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List(3) 				  OCaml library 				  List(3)

NAME
       List - List operations.

Module
       Module	List

Documentation
       Module List
	: sig end

       List operations.

       Some functions are flagged as not tail-recursive.  A tail-recursive function uses constant
       stack space, while a non-tail-recursive function uses  stack  space  proportional  to  the
       length  of its list argument, which can be a problem with very long lists.  When the func-
       tion takes several list arguments, an approximate formula  giving  stack  usage	(in  some
       unspecified constant unit) is shown in parentheses.

       The  above  considerations  can usually be ignored if your lists are not longer than about
       10000 elements.

       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.  Raise Invalid_argument List.nth
       if n is negative.

       val rev : 'a list -> 'a list

       List reversal.

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

       Catenate 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

       List.rev_append	l1  l2	reverses  l1  and  concatenates it to 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 concat .  Not tail-recursive (length of the  argument  +  length  of  the  longest
       sub-list).

       === Iterators ===

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

       List.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 argu-
       ment (counting from 0), and the element itself as second argument.

       Since 4.00.0

       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 .  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  argu-
       ment (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

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

       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) ...))   .	 Not  tail-recur-
       sive.

       === Iterators on two lists ===

       val iter2 : ('a -> 'b -> unit) -> 'a list -> 'b list -> unit

       List.iter2  f  [a1;  ...;  an]  [b1; ...; bn] calls in turn f a1 b1; ...; f an bn .  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_argu-
       ment if the two lists have different lengths.  Not tail-recursive.

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

       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

       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.  Not tail-recur-
       sive.

       === 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) || (p a2) || ... || (p an) .

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

       Same  as  List.for_all  , but for a two-argument predicate.  Raise Invalid_argument if the
       two lists have different lengths.

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

       Same as List.exists , but for a two-argument predicate.	Raise Invalid_argument if the two
       lists have different lengths.

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

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

       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 p l returns the first element of the list l that satisfies the predicate p	.   Raise
       Not_found if there is no value that satisfies p in the list l .

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

       filter  p  l  returns  all  the elements of the list l that satisfy the predicate p .  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 partition : ('a -> bool) -> 'a list -> 'a list * 'a list

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

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

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

       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 com-
       pare 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)] .  Raise 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  func-
       tion  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, Pervasives.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 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 containting 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).

OCamldoc				    2014-06-09					  List(3)
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