Below is my code for building the collatz sequence so a given number. I’m trying to make the function tail recursive and I believe that this impelemtation is tail recursive but I’m not yet so comfortable with F# that I can convince myself 100%.

let collatzSeq n =     let collatz m =         match m%2 with         | 0 -> m/2         | _ -> 3*m + 1     let rec loop (l,acc) =         match l with         | 1 -> acc         | _ -> let l' = (collatz l) in loop (l',l'::acc)     loop (n,[n]) |> List.rev  [<EntryPoint>] let main argv =      let col12 = collatzSeq 12     printfn "%A %d" col12 col12.Length     0 // return an integer exit code 

My concern is does the let .. in loop construct stop this being tail recursive and if it does how do I improve the code to make it tail recursive?