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package travesty
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S_monadic contains the core operations of a zipper, parametrised over a particular failure monad.

type 'a t
module M : Base.Monad.S
val pop_m : 'a t -> on_empty:('a t -> ('a * 'a t) M.t) -> ('a * 'a t) M.t

pop_m zipper ~on_empty behaves like pop, but executes a custom monadic action on_empty, instead of returning an error, when the cursor is empty.

val peek_m : ?steps:Base.int -> 'a t -> on_empty:('a t -> 'a M.t) -> 'a M.t

peek_m ?steps zipper ~on_empty behaves like peek_opt, but executes a custom monadic action on_empty, instead of returning None, when the cursor is empty.

val step_m : ?steps:Base.int -> 'a t -> on_empty:('a t -> 'a t M.t) -> 'a t M.t

step_m ?steps zipper ~on_empty behaves like step, but executes a custom monadic action on_empty, instead of returning an error, when the cursor is empty.

val map_m_head : 'a t -> f:('a -> 'a Base.option M.t) -> on_empty:('a t -> 'a t M.t) -> 'a t M.t

map_m_head ?steps zipper ~on_empty behaves like map_head, but executes a custom monadic action on_empty, instead of leaving the zipper unchanged, when the cursor is empty.