F#:此"let"之后的块未完成.期待表达 [英] F#:Block following this 'let' is unfinished. Expect an expression

问题描述

我知道在F#中，我们应该将每个值绑定到一个名称. 而且我认为我还可以吗?

I know in F# we should bind every single value to a name. And I think mine is ok???

但是在 if语句中，我遇到了以下错误.

But in the if statement I have the following error.

Block following this 'let' is unfinished. Expect an expression

，它来自let min= List.nth list i. 据我所知，我将 min 限制为List.nth list i.那么为什么应该是一个错误呢?

and it comes from let min= List.nth list i. As far as I know I bounded the min to List.nth list i. So why it should be an error?

let mutable list =[-1;2;3;4]
let mutable min=list.[0]
let mutable i=1

if min<=0  then   let  min= List.nth list i  

推荐答案

如果要变异可变变量，可以使用<-运算符:

If you want to mutate a mutable variable, you can use the <- operator:

if min <= 0 then min <- List.nth list i  

但这不是一种非常实用的方法.更好的方法是定义一个新值:

But this is not a very functional approach. A better method is to define a new value:

let minUpdated = if min <= 0 then List.nth list i else min

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