相关疑难解决方法(0)

我之间的差异的理解List.fold,并List.foldBack为在其相反的顺序列表折返迭代.这两个函数都会累积列表中项目的结果.

我很难想出一个很好的例子,最好将foldBack放在列表上.在我提出的示例中,如果函数逻辑执行相同的操作,则fold和foldBack的结果相同.

[<Fact>]
let ``List.foldBack accumulating a value from the right to the left``() =
    let list = [1..5]       
    let fFoldBack x acc =
        acc - x

    let fFold acc x =
        acc - x

    let foldBackResult = List.foldBack fFoldBack list 0
    let foldResult = List.fold fFold 0 list

    Assert.Equal( -15, foldBackResult ) //  0 - 5 - 4 - 3 - 2 - 1
    Assert.Equal( -15, foldResult ) //      0 - 1 - 2 - …