GroupAdjacent for sequences in F#

groupAdjacent.fs

open System.Collections.Generic

let groupAdjacent projection (source : _ seq) = seq {
    let rec loop (e : IEnumerator<_>) g (members : List<_>) = seq {        
        members.Add(e.Current)
        if e.MoveNext() then
            let key = projection e.Current
            if key = g then
                yield! loop e key members
            else
                yield g, seq members
                yield! loop e key (List())
        else
            yield g, seq members
    }
    use e = source.GetEnumerator()
    if e.MoveNext() then
        yield! loop e (projection e.Current) (List())
}