double apply(IndexedTensor.Indexes indexes) {
            if (freeGenerator != null) {
                return freeGenerator.apply(indexes.toList());
            }
            else {
                this.indexes = indexes;
                return boundGenerator.apply(this);
            }
        }
A context for generating all the values of a tensor produced by evaluating Generate.
This returns all the current index values as variables and falls back to delivering from the given
evaluation context.
vespajlib/src/main/java/com/yahoo/tensor/functions/Generate.java