Motivation: in 64-bit machines, we can store boxed uint32 values as a
tagged pointer. In 32-bit machines, we need to allocated an object (like
Haskell) to store the uint32 value. So, the generated bytecode is quite
different in each platform.
This change also allow us to simplify the IR. Example: we don't need the
type `sizet` anymore.
Impact: To be able to bootstrap in both platforms,
we will have to store two versions of the generated code: 32 and 64
versions. In principle, we only need to store the 64-bit version,
and use cross-compilation to build the 32-bit version.
We will use this instruction for compiling inductive datatypes such as
`option A` where `A` is represented as an `object`.
In this case, we can represent `some a` as `a` (without any extra memory
allocation), and `none` as the null pointer.
@Kha, I was having to use `(run ...).1` in many places
in my code. So, I changed the instance
```
instance (σ m out) [monad_run out m] : monad_run (λ α, σ → out (α × σ)) (state_t σ m) :=
⟨λ α x, run ∘ (λ σ, x.run σ)⟩
```
to
```
instance (σ : Type u) (m out : Type u → Type v) [functor m] [monad_run out m] : monad_run (λ α, σ → out α) (state_t σ m) :=
⟨λ α x, run ∘ (λ σ, prod.fst <$> (x.run σ))⟩
```
If we want to get the resultant state in an action `act`, we can just
use `run (act >> get) init_state`.
Without these annotations, Lean will timeout when trying to synthesize
the type class instance `decidable_eq uint32`. The type class resolution
problem will produce the unification problem:
```
decidable (@eq uint32 a b) =?= decidable (@eq usize ?x ?y)
```
which Lean tries to solve by assigning `?x := a`.
During the assignment, the types of `?x` and `a` are unified with "full
force". Thus, we get the constraint
```
usize_sz =?= uint32_sz
```
which will take forever to be solved when peforming the computation in
unary arithmetic.
Remark: this commit also makes sure that `type_context` will not unfold
irreducible definitions when trying to unify/match the types.
The new test `type_class_performance1.lean` exposes the problem fixed
by this commit.
