I'd argue that he's using a bad FP approach. He focuses on one aspect of shapes: testing whether a point is inside it or not. But this is far from a complete,

I'd argue that he's using a bad FP approach. He focuses on one aspect of shapes: testing whether a point is inside it or not. But this is far from a complete, usable representation. How do you draw a shape? Find its edge? Find its bounds? Convex hull? Transform? Test for convexity? Basically, the original post is just another newbie FP realising that - hey - if you're only every going to call one function of a class then the class is completely defined by that function. He presents a poor and incomplete solution. There are much better blog posts on FP design than this. Please don't upvote this one.