@kha @dselsam: I added a small repro for the bug reported by Daniel on
Zulip. The current fix is not polished at all since we will replace
the equation compiler with one implemented in Lean. The bug is once
again on the code that handle nested `match`-expressions containing
recursive calls. We had problems in this module before, and the
current compilation strategy using auxiliary `*._match_<id>` functions
is also very inconvenient for users. They are often puzzled when they
see these auxiliary functions appearing in proof goals after unfolding
and/or simplification. They usually don't know what to do with these
auxiliary definitions, and have no idea how they were defined and what
they correspond to if the function has several nested
`match`-expression. Right now, the best option is to use `#print
<fun-name>._match_<id>` which is far from ideal.
@kha: @dselsam and I discussed an alternative approach where we do not
create the auxiliary definitions, annotate the generated `cases_on`
applications with meta-data indicating they correspond to a nested
match, and modify the pretty printer to display these annotated
`cases_on` applications using the `match` syntax. With these
modifications, the behavior will be similar to the one in Coq where
complex `match`-expressions are reduced to atomic ones. The only
difference is that we represent these "atomic" `match`-expressions
using `cases_on` applications.
This commit uses a simpler version of this approach where we do not
create auxiliary `*._match_<id>` functions, and more importantly do
not use the dreadful `pull_nested_rec_fn` code.
This is a temporary hack. After we eliminate the old elaborator,
we will delete the C++ class `local_context`.
In Lean4, we will not have two different kinds of local context:
`local_ctx` and `local_context`.
The datastructures at `local_context` used to manage used user_names
introduce a lot of overhead. They do guarantee that `get_unused_name` is
`O(log(n))`, but they slowdown much more common operations such as:
local declaration creation/deletion. We create/delete local declarations
much more often than we use `get_unused_name`.
The corelib build time is now 34.18 secs on my desktop. It was 39.5 secs.
The idea is to mimic the behavior of meta definitions.
This is a temporary fix. The new equation compiler will have to provide
a better solution for this problem.
We will re-implement the type class resolution algorithm, and the new
implementation will not rely on a persistent cache. We will improve
performance by:
1) Using better indexing data-structures.
2) Using a local cache during the search.
