记录清单上的SML功能 [英] SML function on record list

问题描述

我正在尝试声明一个函数，该函数将元组内的记录列表作为参数，但是语法不如我所希望的直观.

I'm trying to declare a function that takes a list of records inside a tuple as an argument but the syntax is not as intuitive as I would have liked.

这就是我想要做的:

type Player = {id:int, privateStack:int list};
fun foo(({id, x::xs}:Player)::players, ...) = (* wrong syntax *)
    (* do something *)

推荐答案

模式匹配需要将记录字段绑定到某些值，因此您必须使用显式记录语法.因此，

Pattern matching requires binding record fields to some values so you have to use explicit record syntax. Therefore,

fun foo(({id = id, privateStack = x::xs})::players, ...) =
    (* do something *)

会工作的.

请注意，上面的模式匹配并不详尽，请注意players的空白列表和privateStack的空白列表:

Note that above pattern matching is not exhaustive, be aware of empty list for players and empty list for privateStack:

fun foo([], ...) = (* do something *)
   | foo({id = id, privateStack = []}::players, ...) = (* do something else *)
   | foo({id = id, privateStack = x::xs}::players, ...) = (* do something else *)

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