spotlib

Useful functions for OCaml programming used by @camlspotter
IN THIS PACKAGE
Module Spotlib . Spot . List
include module type of struct include List end
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 itering on 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 n is equivalent to compare (length l) n, except that the computation stops after at most n 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
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 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.

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 argument (counting from 0), and the element itself as second argument.

  • 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_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

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

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 Invalid_argument

    if the two lists are determined to have different lengths.

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.

  • 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

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

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

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) 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 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.

  • raises Not_found

    if there is no value that satisfies p in the list l.

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 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 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 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.

  • raises 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 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
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.

Lists of pairs

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. 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

Iterators

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 the iterator

  • since 4.07
include module type of struct include Xlist end

Type

type 'a t = 'a list

Construction

val empty : 'a t

empty = []

val singleton : 'a -> 'a t

singleton x = [x]

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

make n x returns a list of length n filled with x. Throws Invalid_argument "List.make" when n < 0.

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

init n f returns a list of [f 0; f 1; ..; f (n-1)]. Throws Invalid_argument "List.init" when n < 0.

Conversions

val to_list : 'a t -> 'a list
val to_array : 'a t -> 'a array
val of_list : 'a list -> 'a t
val of_array : 'a array -> 'a t

Basics

val append : 'a t -> 'a t -> 'a t

Tail recursive version of List.append

val (@) : 'a t -> 'a t -> 'a t

Tail recursive version of List.(@)

val concat : 'a t t -> 'a t

Tail recursive version of List.concat

val flatten : 'a t t -> 'a t

Tail recursive version of List.flatten

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

replicate xs n concatenates the list xs n-times

Folding

val map : ( 'a -> 'b ) -> 'a list -> 'b list
val mapi : ( int -> 'a -> 'b ) -> 'a list -> 'b list
val map2 : ( 'a -> 'b -> 'c ) -> 'a list -> 'b list -> 'c list
val split : ('a * 'b) list -> 'a list * 'b list
val merge : ( 'a -> 'a -> int ) -> 'a list -> 'a list -> 'a list
val fold_right : ( 'a -> 'st -> 'st ) -> 'a t -> 'st -> 'st
val fold_left1 : ( 'a -> 'a -> 'a ) -> 'a list -> 'a

List must be non-empty. Otherwise, it raises Invalid_argment "fold_left1".

val fold_right1 : ( 'a -> 'a -> 'a ) -> 'a list -> 'a

List must be non-empty. Otherwise, it raises Invalid_argment "fold_left1".

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

concat_map f xs = concat @@ map f xs but much faster.

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

concat_map f xs = rev @@ concat @@ map f xs but much faster.

val map_accum_left : ( 'acc -> 'a -> 'acc * 'b ) -> 'acc -> 'a t -> 'acc * 'b list

mapAccumL f acc t behaves like a combination of map and fold_left; it applies a function f to each element of a list t, passing an accumulating parameter acc from left to right, and returning a final value of this accumulator together with the new list.

Access

val last : 'a list -> 'a

The last element of the list. Raises Failure when the argument is . last [1;2;3] = 3

Find and assoc

val find_opt : ( 'a -> bool ) -> 'a list -> 'a option
val find_map_opt : ( 'a -> 'b option ) -> 'a list -> 'b option
val remove_first_match : ( 'a -> bool ) -> 'a list -> 'a list
val assoc_all : 'a -> ('a * 'b) list -> 'b list
val assoc_opt : 'a -> ('a * 'b) list -> 'b option
val remove_assoc : 'a -> ('a * 'b) list -> ('a * 'b) list
val remove_assq : 'a -> ('a * 'b) list -> ('a * 'b) list

Sublist by index

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

sub_default t pos len returns a sublist of t from the position pos (0-start) and length len.

The region specified by pos and len is trimmed by t: if it exceeds the size of t, it is intersected with the region from 0 and length List.length t. One tricky example is:

sub_default [0;1;2;3;4;5] (-1) 3 = [0;1]

val take_exn : int -> 'a list -> 'a list
val drop_exn : int -> 'a list -> 'a list
val sub : 'a list -> int -> int -> 'a list
val split_at : int -> 'a list -> 'a list * 'a list

Haskell's splitAt. Always succeeds.

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

Split a list into sub-lists of the fixed length

Sublist by predicate

val filter_map : ( 'a -> 'b option ) -> 'a list -> 'b list
val rev_filter_map : ( 'a -> 'b option ) -> 'a list -> 'b list
val span : ( 'a -> bool ) -> 'a list -> 'a list * 'a list

span p xs extract the longest prefix of xs whose elements satisfy p.

val partition_map : ( 'a -> [< `Left of 'left | `Right of 'right ] ) -> 'a list -> 'left list * 'right list

Sort and uniq

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

Filter out duplicate elements using the given equality. The first result list is the list of first unique occurrences, the second result list is the rest, the duplications removed from the first result list, paired with the corresponding element of the first result list.

O(n^2).

val uniq_dup_sorted : ( 'a -> 'a -> int ) -> 'a list -> 'a list * ('a * 'a) list

Same as uniq_dup but only works for already sorted by the same ordering. O(n log n)

val unique : 'a list -> 'a list

Haskell's nub. O(n^2)

val unique_by : ( 'a -> 'a -> bool ) -> 'a list -> 'a list
val has_dup : ( 'a -> 'a -> bool ) -> 'a list -> ('a * 'a) option

Check the list is a unique list or not, wrt the equality function. If not, it returns a dupe example.

has_dup (fun x y -> fst x = fst y) [(1,2); (2,3); (4,5)] = None has_dup (fun x y -> fst x = fst y) [(1,2); (2,3); (2,5)] = Some ( (2,3), (2,5) )

O(n^2)

val group : 'a list -> 'a list list

group xs returns a list of lists such that the concatenation of the result is equal to the argument. Moreover, each sublist in the result contains only equal elements:

group ['M'; 'i'; 's'; 's'; 'i'; 's'; 's'; 'i'; 'p'; 'p'; 'i'] = [['M'],['i'],['s';'s'];['i'];['s';'s'];['i'];['p';'p'];['i']]

Haskell's group.

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

Same as group but equality can be given. Haskell's groupBy

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

sort then group_by

Composition

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

Haskell's zip. Like List.combine but does not raise when the lengths are not equal. Tail recursive.

With reference

val accum : 'a list ref -> 'a -> unit

accum xsref x is equivalent with xsref := x :: !xsref

val (+::=) : 'a list ref -> 'a -> unit

Same as accum

Integer ranges

val from_to : int -> int -> int list

from_to f t = [f..t]

val (--) : int -> int -> int list

Same as from_to. f--t = [f..t]

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

init_from_to f t fn = [fn x | x <- [f..t] ]

Misc

val intersperse : 'a -> 'a list -> 'a list
val sum : int list -> int

Modules

module Infix : sig ... end
module Stdlib : sig ... end

Non tail recursive versions

These non tail recursive versions are from stdlib.

val (@.) : 'a t -> 'a t -> 'a t

Non tail recursive version of (@)

val append_ntr : 'a t -> 'a t -> 'a t
val concat_ntr : 'a t t -> 'a t
val flatten_ntr : 'a t t -> 'a t
val map_ntr : ( 'a -> 'b ) -> 'a t -> 'b t
val mapi_ntr : ( int -> 'a -> 'b ) -> 'a t -> 'b t
val fold_right_ntr : ( 'a -> 'b -> 'b ) -> 'a list -> 'b -> 'b
val map2_ntr : ( 'a -> 'b -> 'c ) -> 'a list -> 'b list -> 'c list
val fold_right2_ntr : ( 'a -> 'c -> 'b -> 'b ) -> 'a list -> 'c list -> 'b -> 'b
val remove_assoc_ntr : 'a -> ('a * 'b) list -> ('a * 'b) list
val remove_assq_ntr : 'a -> ('a * 'b) list -> ('a * 'b) list
val split_ntr : ('a * 'b) list -> 'a list * 'b list
val combine_ntr : 'a list -> 'b list -> ('a * 'b) list
val merge_ntr : ( 'a -> 'a -> int ) -> 'a list -> 'a list -> 'a list

Deprecated

val iter_until : ( 'a -> [ `Break of 'b | `Continue ] ) -> 'a list -> 'b option
val scani_left : ( int -> 'a -> 'b -> [< `Continue of 'a | `Stop of 'a ] ) -> 'a -> 'b list -> 'a
val is_unique : ( 'a -> 'b ) -> 'a list -> ('a * 'a) option

Check the list is a unique list or not, wrt the key function. If not, it returns a dupe example.

is_unique fst [(1,2); (2,3); (4,5)] = None is_unique fst [(1,2); (2,3); (2,5)] = Some ( (2,3), (2,5) )

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