Pack consecutive duplicates of list elements into sublists.

sublist

//P09  Pack consecutive duplicates of list elements into sublists.
// https://sites.google.com/site/prologsite/prolog-problems/1
let packDups l = 
       let result =  List.foldBack (
                            fun ele (flist,(mainlist:List<List<_>>)) -> 
                                    match (flist,mainlist) with
                                    |([],_)   ->  (ele::flist,mainlist) 
                                    |(h::_,_) when ele = h -> ((ele::flist),mainlist)
                                    |(_::_,[]) -> ([ele], [flist])
                                    |(_::_,_) -> ([ele],flist::mainlist)
                                    ) l ([], [[]] )  
       fst(result)::snd(result)   


packDups ["a";"a";"a";"a";"b";"c";"c";"a";"a";"d";"e";"e";"e";"e"]