F# XML parsing

Question

this c# code is probably not the most efficient but gets what I want done.

How do I accomplish the same thing in F# code?

    string xml = " <EmailList> " +
               "      <Email>[email protected]</Email> " +
               "      <Email>[email protected]</Email> " +
               " </EmailList> ";

    XmlDocument xdoc = new XmlDocument();
    XmlNodeList nodeList;
    String emailList = string.Empty;
    xdoc.LoadXml(xml);
    nodeList = xdoc.SelectNodes("//EmailList");
    foreach (XmlNode item in nodeList)
    {
        foreach (XmlNode email in item)
        {
             emailList +=  email.InnerText.ToString() +  Environment.NewLine ;
        }               
    }

Answer 1

If you look at your code, you have a couple of things going on. The first is loading the collection for the Email nodes, and the second is actually doing something meaningful with them.

First, you'd want to have your function return a collection. Something like (and I'm on my Mac, so this may not work):

List<string> EmailAddresses(string xml)
{
    XmlDocument xdoc = new XmlDocument();
    XmlNodeList nodeList;
    String emailList = string.Empty;
    xdoc.LoadXml(xml);
    nodeList = xdoc.SelectNodes("//EmailList");
    foreach (XmlNode item in nodeList)
    {
        foreach (XmlNode email in item)
        {
             yield email.InnerText.ToString();
        }               
    }
}

Now the question comes around what you want to do with that collection. In your example above, you were concatenating it, or basically storing state.

From a C# perspective, you can then start using things like the answers from this question (using LINQ) and this one.

From an F# perspective, you now have a list and can simply use the normal procedures for a list like this one or here.

You can also look at LINQ to XML (or at the 5 minute overview) to get some more ideas.

Answer 2

How about something along the lines of:

#light
open System.XML

let xml = "..."

let emailList = 
    let xdoc = new XmlDocument()
    xdoc.LoadXml(xml)

    let mutable list = []
    let addEmail e = list <- e :: emailList

    xdoc.SelectNodes("//EmailList")
    |> IEnumerable.iter(fun(item:XmlNode) ->
        item
        |> IEnumerable.iter(fun(e:XmlNode) ->
            addEmail e.InnerText; ()))

    list

Answer 3

Here is similar code to do this in F#. I'm sure one of the F# ninja's will put a better version up here in a minute.

open System.Xml

let getList x = 
    let getDoc =
        let doc = new XmlDocument()
        doc.LoadXml(x) |> ignore
        doc
    let getEmail (n:XmlNode) = n.InnerText.ToString() 
    let doc = getDoc
    let build = new System.Text.StringBuilder()
    doc.SelectNodes("//EmailList") 
        |> Seq.cast<XmlNode>
        |> Seq.map (fun n -> n.ChildNodes )
        |> Seq.map_concat (Seq.cast<XmlNode>)
        |> Seq.map(fun (n:XmlNode) -> getEmail n) 
        |> Seq.iter (fun e -> build.AppendLine(e) |> ignore )
    build.ToString()

Answer 4

let doc = new XmlDocument() in
    doc.LoadXml xml;
    doc.SelectNodes "/EmailList/Email/text()"
        |> Seq.cast<XmlNode>
        |> Seq.map (fun node -> node.Value)
        |> String.concat Environment.NewLine

If you actually want the final trailing newline you can add it in the map and String.concat with the empty string.