When I was in college I sometimes helped people (friends of friends, etc.) with their programming homework. I remember J was in an intro class and needed to find an element in an array. I tried to explain to him how linear search works: first you look at the first element, then then the next, and you stop the loop if you find what you're looking for. No matter how I phrased it, it seemed he didn't get it. It was like there was a floor of complexity, a minimum level of understanding and I couldn't express ideas any simpler.
(Yes, I've seen that paper that argues that programming is simply "beyond" some people. I think it's bunk: their testing methodology measures something that correlates with a bunch of other explanatory but unmentioned skills.)
Sometimes Meena will see me programming and say "I can't believe you think this way", but to me it's so natural I can't imagine thinking another way. I remember taking a logic class in college (part of the philosophy department) and wondering why other people couldn't do the proofs.
I almost feel the same way about types now, except that I can still vaguely remember before. If I look at the official Haskell tutorial on IO, I remember that it was confusing but the memory is strongly overridden by how straightforward and sensible it seems now. If I were to try to explain IO to myself I'd just say that the => operator from my previous post had type
IO a → (a → IO b) → IO b and I'd be mostly done.
So since I can't remember what about typing was confusing, I made a point in my previous post of not talking about types at all and instead phrasing it in runtime terms ("if this produces a value, then next ..."). This is not at all how I really think about it. It is a stretch of my imagination, which is part of why I tried to write it.