gistfile1.txt

let rec nums = seq { yield 1
                     printfn "yield 1"
                     for n in nums do 
                        printfn "(for)yield %d" (n)
                        yield n+1 } 

> Seq.take 5 nums |> Seq.iter (printfn "%d");;
1
yield 1
(for)yield 1
2
yield 1
(for)yield 1
(for)yield 2
3
yield 1
(for)yield 1
(for)yield 2
(for)yield 3
4
yield 1
(for)yield 1
(for)yield 2
(for)yield 3
(for)yield 4
5

-------

let rec nums = seq { yield 1
                     printfn "yield 1"
                     for n in nums do 
                        printfn "(for)yield %d" (n)
                        yield n+1 }  |> Seq.cache

> Seq.take 5 nums |> Seq.iter (printfn "%d");;
1
yield 1
(for)yield 1
2
(for)yield 2
3
(for)yield 3
4
(for)yield 4
5