Get Levenshtein distance

Levenshtein.fsx

// Formula from https://en.wikipedia.org/wiki/Levenshtein_distance
let lev (a : string) (b : string) =
    let rec loop (a : char list) (b : char list) =
        match a, b with
        | a, [] -> a.Length
        | [], b -> b.Length
        | (aHead :: aTail), (bHead :: bTail) when aHead = bHead -> loop aTail bTail
        | (_ :: aTail), (_ :: bTail) -> 1 + List.min [loop aTail b ; loop a bTail ; loop aTail bTail]

    loop (List.ofSeq a) (List.ofSeq b)

match List.ofArray fsi.CommandLineArgs with
| []
| [_] -> printfn "Please provide 2 words"
| [_ ; a] -> lev a "" |> printfn "%i"
| [_ ; a ; b] -> lev a b |> printfn "%i"
| args -> lev args[1] args[2] |> printfn "%i"