lean4-htt/tests/lean/1079.lean
jrr6 d1ec806834
feat: improve error messages in invalid match alternatives (#8368)
This PR improves the error messages produced by invalid pattern-match
alternatives and improves parity in error placement between
pattern-matching tactics and elaborators.

Closes #7170
2025-05-19 17:40:41 +00:00

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Text

theorem bad : ∀ (m n : Nat), (if m = n then Ordering.eq else Ordering.gt) = Ordering.lt → False := by
intros m n
cases (Nat.decEq m n) with -- an error as expected: "Alternative `isFalse` has not bee provided"
| isTrue h =>
set_option trace.Meta.Tactic.simp true in
simp [h]
theorem bad' : ∀ (m n : Nat), (if m = n then Ordering.eq else Ordering.gt) = Ordering.lt → False := by
intros m n
cases (Nat.decEq m n) with
| isTrue h =>
simp [h]
| isFalse h =>
simp [h]