Type system problems
====================

Mutable structs with immutable fields
-------------------------------------

Assume that we have a struct:

    type S = struct {
        var int a
        int b     # <--- not modifiable
    }

Assume that we have two definitions of it, where one is "var":

    var S a
    S b

Since S has a const field, this means that we can't do the following:

    a = b

The type system should enforce this