将F#seq表达式转换为OCaml

Question

在我试图转换为OCaml的F#代码中,我遇到了以下问题:

    let rec parseList lst off =
        seq {
            if List.isEmpty lst then ()
            else
                match parse off <| List.head lst with
                | (Unmatched, _) as y -> yield y
                | (y, z) -> yield (y, z)
                            yield! parseList (List.tail lst) z
        }

我想知道如何将 带有yield的seq {...}表达式转换为OCaml？我的第一个猜测是seq必须成为一个列表.

Answer 1

最简单的翻译(不是尾递归)是:

let rec parseList lst off =
  match lst with
  | [] -> []
  | x::xs ->
      match parse off x with
      | Unmatched, _ as y -> [y]
      | y, z -> (y, z)::parseList xs z

尾递归版是:

let parseList lst off =
  let rec loop xs off = function
    | [] -> xs
    | y::ys ->
        match parse off y with
        | Unmatched, _ as x -> x::xs
        | _, z as x -> loop (x::xs) z ys in
  List.rev (loop [] off lst)

请注意,您开始使用的F#代码有很多不足之处.当您可以更轻松地使用模式匹配时,调用List.head并且List.tail是不必要的潜在异常来源.并且有多余的括号.