Thymeleaf - comment boucler une liste par index

Comment puis-je boucler par index?

Foo.java

public Foo {
    private List<String> tasks;
    ...
}

index.html

<p>Tasks:
    <span th:each="${index: #numbers.sequence(0, ${foo.tasks.length})}">
        <span th:text="${foo.tasks[index]}"></span>
    </span>
</p>

je suis parse error

org.thymeleaf.exceptions.TemplateProcessingException: Could not parse as each: "${index: #numbers.sequence(0,  ${student.tasks.length})}"