steps.fsx

// sequence of steps

type Step =
| Next
| Ask1 of string ref
| Ask2 of string ref

let steps = seq {
    printfn "step 0"

    yield Next
    printfn "step 1"

    let ask1 = ref ""
    yield Ask1 ask1
    if !ask1 = "n" then () else
    printfn "step 2"

    let ask2 = ref ""
    yield Ask2 ask2
    if !ask2 = "c" then
        printfn "step 3 custom"
        yield Next
        printfn "step 4 extra"
    else
        printfn "step 3 default"
}

// go default steps
printfn "--- default steps"
for step in steps do ()

// go with a custom step
printfn "--- stop at Ask1"
for step in steps do
    match step with
    | Ask1 res -> res := "n"
    | _ -> ()

// go with a custom step
printfn "--- custom at Ask2"
for step in steps do
    match step with
    | Ask2 res -> res := "c"
    | _ -> ()

// go to Ask2 then pause and continue
printfn "--- pause and continue"
let it = steps.GetEnumerator ()
let rec step () =
    if it.MoveNext () then
        match it.Current with
        | Ask2 _ -> ()
        | _ -> step ()
step ()
printfn "pause"
while it.MoveNext () do ()