Traversable containers, monad extensions, and more
include S_non_monadic
type 'a t

The opaque type of zippers.

include Sexplib0.Sexpable.S1 with type 'a t := 'a t
val t_of_sexp : ( Sexplib0.Sexp.t -> 'a ) -> Sexplib0.Sexp.t -> 'a t
val sexp_of_t : ( 'a -> Sexplib0.Sexp.t ) -> 'a t -> Sexplib0.Sexp.t

Construction and destruction

val make : left:'a Base.list -> right:'a Base.list -> 'a t

make ~left ~right constructs a zipper with left list left and right list right.

These lists go directly into the zipper itself, so left, if non-empty, should be in the reverse order to how it should appear when fully rewound.

val of_list : 'a Base.list -> 'a t

of_list xs converts a list xs to a fully-rewound zipper.

It is equivalent to make with an empty left.

val to_list : 'a t -> 'a Base.list

to_list zipper returns the list of _all_ items in the zipper, including those in the left list.

All items appear in the same order that they would take in the right list if the zipper was fully rewound. In other words, the left list appears first (in reverse order), followed by the right list (in forwards order).

To get only the items in the right list, use right_list; to get only the items in the left list (reversed), use left_list.

Querying the left and right lists

val left_list : 'a t -> 'a Base.list

left_list zipper gets the raw left list of the zipper: all of the already-processed items in reverse order.

val right_list : 'a t -> 'a Base.list

right_list zipper gets the right list of the zipper: all of the not-yet-processed items in forwards order.

val to_two_lists : 'a t -> 'a Base.list * 'a Base.list

to_two_lists zipper is (left_list zipper, right_list zipper).

val left_length : 'a t ->

left_length zipper gets the length of zipper's left list.

val right_length : 'a t ->

right_length zipper gets the length of zipper's right list.


val is_at_start : 'a t -> Base.bool

is_at_start zipper tests whether zipper's left list is empty.

val is_at_end : 'a t -> Base.bool

is_at_end zipper tests whether zipper's right list is empty.


val push : 'a t -> value:'a -> 'a t

push zipper ~value pushes value into zipper at the cursor. The current cursor becomes the second item in the right list, and so on.

val push_left : 'a t -> value:'a -> 'a t

push_left zipper ~value pushes value into zipper just to the left of the cursor.

Peeking and popping

val peek_opt : ? -> 'a t -> 'a Base.option

peek_opt ?steps zipper retrieves the cursor value without popping it from the zipper. If the cursor is empty, None is returned.

If steps is given, it shifts the effective cursor steps places forwards.

val pop : 'a t -> ('a * 'a t) Base.Or_error.t

pop zipper returns an error if zipper has no cursor, or Ok (a, zipper') where a is zipper's cursor and zipper' is the new zipper formed by removing a.

val pop_opt : 'a t -> ('a * 'a t) Base.option

pop_opt zipper behaves as pop, but returns None if zipper has no cursor and Some (a, zipper') otherwise.

val map_head : 'a t -> f:( 'a -> 'a Base.option ) -> 'a t

map_head zipper ~f maps f across the cursor of zipper, if it exists, and replaces the cursor with the result (or drops it if f returns None).


val step : ? -> 'a t -> 'a t Base.Or_error.t

step ?steps zipper ~on_empty takes one or more steps across zipper. The number of steps defaults to 1 (forwards), but can be given by steps; negative numbers step backwards through the zipper. If the number of steps exceeds the bounds of the zipper, an error is returned.

type mark

The type of marks.

val mark : 'a t -> mark:mark -> 'a t Base.Or_error.t

mark zipper ~mark marks the cursor with mark, and returns the marked-up zipper.

If the cursor is empty, an error is returned.

val recall : 'a t -> mark:mark -> 'a t Base.Or_error.t

recall zipper ~mark rewinds zipper until the cursor is on an element previously marked with mark.

If recall runs out of left-list to rewind before finding mark, an error is returned.

val fold_until : 'a t -> f:( 'acc -> 'a -> 'a t -> ( mark, 'a, 'acc, 'final ) fold_outcome ) -> init:'acc -> finish:( 'acc -> 'a t -> 'final ) -> 'final

fold_until zipper ~f ~init ~finish behaves conceptually like List.fold_until, but folds f through the remaining elements of a zipper.

f receives the current accumulator, current cursor, and zipper with cursor popped at each stage. It can't directly modify the zipper mid-fold, but can influence the value of the final zipper provided to the finish continuation by using the various legs of fold_outcome.

val delete_to_mark : 'a t -> mark:mark -> 'a t Base.Or_error.t

delete_to_mark zipper ~mark deletes every item in the left-list up to, and including, the element previously marked with mark.

If delete_to_mark runs out of left-list to rewind before finding mark, an error is returned.