> intuitively seems to have the length 2 whereas the correct length is 3. I find 3 more intuitive though. It could be because right from my early days of learning various Lisps, I learnt about lists in terms of cons cells.
That's just how cons is defined. the first argument is a list and the second is an arbitrary object, and the result has the elements from the list plus the other object. It doesn't take a bunch of algebraic manipulation to understand this definition. It just takes a recognition that an "arbitrary object" could be a list, as well as a recognition that the other definition you imply ("make a new list with both arguments as elements") would have to either be variadic (which in turn would obviate `list`) or would only ever be able to make lists of exactly 2 elements. (The point is that `cons` can serve as a simpler primitive, and `list` can be implemented in terms of it.)
That's just how cons is defined. the first argument is a list and the second is an arbitrary object, and the result has the elements from the list plus the other object. It doesn't take a bunch of algebraic manipulation to understand this definition. It just takes a recognition that an "arbitrary object" could be a list, as well as a recognition that the other definition you imply ("make a new list with both arguments as elements") would have to either be variadic (which in turn would obviate `list`) or would only ever be able to make lists of exactly 2 elements. (The point is that `cons` can serve as a simpler primitive, and `list` can be implemented in terms of it.)