ocaml/stdlib/list.mli

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(*                                                                     *)
(*                         Caml Special Light                          *)
(*                                                                     *)
(*            Xavier Leroy, projet Cristal, INRIA Rocquencourt         *)
(*                                                                     *)
(*  Copyright 1995 Institut National de Recherche en Informatique et   *)
(*  Automatique.  Distributed only by permission.                      *)
(*                                                                     *)
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(* $Id$ *)

(* Module [List]: list operations *)

val length : 'a list -> int
        (* Return the length (number of elements) of the given list. *)
val hd : 'a list -> 'a
        (* Return the first element of the given list. Raise
           [Failure "hd"] if the list is empty. *)
val tl : 'a list -> 'a list
        (* Return the given list without its first element. Raise
           [Failure "tl"] if the list is empty. *)
val nth : 'a list -> int -> 'a
        (* Return the n-th element of the given list.
           The first element (head of the list) is at position 0.
           Raise [Failure "nth"] if the list is too short. *)
val rev : 'a list -> 'a list
        (* List reversal. *)
val flatten : 'a list list -> 'a list
        (* Catenate (flatten) a list of lists. *)

(** Iterators *)

val iter : ('a -> 'b) -> 'a list -> unit
        (* [List.iter f [a1; ...; an]] applies function [f] in turn to
           [a1; ...; an], discarding all the results. It is equivalent to
	   [begin f a1; f a2; ...; f an; () end]. *)
val map : ('a -> 'b) -> 'a list -> 'b list
        (* [List.map f [a1; ...; an]] applies function [f] to [a1, ..., an],
           and builds the list [[f a1; ...; f an]]
           with the results returned by [f]. *)
val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a
        (* [List.fold_left f a [b1; ...; bn]] is
           [f (... (f (f a b1) b2) ...) bn]. *)
val fold_right : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b
        (* [List.fold_right f [a1; ...; an] b] is
           [f a1 (f a2 (... (f an b) ...))]. *)

(** Iterators on two lists *)

val iter2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> unit
        (* [List.iter2 f [a1; ...; an] [b1; ...; bn]] calls in turn
           [f a1 b1; ...; f an bn], discarding the results.
	   Raise [Invalid_argument] if the two lists have
	   different lengths. *)
val map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
        (* [List.map2 f [a1; ...; an] [b1; ...; bn]] is
           [[f a1 b1; ...; f an bn]].
	   Raise [Invalid_argument] if the two lists have
           different lengths. *)
val fold_left2 : ('a -> 'b -> 'c -> 'a) -> 'a -> 'b list -> 'c list -> 'a
        (* [List.fold_left2 f a [b1; ...; bn] [c1; ...; cn]] is
           [f (... (f (f a b1 c1) b2 c2) ...) bn cn].
	   Raise [Invalid_argument] if the two lists have
	   different lengths. *)
val fold_right2 : ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'c
        (* [List.fold_right2 f [a1; ...; an] [b1; ...; bn] c] is
           [f a1 b1 (f a2 b2 (... (f an bn c) ...))].
	   Raise [Invalid_argument] if the two lists have
	   different lengths. *)

(** List scanning *)

val for_all : ('a -> bool) -> 'a list -> bool
        (* [for_all p [a1; ...; an]] checks if all elements of the list
           satisfy the predicate [p]. That is, it returns
           [(p a1) & (p a2) & ... & (p an)]. *)
val exists : ('a -> bool) -> 'a list -> bool
        (* [exists p [a1; ...; an]] checks if at least one element of the list
           satisfies the predicate [p]. That is, it returns
           [(p a1) or (p a2) or ... or (p an)]. *)
val mem : 'a -> 'a list -> bool
        (* [mem a l] is true if and only if [a] is equal
           to an element of [l]. *)

(** Association lists *)

val assoc : 'a -> ('a * 'b) list -> 'b
        (* [assoc a l] returns the value associated with key [a] in the list of
           pairs [l]. That is,
             [assoc a [ ...; (a,b); ...] = b]
           if [(a,b)] is the leftmost binding of [a] in list [l].
           Raise [Not_found] if there is no value associated with [a] in the
           list [l]. *)
val mem_assoc : 'a -> ('a * 'b) list -> bool
        (* Same as [assoc], but simply return true if a binding exists,
           and false if no bindings exist for the given key. *)
val assq : 'a -> ('a * 'b) list -> 'b
        (* Same as [assoc], but use physical equality instead of structural
           equality to compare keys. *)

(** Lists of pairs *)

val split : ('a * 'b) list -> 'a list * 'b list
        (* Transform a list of pairs into a pair of lists:
           [split [(a1,b1); ...; (an,bn)]] is [([a1; ...; an], [b1; ...; bn])]
        *)
val combine : 'a list -> 'b list -> ('a * 'b) list
        (* Transform a pair of lists into a list of pairs:
           [combine ([a1; ...; an], [b1; ...; bn])] is
              [[(a1,b1); ...; (an,bn)]].
           Raise [Invalid_argument] if the two lists
           have different lengths. *)