Section Definitions.
Definition eq_dec X := forall x y : X, {x=y} + {x <> y}.
Existing Class eq_dec.
(* Any function that uses eq_dec. Doesn't matter -- ↓ ↓ ↓ *)
Definition f {X: Type} {DecX: eq_dec X} (x y: X) := x = y.
End Definitions.
Section MySection.
Context {T: Type}.
Hypothesis TEqDec: eq_dec T.
Inductive myType :=
| C: T -> myType.
Instance myTypeEqDec : eq_dec myType.
Proof. ... Defined.
(* Everything is ok *)
Example example1: forall (t1 t2: myType), f t1 t2.
Proof. ... Qed.
End MySection.
Section AnotherSection.
Context {T: Type}.
Hypothesis TEqDec: eq_dec T.
(* Now I must explicitly specify this -- ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
Example example2: forall (t1 t2: @myType T), @f _ (@myTypeEqDec _ TEqDec) t1 t2.
Proof. ... Qed.
End AnotherSection.
正如您在example1中看到的,Coq能够找到有关myType的实例信息。但是在我更改了部分之后,有关实例的所有信息都消失了,我必须明确指定它。因此,当我有许多类型类和实例时,代码会迅速变得混乱。显然,我应该以某种方式将这些信息反馈到上下文中。这样做的正确方法是什么?
答案 0 :(得分:1)
只需将Global
修饰符添加到您的实例声明中,如下所示:
Global Instance myTypeEqDec : eq_dec myType.
(* ... *)
如reference manual中所述,
可以在节中声明的实例上使用
Global
修饰符,以便在节关闭后自动重新声明它们的泛化。