3878432ac7
This PR make sure that the local instance cache calculation applies more reductions. In #2199 there was an issue where metavariables could prevent local variables from being considered as local instances. We use a slightly different approach that ensures that, for example, `let`s at the ends of telescopes do not cause similar problems. These reductions were already being calculated, so this does not require any additional work to be done. Metaprogramming interface addition: the various forall telescope functions that do reduction now have a `whnfType` flag (default false). If it's true, then the callback `k` is given the WHNF of the type. This is a free operation, since the telescope function already computes it.
44 lines
1.1 KiB
Text
44 lines
1.1 KiB
Text
/-!
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# Make sure local instance detection can handle metavariables and other reductions
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-/
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/-!
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Reported in https://github.com/leanprover/lean4/issues/2199
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The `inferInstance` was failing due to metavariables introduced by `cases`.
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-/
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theorem exists_foo : ∃ T : Type, Nonempty T := ⟨Unit, ⟨()⟩⟩
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example : True := by
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cases exists_foo
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rename_i T hT
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have : Nonempty T := inferInstance
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trivial
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/-!
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The `let` would inhibit `inst` from being seen as a local `Decidable` instance.
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Two tests: one where `let` starts a telescope, and another where it's at the end.
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(Having `let`s in the middle of a forall telescope always worked.)
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-/
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axiom p : Nat → Prop
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axiom inst : let n := 5; Decidable (p n)
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example : True := by
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have := inst
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have : Decidable (p 5) := inferInstance
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trivial
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axiom inst' : ∀ k, let n := k; Decidable (p n)
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example : True := by
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have := inst'
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have : Decidable (p 5) := inferInstance
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trivial
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/-!
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This worked before, but here's an extra test that abbreviations are correctly handled.
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-/
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abbrev D (p : Prop) := Decidable p
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example (p : Prop) [D p] : (if p then True else False) ↔ p := by
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split <;> simp_all
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