> However, one problem with it is that a polymorphic type, such as [] of kind "* -> ", or a function like map of type "forall a b. (a -> b) -> [a] -> [b]" reall

> However, one problem with it is that a polymorphic type, such as [] of kind "* -> ", or a function like map of type "forall a b. (a -> b) -> [a] -> [b]" really only works with boxed types. Can you explain why this is, or provide a reference to literature where it was investigated? I still (even after getting a PhD in compiling functional languages!) do not understand why you could not create code parameterised over the sizes of the arguments. For example, a 'cons' cell could be represented as first the size of the 'car' in bytes, then the 'car' value inline/unboxed, then a pointer to the 'cdr' cell. The Sixten language[0] does this, although it's still very early in its development. I'm not saying this is necessarily a good solution, I just wonder why I have never seen it seriously considered (and perhaps rejected). In practice, I do believe that monomorphisation is very often a good strategy. [0]: https://github.com/ollef/sixten https://github.com/ollef/sixten