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Good examples of implementing For and Yield in a computation expression / monad

Hi,

I've seen plenty of good examples of implementing Bind, Return, Let etc for a computation expression builder, but haven't yet come across good examples of For, Yield and YieldFrom.

Could anyone point me in the right direction?

A simple example of adding for and yield to the AttemptBuilder example would be great. In particular I'd like the yield only to yield if the attempt was successful

        let ofType<'T> x =
            match box x with
            | :? 'T as t -> fun () -> Some t
            | _          -> fun () -> None     

        let mapOfNameTuplePairs = 
            attempt { 
                for item in collection.Items do
                    let! a = item |> ofType<A>
                    let! b = a.Property.Item |> ofType<B>
                    let! c = b.Item |> ofType<C>
                    yield c.Name, (a, b, c) } 
                    |> run
                    |> Map.ofList

I'll post here if I come up with anything...

many thanks,

Danny

Two excellent article series are:

[link:codebetter.com]

[link:techneilogy.blogspot.com]

By DannyAsher on 11/1/2010 2:02 AM (permalink)