我在用:
$ coqtop -v
The Coq Proof Assistant, version 8.4pl5 (February 2015)
compiled on Feb 06 2015 17:44:41 with OCaml 4.02.1
我定义了以下CoInductive
类型stream
:
$ coqtop
Welcome to Coq 8.4pl5 (February 2015)
Coq < CoInductive stream (A : Type) : Type :=
Coq < | Cons : A -> stream A -> stream A.
stream is defined
Coq < Check stream.
stream
: Type -> Type
Coq < Check Cons.
Cons
: forall A : Type, A -> stream A -> stream A
然后,我尝试定义以下CoFixpoint
定义zeros
:
Coq < CoFixpoint zeros : stream nat := Cons 0 zeros.
但是,我收到了以下错误:
Toplevel input, characters 38-39:
> CoFixpoint zeros : stream nat := Cons 0 zeros.
> ^
Error: In environment
zeros : stream nat
The term "0" has type "nat" while it is expected to have type
"Type".
我发现我必须显式实例化变量A
:
Coq < CoFixpoint zeros : stream nat := Cons nat 0 zeros.
zeros is corecursively defined
为什么 Coq 不A
自己推断类型?我如何让它推断出的类型A
?