| Because it reduces the number of things you have to keep in your head and the uncertainty about what you don't know. Using monads and a "state box", it's not enough to make a change to the context of the box, you also have to pass the box onto the next entity/process that wants to change it, or nothing will effectively change (other than burning cpu cycles). This also means that it suddenly becomes easy to find out what things happened to the box content before, because all you have to do is check what the one who was passing the box to you was doing with it. If your program is strictly linear than using state boxes is merely syntactic overhead. But as soon as that's not the case anymore, it suddenly becomes important. I remember very well the time when I had to deal with bugs where I was operating on data that looked different than I expected and I had a hard time to figure out how it came to that. But even worse are bugs from concurrency and also the "magic" and workarounds for dealing with it when "state boxes" are not available or known to the developer. Now you look at a line of code while knowing that stuff is running somewhere else, impacting what you are working on in a potentially uncontrolled manner. I find that very unproductive. |