Container_exts.Extend0
Extend0
creates extensions for a Container.S0
.
include Generic_types.S0 with type t := C.t with type elt := C.elt
include Container_exts_types.Generic
with type ('a, 'phantom) t := C.t
and type 'a elt := C.elt
Generic
refers to the container type as 'a t
, and the element type as 'a elt
; substitute t
/elt
(arity-0) or 'a t
/'a
(arity-1) accordingly below.
include Generic_types.Generic
with type ('a, 'phantom) t := C.t
with type 'a elt := C.elt
The following functions help in checking whether a container has a particular, commonly-required number of elements (zero or one, one, two, and so on).
at_most_one xs
returns Ok None
if xs
is empty; Ok Some(x)
if it contains only x
; and an error otherwise.
Examples (using an extended version of List):
(* ok None *)
List.at_most_one []
(* ok (Some 1) *)
List.at_most_one [1]
(* error -- too many *)
List.at_most_one [1; 2]
one xs
returns Ok x
if xs
contains only x
, and an error otherwise.
Examples (using an extended version of List):
(* error -- not enough *)
List.one []
(* ok 1 *)
List.one [1]
(* error -- too many *)
List.one [1; 2]
two xs
returns Ok (x, y)
if xs
is a list containing only x
and y
in that order, and an error otherwise.
Examples (using an extended version of List):
(* error -- not enough *)
List.two []
(* error -- not enough *)
List.two [1]
(* ok (1, 2) *)
List.two [1; 2]
(* error -- too many *)
List.two [1; 2; 3]