Question

以下代码用于替换数组的第一个元素，但我想指定值1而不是值0到删除数组的第一个元素。

let rec replace index value list =
    match index, list with
    | 0, x::xs -> value::xs
    | index, x::xs -> x::replace (index - 1) value xs
    | index, [] -> failwith "index out of range"

let replaceCharArray = replace 0 'd' ['a';'b';'c']
printfn "%A" replaceCharArray

我修改了上面的代码工作代码，以便我可以这样做，但现在我我的范围超出范围。

let rec replace index value list =
    match index, list with
    | 0, x::xs -> value::xs
    | index, x::xs -> x::replace ((index - 1) - 1) value xs
    | index, [] -> failwith "index out of range"

let replaceCharArray = replace 1 'd' ['a';'b';'c']
printfn "%A" replaceCharArray

有人可以帮我弄清楚为什么我会超出范围异常？

Answer 1

let rec replace index value list =
    match index, list with
    | 0, _ -> failwith "index out of range"
    | 1, x::xs -> value::xs
    | index, x::xs -> x::replace (index - 1) value xs
    | index, [] -> failwith "index out of range"

起始值为1的递归反向函数

1 个答案: