Lean 4 fork for HoTT-compatible kernel extensions (Path types, transport, HITs). Maintained against upstream leanprover/lean4.
5f4d724c2d
This PR improves `match` generalization such that it abstracts metavariables in types of local variables and in the result type of the match over the match discriminants. Previously, a metavariable in the result type would silently default to the behavior of `generalizing := false`, and a metavariable in the type of a free variable would lead to an error (#8099). Example of a `match` that elaborates now but previously wouldn't: ```lean example (a : Nat) (ha : a = 37) := (match a with | 42 => by contradiction | n => n) = 37 ``` This is because the result type of the `match` is a metavariable that was not abstracted over `a` and hence generalization failed; the result is that `contradiction` cannot pick up the proof `ha : 42 = 37`. The old behavior can be recovered by passing `(generalizing := false)` to the `match`. Furthermore, programs such as the following can now be elaborated: ```lean example (n : Nat) : Id (Fin (n + 1)) := have jp : ?m := ?rhs match n with | 0 => ?jmp1 | n + 1 => ?jmp2 where finally case m => exact Fin (n + 1) → Id (Fin (n + 1)) case jmp1 => exact jp ⟨0, by decide⟩ case jmp2 => exact jp ⟨n, by omega⟩ case rhs => exact pure ``` This is useful for the `do` elaborator. Fixes #8099. |
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