Q:

How do I get the current sequence number in an iteration in F#? 

Consider the following code to demonstrate the question:

let sequence = Seq.initInfinite (fun _ -> "Element")
Seq.iter (fun _ -> printf "Element no: ?")  sequence 

Is it in any way possible to get the current sequence number (e.g. its rank) to print? 

A:

Use the iteri function:
let sequence = Seq.initInfinite (fun _ -> "Element")
sequence |> Seq.iteri (fun i _ -> printfn "Element no. % d" i) 

