I came across this problem on Daily Coding Problem
This problem was asked by Squarespace.
Write a function, add_subtract, which alternately adds and subtracts curried arguments. Here are some sample operations:
add_subtract(7) -> 7
add_subtract(1)(2)(3) -> 1 + 2 - 3 -> 0
add_subtract(-5)(10)(3)(9) -> -5 + 10 - 3 + 9 -> 11
I didn't have an answer from the top of my head. I decided to get some help from Google and see what I could learn in the process. Before going further in my blog post, see if you can come up with a solution and comment how that went. First thing for me was to learn about currying in javascript. The first link I came across was this one
But it does not cover infinite currying which is what I needed. I then went through a bunch of searches and articles trying to understand as much as I could. This next article stood out to me because of how simple the solution was but it could not be modified to cater for alternating addition and subtraction. To do this I figured I needed access the position in the arguments list.
Some of the things you might come across while researching are perpetual curry or infinite curry, variadic currying, partial application vs currying, arity, single level currying, composition and closure. This final link did the best in explaining currying to me and had an example of infinite currying.
I was able to modify the example to come up with a solution. This is what I have so far with minimal testing in replit.
Replit now has a mobile app which I talked about on my youtube channel - Replit Mobile App - Coding on my aging budget Android phone in Trinidad
Basically I had to check for every even argument and make that argument negative as follows
args.reduce((acc, a, l) => {
if (l%2 == 0 && l != 0) a=a*-1;
At first I had l=args.length. This was a mistake but did not matter because l is replaced by index. The 3rd parameter of reduce is the index and refers to the number of times the reducer has looped over the array. The problem does not use a terminator and an improvement to my solution would be to not use a terminator. I have never had to use currying before and there are articles that discuss real world examples of using currying. Share your thoughts with us in the comments below.
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