It just adds extra complexity and is in conflict for our plans for
Lean4. Moreover, in our experiments it impacts negatively on
performance: master and lean4 branches. The negative impact has been
confirmed by @kha too.
This field was originally added to create hashtables based on pointer
equality. We don't use them anymore, and the caches based on
m_hash_alloc can be implemented using m_hash without any performance
impact. This commit also fixes two places where `expr_set` was used
instead of `expr_struct_set`.
This commit is also important for the Lean4 plans where `expr` will
be implemented in Lean, and fields like `m_hash_alloc` would require us
to track state.
`{s with ...}` is now `{..., ..s}`, which more clearly expresses that the
result type is not necessarily equal to the type of `s` (in absence of an
expected type and a structure name, we still default to the type of `s`).
Multiple fallback sources can be given: `{..., ..s, ..t}` will fall back to
searching a field in `s`, then in `t`. The last component can also be `..`,
which will replace any missing fields with a placeholder.
The old notation will be removed in the future.
TODO: we are not checking if the unicode escape values provide by the
user correspond to valud unicode scalar values. We should check how
other languanges handle this case.
Comment from parser.h
This commit makes sure that all declaration parameters must be surrounded with some kind of bracket. (e.g., '()', '{}', '[]').
The goal is to avoid counter-intuitive declarations such as:
example p : false := trivial
def main proof : false := trivial
which would be parsed as
example (p : false) : _ := trivial
def main (proof : false) : _ := trivial
where `_` in both cases is elaborated into `true`. This issue was raised by @gebner in the slack channel.
Remark: we still want implicit delimiters for lambda/pi expressions. That is, we want to write
fun x : t, s
or
fun x, s
instead of
fun (x : t), s
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
Older gcc compilers generate a warning when the attribute is used.
I found out that GCC 7 will not produce a warning if comments
such as /* fall-thru */ or /* FALLTHRU */ are used instead of the
attribute [[fallthrough]]
