@kha The runtime folder includes what is needed to link a
standalone Lean program. It is still contains some unnecessary files.
We will be able to remove them after we release Lean4.
We need this feature for:
1) Defining nonlinear search patterns. Example: (?m <= ?m + 1)
2) Preprocessing recursive equations and support the pattern
refinement approach used in Agda. Example: in Agda, they accept
```
def append {A : Type} : Π (m n : nat), Vec A m -> Vec A n -> Vec A (m + n)
| m n nil ys := ys
| m n (cons m' x xs) ys := cons x (append m' n xs ys)
```
These equations have to be refined. For example, `m` has to be
replaced with `0` (in the first equation), and `succ m'` in the
second. To implement this kind of refinement, we need to convert
the pattern variables (local constants) into metavariables during
elaboration. Then, the unassigned metavariables become local constants
again. This preprocessing step will fix some of the issues on #1594.
To completely fix#1594, we will need yet another preprocessing step
which will implement "complete transition" used in the equation
compiler before we start elim_match.cpp
@kha I had to add yet another hack to fix this issue.
In notation declarations, names are resolved at notation declaration time.
So, users do not expect them to be resolved again at tactic execution time.
I addressed this problem by wrapping constants occurring in notation
declarations with a "frozen_name" annotation. This transformation is
only performed if m_in_quote is true.
Then resolve_names_fn at elaborator.cpp will not try to resolve the
names again.
This change broke two other modules. `-` notation for inverting
equations at `rw`, and `calc` expressions inside quotes.
The broke for the same reason. They were not expecting the constants
to be wrapped with an annotation.
Now, eta and impredicativity are assumed to be always true.
Motivation: the rest of the system assumes eta.
Regarding impredicativity, we decided to support only the standard library.
In the standard library, we should use explicit universe variables for
universe polymorphic definitions.
Users that want to declare universe polymorphic definitions but do not
want to provide universe level parameters should use
Type _
or
Type*
