This PR adds the function `Std.Iter.first?` and proves the specification
lemma `Std.Iter.first?_eq_match_step` if the iterator is productive.
The monadic variant on `Std.IterM` is also provided.
We use this new function to fix the default implementation for
`startsWith` and `dropPrefix` on `String` patterns, which used to fail
if the searcher returned a `skip` at the beginning. None of the patterns
we ship out of the box were affected by this, but user-defined patterns
were vulnerable.
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Co-authored-by: Paul Reichert <6992158+datokrat@users.noreply.github.com>
This PR makes the `FinitenessRelation` structure, which is helpful when
proving the finiteness of iterators, part of the public API. Previously,
it was marked internal and experimental.
This PR migrates usages of `Std.Range` to the new polymorphic ranges.
This PR unfortunately increases the transitive imports for
frequently-used parts of `Init` because the ranges now rely on iterators
in order to provide their functionality for types other than `Nat`.
However, iteration over ranges in compiled code is as efficient as
before in the examples I checked. This is because of a special
`IteratorLoop` implementation provided in the PR for this purpose.
There were two issues that were uncovered during migration:
* In `IndPredBelow.lean`, migrating the last remaining range causes
`compilerTest1.lean` to break. I have minimized the issue and came to
the conclusion it's a compiler bug. Therefore, I have not replaced said
old range usage yet (see #9186).
* In `BRecOn.lean`, we are publicly importing the ranges. Making this
import private should theoretically work, but there seems to be a
problem with the module system, causing the build to panic later in
`Init.Data.Grind.Poly` (see #9185).
* In `FuzzyMatching.lean`, inlining fails with the new ranges, which
would have led to significant slowdown. Therefore, I have not migrated
this file either.
This PR adjusts the experimental module system to make `private` the
default visibility modifier in `module`s, introducing `public` as a new
modifier instead. `public section` can be used to revert the default for
an entire section, though this is more intended to ease gradual adoption
of the new semantics such as in `Init` (and soon `Std`) where they
should be replaced by a future decl-by-decl re-review of visibilities.
This PR moves parts of the iterator library from `Std` to `Init`. The
reason is that the polymorphic range API must be in `Init` and it
depends on the iterators.
