Split seq in F#

Question

I should split seq into seq> by an attribute of the elements. If this attribute equals by a given value it must be \'sp

Answer 1

The following is an impure implementation but yields immutable sequences lazily:

let unflatten f s = seq {
    let buffer = ResizeArray()

    let flush() = seq { 
        if buffer.Count > 0 then 
            yield Seq.readonly (buffer.ToArray())
            buffer.Clear() }

    for item in s do
        if f item then yield! flush()
        buffer.Add(item)

    yield! flush() }

f is the function used to test whether an element should be a split point:

[1;2;3;4;1;5;6;7;1;9] |> unflatten (fun item -> item = 1)