Question

mySequence
|> Seq.iteri (fun i x -> ...)
...

How do I bind i at the end of the sequence? In other words how do I bind the value representing the number of iterations iterated by iteri?

Of course I could create a ref and assign i for all iterations, but I wonder if there is a more elegant way?

Answer 1

You could use fold, so that

Seq.iteri (fun i x -> ...)

becomes

Seq.fold (fun i x -> ... ; i+1) 0

along these lines:

let aSeq = 
    seq {
        for i in 1..10 do
            printfn "eval %d" i
            yield i
    }

let r = 
    aSeq 
    |> Seq.fold (fun i x ->
        printfn "iter %d" x // or whatever is "..."
        i+1) 0     

printfn "result: %d" r