NAME

       Stdlib.List - no description

Module

       Module   Stdlib.List

Documentation

       Module List
        : (module Stdlib__List)

       type 'a t = 'a list =
        | []
        | (::) of 'a * 'a list

       An alias for the type of lists.

       val length : 'a list -> int

       Return the length (number of elements) of the given list.

       val compare_lengths : 'a list -> 'b list -> int

       Compare  the lengths of two lists.  compare_lengths l1 l2 is equivalent to compare (length
       l1) (length l2) , except that the computation stops after reaching the end of the shortest
       list.

       Since 4.05.0

       val compare_length_with : 'a list -> int -> int

       Compare  the  length  of a list to an integer.  compare_length_with l len is equivalent to
       compare (length l) len , except that the computation stops after at most len iterations on
       the list.

       Since 4.05.0

       val cons : 'a -> 'a list -> 'a list

       cons x xs is x :: xs

       Since 4.03.0 (4.05.0 in ListLabels)

       val hd : 'a list -> 'a

       Return the first element of the given list.

       Raises Failure if the list is empty.

       val tl : 'a list -> 'a list

       Return the given list without its first element.

       Raises Failure 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.

       Raises Failure if the list is too short.

       Raises Invalid_argument if n is negative.

       val nth_opt : 'a list -> int -> 'a option

       Return the n -th element of the given list.  The first element (head of the  list)  is  at
       position 0.  Return None if the list is too short.

       Since 4.05

       Raises Invalid_argument if n is negative.

       val rev : 'a list -> 'a list

       List reversal.

       val init : int -> (int -> 'a) -> 'a list

       init len f is f 0; f 1; ...; f (len-1) , evaluated left to right.

       Since 4.06.0

       Raises Invalid_argument if len < 0 .

       val append : 'a list -> 'a list -> 'a list

       Concatenate two lists. Same function as the infix operator @ .  Not tail-recursive (length
       of the first argument). The @ operator is not tail-recursive either.

       val rev_append : 'a list -> 'a list -> 'a list

       rev_append l1 l2 reverses l1 and concatenates it with  l2  .   This  is  equivalent  to  (
       List.rev l1) @ l2 , but rev_append is tail-recursive and more efficient.

       val concat : 'a list list -> 'a list

       Concatenate  a  list  of lists. The elements of the argument are all concatenated together
       (in the same order) to give the result.  Not tail-recursive  (length  of  the  argument  +
       length of the longest sub-list).

       val flatten : 'a list list -> 'a list

       Same  as  List.concat . Not tail-recursive (length of the argument + length of the longest
       sub-list).

   Comparison
       val equal : ('a -> 'a -> bool) -> 'a list -> 'a list -> bool

       equal eq [a1; ...; an] [b1; ..; bm] holds when the two input lists have the  same  length,
       and for each pair of elements ai , bi at the same position we have eq ai bi .

       Note:  the  eq function may be called even if the lists have different length. If you know
       your equality function is costly, you may want to check List.compare_lengths first.

       Since 4.12.0

       val compare : ('a -> 'a -> int) -> 'a list -> 'a list -> int

       compare cmp [a1; ...; an] [b1; ...; bm] performs a lexicographic  comparison  of  the  two
       input lists, using the same 'a -> 'a -> int interface as compare :

       -  a1  ::  l1  is smaller than a2 :: l2 (negative result) if a1 is smaller than a2 , or if
       they are equal (0 result) and l1 is smaller than l2

       -the empty list [] is strictly smaller than non-empty lists

       Note: the cmp function will be called even if the lists have different lengths.

       Since 4.12.0

   Iterators
       val iter : ('a -> unit) -> 'a list -> unit

       iter f [a1; ...; an] applies function f in turn to a1; ...; an . It is equivalent to begin
       f a1; f a2; ...; f an; () end .

       val iteri : (int -> 'a -> unit) -> 'a list -> unit

       Same  as  List.iter  ,  but  the  function is applied to the index of the element as first
       argument (counting from 0), and the element itself as second argument.

       Since 4.00.0

       val map : ('a -> 'b) -> 'a list -> 'b 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 . Not tail-recursive.

       val mapi : (int -> 'a -> 'b) -> 'a list -> 'b list

       Same  as  List.map  ,  but  the  function  is applied to the index of the element as first
       argument (counting from 0), and the element itself as second argument. Not tail-recursive.

       Since 4.00.0

       val rev_map : ('a -> 'b) -> 'a list -> 'b list

       rev_map f l gives the same result as List.rev ( List.map f l) , but is tail-recursive  and
       more efficient.

       val filter_map : ('a -> 'b option) -> 'a list -> 'b list

       filter_map f l applies f to every element of l , filters out the None elements and returns
       the list of the arguments of the Some elements.

       Since 4.08.0

       val concat_map : ('a -> 'b list) -> 'a list -> 'b list

       concat_map f l gives the same result as List.concat ( List.map f l) . Tail-recursive.

       Since 4.10.0

       val fold_left_map : ('a -> 'b -> 'a * 'c) -> 'a -> 'b list -> 'a * 'c list

       fold_left_map is  a combination of fold_left and map that threads an  accumulator  through
       calls to f .

       Since 4.11.0

       val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a

       fold_left f init [b1; ...; bn] is f (... (f (f init b1) b2) ...) bn .

       val fold_right : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b

       fold_right  f  [a1;  ...;  an]  init  is  f  a1  (f  a2  (...  (f  an  init)  ...))  . Not
       tail-recursive.

   Iterators on two lists
       val iter2 : ('a -> 'b -> unit) -> 'a list -> 'b list -> unit

       iter2 f [a1; ...; an] [b1; ...; bn] calls in turn f a1 b1; ...; f an bn .

       Raises Invalid_argument if the two lists are determined to have different lengths.

       val map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list

       map2 f [a1; ...; an] [b1; ...; bn] is [f a1 b1; ...; f an bn] .

       Raises Invalid_argument if the two lists are determined to  have  different  lengths.  Not
       tail-recursive.

       val rev_map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list

       rev_map2  f  l1  l2  gives  the  same  result  as  List.rev  ( List.map2 f l1 l2) , but is
       tail-recursive and more efficient.

       val fold_left2 : ('a -> 'b -> 'c -> 'a) -> 'a -> 'b list -> 'c list -> 'a

       fold_left2 f init [a1; ...; an] [b1; ...; bn] is f (... (f (f init a1 b1) a2 b2)  ...)  an
       bn .

       Raises Invalid_argument if the two lists are determined to have different lengths.

       val fold_right2 : ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'c

       fold_right2  f  [a1;  ...;  an] [b1; ...; bn] init is f a1 b1 (f a2 b2 (... (f an bn init)
       ...))  .

       Raises Invalid_argument if the two lists are determined to  have  different  lengths.  Not
       tail-recursive.

   List scanning
       val for_all : ('a -> bool) -> 'a list -> bool

       for_all  f [a1; ...; an] checks if all elements of the list satisfy the predicate f . That
       is, it returns (f a1) && (f a2) && ... && (f an) for a non-empty list and true if the list
       is empty.

       val exists : ('a -> bool) -> 'a list -> bool

       exists  f [a1; ...; an] checks if at least one element of the list satisfies the predicate
       f . That is, it returns (f a1) || (f a2) || ... || (f an) for a non-empty list  and  false
       if the list is empty.

       val for_all2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool

       Same as List.for_all , but for a two-argument predicate.

       Raises Invalid_argument if the two lists are determined to have different lengths.

       val exists2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool

       Same as List.exists , but for a two-argument predicate.

       Raises Invalid_argument if the two lists are determined to have different lengths.

       val mem : 'a -> 'a list -> bool

       mem a set is true if and only if a is equal to an element of set .

       val memq : 'a -> 'a list -> bool

       Same  as  List.mem  , but uses physical equality instead of structural equality to compare
       list elements.

   List searching
       val find : ('a -> bool) -> 'a list -> 'a

       find f l returns the first element of the list l that satisfies the predicate f .

       Raises Not_found if there is no value that satisfies f in the list l .

       val find_opt : ('a -> bool) -> 'a list -> 'a option

       find f l returns the first element of the list l that satisfies the predicate f .  Returns
       None if there is no value that satisfies f in the list l .

       Since 4.05

       val find_map : ('a -> 'b option) -> 'a list -> 'b option

       find_map  f l applies f to the elements of l in order, and returns the first result of the
       form Some v , or None if none exist.

       Since 4.10.0

       val filter : ('a -> bool) -> 'a list -> 'a list

       filter f l returns all the elements of the list l that satisfy the predicate f . The order
       of the elements in the input list is preserved.

       val find_all : ('a -> bool) -> 'a list -> 'a list

       find_all is another name for List.filter .

       val filteri : (int -> 'a -> bool) -> 'a list -> 'a list

       Same  as  List.filter  , but the predicate is applied to the index of the element as first
       argument (counting from 0), and the element itself as second argument.

       Since 4.11.0

       val partition : ('a -> bool) -> 'a list -> 'a list * 'a list

       partition f l returns a pair of lists (l1, l2) , where l1 is the list of all the  elements
       of  l  that  satisfy the predicate f , and l2 is the list of all the elements of l that do
       not satisfy f .  The order of the elements in the input list is preserved.

       val partition_map : ('a -> ('b, 'c) Either.t) -> 'a list -> 'b list * 'c list

       partition_map f l returns a pair of lists (l1, l2) such that, for each element  x  of  the
       input list l :

       -if f x is Left y1 , then y1 is in l1 , and

       -if f x is Right y2 , then y2 is in l2 .

       The  output  elements  are  included  in  l1  and  l2  in  the  same relative order as the
       corresponding input elements in l .

       In particular, partition_map (fun x -> if f x then Left x else Right x) l is equivalent to
       partition f l .

       Since 4.12.0

   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 .

       Raises Not_found if there is no value associated with a in the list l .

       val assoc_opt : 'a -> ('a * 'b) list -> 'b option

       assoc_opt a l returns the value associated with key a in the list of pairs l  .  That  is,
       assoc_opt  a [ ...; (a,b); ...] = Some b if (a,b) is the leftmost binding of a in list l .
       Returns None if there is no value associated with a in the list l .

       Since 4.05

       val assq : 'a -> ('a * 'b) list -> 'b

       Same as List.assoc , but uses physical equality instead of structural equality to  compare
       keys.

       val assq_opt : 'a -> ('a * 'b) list -> 'b option

       Same  as  List.assoc_opt  ,  but  uses physical equality instead of structural equality to
       compare keys.

       Since 4.05.0

       val mem_assoc : 'a -> ('a * 'b) list -> bool

       Same as List.assoc , but simply return true if a binding exists, and false if no  bindings
       exist for the given key.

       val mem_assq : 'a -> ('a * 'b) list -> bool

       Same  as  List.mem_assoc  ,  but  uses physical equality instead of structural equality to
       compare keys.

       val remove_assoc : 'a -> ('a * 'b) list -> ('a * 'b) list

       remove_assoc a l returns the list of pairs l without the first pair with key a ,  if  any.
       Not tail-recursive.

       val remove_assq : 'a -> ('a * 'b) list -> ('a * 'b) list

       Same  as  List.remove_assoc , but uses physical equality instead of structural equality to
       compare keys. Not tail-recursive.

   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]) .  Not tail-recursive.

       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)] .

       Raises Invalid_argument if the two lists have different lengths. Not tail-recursive.

   Sorting
       val sort : ('a -> 'a -> int) -> 'a list -> 'a list

       Sort a list in increasing  order  according  to  a  comparison  function.  The  comparison
       function  must return 0 if its arguments compare as equal, a positive integer if the first
       is greater, and a negative integer if the first is smaller (see Array.sort for a  complete
       specification).  For  example,  compare  is a suitable comparison function.  The resulting
       list is sorted in increasing order.  List.sort is guaranteed to run in constant heap space
       (in addition to the size of the result list) and logarithmic stack space.

       The current implementation uses Merge Sort. It runs in constant heap space and logarithmic
       stack space.

       val stable_sort : ('a -> 'a -> int) -> 'a list -> 'a list

       Same as List.sort , but the sorting algorithm is guaranteed to be  stable  (i.e.  elements
       that compare equal are kept in their original order).

       The current implementation uses Merge Sort. It runs in constant heap space and logarithmic
       stack space.

       val fast_sort : ('a -> 'a -> int) -> 'a list -> 'a list

       Same as List.sort or List.stable_sort , whichever is faster on typical input.

       val sort_uniq : ('a -> 'a -> int) -> 'a list -> 'a list

       Same as List.sort , but also remove duplicates.

       Since 4.02.0 (4.03.0 in ListLabels)

       val merge : ('a -> 'a -> int) -> 'a list -> 'a list -> 'a list

       Merge two lists: Assuming that l1 and l2 are sorted according to the  comparison  function
       cmp , merge cmp l1 l2 will return a sorted list containing all the elements of l1 and l2 .
       If several elements compare equal, the elements of l1 will be before the elements of l2  .
       Not tail-recursive (sum of the lengths of the arguments).

   Lists and Sequences
       val to_seq : 'a list -> 'a Seq.t

       Iterate on the list.

       Since 4.07

       val of_seq : 'a Seq.t -> 'a list

       Create a list from a sequence.

       Since 4.07