Module BatList

module BatList: sig .. end

Additional and modified functions for lists.

The OCaml standard library provides a module for list functions. This BatList module can be used to extend the List module or as a standalone module. It provides new functions and modify the behavior of some other ones (in particular all functions are now tail-recursive).

The following functions have the same behavior as the List module ones but are tail-recursive: map, append, concat, flatten, fold_right, remove_assoc, remove_assq, split. That means they will not cause a Stack_overflow when used on very long list.

The implementation might be a little more slow in bytecode, but compiling in native code will not affect performances.

This module extends Stdlib's List module, go there for documentation on the rest of the functions and types.

type 'a t = 'a list

List operations.

The type of lists
Author(s): Xavier Leroy (base module), Brian Hurt, Nicolas Cannasse, Richard W.M. Jones, David Teller

include BatEnum.Enumerable

include BatInterfaces.Mappable

Base operations

val is_empty : 'a list -> bool

is_empty e returns true if e does not contains any element.

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

cons h t returns the list starting with h and continuing as t

val first : 'a list -> 'a

Returns the first element of the list, or raise Empty_list if the list is empty (similar to hd).

val last : 'a list -> 'a

Returns the last element of the list, or raise Empty_list if the list is empty. This function takes linear time.

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

at l n returns the n-th element of the list l or raise Invalid_index is the index is outside of l bounds.

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

Catenate two lists. Same function as the infix operator @. Tail-recursive (length of the first argument).

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. Tail-recursive (length of the argument + length of the longest sub-list).

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

Same as concat.

Constructors

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

Similar to String.make, make n x returns a list containing n elements x.

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

Similar to Array.init, init n f returns the list containing the results of (f 0),(f 1).... (f (n-1)). Raise Invalid_arg "BatList.init" if n < 0.

Iterators

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

iteri f l will call (f 0 a0);(f 1 a1) ... (f n an) where a0..an are the elements of the list l.

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. Tail-recursive.

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

mapi f l will build the list containing (f 0 a0);(f 1 a1) ... (f n an) where a0..an are the elements of the list l.

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) ...)). Tail-recursive.

val reduce : ('a -> 'a -> 'a) -> 'a list -> 'a

List.reduce f h::t is fold_left f h t.
Raises Empty_list on empty lists.

val max : 'a list -> 'a

max l returns the largest value in l as judged by Pervasives.compare

val min : 'a list -> 'a

min l returns the smallest value in l as judged by Pervasives.compare

val sum : int list -> int

sum l returns the sum of the elements of l

val fsum : float list -> float

sum l returns the sum of the elements of l

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.
Raises Different_list_size 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].
Raises Different_list_size if the two lists have different lengths. Tail-recursive.

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.
Raises Different_list_size 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) ...)).
Raises Different_list_size if the two lists have different lengths. Tail-recursive.

List scanning

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 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 have different lengths.

List searching

val find_exn : ('a -> bool) -> exn -> 'a list -> 'a

find_exn p e l returns the first element of l such as p x returns true or raises e if such an element has not been found.

val findi : (int -> 'a -> bool) -> 'a list -> int * 'a

findi p e l returns the first element ai of l along with its index i such that p i ai is true, or raises Not_found if no such element has been found.

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

find_map pred list finds the first element of list for which pred element returns Some r. It returns r immediately once found or raises Not_found if no element matches the predicate. See also BatList.filter_map.

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

rfind p l returns the last element x of l such as p x returns true or raises Not_found if such element as not been found.

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

filter_map f l calls (f a0) (f a1).... (f an) where a0..an are the elements of l. It returns the list of elements bi such as f ai = Some bi (when f returns None, the corresponding element of l is discarded).

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.

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

index_of e l returns the index of the first occurrence of e in l, or None if there is no occurrence of e in l

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

index_ofq e l behaves as index_of e l except it uses physical equality

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

rindex_of e l returns the index of the last occurrence of e in l, or None if there is no occurrence of e in l

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

rindex_ofq e l behaves as rindex_of e l except it uses physical equality

val unique : ?cmp:('a -> 'a -> bool) -> 'a list -> 'a list

unique cmp l returns the list l without any duplicate element. Default comparator ( = ) is used if no comparison function specified.

This function takes O(n²) time.
See also sort_unique to save time in cases when reordering the list is acceptable

Association lists

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

assoc_inv b l returns the key associated with value b in the list of pairs l. That is, assoc b [ ...; (a,b); ...] = a if (a,b) is the leftmost binding of a in list l. Raise Not_found if there is no key associated with b in the list l.

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. 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. Tail-recursive.

List transformations

val split_at : int -> 'a list -> 'a list * 'a list

split_at n l returns two lists l1 and l2, l1 containing the first n elements of l and l2 the others. Raise Invalid_index if n is outside of l size bounds.

val split_nth : int -> 'a list -> 'a list * 'a list

Obsolete. As split_at.

val remove : 'a list -> 'a -> 'a list

remove l x returns the list l without the first element x found or returns l if no element is equal to x. Elements are compared using ( = ).

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

remove_if cmp l is similar to remove, but with cmp used instead of ( = ).

val remove_all : 'a list -> 'a -> 'a list

remove_all l x is similar to remove but removes all elements that are equal to x and not only the first one.

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

take n l returns up to the n first elements from list l, if available.

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

drop n l returns l without the first n elements, or the empty list if l have less than n elements.

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

takewhile f xs returns the first elements of list xs which satisfy the predicate f.

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

dropwhile f xs returns the list xs with the first elements satisfying the predicate f dropped.

val interleave : ?first:'a -> ?last:'a -> 'a -> 'a list -> 'a list

interleave ~first ~last sep [a1;a2;a3;...;an] returns first; a1; sep; a2; sep; a3; sep; ...; sep; an

BatEnum functions

Abstraction layer.

val enum : 'a list -> 'a BatEnum.t

Returns an enumeration of the elements of a list. This enumeration may be used to visit elements of the list in forward order (i.e. from the first element to the last one)

val of_enum : 'a BatEnum.t -> 'a list

Build a list from an enumeration. In the result, elements appear in the same order as they did in the source enumeration.

val backwards : 'a list -> 'a BatEnum.t

Returns an enumeration of the elements of a list. This enumeration may be used to visit elements of the list in backwards order (i.e. from the last element to the first one)

val of_backwards : 'a BatEnum.t -> 'a list

Build a list from an enumeration. The first element of the enumeration becomes the last element of the list, the second element of the enumeration becomes the second-to-last element of the list...

List 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]). 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 Different_list_size if the two lists have different lengths. Tail-recursive.

Utilities

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

make_compare c generates the lexicographical order on lists induced by c

val sort : ?cmp:('a -> 'a -> int) -> 'a list -> 'a list

Sort the list using optional comparator (by default compare).

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

sort_unique cmp l returns the list l sorted and without any duplicate element. cmp is a usual comparison function providing linear order.

This function takes O(n log n) time.

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

group cmp l returns list of groups and each group consists of elements judged equal by comparison function cmp. Groups in the resulting list appear in order given by cmp. All groups are always nonempty. group returns [] only if l is empty.

For example group cmp [f;c;b;e;d;a] can give [[a;b];[c];[d;e;f]] if following conditions are met: cmp a b = 0, cmp b c = -1, cmp c d = -1, cmp d e = 0,...

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

Different from List.combine, this returns every pair of elements formed out of the two lists.

cartesian_product
	      [a1; ...; an] [b1; ...; bn] = [(a1,b1);(a1,b2); ...;
	      (a1,bn); (a2,b1); ...; (an,bn)]

. The lists can be of unequal size.

val n_cartesian_product : 'a list list -> 'a list list

Given n lists, return the n-way cartesian product of these lists. Given [a;b];[c];[d;e;f], returns [a;c;d];[a;c;e];[a;c;f];[b;c;d];[b;c;e];[b;c;f], all ways of choosing one element from each input list.

Boilerplate code

Printing

val print : ?first:string ->
       ?last:string ->
       ?sep:string ->
       ('a BatInnerIO.output -> 'b -> unit) ->
       'a BatInnerIO.output -> 'b list -> unit

Print the contents of a list

val sprint : ?first:string ->
       ?last:string ->
       ?sep:string -> ('a BatInnerIO.output -> 'b -> unit) -> 'b list -> string

Using a string printer, print a list to a string (as sprintf vs. printf)

val t_printer : 'a BatValue_printer.t -> 'a t BatValue_printer.t

Obsolete functions

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

Obsolete. As at.

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

obsolete, as BatList.take_while

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

obsolete, as BatList.drop_while

Override modules

The following modules replace functions defined in List with functions behaving slightly differently but having the same name. This is by design: the functions meant to override the corresponding functions of List.

module Exceptionless: sig .. end

Exceptionless counterparts for error-raising operations

module Labels: sig .. end

Operations on List with labels.

val (@) : 'a list -> 'a list -> 'a list

the new implementation for ( @ ) operator, see List.append.