Tradeoff of defining types as subobjects #86
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YaelDillies
commented
Jul 25, 2024
fpvandoorn
reviewed
Jul 25, 2024
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| ## Typeclass search | ||
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| In the Subobject design, all instances about `circle` are actually about `↥circle` where `↥` is [`CoeSort.coe`](https://leanprover-community.github.io/mathlib4_docs/find/?pattern=CoeSort.coe#doc). Eg `Foo circle` is secretly `Foo ↥circle`. This makes the head symbol be `CoeSort.coe`, meaning that typeclass search will try unifying *every* `Foo ↥someSubobject` instance with `Foo ↥circle`. In doing so, it will try unifying *every* subobject `someSubobject` with a `Foo` instance with `circle`. This is potentially really expensive. |
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Is this still the case in Lean 4? I thought discrimination trees avoided this...
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Very much so. Else why would leanprover-community/mathlib4#12386 have achieved anything perf-wise? The problem I believe is that the discr tree key is [CoeSort.coe, *]
adomani
approved these changes
Jul 25, 2024
Co-authored-by: damiano <[email protected]>
YaelDillies
commented
Jul 25, 2024
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| author: 'Yaël Dillies' | |||
| category: 'Papers' | |||
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