com.yahoo.searchlib.rankingexpression.rule.TensorFunctionNode$ExpressionTensorFunction wrap(com.yahoo.searchlib.rankingexpression.rule.ExpressionNode)",
       "public static java.util.Map wrap(java.util.Map)",
       "public static java.util.List wrap(java.util.List)"
     ],
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java
index e6e49e07c34..4ffd40f00f7 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/TensorFunctionNode.java
@@ -12,6 +12,7 @@ import com.yahoo.tensor.TensorType;
 import com.yahoo.tensor.evaluation.EvaluationContext;
 import com.yahoo.tensor.evaluation.TypeContext;
 import com.yahoo.tensor.functions.PrimitiveTensorFunction;
+import com.yahoo.tensor.functions.ScalarFunction;
 import com.yahoo.tensor.functions.TensorFunction;
 import com.yahoo.tensor.functions.ToStringContext;
 
@@ -21,7 +22,6 @@ import java.util.Deque;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.function.Function;
 import java.util.stream.Collectors;
 
 /**
@@ -49,8 +49,8 @@ public class TensorFunctionNode extends CompositeNode {
     }
 
     private ExpressionNode toExpressionNode(TensorFunction f) {
-        if (f instanceof TensorFunctionExpressionNode)
-            return ((TensorFunctionExpressionNode)f).expression;
+        if (f instanceof ExpressionTensorFunction)
+            return ((ExpressionTensorFunction)f).expression;
         else
             return new TensorFunctionNode(f);
     }
@@ -58,7 +58,7 @@ public class TensorFunctionNode extends CompositeNode {
     @Override
     public CompositeNode setChildren(List<ExpressionNode> children) {
         List<TensorFunction> wrappedChildren = children.stream()
-                                                        .map(TensorFunctionExpressionNode::new)
+                                                        .map(ExpressionTensorFunction::new)
                                                         .collect(Collectors.toList());
         return new TensorFunctionNode(function.withArguments(wrappedChildren));
     }
@@ -66,7 +66,7 @@ public class TensorFunctionNode extends CompositeNode {
     @Override
     public StringBuilder toString(StringBuilder string, SerializationContext context, Deque<String> path, CompositeNode parent) {
         // Serialize as primitive
-        return string.append(function.toPrimitive().toString(new ExpressionNodeToStringContext(context, path, this)));
+        return string.append(function.toPrimitive().toString(new ExpressionToStringContext(context, path, this)));
     }
 
     @Override
@@ -77,29 +77,29 @@ public class TensorFunctionNode extends CompositeNode {
         return new TensorValue(function.evaluate(context));
     }
 
-    public static TensorFunctionExpressionNode wrap(ExpressionNode node) {
-        return new TensorFunctionExpressionNode(node);
+    public static ExpressionTensorFunction wrap(ExpressionNode node) {
+        return new ExpressionTensorFunction(node);
     }
 
-    public static Map<TensorAddress, Function<EvaluationContext<?>, Double>> wrap(Map<TensorAddress, ExpressionNode> nodes) {
-        Map<TensorAddress, Function<EvaluationContext<?>, Double>> closures = new LinkedHashMap<>();
+    public static Map<TensorAddress, ScalarFunction> wrap(Map<TensorAddress, ExpressionNode> nodes) {
+        Map<TensorAddress, ScalarFunction> functions = new LinkedHashMap<>();
         for (var entry : nodes.entrySet())
-            closures.put(entry.getKey(), new ExpressionClosure(entry.getValue()));
-        return closures;
+            functions.put(entry.getKey(), new ExpressionScalarFunction(entry.getValue()));
+        return functions;
     }
 
-    public static List<Function<EvaluationContext<?>, Double>> wrap(List<ExpressionNode> nodes) {
-        List<Function<EvaluationContext<?>, Double>> closures = new ArrayList<>();
+    public static List<ScalarFunction> wrap(List<ExpressionNode> nodes) {
+        List<ScalarFunction> functions = new ArrayList<>();
         for (var entry : nodes)
-            closures.add(new ExpressionClosure(entry));
-        return closures;
+            functions.add(new ExpressionScalarFunction(entry));
+        return functions;
     }
 
-    private static class ExpressionClosure implements java.util.function.Function<EvaluationContext<?> , Double> {
+    private static class ExpressionScalarFunction implements ScalarFunction {
 
         private final ExpressionNode expression;
 
-        public ExpressionClosure(ExpressionNode expression) {
+        public ExpressionScalarFunction(ExpressionNode expression) {
             this.expression = expression;
         }
 
@@ -110,7 +110,18 @@ public class TensorFunctionNode extends CompositeNode {
 
         @Override
         public String toString() {
-            return expression.toString();
+            return toString(ExpressionToStringContext.empty);
+        }
+
+        @Override
+        public String toString(ToStringContext c) {
+            if (c instanceof ExpressionToStringContext) {
+                ExpressionToStringContext context = (ExpressionToStringContext) c;
+                return expression.toString(new StringBuilder(),context.context, context.path, context.parent).toString();
+            }
+            else {
+                return expression.toString();
+            }
         }
 
     }
@@ -119,12 +130,12 @@ public class TensorFunctionNode extends CompositeNode {
      * A tensor function implemented by an expression.
      * This allows us to pass expressions as tensor function arguments.
      */
-    public static class TensorFunctionExpressionNode extends PrimitiveTensorFunction {
+    public static class ExpressionTensorFunction extends PrimitiveTensorFunction {
 
         /** An expression which produces a tensor */
         private final ExpressionNode expression;
 
-        public TensorFunctionExpressionNode(ExpressionNode expression) {
+        public ExpressionTensorFunction(ExpressionNode expression) {
             this.expression = expression;
         }
 
@@ -132,7 +143,7 @@ public class TensorFunctionNode extends CompositeNode {
         public List<TensorFunction> arguments() {
             if (expression instanceof CompositeNode)
                 return ((CompositeNode)expression).children().stream()
-                                                             .map(TensorFunctionExpressionNode::new)
+                                                             .map(ExpressionTensorFunction::new)
                                                              .collect(Collectors.toList());
             else
                 return Collections.emptyList();
@@ -142,9 +153,9 @@ public class TensorFunctionNode extends CompositeNode {
         public TensorFunction withArguments(List<TensorFunction> arguments) {
             if (arguments.size() == 0) return this;
             List<ExpressionNode> unwrappedChildren = arguments.stream()
-                                                              .map(arg -> ((TensorFunctionExpressionNode)arg).expression)
+                                                              .map(arg -> ((ExpressionTensorFunction)arg).expression)
                                                               .collect(Collectors.toList());
-            return new TensorFunctionExpressionNode(((CompositeNode)expression).setChildren(unwrappedChildren));
+            return new ExpressionTensorFunction(((CompositeNode)expression).setChildren(unwrappedChildren));
         }
 
         @Override
@@ -163,13 +174,13 @@ public class TensorFunctionNode extends CompositeNode {
 
         @Override
         public String toString() {
-            return toString(ExpressionNodeToStringContext.empty);
+            return toString(ExpressionToStringContext.empty);
         }
 
         @Override
         public String toString(ToStringContext c) {
-            if (c instanceof ExpressionNodeToStringContext) {
-                ExpressionNodeToStringContext context = (ExpressionNodeToStringContext) c;
+            if (c instanceof ExpressionToStringContext) {
+                ExpressionToStringContext context = (ExpressionToStringContext) c;
                 return expression.toString(new StringBuilder(),context.context, context.path, context.parent).toString();
             }
             else {
@@ -180,17 +191,17 @@ public class TensorFunctionNode extends CompositeNode {
     }
 
     /** Allows passing serialization context arguments through TensorFunctions */
-    private static class ExpressionNodeToStringContext implements ToStringContext {
+    private static class ExpressionToStringContext implements ToStringContext {
 
         final SerializationContext context;
         final Deque<String> path;
         final CompositeNode parent;
 
-        public static final ExpressionNodeToStringContext empty = new ExpressionNodeToStringContext(new SerializationContext(),
-                                                                                                    null,
-                                                                                                    null);
+        public static final ExpressionToStringContext empty = new ExpressionToStringContext(new SerializationContext(),
+                                                                                            null,
+                                                                                            null);
 
-        public ExpressionNodeToStringContext(SerializationContext context, Deque<String> path, CompositeNode parent) {
+        public ExpressionToStringContext(SerializationContext context, Deque<String> path, CompositeNode parent) {
             this.context = context;
             this.path = path;
             this.parent = parent;
diff --git a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/transform/TensorMaxMinTransformer.java b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/transform/TensorMaxMinTransformer.java
index 6d687b015f1..9a38b5efc1f 100644
--- a/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/transform/TensorMaxMinTransformer.java
+++ b/searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/transform/TensorMaxMinTransformer.java
@@ -83,7 +83,7 @@ public class TensorMaxMinTransformer<CONTEXT extends TransformContext> extends E
         ExpressionNode arg1 = node.children().get(0);
         ExpressionNode arg2 = node.children().get(1);
 
-        TensorFunctionNode.TensorFunctionExpressionNode expression = TensorFunctionNode.wrap(arg1);
+        TensorFunctionNode.ExpressionTensorFunction expression = TensorFunctionNode.wrap(arg1);
         Reduce.Aggregator aggregator = Reduce.Aggregator.valueOf(node.getFunction().name());
         String dimension = ((ReferenceNode) arg2).getName();
 
diff --git a/searchlib/src/test/java/com/yahoo/searchlib/rankingexpression/RankingExpressionTestCase.java b/searchlib/src/test/java/com/yahoo/searchlib/rankingexpression/RankingExpressionTestCase.java
index efebdb310f7..e7024b87452 100755
--- a/searchlib/src/test/java/com/yahoo/searchlib/rankingexpression/RankingExpressionTestCase.java
+++ b/searchlib/src/test/java/com/yahoo/searchlib/rankingexpression/RankingExpressionTestCase.java
@@ -1,20 +1,16 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.searchlib.rankingexpression;
 
-import com.yahoo.searchlib.rankingexpression.evaluation.DoubleValue;
 import com.yahoo.searchlib.rankingexpression.parser.ParseException;
 import com.yahoo.searchlib.rankingexpression.rule.ArithmeticNode;
 import com.yahoo.searchlib.rankingexpression.rule.ArithmeticOperator;
 import com.yahoo.searchlib.rankingexpression.rule.CompositeNode;
-import com.yahoo.searchlib.rankingexpression.rule.ConstantNode;
-import com.yahoo.searchlib.rankingexpression.rule.Function;
 import com.yahoo.searchlib.rankingexpression.rule.IfNode;
 import com.yahoo.searchlib.rankingexpression.rule.ExpressionNode;
 import com.yahoo.searchlib.rankingexpression.rule.FunctionNode;
 import com.yahoo.searchlib.rankingexpression.rule.ReferenceNode;
 import com.yahoo.searchlib.rankingexpression.rule.TensorFunctionNode;
 import com.yahoo.tensor.functions.Reduce;
-import com.yahoo.tensor.functions.TensorFunction;
 import org.junit.Test;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
@@ -65,7 +61,7 @@ public class RankingExpressionTestCase {
         ReferenceNode input = new ReferenceNode("input");
         ReferenceNode constant = new ReferenceNode("constant");
         ArithmeticNode product = new ArithmeticNode(input, ArithmeticOperator.MULTIPLY, constant);
-        Reduce sum = new Reduce(new TensorFunctionNode.TensorFunctionExpressionNode(product), Reduce.Aggregator.sum);
+        Reduce sum = new Reduce(new TensorFunctionNode.ExpressionTensorFunction(product), Reduce.Aggregator.sum);
         RankingExpression expression = new RankingExpression(new TensorFunctionNode(sum));
 
         RankingExpression expected = new RankingExpression("sum(input * constant)");
diff --git a/vespajlib/abi-spec.json b/vespajlib/abi-spec.json
index 8b87c5dc79f..47b066b15a6 100644
--- a/vespajlib/abi-spec.json
+++ b/vespajlib/abi-spec.json
@@ -1606,6 +1606,7 @@
       "public java.util.List arguments()",
       "public com.yahoo.tensor.functions.TensorFunction withArguments(java.util.List)",
       "public com.yahoo.tensor.functions.PrimitiveTensorFunction toPrimitive()",
+      "public java.lang.String toString(com.yahoo.tensor.functions.ToStringContext)",
       "public static com.yahoo.tensor.functions.DynamicTensor from(com.yahoo.tensor.TensorType, java.util.Map)",
       "public static com.yahoo.tensor.functions.DynamicTensor from(com.yahoo.tensor.TensorType, java.util.List)"
     ],
@@ -1835,6 +1836,23 @@
     ],
     "fields": []
   },
+  "com.yahoo.tensor.functions.ScalarFunction": {
+    "superClass": "java.lang.Object",
+    "interfaces": [
+      "java.util.function.Function"
+    ],
+    "attributes": [
+      "public",
+      "interface",
+      "abstract"
+    ],
+    "methods": [
+      "public abstract java.lang.Double apply(com.yahoo.tensor.evaluation.EvaluationContext)",
+      "public java.lang.String toString(com.yahoo.tensor.functions.ToStringContext)",
+      "public bridge synthetic java.lang.Object apply(java.lang.Object)"
+    ],
+    "fields": []
+  },
   "com.yahoo.tensor.functions.ScalarFunctions$Abs": {
     "superClass": "java.lang.Object",
     "interfaces": [
diff --git a/vespajlib/src/main/java/com/yahoo/tensor/functions/DynamicTensor.java b/vespajlib/src/main/java/com/yahoo/tensor/functions/DynamicTensor.java
index 1154f962a6f..b8b644f8b49 100644
--- a/vespajlib/src/main/java/com/yahoo/tensor/functions/DynamicTensor.java
+++ b/vespajlib/src/main/java/com/yahoo/tensor/functions/DynamicTensor.java
@@ -46,21 +46,28 @@ public abstract class DynamicTensor extends PrimitiveTensorFunction {
 
     TensorType type() { return type; }
 
+    @Override
+    public String toString(ToStringContext context) {
+        return type().toString() + ":" + contentToString(context);
+    }
+
+    abstract String contentToString(ToStringContext context);
+
     /** Creates a dynamic tensor function. The cell addresses must match the type. */
-    public static DynamicTensor from(TensorType type, Map<TensorAddress, Function<EvaluationContext<?> , Double>> cells) {
+    public static DynamicTensor from(TensorType type, Map<TensorAddress, ScalarFunction> cells) {
         return new MappedDynamicTensor(type, cells);
     }
 
     /** Creates a dynamic tensor function for a bound, indexed tensor */
-    public static DynamicTensor from(TensorType type, List<Function<EvaluationContext<?> , Double>> cells) {
+    public static DynamicTensor from(TensorType type, List<ScalarFunction> cells) {
         return new IndexedDynamicTensor(type, cells);
     }
 
     private static class MappedDynamicTensor extends DynamicTensor {
 
-        private final ImmutableMap<TensorAddress, Function<EvaluationContext<?> , Double>> cells;
+        private final ImmutableMap<TensorAddress, ScalarFunction> cells;
 
-        MappedDynamicTensor(TensorType type, Map<TensorAddress, Function<EvaluationContext<?> , Double>> cells) {
+        MappedDynamicTensor(TensorType type, Map<TensorAddress, ScalarFunction> cells) {
             super(type);
             this.cells = ImmutableMap.copyOf(cells);
         }
@@ -74,11 +81,7 @@ public abstract class DynamicTensor extends PrimitiveTensorFunction {
         }
 
         @Override
-        public String toString(ToStringContext context) {
-            return type().toString() + ":" + contentToString();
-        }
-
-        private String contentToString() {
+        String contentToString(ToStringContext context) {
             if (type().dimensions().isEmpty()) {
                 if (cells.isEmpty()) return "{}";
                 return "{" + cells.values().iterator().next() + "}";
@@ -86,7 +89,7 @@ public abstract class DynamicTensor extends PrimitiveTensorFunction {
 
             StringBuilder b = new StringBuilder("{");
             for (var cell : cells.entrySet()) {
-                b.append(cell.getKey().toString(type())).append(":").append(cell.getValue());
+                b.append(cell.getKey().toString(type())).append(":").append(cell.getValue().toString(context));
                 b.append(",");
             }
             if (b.length() > 1)
@@ -100,9 +103,9 @@ public abstract class DynamicTensor extends PrimitiveTensorFunction {
 
     private static class IndexedDynamicTensor extends DynamicTensor {
 
-        private final List<Function<EvaluationContext<?>, Double>> cells;
+        private final List<ScalarFunction> cells;
 
-        IndexedDynamicTensor(TensorType type, List<Function<EvaluationContext<?> , Double>> cells) {
+        IndexedDynamicTensor(TensorType type, List<ScalarFunction> cells) {
             super(type);
             if ( ! type.dimensions().stream().allMatch(d -> d.type() == TensorType.Dimension.Type.indexedBound))
                 throw new IllegalArgumentException("A dynamic tensor can only be created from a list if the type has " +
@@ -119,11 +122,7 @@ public abstract class DynamicTensor extends PrimitiveTensorFunction {
         }
 
         @Override
-        public String toString(ToStringContext context) {
-            return type().toString() + ":" + contentToString();
-        }
-
-        private String contentToString() {
+        String contentToString(ToStringContext context) {
             if (type().dimensions().isEmpty()) {
                 if (cells.isEmpty()) return "{}";
                 return "{" + cells.get(0) + "}";
@@ -133,7 +132,7 @@ public abstract class DynamicTensor extends PrimitiveTensorFunction {
             StringBuilder b = new StringBuilder("{");
             for (var cell : cells) {
                 indexes.next();
-                b.append(indexes.toAddress().toString(type())).append(":").append(cell);
+                b.append(indexes.toAddress().toString(type())).append(":").append(cell.toString(context));
                 b.append(",");
             }
             if (b.length() > 1)
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
--- /dev/null
+++ 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();
+    }
+
+}
diff --git a/vespajlib/src/test/java/com/yahoo/tensor/functions/DynamicTensorTestCase.java b/vespajlib/src/test/java/com/yahoo/tensor/functions/DynamicTensorTestCase.java
index 474e6200676..925da9d3c89 100644
--- a/vespajlib/src/test/java/com/yahoo/tensor/functions/DynamicTensorTestCase.java
+++ b/vespajlib/src/test/java/com/yahoo/tensor/functions/DynamicTensorTestCase.java
@@ -34,7 +34,7 @@ public class DynamicTensorTestCase {
         assertEquals("tensor(x{}):{{x:a}:5.0}", t2.toString());
     }
 
-    private static class Constant implements Function<EvaluationContext<?>, Double> {
+    private static class Constant implements ScalarFunction {
 
         private final double value;