protected Expression expectOneArgument() {
        List<Expression> argv = functionNode.getArguments();
        if (argv.size() == 1) {
            return argv.get(0);
        }
        throw new RuleError(new SourceException("expected 1 argument but found " + argv.size(), functionNode));
    }
@return The arguments to this function
smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/expressions/functions/LibraryFunction.java