Builtin Types
=============
Bitsy includes the following built-in types:

`Word[n]`
---------
A `Word[n]` is an n-bit number.
It is nominally interpreted to be unsigned.
However, operators and functions may re-interpret it as a signed number or as a bitvector.

`Vec[T, n]`
-----------
A `Vec[T, n]` is an n-element vector of elements of a type `S`.

It's values are written as `[v1, v2, ..., vn]`.
For example, `[1, 2, 3]` is a value for `Vec[Word[8], 3]`.

`Valid[T]`
----------
A `Valid[T]` is a type for values which may or may not be valid.

If you have an expression `t` of type `T`, you can construct a `Valid[T]` with `@Valid(t)`.
You can use `@Invalid` to construct a `Valid[T]` with no value.

You can use `match` expressions to get access to the payload inside `Valid[T]`:

.. code-block:: bitsy

    mod Top {
        incoming in  of Valid[Word[8]];
        outgoing out of Word[8];

        match in {
            @Valid(t) => t;
            @Invalid  => 0;
        }
    }