BOOL local fn IsGoodISBN( isbn as CFStringRef )
  int sum = 0
  for int i = 0 to len(isbn) - 1
    unichar chr = ucc(isbn,i) - 48
    if ( chr > 0 && chr <= 9 )
      if ( i % 2 == 0 ) then sum += chr * 3 else sum += chr
    end if
  next
end fn = sum % 10 == 0

void local fn DoIt
  CFArrayRef a = @[@"978-0596528126",@"978-0596528120",@"978-1788399081",@"978-1788399083"]
  for CFStringRef s in a
    print s,
    if ( fn IsGoodISBN(s) ) then print @"good" else print @"bad"
  next
end fn

fn DoIt

HandleEvents