Applescript using if then statements and choose from list

Question

I'm working on a course selection script and each person should only be able to select three courses. I am having issues figuring out how to repeat choose from list if the user selects less than or more than three courses, and only proceed if three choices are selected. Converting the choices from the list to string should work however nothing happens after choosing from list

set theClassList to {"Math ", "English ", "Science ", "I&S ", "Design "}

repeat

set theClass to choose from list theClassList with prompt "Select three courses" with multiple selections allowed

set theClassString to theClass as string

if words in theClassString ≠ 3 then

    display dialog "Please select three courses"
    exit repeat

else if words in theClassString = 3 then
    display dialog "Ok"

end if
end repeat

Answer 1

It's a clever idea to count the words in the theClassString (which would be done using number of words in theClassString, instead of simply words in theClassString). This would work the majority of the time, until a user includes "I&S" as one of their options, which sadly counts as two words, "I" and "S", since the ampersand is not a word character.

You also had your exit repeat in the wrong half of the if...then...else block, since you want to break the loop when the user selects 3 courses, not when they fail to select 3 courses.

Rather than attempting to coerce the result of the list selection into a string, you ought to just count the number of items in the result, which can be done in one of three ways:

1. count theClass
2. length of theClass
3. number in theClass

Here's a reworked version of your script:

property theClassList : {"Math ", "English ", "Science ", "I&S ", "Design "}
property text item delimiters : linefeed

set choices to missing value

repeat
    if choices ≠ missing value then display dialog ¬
        "You must select precisely three courses"

    set choices to choose from list theClassList with prompt ¬
        "Select three courses" with multiple selections allowed

    if choices = false or the number of choices = 3 then exit repeat
end repeat

if choices = false then return
display dialog choices as text

---

...And here's a version that uses a recursive handler instead of a repeat loop:

property theClassList : {"Math", "English", "Science", "I&S", "Design"}
property text item delimiters : linefeed

to choose()
    tell (choose from list theClassList ¬
        with prompt ("Select three courses") ¬
        with multiple selections allowed) to ¬
        if it = false or its length = 3 then ¬
            return it

    display dialog "You must select precisely three courses"
    choose()
end choose

display alert (choose() as text)