Lean 4 fork for HoTT-compatible kernel extensions (Path types, transport, HITs). Maintained against upstream leanprover/lean4.
fc963ffceb
This implements the first half of #3302: It improves the extensible `apply_rfl` tactic (the one that looks at `refl` attributes, part of the `rfl` macro) to * Check itself and ahead of time that the lhs and rhs are defEq, and give a nice consistent error message when they don't (instead of just passing on the less helpful error message from `apply Foo.refl`), and using the machinery that `apply` uses to elaborate expressions to highlight diffs in implicit arguments. * Also handle `Eq` and `HEq` (built in) and `Iff` (using the attribute) Care is taken that, as before, the current transparency setting affects comparing the lhs and rhs, but not the reduction of the relation So before we had ```lean opaque P : Nat → Nat → Prop @[refl] axiom P.refl (n : Nat) : P n n /-- error: tactic 'apply' failed, failed to unify P ?n ?n with P 42 23 ⊢ P 42 23 -/ #guard_msgs in example : P 42 23 := by apply_rfl opaque withImplicitNat {n : Nat} : Nat /-- error: tactic 'apply' failed, failed to unify P ?n ?n with P withImplicitNat withImplicitNat ⊢ P withImplicitNat withImplicitNat -/ #guard_msgs in example : P (@withImplicitNat 42) (@withImplicitNat 23) := by apply_rfl ``` and with this PR the messages we get are ``` error: tactic 'apply_rfl' failed, The lhs 42 is not definitionally equal to rhs 23 ⊢ P 42 23 ``` resp. ``` error: tactic 'apply_rfl' failed, The lhs @withImplicitNat 42 is not definitionally equal to rhs @withImplicitNat 23 ⊢ P withImplicitNat withImplicitNat ``` A test file checks the various failure modes and error messages. I believe this `apply_rfl` can serve as the only implementation of `rfl`, which would then complete #3302, and actually expose these improved error messages to the user. But as that seems to require a non-trivial bootstrapping dance, it’ll be separate. |
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