Module `Soteria_std.List`

Extensions to Stdlib.List with utility functions.

include module type of struct include List end

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

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

val is_empty : 'a list -> bool

is_empty l is true if and only if l has no elements. It is equivalent to compare_length_with l 0 = 0.

since 5.1

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

cons x xs is x :: xs

since 4.03 (4.05 in ListLabels)

val singleton : 'a -> 'a list

singleton x returns the one-element list [x].

since 5.4

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.

raises Invalid_argument
if n is negative.

since 4.05

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.

raises Invalid_argument
if len < 0.

since 4.06

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

append l0 l1 appends l1 to l0. Same function as the infix operator @.

since 5.1 this function is tail-recursive.

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

rev_append l1 l2 reverses l1 and concatenates it with l2. This is equivalent to (rev l1) @ l2.

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).

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 compare_lengths first.

since 4.12

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 Stdlib.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

Iterators

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

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

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

Same as 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

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.

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

Same as 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.

since 4.00

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

rev_map f l gives the same result as rev (map f l), but is 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

val filter_mapi : (int -> 'a -> 'b option) -> 'a list -> 'b list

Same as filter_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.

since 5.5

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

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

since 4.10

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

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

since 4.11

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

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

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

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.

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

rev_map2 f l1 l2 gives the same result as rev (map2 f l1 l2), but is more efficient.

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

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 -> 'acc -> 'acc) ->
  'a list ->
  'b list ->
  'acc ->
  'acc

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 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 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 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_index : ('a -> bool) -> 'a list -> int option

find_index f xs returns Some i, where i is the index of the first element of the list xs that satisfies f x, if there is such an element.

It returns None if there is no such element.

since 5.1

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

val find_mapi : (int -> 'a -> 'b option) -> 'a list -> 'b option

Same as find_map, 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 5.1

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 filter.

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

Same as 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

List manipulation

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

take n l returns the prefix of l of length n, or a copy of l if n > length l. This is the empty list if n is negative.

Warning. In version 5.3 only, this function raises Invalid_argument for negative n values.

since 5.3

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

drop n l returns the suffix of l after n elements, or [] if n > length l. This is l if n is negative.

Warning. In version 5.3 only, this function raises Invalid_argument for negative n values.

since 5.3

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

take_while p l is the longest (possibly empty) prefix of l containing only elements that satisfy p.

since 5.3

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

drop_while p l is the longest (possibly empty) suffix of l starting at the first element that does not satisfy p.

since 5.3

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

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

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

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

since 4.05

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

Same as 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 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 split_map : ('c -> 'a * 'b) -> 'c list -> 'a list * 'b list

split_map f l is equivalent to split (map f l) but avoids allocating intermediate lists.

since 5.5

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, Stdlib.compare is a suitable comparison function. The resulting list is sorted in increasing order. 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 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 sort or stable_sort, whichever is faster on typical input.

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

Same as sort, but also remove duplicates: if multiple elements compare equal, keep only the first.

since 4.02 (4.03 in ListLabels)

before 5.4
the element kept was not necessarily the first one.

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

val return : 'a -> 'a list

The singleton list containing the given element

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

The bind operator for lists, also known as concat_map.

val take_count : int -> 'a t -> 'a t * int

Take a prefix of a list of at most n elements, or the entire list if the list is shorter than n.

returns
(prefix, count) where prefix is the prefix of the list and count is the number of elements taken.

raises Invalid_argument
if n is negative.

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

Combine two lists into a list of pairs.

val combine_or : 
  ok:(('a * 'b) list -> 'c) ->
  err:(unit -> 'c) ->
  'a list ->
  'b list ->
  'c

val join_results : ('a, 'b) result list -> ('a list, 'b list) result

Aggregates results, returning all errors if any, otherwise all successful values.

val combine3 : 'a t -> 'b t -> 'c t -> ('a * 'b * 'c) t

Combine three lists into a list of triples.

val combine3_opt : 'a t -> 'b t -> 'c t -> ('a * 'b * 'c) t option

Combine three lists into a list of triples.

val combinei : 'a t -> 'b t -> (int * 'a * 'b) t

val map2i : (int -> 'a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t

Map a function over two lists simultaneously, passing the current index as the first argument to the function. The function f receives arguments index element1 element2.

returns
the resulting list.

raises Invalid_argument
if the lists have different lengths.

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

Map a function over a list and return both the resulting list and a boolean indicating whether any element was changed (using physical equality !=).

returns
(res, changed) where res is the resulting list and changed is a boolean indicating whether any element was changed.

val last : 'a t -> 'a

Return the last element of a list.

raises Invalid_argument
if the list is empty.

val last_opt : 'a t -> 'a option

Return the last element of a list, if any.

val hd_opt : 'a t -> 'a option

Return the head of a list, if any.

val concat_map2 : ('a -> 'b -> 'c t) -> 'a t -> 'b t -> 'c t

Apply a function to each pair of elements from two lists, concatenating all resulting lists.

returns
the resulting list.

raises Invalid_argument
if the lists have different lengths.

val prepend_concat_map2 : 'a t -> ('b -> 'c -> 'a t) -> 'b t -> 'c t -> 'a t

val sub : from:int -> len:int -> 'a list -> 'a list

sub ~from ~len l returns the sublist of l, from index from (inclusive), of length n.

val group_by : ?compare:??? -> ('a * 'b) list -> ('a * 'b t) list

Group a list of pairs by their first component, using the provided comparison function to determine equality of keys. The resulting list contains pairs of keys and lists of corresponding values. The complexity is O(n log n), the list is traversed only once.

val find_with_rest : ('a -> bool) -> 'a t -> ('a * 'a t) option

find_with_rest f l will look for the first element of l that satisfies the predicate f. If one is found, returns Some (x, l'), where f x = true and l' is l with x removed (order is preserved).

val take_nth_exn : int -> 'a t -> 'a * 'a t

val update_at : int -> ('a -> 'a) -> 'a t -> 'a t

update_at i f l updates the element at index i in list l with function f. This is more efficient than e.g. mapi, as it only traverses and rebuilds the list up to index i; the list is shared after index i.

raises Invalid_argument
if i is negative or greater than or equal to the length of l.

val set_nth : int -> 'a -> 'a t -> 'a t

set_nth i v l sets the value at index i in l to v. This is more efficient than using mapi, as the part of the list after i is shared.

raises Invalid_argument
if i is negative or greater than or equal to the length of l.

val split_around : 'a t -> int -> 'a list * 'a * 'a list

split_around l i splits the list l into three parts: the elements before index i, the element at index i, and the elements after index i.

raises Invalid_argument
if i is negative or greater than or equal to the length of l.

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

Equivalent to fold_left; we re-export is as fold for compatibility with Sigs.Foldable.

Install

dune-project
Dependency

Authors

Maintainers

Sources

doc/soteria/Soteria/Soteria_std/List/index.html

Module `Soteria_std.List`

Comparison

Iterators

Iterators on two lists

List scanning

List searching

List manipulation

Association lists

Lists of pairs

Sorting

Lists and Sequences

package soteria

Install

dune-project Dependency

Authors

Maintainers

Sources

doc/soteria/Soteria/Soteria_std/List/index.html

Module Soteria_std.List

Comparison

Iterators

Iterators on two lists

List scanning

List searching

List manipulation

Association lists

Lists of pairs

Sorting

Lists and Sequences

dune-project
Dependency

Module `Soteria_std.List`