How To Compute On-Balance Volume (OBV) using F#?

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let calculateOBV (prices : float list) (volumes : float list) =
    let rec calculateOBVHelper (prices : float list) (volumes : float list) (obv : float list) =
        match prices, volumes with
        | [], _ -> obv |> List.rev
        | price :: restPrices, volume :: restVolumes ->
            let change = 
                match restPrices with
                | [] -> 0.0
                | hd :: _ -> if price > hd then volume else if price < hd then -volume else 0.0
            let newObv = 
                match obv with
                | [] -> change
                | hd :: _ -> hd + change
            calculateOBVHelper restPrices restVolumes (newObv :: obv)
    calculateOBVHelper prices volumes []

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let prices = [100.0; 105.0; 110.0; 105.0; 115.0]
let volumes = [500.0; 600.0; 700.0; 300.0; 800.0]
let obv = calculateOBV prices volumes
printfn "On-Balance Volume (OBV): %A" obv