记录列表上的SML功能

发布于 2024-12-23 19:50:30 字数 227 浏览 5 评论 0原文

我试图声明一个函数，该函数将元组内的记录列表作为参数，但语法并不像我希望的那样直观。

这就是我想做的：

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

原文

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.

Here's what I'm trying to do:

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

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坐在坟头思考人生 2024-12-30 19:50:30

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，

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

会起作用。

请注意，上述模式匹配并不详尽，请注意 players 的空列表和 privateStack 的空列表：

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

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 *)

would work.

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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