travesty

Traversable containers, monad extensions, and more
IN THIS PACKAGE
Module type Travesty . Traversable_types . S0
module Elt : Base.Equal.S

Elements must have equality. While this is an extra restriction on top of the Base equivalent, it is required by Make0, and helps us define chaining operations.

We export Elt.t as elt for compatibility with Core-style containers.

include Generic_types.S0 with type elt = Elt.t
type t

The container type.

type elt = Elt.t

The element type.

include Generic with type 'a t := t and type 'a elt := Elt.t
include Generic_types.Generic with type 'a t := t with type 'a elt := Elt.t
module On (M : Base.Applicative.S) : Generic_on_applicative with type 'a t := t and type 'a elt := Elt.t and module M := M

On implements traversal operators for a given applicative M.

module On_monad (M : Base.Monad.S) : Generic_on_monad with type 'a t := t and type 'a elt := Elt.t and module M := M

On_monad implements traversal operators for a given monad M. Compared to On(Monad_exts.App(M)), this adds various derived operators available only for monads.

We can do generic container operations.

include Base.Container.Generic with type 'a t := t and type 'a elt := Elt.t

We can do non-applicative mapping operations.

include Mappable_types.Generic with type 'a t := t and type 'a elt := Elt.t

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 t := t with type 'a elt := Elt.t
val fold_map : t -> f:( 'acc -> Elt.t -> 'acc * Elt.t ) -> init:'acc -> 'acc * t

fold_map c ~f ~init folds f over every t in c, threading through an accumulator with initial value init.

val mapi : f:( Base.int -> Elt.t -> Elt.t ) -> t -> t

mapi ~f t maps f across t, passing in an increasing position counter.

module With_errors : Generic_on_monad with type 'a t := t and type 'a elt := Elt.t and module M := Base.Or_error

With_errors specialises On_applicative to the error applicative.

include Mappable_types.S0_container with type t := t and type elt := Elt.t
include Mappable_types.S0 with type t := t with type elt := Elt.t
include Generic_types.S0 with type t := t with type elt := Elt.t
include Mappable_types.Generic with type 'a t := t and type 'a elt := Elt.t

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 t := t with type 'a elt := Elt.t
val map : t -> f:( Elt.t -> Elt.t ) -> t

map c ~f maps f over every t in c.

include Base.Container.S0 with type t := t and type elt := Elt.t
val mem : t -> Elt.t -> bool

Checks whether the provided element is there, using equality on elts.

val length : t -> int
val is_empty : t -> bool
val iter : t -> f:( Elt.t -> unit ) -> unit

iter must allow exceptions raised in f to escape, terminating the iteration cleanly. The same holds for all functions below taking an f.

val fold : t -> init:'accum -> f:( 'accum -> Elt.t -> 'accum ) -> 'accum

fold t ~init ~f returns f (... f (f (f init e1) e2) e3 ...) en, where e1..en are the elements of t.

val fold_result : t -> init:'accum -> f:( 'accum -> Elt.t -> ( 'accum, 'e ) Base.Result.t ) -> ( 'accum, 'e ) Base.Result.t

fold_result t ~init ~f is a short-circuiting version of fold that runs in the Result monad. If f returns an Error _, that value is returned without any additional invocations of f.

val fold_until : t -> init:'accum -> f:( 'accum -> Elt.t -> ( 'accum, 'final ) Base.Container.Continue_or_stop.t ) -> finish:( 'accum -> 'final ) -> 'final

fold_until t ~init ~f ~finish is a short-circuiting version of fold. If f returns Stop _ the computation ceases and results in that value. If f returns Continue _, the fold will proceed. If f never returns Stop _, the final result is computed by finish.

Example:

type maybe_negative =
  | Found_negative of int
  | All_nonnegative of { sum : int }

(** [first_neg_or_sum list] returns the first negative number in [list], if any,
    otherwise returns the sum of the list. *)
let first_neg_or_sum =
  List.fold_until ~init:0
    ~f:(fun sum x ->
      if x < 0
      then Stop (Found_negative x)
      else Continue (sum + x))
    ~finish:(fun sum -> All_nonnegative { sum })
;;

let x = first_neg_or_sum [1; 2; 3; 4; 5]
val x : maybe_negative = All_nonnegative {sum = 15}

let y = first_neg_or_sum [1; 2; -3; 4; 5]
val y : maybe_negative = Found_negative -3
val exists : t -> f:( Elt.t -> bool ) -> bool

Returns true if and only if there exists an element for which the provided function evaluates to true. This is a short-circuiting operation.

val for_all : t -> f:( Elt.t -> bool ) -> bool

Returns true if and only if the provided function evaluates to true for all elements. This is a short-circuiting operation.

val count : t -> f:( Elt.t -> bool ) -> int

Returns the number of elements for which the provided function evaluates to true.

val sum : (module Base.Container.Summable with type t = 'sum) -> t -> f:( Elt.t -> 'sum ) -> 'sum

Returns the sum of f i for all i in the container.

val find : t -> f:( Elt.t -> bool ) -> Elt.t option

Returns as an option the first element for which f evaluates to true.

val find_map : t -> f:( Elt.t -> 'a option ) -> 'a option

Returns the first evaluation of f that returns Some, and returns None if there is no such element.

val to_list : t -> Elt.t list
val to_array : t -> Elt.t array
val min_elt : t -> compare:( Elt.t -> Elt.t -> int ) -> Elt.t option

Returns a min (resp. max) element from the collection using the provided compare function. In case of a tie, the first element encountered while traversing the collection is returned. The implementation uses fold so it has the same complexity as fold. Returns None iff the collection is empty.

val max_elt : t -> compare:( Elt.t -> Elt.t -> int ) -> Elt.t option