F#查询表达式:如何在连接表为空的记录上执行左连接并返回？

let leftJoin (table1: 'a seq) (table2: 'b seq) (joinCondition: 'a -> 'b -> bool) (select: 'a -> 'b -> 'c) : 'c seq =
    table1
    |> Seq.collect (fun row1 ->
        match Seq.tryFind (fun row2 -> joinCondition row1 row2) table2 with
        | Some row2 -> Seq.singleton (select row1 row2)
        | None -> Seq.singleton (select row1 (Option.defaultValue row2)))

type Person = { Name: string; Age: int }
type Address = { Name: string; City: string }

let people = [
    { Name = "John"; Age = 25 }
    { Name = "Alice"; Age = 30 }
]

let addresses = [
    { Name = "John"; City = "New York" }
    { Name = "Bob"; City = "Los Angeles" }
]

let result = leftJoin people addresses (fun p a -> p.Name = a.Name) (fun p a -> (p.Name, a.City))

for (name, city) in result do
    printfn "%s - %s" name city

John - New York
Alice -