type-tag → type-value

[vekatze]

before:

let tag = magic get-type-tag(a);
match tag {
| Vector =>
  let t = magic get-vector-content-type(a);
  ...
| Algebraic =>
  let data-args = magic get-data-args(a);
  let num = magic get-cons-size(a);
  let ts = magic get-constructor-arg-types(a, i); // 0 <= i < num
  ...
| _ =>
  ...
}

after:

let type-value = magic inspect-type(a);
match type-value {
| Vector(t) =>
  ...
| Algebraic(data-name, data-args, construtors) => // constructors: list(constructor-info)
  ...
| _ =>
  ...
}