module Doubly_linked:`sig`

..`end`

doubly-linked lists

There is a fundamental problem with a data structure (like doubly-linked lists) that is both mutable and provides iteration function that call back to user-supplied functions. If those user-supplied functions modify the data structure, what is the semantics of the remainder of the iteration? This module sidesteps this issue by detecting attempts by user-supplied functions to modify a doubly-linked list while in the middle of iterating over it.

Modification functions include: insert_*, remove*, transfer Iteration functions include: exists, fold*, for_all, find

Calls to modification functions detect if the list is being iterated over, and if so raise an exception rather than modify the list. For example, a use like the following would raise.

iter t ~f:(fun _ -> ... remove t e ...)

module Elt:`sig`

..`end`

`type ``'a`

t

`include Container.S1`

`val invariant : ``'a t -> unit`

`val create : ``unit -> 'a t`

creating doubly-linked lists

`val of_list : ``'a list -> 'a t`

`of_list l`

returns a doubly-linked list `t`

with the same elements as `l`

and in the
same order (i.e. the first element of `l`

is the first element of `t`

). It is always
the case that `l = to_list (of_list l)`

.`val equal : ``'a t -> 'a t -> bool`

predicates

`val is_first : ``'a t -> 'a Elt.t -> bool`

`val is_last : ``'a t -> 'a Elt.t -> bool`

`val first_elt : ``'a t -> 'a Elt.t option`

constant-time extraction of first and last elements.

`val last_elt : ``'a t -> 'a Elt.t option`

`val first : ``'a t -> 'a option`

`val last : ``'a t -> 'a option`

`val next : ``'a t -> 'a Elt.t -> 'a Elt.t option`

constant-time move to next or previous element.

`val prev : ``'a t -> 'a Elt.t -> 'a Elt.t option`

`val insert_before : ``'a t -> 'a Elt.t -> 'a -> 'a Elt.t`

constant-time insertion of a new element. It is an error to call

```
insert_before t e
a
```

or `insert_after t e a`

if `e`

is not an element in `t`

.`val insert_after : ``'a t -> 'a Elt.t -> 'a -> 'a Elt.t`

`val insert_first : ``'a t -> 'a -> 'a Elt.t`

`val insert_last : ``'a t -> 'a -> 'a Elt.t`

`val remove : ``'a t -> 'a Elt.t -> unit`

constant-time removal of an element. It is an error to call

`remove t e`

when `e`

is
not in `t`

.`val remove_first : ``'a t -> 'a option`

`val remove_last : ``'a t -> 'a option`

`val fold_elt : ``'a t -> init:'b -> f:('b -> 'a Elt.t -> 'b) -> 'b`

`fold_elt t ~init ~f`

is the same as fold, except `f`

is called with the `'a Elt.t`

's
from the list instead of the contained `'a`

values.
Note that like other iteration functions, it is an error to mutate `t`

inside the
fold. If you'd like to call `remove`

on any of the `'a Elt.t`

's, accumulate them here
and do so after `fold_elt`

returns.

`val iter_elt : ``'a t -> f:('a Elt.t -> unit) -> unit`

`val fold_right : ``'a t -> init:'b -> f:('a -> 'b -> 'b) -> 'b`

`val find_elt : ``'a t -> f:('a -> bool) -> 'a Elt.t option`

`find_elt t ~f`

finds the first element in `t`

that satisfies `f`

, by testing each of
element of `t`

in turn until `f`

succeeds.`val clear : ``'a t -> unit`

`clear t`

removes all elements from the list in constant time.`val copy : ``'a t -> 'a t`

`copy t`

returns a copy of `t`

.`val transfer : ``src:'a t -> dst:'a t -> unit`

`transfer ~src ~dst`

has the same behavior as
`iter src ~f:(insert_last dst); clear src`

except that it runs in constant time.
If `s = to_list src`

and `d = to_list dst`

, then after `transfer ~src ~dst`

:
`to_list src = []`

`to_list dst = d @ s`

`val filter_inplace : ``'a t -> f:('a -> bool) -> unit`

`filter_inplace t ~f`

removes all elements of `t`

that don't satisfy `f`

.`val unchecked_iter : ``'a t -> f:('a -> unit) -> unit`

`unchecked_iter t ~f`

behaves like `iter t ~f`

except that `f`

is allowed to modify
`t`

. Adding or removing elements before the element currently being visited has no
effect on the traversal. Elements added after the element currently being visited
will be traversed. Elements deleted after the element currently being visited will
not be traversed. Deleting the element currently visited is an error that is not
detected (presumably leading to an infinite loop) .`val t_of_sexp : ``(Sexplib.Sexp.t -> 'a) -> Sexplib.Sexp.t -> 'a t`

`val sexp_of_t : ``('a -> Sexplib.Sexp.t) -> 'a t -> Sexplib.Sexp.t`

creating doubly-linked lists

`of_list l`

returns a doubly-linked list `t`

with the same elements as `l`

and in the
same order (i.e. the first element of `l`

is the first element of `t`

). It is always
the case that `l = to_list (of_list l)`

.predicates

constant-time extraction of first and last elements.

constant-time move to next or previous element.

constant-time insertion of a new element. It is an error to call

```
insert_before t e
a
```

or `insert_after t e a`

if `e`

is not an element in `t`

.constant-time removal of an element. It is an error to call

`remove t e`

when `e`

is
not in `t`

.`fold_elt t ~init ~f`

is the same as fold, except `f`

is called with the `'a Elt.t`

's
from the list instead of the contained `'a`

values.
Note that like other iteration functions, it is an error to mutate `t`

inside the
fold. If you'd like to call `remove`

on any of the `'a Elt.t`

's, accumulate them here
and do so after `fold_elt`

returns.

`find_elt t ~f`

finds the first element in `t`

that satisfies `f`

, by testing each of
element of `t`

in turn until `f`

succeeds.

`clear t`

removes all elements from the list in constant time.

`copy t`

returns a copy of `t`

.

`transfer ~src ~dst`

has the same behavior as
`iter src ~f:(insert_last dst); clear src`

except that it runs in constant time.

If `s = to_list src`

and `d = to_list dst`

, then after `transfer ~src ~dst`

:
`to_list src = []`

`to_list dst = d @ s`

`filter_inplace t ~f`

removes all elements of `t`

that don't satisfy `f`

.

`unchecked_iter t ~f`

behaves like `iter t ~f`

except that `f`

is allowed to modify
`t`

. Adding or removing elements before the element currently being visited has no
effect on the traversal. Elements added after the element currently being visited
will be traversed. Elements deleted after the element currently being visited will
not be traversed. Deleting the element currently visited is an error that is not
detected (presumably leading to an infinite loop) .