Номер минимального элемента

[|1;8;9;5;3|]
|> Array.min
|> Array.findIndex [Array.min];;

let seek xs = 
    let rec loop i min indexes =
        if i >= Array.length xs then (min, List.rev indexes) else
        let e = xs.[i]
        match indexes with 
        | []              -> loop (i + 1) e [i] 
        | xs when e < min -> loop (i + 1) e [i] 
        | xs when e = min -> loop (i + 1) e (i :: xs) 
        | _               -> loop (i + 1) min indexes
    loop 0 0 []  
 
 
do 
    printfn "%A" <| seek [| 1; 2; 3; 2; 0; 4; 5; 0; 1 |]
    System.Console.ReadKey() |> ignore

let seek xs = 
    let min     = xs |> Array.min 
    let indexes = xs |> Seq.mapi (fun i e -> (i, e)) 
                     |> Seq.choose (fun (i, e) -> if e = min then Some i else None)
                     |> Seq.toList
    min, indexes