小编dum*_*ulo的帖子

我正在玩写结果类型和各种功能,并遇到了我无法解释的类型不匹配错误.这是一个最小的例子:

type ('a, 'b) result =
    | Success of 'a
    | Failure of 'b list

let apply fr xr =
    match fr, xr with
    | Success f, Success x -> Success (f x)
    | Failure _, Success _ -> fr
    | Success _, Failure _ -> xr
    | Failure a, Failure b -> Failure (List.concat [a; b])

编译此代码会产生以下错误:

init.fsx(8,31): error FS0001: Type mismatch. Expecting a
('a,'b) result
but given a
(('c -> 'a),'d) result
The resulting type would be infinite …