Coq 将模式传递给战术

我正在编写一种策略，在绑定列表中查找与键关联的值。比如：

Require Import String List Program.

Ltac assoc needle haystack :=
  match haystack with
  | @nil (_ * ?T) => constr:(@None T)
  | cons (?k, ?v) ?t => let pr := constr:(eq_refl k : k = needle) in constr:(Some v)
  | cons _        ?t => let res := assoc needle t in constr:res
  end.

不幸的是，我不知道钥匙的确切形式；相反，我知道一个与之匹配的模式。更准确地说，我要寻找的关键是调用类型类方法的结果，但我事先不知道将使用哪个实例。在下面的示例中，我知道键是调用

show“a”

，但我不知道使用什么实例：

Open Scope string_scope.
Open Scope list_scope.

Class Show A := { show: A -> string }.
Instance Show1 : Show string := {| show := fun x => x |}.
Instance Show2 : Show string := {| show := fun x => x ++ x |}.

Goal True.
  (* Works (poses Some 1) *)
  let v := assoc (show "a") [(show (Show := Show2) "a", 1); ("b", 2)] in pose v.
  (* Does not work (poses None) *)
  let v := assoc (show "a") [(show (Show := Show1) "a", 1); ("b", 2)] in pose v.

---

除了传递检查匹配的ltac

assoc

之外，还有什么技巧可以在这里使用吗？理想情况下，它看起来像是

（show（show:=“a”）

，或者可能是

（fun inst=>show（show:=inst）”a”）

，看起来像是传递函数，实际上：

Ltac assoc needlef haystack :=
  match haystack with
  | @nil (_ * ?T) => constr:(@None T)
  | cons (?k, ?v) ?t => let pr := constr:(eq_refl k : k = needlef _) in constr:(Some v)
  | cons _        ?t => let res := assoc needlef t in constr:res
  end.

Goal False.
  let v := assoc (fun i => show (Show := i) "a") [(show (Show := Show2) "a", 1); ("b", 2)] in pose v.
  let v := assoc (fun i => show (Show := i) "a") [(show (Show := Show1) "a", 1); ("b", 2)] in pose v.

整洁的（我必须添加

打开范围列表。

才能解析它。）