you might be right, though i understood it as "every call to a recursive function must be prefixed with `rec`", which would mean that, say, ,`last xs` [assuming

you might be right, though i understood it as "every call to a recursive function must be prefixed with `rec`", which would mean that, say, ,`last xs` [assuming that `last` is implemented recursively and xs is a linked list] would have to look like `rec last xs` instead, de facto making the recursiveness of `last` a part of its public API.