JonC

https://mitpress.mit.edu/9780262046305/introduction-to-algorithms/

This one is pretty hardcore. I bought the 2nd edition of it over 20 years ago when I started my career as a developer due to not doing a CS degree.

Also take a look at the Specification Pattern for something similar.

That’s something I would only use if the logic becomes very complex, but it can help break things down nicely in those cases.

Why the assumption that reactivity is only a front-end thing?

I’ve used it plenty on the back-end when dealing with streams of data that need to trigger other processing steps.

I mean, why does anything have value?

In the strict financial sense, something is only worth what somone else is willing to pay for it. That’s the whole premise of financial trading. Getting a bit beyond ELI5 now, but most exchanges use something called a Central Limit Order Book (CLOB) to let the participants in the market see who wants to buy and sell what and for how much, and also to match those buyers and sellers. This is a good intro: https://optiver.com/explainers/orders-and-the-order-book/

In terms of shares in companies, then they do have some fundamental value according to the market. If you buy a share in the company, you get a share of the profits (paid as dividends), which gives those shares some value. Obviously, there’s a lot of speculation too as people are involved, so emotions and wild predictions can come into play!

Financial instruments that get traded aren’t limited to shares in companies though. There are all kind of other financial instruments that get traded every day, some are pretty basic like buying and selling different currencies. Others involve all kinds of crazy financial engineering , like the sort that caused the crash in 2008!

Most have some fundamental value based on their attributes, so it’s a little different to the likes of an NFT. The big issues come if the values that the market has agreed upon don’t match reality, which is what happened in 2008.

If you strip things back, the most fundamental point of a market is to bring buyers and sellers together and to enable price discovery.

The price of a financial instrument you see on a stock exchange or similar is simply the last traded price between a buyer and a seller. If you want to buy or sell something, then the price you get depends on who wants to sell/buy on the other side and what price they have put an order in for.

The more trades going on in the market, the more likely it is that you will be able to buy at a price close to what you see as the last price in the market.

If you only allow trading every hour, then you lose some of that price discovery.

Additionally, as already mentioned, trades would likely still happen, but away from the designated marketplace. If I want to sell something, then I may just ask who else has the thing I want to sell and try to negotiate a price directly with them.

That way, fewer trades happen in the marketplace and more trades happen in private away from there.

That sort of limited trading does happen for some very niche products that don’t have a lot of potential buyers and sellers. For common financial instruments, have a lot of participants wanting to trade, having a centralised marketplace helps avoid the issues that would come otherwise.

Now, you can argue that in practice it doesn’t work as well as the theory, and I would agree there. If you are a HFT, then you can make money by getting in milli or microseconds ahead of others.

For a lot of market participants, that doesn’t really matter though. The big banks typically don’t do that sort of trading. They are buying and selling on behalf of their clients, both individuals and companies that want access to the market. The bank makes their money by charging a margin to their client (similar to how it works for pretty much any retailer), and the fact that the HFTs are making all these trades helps them with price discovery and liquidity (ensuring there is someone to buy what they want to sell, or sell what they want to buy)

And he created Trello

Same, using Chat GPT 4. It explained the steps without prompting, which is different from the single line answer shown in the post too. I got this…

Let’s break this down step by step:

1. Sally has 3 brothers.
2. Each of those brothers has 2 sisters.

Sally is one of those sisters for each of her 3 brothers. Therefore, the second sister that each brother has would be the same other sister.

This means that Sally has only 1 other sister, making a total of 2 sisters in the family (including Sally herself).

So, Sally has 1 sister.