private static ExpressionFunction asExpressionFunction(ImportedMlFunction function) {
        try {
            Map<String, TensorType> argumentTypes = new HashMap<>();
            for (Map.Entry<String, String> entry : function.argumentTypes().entrySet())
                argumentTypes.put(entry.getKey(), TensorType.fromSpec(entry.getValue()));

            return new ExpressionFunction(function.name(),
                                          function.arguments(),
                                          new RankingExpression(function.expression()),
                                          argumentTypes,
                                          function.returnType().map(TensorType::fromSpec));
        }
        catch (ParseException e) {
            throw new IllegalArgumentException("Got an illegal argument from importing " + function.name(), e);
        }
    }
Returns the expression matching the given arguments.
config-model/src/main/java/com/yahoo/vespa/model/ml/ConvertedModel.java