module Seq =
    let groupAdjacent f input = 
        let prev = Seq.head input
        let sgs,n = 
            (([],prev),input |> Seq.tail)
            ||> Seq.fold(fun (acc,prev) next -> 
                if f (prev,next) then 
                    match acc with
                    | [] -> [[prev]],next
                    | xs::rest -> (prev::xs)::rest,next
                else
                    match acc with 
                    | [] -> [[];[prev]],next
                    | xs::rest -> []::(prev::xs)::rest,next)
        let sgs = 
            match sgs with 
            | [] -> [[n]]
            | xs::rest -> 
                match xs with
                | [] -> [n]::rest
                | ys -> (n::ys)::rest
        sgs |> List.map List.rev |> List.rev

(*
["a"; "a"; "a"; "b"; "c"; "c"] |> Seq.groupAdjacent (fun (a,b)->a=b)
val it : seq<seq<string>> = seq [["a"; "a"; "a"]; ["b"]; ["c"; "c"]]
*)