Code Review: a lot of if else

[cd155]

Hi, I am currently taking an online class, and I would like to hear some feedback on the code I made. The code is made by Standard ML.

In the following three functions, each of them takes two arguments and returns a bool. Two arguments, named date1 and date2, are a tuple with 3 int type. The first int is year, the second int is month, and the last int is day. The following three functions will check if date1 is order than date2. Which one do you prefer?

fun is_older (date1: int*int*int, date2: int*int*int) = 
    if #1 date1 < #1 date2
    then true
    else if #1 date1 > #1 date2
    then false
    else (* when year equal *)
        if #2 date1 < #2 date2
        then true
        else if #2 date1 > #2 date2
        then false
        else (* when month equal *)
            if #3 date1 < #3 date2
            then true
            else if #2 date1 > #2 date2
            then false
            else false (* when day equal *)

fun is_older' (date1: int*int*int, date2: int*int*int) = 
    if #1 date1 = #1 date2
    then
        if #2 date1 = #2 date2
        then 
            if #3 date1 = #3 date2
            then
                false
            else
                #3 date1 < #3 date2
        else
            #2 date1 < #2 date2
    else 
        #1 date1 < #1 date2

fun is_older'' (date1: int*int*int, date2: int*int*int) = 
    let
        val year = (#1 date1, #1 date2)
        val month = (#2 date1, #2 date2)
        val date = (#3 date1, #3 date2)
        val xs = [year, month, date]

        fun is_older_Helper (xs: (int*int) list) =
            if null xs 
            then false
            else
                if #1 (hd xs) = #2 (hd xs) 
                then true andalso is_older_Helper (tl xs)
                else #1 (hd xs) < #2 (hd xs)
    in
        is_older_Helper xs
    end

[JacquesCarette]

To me, the best version would take in 2 records, each with 3 fields, called year, month and day. Taking a 3-tuple of ints is a very old style of coding.

Then I would write a boolean predicate, using 'and', and not use if-then-else at all.

[JacquesCarette]

 (x.year < y.year) || 
((x.year == y.year) && 
    ( (x.month < y.month) || 
      ( (x.month == y.month) && (x.day < y.day)) ) )

[JacquesCarette]

Preferably with proper comments...

[cd155]

I see. With a combination of or and and, it would work, thanks.

By the way, tuples are syntactic sugar of record, so technically, the code already uses record.

[JacquesCarette]

While it is true that tuples are like records with accessors fst and snd (or .1 and .2), most people don't see it that way. Positional access doesn't have the same affordability (a technical word from HCI) as more meaningful field names.

[cd155]

I see, thanks for mentioning it.