f9b2f6b597
This PR fixes universe unification for `for` loops with `mut` variables whose types span multiple implicit universes. The old approach used `ensureHasType (mkSort mi.u.succ)` per variable, which generated constraints like `max (?u+1) (?v+1) =?= ?u+1` that the universe solver cannot decompose. The new approach uses `getDecLevel`/`isLevelDefEq` on the decremented level, producing `max ?u ?v =?= ?u` which `solveSelfMax` handles directly. Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
45 lines
1.6 KiB
Text
45 lines
1.6 KiB
Text
import Std.Data.HashSet
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/-!
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Test that `for` loops with `mut` variables whose type spans multiple implicit universes
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do not get stuck on `max (?u+1) (?v+1) =?= ?u+1`. This is solved by instead solving the decremented
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constraint `max ?u ?v =?= ?u` eagerly, which solves by `solveSelfMax`.
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-/
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-- Works with explicit universe variables
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example {α : Type (max u v)} {β : Type v} [Inhabited α] [Inhabited β] (as : Array α) : Array α := Id.run do
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let mut m : α × β := default
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for a in as do
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m := (a, m.2)
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return #[m.1]
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-- Works with legacy do elaborator
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set_option backward.do.legacy true in
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example [Inhabited α] [Inhabited β] (as : Array α) : Array α := Id.run do
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let mut m : α × β := default
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for a in as do
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m := (a, m.2)
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return #[m.1]
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-- Also works with implicit universe variables (the actual regression case)
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example [Inhabited α] [Inhabited β] (as : Array α) : Array α := Id.run do
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let mut m : α × β := default
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for a in as do
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m := (a, m.2)
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return #[m.1]
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-- Closer to the real world reproducer from aesop's UnionFind data structure:
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def cluster [BEq α] [Hashable α] [BEq β] [Hashable β] (f : α → Array β)
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(as : Array α) : Array (Array α) := Id.run do
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let mut clusters := Std.HashSet.ofArray as
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let mut aOccs : Std.HashMap β (Array α) := {}
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for a in as do
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for b in f a do
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match aOccs[b]? with
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| some as' =>
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for a' in as' do
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clusters := clusters.insert a'
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aOccs := aOccs.insert b (as'.push a)
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| none =>
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aOccs := aOccs.insert b #[a]
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return #[clusters.toArray]
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