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Recursive tree
f#functional

Hi,
I have a XElement roughly done like this:

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    <Tasks>
      <Task>
        0
        <Id>1</Id>
      </Task>
      <Task>
        1
        <Id>2</Id>
      </Task>
      <Task>
        1
        <Id>3</Id>
      </Task>
      <Task>
        3
        <Id>5</Id>
      </Task>
      [..]

Each Task Element has a unique Id, some informations I'm not reporting and a parent id. The parent id refers to another task so that it is possible to represent a tree.

I already have a C# function to sort this structure:

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private void SortTask(ref XElement taskOutput, XElement tasks, string parent)
{
	var children = from t in tasks.Elements("Task")
								 where t.Element("Parent").Value == parent
								 select t;
	foreach (XElement task in children.AsEnumerable())
	{
		taskOutput.Add(task);
		SortTask(ref taskOutput, tasks, task.Element("Id").Value);
	}
}

Here I keep invoking recursively the function searching the children elements of each node and adding the to a new XElement called taskOutput. Each time I pass a reference to this new object, the id of the current element (that represent the parent in the next call) and the original XElement with all the tasks.

Now, I thought this would be a good test case to learn a bit about F# simply rewriting this thing in a functional way, but I'm having trouble with it.

This is what I got so far:

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    type TaskManager(taskListXml) = 
        member o.taskList = XElement.Parse(taskListXml).Elements(XName.op_Implicit("Task"))
        
        member o.Sort =
            let parent =
                o.taskList
                |> Seq.find (fun t -> t.Element(XName.op_Implicit("Parent")).Value.Equals("0"))
            let rec doSort t =
                let parId = t.Element(XName.op_Implicit("Id")).Value
                let children = 
                    o.tasklist
                    |> Seq.filter (fun x -> x.Element(XName.op_Implicit("Parent")).Value.Equals(parId))
                    |> Seq.iter (fun x -> Console.WriteLine(x))
                    |> Seq.iter (fun x -> doSort x)

It does not compile specifying that the return type for let (in `let children`) has an error.
Any help in let me understand this better?

Thank you very much

.

Looks like

[link:stackoverflow.com]

is the canonical URL for this question now.

By on 7/18/2009 3:37 PM ()

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