package extlib

  1. Overview
  2. Docs
type 'a t = 'a list
New functions
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 "ExtList.init" if n < 0. Uses stdlib implementation in OCaml 4.06.0 and newer.

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

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

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

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

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 are the elements of the list l.

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 find_exc : ('a -> bool) -> exn -> 'a list -> 'a

find_exc p e l returns the first element of l such as p x returns true or raises e if such element as 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 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.

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

filter_map f l call (f a0) (f a1).... (f an) where 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_map_exn : ('a -> 'b option) -> 'a list -> 'b

find_map_exn 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 filter_map. This function was called find_map prior to extlib 1.7.7, but had to be renamed to stay compatible with OCaml 4.10.

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

same as find_map_exn but returning option

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

same as find_map_opt

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

split_nth 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 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.

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

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

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

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

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

Enum functions

Enumerations are important in ExtLib, they are a good way to work with abstract enumeration of elements, regardless if they are located in a list, an array, or a file.

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

Returns an enumeration of the elements of a list.

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

Build a list from an enumeration.

Compatibility functions
val cons : 'a -> 'a list -> 'a list
val assoc_opt : 'a -> ('a * 'b) list -> 'b option
val assq_opt : 'a -> ('a * 'b) list -> 'b option
val find_opt : ('a -> bool) -> 'a list -> 'a option
val nth_opt : 'a list -> int -> 'a option
val compare_lengths : 'a list -> 'b list -> int
val compare_length_with : 'a list -> int -> int
Modified functions

Some minor modifications have been made to the specification of some functions, especially concerning exceptions raised.

val hd : 'a list -> 'a

Returns the first element of the list or raise Empty_list if the list is empty.

val tl : 'a list -> 'a list

Returns the list without its first elements or raise Empty_list if the list is empty.

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

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

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

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

The following functions have been improved so all of them are tail-recursive. They have also been modified so they no longer raise Invalid_arg but Different_list_size when used on two lists having a different number of elements.

val map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
val rev_map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
val iter2 : ('a -> 'b -> unit) -> 'a list -> 'b list -> unit
val fold_left2 : ('a -> 'b -> 'c -> 'a) -> 'a -> 'b list -> 'c list -> 'a
val fold_right2 : ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'c
val for_all2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool
val exists2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool
val combine : 'a list -> 'b list -> ('a * 'b) list
Improved functions

The following functions have the same behavior as the List module ones but are tail-recursive. 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.

val map : ('a -> 'b) -> 'a list -> 'b list
val append : 'a list -> 'a list -> 'a list
val flatten : 'a list list -> 'a list
val concat : 'a list list -> 'a list
val fold_right : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b
val remove_assoc : 'a -> ('a * 'b) list -> ('a * 'b) list
val remove_assq : 'a -> ('a * 'b) list -> ('a * 'b) list
val split : ('a * 'b) list -> 'a list * 'b list

The following functions were already tail-recursive in the List module but were using List.rev calls. The new implementations have better performances.

val filter : ('a -> bool) -> 'a list -> 'a list
val find_all : ('a -> bool) -> 'a list -> 'a list
val partition : ('a -> bool) -> 'a list -> 'a list * 'a list
Older functions

These functions are already part of the Ocaml standard library and have not been modified. Please refer to the Ocaml Manual for documentation.

val length : 'a list -> int
val rev_append : 'a list -> 'a list -> 'a list
val rev : 'a list -> 'a list
val rev_map : ('a -> 'b) -> 'a list -> 'b list
val iter : ('a -> unit) -> 'a list -> unit
val fold_left : ('b -> 'a -> 'b) -> 'b -> 'a list -> 'b
val for_all : ('a -> bool) -> 'a list -> bool
val exists : ('a -> bool) -> 'a list -> bool
val find : ('a -> bool) -> 'a list -> 'a
val mem : 'a -> 'a list -> bool
val memq : 'a -> 'a list -> bool
val assoc : 'a -> ('a * 'b) list -> 'b
val assq : 'a -> ('a * 'b) list -> 'b
val mem_assoc : 'a -> ('a * 'b) list -> bool
val mem_assq : 'a -> ('a * 'b) list -> bool
val stable_sort : ('a -> 'a -> int) -> 'a list -> 'a list
val fast_sort : ('a -> 'a -> int) -> 'a list -> 'a list
val merge : ('a -> 'a -> int) -> 'a list -> 'a list -> 'a list
val sort_uniq : ('a -> 'a -> int) -> 'a list -> 'a list

Same as List.sort, but also remove duplicates.

  • since 4.02.0
val concat_map : ('a -> 'b list) -> 'a list -> 'b list
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 compare_lengths first.

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

  • 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.

exception Empty_list

Empty_list is raised when an operation applied on an empty list is invalid : hd for example.

exception Invalid_index of int

Invalid_index is raised when an indexed access on a list is out of list bounds.

exception Different_list_size of string

Different_list_size is raised when applying functions such as iter2 on two lists having different size.


Innovation. Community. Security.