Streams

streams.fs

open System

type Stream<'t> = 
    | Empty
    | Stream of 't * (unit -> Stream<'t>)

let takeList count stream = 
    let rec inner remain remainCount tail = 
        match (remain, remainCount) with
        | (Empty, _) -> tail
        | (Stream(item, rest), remainCount) -> 
            if remainCount > 0 then inner (rest()) (remainCount - 1) (item :: tail)
            else tail
    (inner stream count []) |> List.rev

let toList stream = 
    let rec inner remain tail = 
        match remain with
        | Empty -> tail
        | Stream(item, stream) -> inner (stream()) (item :: tail)
    inner stream [] |> List.rev

let rec take count stream = 
    match stream with
    | Empty -> Empty
    | Stream(item, stream) -> 
        Stream(item, 
               fun () -> 
                   if count > 1 then take (count - 1) (stream())
                   else Empty)

let ints = 
    let rec inner (start) = Stream(start, fun () -> inner (start + 1))
    inner 0