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package travesty
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Extensions for a Container.S0 whose elements are predicates.

This signature extends and constrains Extensions0.

type t

Type of predicate containers

type item

Type of items being tested against predicates.

include S0 with type t := t and type elt := item -> Base.bool
include Types_intf.S0 with type t := t with type elt := item -> Base.bool
include Generic with type 'a t := t and type 'a elt := item -> Base.bool

Generic_extensions 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 Types_intf.Generic with type 'a t := t with type 'a elt := item -> Base.bool

Testing for a specific number of elements

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).

val at_most_one : t -> (item -> Base.bool) Base.option Base.Or_error.t

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):

List.at_most_one []     (* ok None *)
     at_most_one [1]    (* ok (Some 1) *)
     at_most_one [1; 2] (* error -- too many *)
val one : t -> (item -> Base.bool) Base.Or_error.t

one xs returns Ok x if xs contains only x, and an error otherwise.

Examples (using an extended version of List):

List.one []     (* error -- not enough *)
     one [1]    (* ok 1 *)
     one [1; 2] (* error -- too many *)
val two : t -> ((item -> Base.bool) * (item -> Base.bool)) Base.Or_error.t

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):

List.two []        (* error -- not enough *)
     two [1]       (* error -- not enough *)
     two [1; 2]    (* ok (1, 2) *)
     two [1; 2; 3] (* error -- too many *)

Miscellaneous extensions

val max_measure : measure:((item -> Base.bool) -> Base.int) -> ?default:Base.int -> t -> Base.int

max_measure ~measure ~default xs measures each item in xs according to measure, and returns the highest measure reported. If xs is empty, return default if given, and 0 otherwise.

include Generic_predicate with type 'a t := t and type 'a item := item
val any : item -> predicates:t -> Base.bool

any x ~predicates tests x against predicates until one returns true, in which case it returns true; or all return false, in which case it returns false.

val all : item -> predicates:t -> Base.bool

any x ~predicates tests x against predicates until one returns false, in which case it returns false; or all return true, in which case it returns true.

val none : item -> predicates:t -> Base.bool

none x ~predicates is the same as any x with all predicates in predicates negated. It tests x against predicates until one returns true, in which case it returns false; or all return false, in which case it returns true.