private ExpressionNode transformFeatureNode(ReferenceNode feature, RankProfileTransformContext context) {
        if (feature.getArguments().size() > 0) return feature;  // From RankProfile: only inline no-arg functions
        RankProfile.RankingExpressionFunction rankingExpressionFunction = context.inlineFunctions().get(feature.getName());
        if (rankingExpressionFunction == null) return feature;
        return transform(rankingExpressionFunction.function().getBody().getRoot(), context); // inline recursively and return
    }
Inlines functions in ranking expressions

@author bratseth
config-model/src/main/java/com/yahoo/schema/expressiontransforms/FunctionInliner.java