For example, `mkFreshExprMVar none MetavarKind.synthetic` should
create a fresh synthetic metavariable `?m` with type `?t` where `?t`
is a fresh natural metavariable. If users want a synthetic
metavariable `?t`, then it must create it themselves.
@Kha I am also tracking `currNamespace` and `openDecls`.
BTW, I also tried an experiment where I added `currNamespace` and
`openDecls` to `Meta.Context`, but it looked weird. This information
is only needed in the elaborator and pretty printer.
The `PPContext` object should contain everything you need. You
can put `currNamespace` and `openDecls` in the `Delaborator.Context`.
@Kha I am using `_shadowed.<idx>` suffix for marking variables that
have been shadowed. It is a bit verbose, but at least it is easy to
understand understand error messages such as
```
shadow.lean:4:0: error: type mismatch
h
has type
x._shadowed.1 = x._shadowed.1
but it is expected to have type
x = x
```
It is better than the old cryptic version
```
shadow.lean:4:0: error: type mismatch
h
has type
x = x
but it is expected to have type
x = x
```
The `matchType` created by the macro is bad for dependent pattern
matching. The `tst8` and `tst9` at `matchTac` failed to be elaborated
when using the macro.
@Kha This one is not as useful as the indented `do`. When writing
interactive proofs I like the error message at the `}` showing the
resulting tactic state. We can simulate it using a `skip` in the end of the sequence :)
We remove the `skip` when the proof is done. Note that, the last `;`
is usually not part of the `by`. Example:
```lean
theorem ex (x y z : Nat) : y = z → y = x → x = z :=
fun _ _ =>
have x = y by apply Eq.symm; assumption; -- <<< the last `;` is part of the `have`
Eq.trans this (by assumption)
```
The idea is to make clear that the field `posponed` is transient
state. It is only used during `isDefEq`.
The refactoring was motivated by a bug I found where the `posponed`
constraints were not being handled correctly. For example,
the `check (e : Expr)` method was returning `true`, but leaving pending
universe constraints at `postponed`.
cc @Kha
