Repeatedly appending to a list is a common, if inefficient pattern in functional programs. Usually the trick we use is to build up the list in reverse, and then to reverse it as the last action of a function.Dlists are a representation of lists as functions that provide for constant time append to either the front or end of a dlist that may be used instead.dlist? : any -> boolean returns #t if its argument is a dlist, #f otherwise.

dlist-append : dlist dlist -> dlist returns a new dlist consisting of all the elements of the first dlist, followed by all the items of the second dlist.dlist-cons : any dlist -> dlist returns a new dlist created by prepending the element to the head of the dlist argument.dlist-snoc : dlist any -> dlist returns a new dlist created by appending the element to the tail of the dlist argument.dlist->list : dlist -> listof(any) returns a list consisting of all the elements of the dlist.list->dlist : listof(any) -> dlist returns a dlist consisting of all the elements of the list.dlist : any ... -> dlist returns a dlist containing all its arguments.