Unfortunately the linebreaks were lost and, as shown that isn't a valid PRQL query. It would have to be either

    from employees
    group role (
        sort join_date 
        take 1
        )

or

    from employees | group role (sort join_date | take 1)

In English:

    Take the 1st employee 
    by (earliest) join_date 
    for each role 
    from the set of employees