This handler will sum what AppleScript doesn’t.
To make it work, you must provide a list of strings (numbers), without any limitation of its number of digits.
OS version: OS X
sumIntegersByHand({"123", "98765432109876543210", "98765432109876543210"})
to sumIntegersByHand(string_list)
--> reverse items to build columns
repeat with i from 1 to string_list's length
set string_list's item i to (reverse of (string_list's item i)'s items as text)
end repeat
set sum_result to {}
set current_digit to 1
set the_rest to 0
repeat
try
--> get column of current digit
set digit_list to {}
repeat with i in string_list
try
set end of digit_list to (i's item current_digit as integer)
end try
end repeat
if digit_list = {} then exit repeat
--> sum column
set partial_result to 0
repeat with i in digit_list
set partial_result to partial_result + i
end repeat
--> sum rest, if exists
set partial_result to partial_result + the_rest
set beginning of sum_result to partial_result mod 10
set the_rest to partial_result div 10
set current_digit to current_digit + 1
on error msg
exit repeat
end try
end repeat
if the_rest is not 0 then set beginning of sum_result to the_rest
return sum_result as text
end sumIntegersByHand