open System.Reflection
 
type T =
    | A of int
    | B of string
 
let collection = [A 10; B "abc"; A 40; B "120"]
 
let sp (col: T list) (str:string) = 
    match col with
    | [] -> []
    | _ ->
        let names = "Is" + str
        col 
        |> List.choose (fun x -> 
            let t = x.GetType()
            match t.GetProperty(names) with
            | null -> None
            | pi when unbox(pi.GetValue(x)) ->
                Some(t.InvokeMember("get_Item", BindingFlags.InvokeMethod, null, x, null))
            | _ -> None)
 
sp collection "A" |> printfn "%A\n"
sp collection "B" |> printfn "%A\n"   
sp collection "C" |> printfn "%A\n"

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