在战术/战术符号中匹配上下文模式

Question

我通过战术在我的目标中找到了一个模式。

为什么会失败：

        Tactic Notation "my_context_match" uconstr(g) :=
          match goal with
          | |- context[g] => idtac
          end.
          my_context_match _.

虽然成功了？

        match goal with
          | |- context[_] => idtac
        end.

---

有没有办法写一个my_context_match，这样我就可以传递不完整的模式（上面有_），看看我的目标内是否有任何与模式匹配的东西？

Answer 1

对

uconstr的支持非常不完整。 我刚刚报告了#9321。 请注意，即使这样也会失败：

Goal True.
  let v := uconstr:(True) in
  lazymatch constr:(v) with
  | v => idtac
  end. (* Error: No matching clauses for match. *)

---

正如@eponier在评论中建议的那样，您可以使用open_constr而不是uconstr。 但是，这将留下未解决的问题。 这是一种行之有效的策略，并且不会留下未解决的 evars：

Tactic Notation "my_context_match" uconstr(g) :=
  (* [match] does not support [uconstr], cf COQBUG(https://github.com/coq/coq/issues/9321),
     so we use [open_constr] *)
  let g := open_constr:(g) in
  (* turning [g] into an [open_constr] creates new evars, so we must
     eventually unify them with the goal *)
  let G := match goal with |- ?G => G end in
  (* We now search for [g] in the goal, and then replace the matching
     subterm with the [open_constr] [g], so that we can unify the
     result with the goal [G] to resolve the new evars we created *)
  match G with
  | context cG[g]
    => let G' := context cG[g] in
       unify G G'
  end.
Goal True / True.
  my_context_match _.
  my_context_match (_ / _).
  Fail my_context_match (_ / _).
  my_context_match True.
  exact (conj I I).
Qed.