LIST setadd(LIST list, ANY value)
This function appends the argument value to the argument list if it is not already in the list, and returns the result. If value is already in the list, it does not add it. Examples:
setadd([2, 3, 4], 'foo)
=> [2, 3, 4, 'foo]
setadd([2, 3, 4], 3)
=> [2, 3, 4]
delete() | insert() | join() | listgraft() | listlen() | replace() | setadd() | setremove() | sublist() | union() | listidx()