It is still broken since we apply attributes before we compile code.
Recall that attributes such as `@[export]` and `@[extern]` must be applied before we
compile code.
On the other hand, any attribute `attrName`
```
@[attrName] def foo := ...
```
which creates auxiliary definitions that depend on `foo` must be applied
AFTER we generate code for `foo`. Otherwise, we will fail to compile the
auxiliary definition since we don't have code for `foo` yet.
I will fix the issue above by allowing attributes to specify when they
should be applied. I will start with only two options: before and after
code compilation. In the future, we may need more options (e.g., before
elaboration), but I don't see the need yet.
cc @kha
Main differences with respect to `tests/playground/parser`
1- There is a single (parametric) parser type: `Parser k`, where `k` is
used to identify whether it is a `nud` or `led` parser.
2- It assumes parsing tables are stored in the `Environment`.
3- We check precedence mismatch, and use the value `none` to represent
"use existing precedence".
4- We have support for silent (aka epsilon) parsing actions.
Remark: the experiments at `tests/playground/parser` demonstrated that the new
parsing infrastructure is at least 10x faster than the one based on the
`Parsec` monad.
In the original parsec paper, they store messages in OK silent/epsilon
results too. This is not necessary, we only need the "expected" field
for the `ok_eps` constructor.
