期望 int return 值

Question

我有以下代码片段，它评估了一个 XML 文件：

open System
open System.IO
open System.Xml.Linq
open FSharp.Data
open System.Net

type InputXml = XmlProvider<"C:\Temp\sample.xml">

[<EntryPoint>]
let main argv =

    let input = InputXml.Load("C:\Temp\sample.xml")

    for customer in input.GetCustomers() do
    for order in customer.GetOrders() do
    for line in order.GetOrderLines() do
        printfn "Customer: %s, Order: %s, Item: %s, Quantity: %d"
                customer.Name order.Number line.Item line.Quantity

    Console.ReadLine() |> ignore
    0 // return an integer exit code

编译器显示以下错误：

Error   1   This expression was expected to have type
    int    
but here has type
    unit    D:\f#\samples\Program.fs    16  5   samples

为什么？我做错了什么？

Answer 1

F# 是用空格分隔的。这意味着：

for customer in input.GetCustomers() do
for order in customer.GetOrders() do
for line in order.GetOrderLines() do

需要更像这样：

for customer in input.GetCustomers() do
  for order in customer.GetOrders() do
    for line in order.GetOrderLines() do

否则第一个 for 的正文范围将一直持续到当前缩进级别结束（包括 0）。您可以使用旧式语法通过执行以下操作来解决此问题：

for customer in input.GetCustomers() do
for order in customer.GetOrders() do
for line in order.GetOrderLines() do

...

done
done
done
0

但这在这一点上是非常不合惯用语的。

期望 int return 值

Expecting int return value

xml

f#