FSharpAux.IO.SeqIO.Seq.CSV: Incorrect collection formatting

proposedSolution.fsx

open BioFSharp
open FSharpAux.IO.SeqIO

///Returns a function to format a given value as string
let inline stringFunction (separator: string) (flatten: bool) (input: 'a) =
    let o = box input
    match o with
    //match string first so that it doesn't get treated as a char array
    | :? string ->
        fun (x: obj) ->
            let sb = new System.Text.StringBuilder()
            sb.Append x |> ignore
            let res = sb.ToString()
            sb.Clear() |> ignore
            res
    | :? System.Collections.IEnumerable ->
        if flatten then
            fun x ->
                let sb = new System.Text.StringBuilder()
                let a = x :?> System.Collections.IEnumerable
                //iterates over Collections.IEnumerable to get entries as objects for the string builder
                let b = [for i in a do yield box i]
                b
                |> Seq.iteri (fun i x ->
                    if i = 0 then
                        sb.AppendFormat("{0}", x) |> ignore
                    else
                        sb.AppendFormat(sprintf "%s{0}" separator, x) |> ignore
                    )
                let res = sb.ToString()
                sb.Clear() |> ignore
                res
        else
            fun x -> 
                let standardSeparators = [";";"\t";","]
                let separator = 
                    standardSeparators
                    |> List.find (fun sep -> sep <> separator)
                let sb = new System.Text.StringBuilder()
                let a = x :?> System.Collections.IEnumerable
                //iterates over Collections.IEnumerable to get entries as objects for the string builder
                let b = [for i in a do yield box i]
                b
                |> Seq.iteri (fun i x ->
                    if i = 0 then
                        sb.AppendFormat("{0}", x) |> ignore
                    else
                        sb.AppendFormat(sprintf "%s{0}" separator, x) |> ignore
                    )
                let res = sb.ToString()
                sb.Clear() |> ignore
                res            
    | _ ->
        fun (x: obj) ->
            let sb = new System.Text.StringBuilder()
            sb.Append x |> ignore
            let res = sb.ToString()
            sb.Clear() |> ignore
            res

let csv separator header flatten data = Seq.CSVwith Seq.valueFunction stringFunction separator header flatten data 

type test = {
    name  : string
    lname : string
    d1    : string []
    d2    : float list 
    d3    : int seq
    }

let x = 
    [
    for i = 1 to 10 do 
        yield
            {
                name  = i.ToString()
                lname = i.ToString()
                d1    = [|i..50|] |> Array.map string
                d2    = [i..50] |> List.map float
                d3    = seq {i.. 50}
            }
    ]

let outFilePath = @"YourPath"

x
|> csv "\t" true false 
|> FSharpAux.IO.SeqIO.Seq.writeOrAppend (outFilePath)