There's a funky thing going on here because of the environment this guy is using: Javascript and a JS library to handle immutability. Because of the way he's c

There's a funky thing going on here because of the environment this guy is using: Javascript and a JS library to handle immutability. Because of the way he's coding, he's doing a lot of horsing around with several things at once. He's not writing functions and then composing them. He's refactoring multiple functions at the same time. As it turns out, this difference is important. Looking at it from one angle, from small pieces into larger pieces, you'll be solving the order of functions almost immediately. Looking at it from another angle, from big pieces into smaller pieces, you solve problems in a different order. You make pieces with names on them that do what you want, then you look at whether there's support in the code to do what you want to do, regardless of how that integrates. In fact, you end up (as he does) integrating later. You're not composing, you're decomposing. This is why one of the recommended ways to do FP is to use the REPL and get the core, toughest function working first. Then start composing. Work outwards from there. The first function you'd probably write in this case would perhaps be moveTheGuy which would move the guy from one place to another. You would immediately be solving the problem of whether or not the guy could actually move. Contrast this with the first function being updateTheWorld, where you can start inventing all kinds of stuff that might or might not happen. Then you horse around trying to figure out what should go under updateTheWorld I remember the first conference talk I saw with a guy talking about F#. It was still new in the industry, and many of the folks who were using it were true-blue OO coders. The guy gets up, shows some code, then goes behind-the-scenes to show us the "real" C# code. "As you can see, all this really is? It's do-while loop. You could code this way with C# and never touch F#" Yeah sure, but the environment you're in can help lead you to write better or worse code. It seems to me if I wanted to do pure functional stuff and Javascript I'd be pretty freaking careful how I coded. Lots of things there that point you in the wrong direction. Functional code just isn't regular code with all sorts of weird syntax; it's actually a different way of looking at solving problems.