streamsthing.fs

type EnumerableFromEnumerator(input: IEnumerator<byte> ) =
    interface IEnumerable<byte> with
        member this.GetEnumerator() = input 
    interface System.Collections.IEnumerable with
        member this.GetEnumerator() = input :> System.Collections.IEnumerator

let takeSkip (sequence: IEnumerable<byte>) (n: int) : (byte[] * IEnumerable<byte>) = 
    let enumerator = sequence.GetEnumerator()
    let data = Array.zeroCreate(n) 
    let rec readSequence i = 
        let moreData = enumerator.MoveNext() 
        if (not moreData || i = n) then i 
        else 
            data.[i] <- enumerator.Current
            readSequence (i+1) 
    let readBytes = readSequence 0
    let sequence' = new EnumerableFromEnumerator(enumerator) :> IEnumerable<byte>
    if (readBytes = n) then 
        (data, sequence') 
    else 
        (data.[0 .. readBytes], sequence') 

Jonas just did it in three lines instead https://gist.github.com/bjartwolf/d1bf94521f48ae74809b