This PR reimplements `mkNoConfusionType` in lean, thus removing the
remaining C code related to this construction.
Also uses the ctor elimination principles only when there are more than
three ctors.
This PR adds “non-branching case statements”: For each inductive
constructor `T.con` this adds a function `T.con.with` that is similar
`T.casesOn`, but has only one arm (the one for `con`), and an additional
`t.toCtorIdx = 12` assumption.
For example:
```lean
inductive Vec (α : Type) : Nat → Type where
| nil : Vec α 0
| cons {n} : α → Vec α n → Vec α (n + 1)
/--
info: @[reducible] protected def Vec.cons.elim.{u} : {α : Type} →
{motive : (a : Nat) → Vec α a → Sort u} →
{a : Nat} →
(t : Vec α a) →
t.ctorIdx = 1 → ({n : Nat} → (a : α) → (a_1 : Vec α n) → motive (n + 1) (Vec.cons a a_1)) → motive a t
-/
#guard_msgs in
#print sig Vec.cons.elim
```
This is a building block for non-quadratic implementations of `BEq` and
`DecidableEq` etc.
Builds on top of #9951.
The compiled code for a these functions could presumably, without
branching on the inductive value, directly access the fields. Achieving
this optimization (and achieving it without a quadratic compilation
cost) is not in scope for this PR.
This PR resurrects the changes from #8978, #8992, #8973 which were
accidentally removed by #8996.
Fixes#8962.
---------
Co-authored-by: Wojciech Rozowski <wojciech@lean-fro.org>
This PR refactors the juggling of universes in the linear
`noConfusionType` construction: Instead of using `PUnit.{…} → ` in the
to get the branches of `withCtorType` to the same universe level, we use
`PULift`.
This fixes https://github.com/leanprover/lean4/issues/8962, although
probably doesn’t solve all issues of that kind while level equality
checking is incomplete.
Although `HEq` was abbreviated as `≍` in #8503, many instances of the
form `HEq x y` still remain.
Therefore, I searched for occurrences of `HEq x y` using the regular
expression `(?<![A-Za-z/@]|``)HEq(?![A-Za-z.])` and replaced as many as
possible with the form `x ≍ y`.
This PR introduces a `noConfusionType` construction that’s sub-quadratic
in size, and reduces faster.
The previous `noConfusion` construction with two nested `match`
statements is quadratic in size and reduction behavior. Using some
helper definitions, a linear size construction is possible.
With this, processing the RISC-V-AST definition from
https://github.com/opencompl/sail-riscv-lean takes 6s instead of 60s.
The previous construction is still used when processing the early
prelude, and can be enabled elsewhere using `set_option
backwards.linearNoConfusionType false`.
