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 function 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.
type'at ='a list=
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[] |
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:: of |
An alias for the type of lists.
val length : 'a list -> intReturn the length (number of elements) of the given list.
val compare_lengths : 'a list -> 'b list -> intCompare 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.
val compare_length_with : 'a list -> int -> intCompare 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.
val cons : 'a -> 'a list -> 'a listcons x xs is x :: xs
val hd : 'a list -> 'aReturn the first element of the given list.
Failure if the list is empty.val tl : 'a list -> 'a listReturn the given list without its first element.
Failure if the list is empty.val nth : 'a list -> int -> 'aReturn the n-th element of the given list.
The first element (head of the list) is at position 0.
Failure if the list is too short.Invalid_argument if n is negative.val nth_opt : 'a list -> int -> 'a optionReturn 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.
Invalid_argument if n is negative.val rev : 'a list -> 'a listList reversal.
val init : int -> (int -> 'a) -> 'a listList.init len f is [f 0; f 1; ...; f (len-1)], evaluated left to right.
Invalid_argument if len < 0.val append : 'a list -> 'a list -> 'a listConcatenate two lists. Same as the infix operator @.
Not tail-recursive (length of the first argument).
val rev_append : 'a list -> 'a list -> 'a listList.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 listConcatenate 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 listAn alias for concat.
val iter : ('a -> unit) -> 'a list -> unitList.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 -> unitSame 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.
val map : ('a -> 'b) -> 'a list -> 'b listList.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 listSame as List.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. Not tail-recursive.
val rev_map : ('a -> 'b) -> 'a list -> 'b listval filter_map : ('a -> 'b option) -> 'a list -> 'b listfilter_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.
val concat_map : ('a -> 'b list) -> 'a list -> 'b listList.concat_map f l gives the same result as
List.concat (List.map f l). Tail-recursive.
val fold_left_map : ('a -> 'b -> 'a * 'c) -> 'a -> 'b list -> 'a * 'c listfold_left_map is a combination of fold_left and map that threads an
accumulator through calls to f
val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'aList.fold_left f a [b1; ...; bn] is
f (... (f (f a b1) b2) ...) bn.
val fold_right : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'bList.fold_right f [a1; ...; an] b is
f a1 (f a2 (... (f an b) ...)). Not tail-recursive.
val iter2 : ('a -> 'b -> unit) -> 'a list -> 'b list -> unitList.iter2 f [a1; ...; an] [b1; ...; bn] calls in turn
f a1 b1; ...; f an bn.
Invalid_argument if the two lists are determined
to have different lengths.val map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c listList.map2 f [a1; ...; an] [b1; ...; bn] is
[f a1 b1; ...; f an bn].
Invalid_argument if the two lists are determined
to have different lengths. Not tail-recursive.val rev_map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c listval fold_left2 : ('a -> 'b -> 'c -> 'a) -> 'a -> 'b list -> 'c list -> 'aList.fold_left2 f a [b1; ...; bn] [c1; ...; cn] is
f (... (f (f a b1 c1) b2 c2) ...) bn cn.
Invalid_argument if the two lists are determined
to have different lengths.val fold_right2 : ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'cList.fold_right2 f [a1; ...; an] [b1; ...; bn] c is
f a1 b1 (f a2 b2 (... (f an bn c) ...)).
Invalid_argument if the two lists are determined
to have different lengths. Not tail-recursive.val for_all : ('a -> bool) -> 'a list -> boolfor_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 -> boolexists 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 -> boolSame as List.for_all, but for a two-argument predicate.
Invalid_argument if the two lists are determined
to have different lengths.val exists2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> boolSame as List.exists, but for a two-argument predicate.
Invalid_argument if the two lists are determined
to have different lengths.val mem : 'a -> 'a list -> boolmem a l is true if and only if a is equal
to an element of l.
val memq : 'a -> 'a list -> boolSame as List.mem, but uses physical equality instead of structural
equality to compare list elements.
val find : ('a -> bool) -> 'a list -> 'afind p l returns the first element of the list l
that satisfies the predicate p.
Not_found if there is no value that satisfies p in the
list l.val find_opt : ('a -> bool) -> 'a list -> 'a optionfind_opt p l returns the first element of the list l that
satisfies the predicate p, or None if there is no value that
satisfies p in the list l.
val find_map : ('a -> 'b option) -> 'a list -> 'b optionfind_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.
val filter : ('a -> bool) -> 'a list -> 'a listfilter 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 listfind_all is another name for List.filter.
val filteri : (int -> 'a -> bool) -> 'a list -> 'a listSame 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 partition : ('a -> bool) -> 'a list -> 'a list * 'a listpartition 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 assoc : 'a -> ('a * 'b) list -> 'bassoc 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.
Not_found if there is no value associated with a in the
list l.val assoc_opt : 'a -> ('a * 'b) list -> 'b optionassoc_opt a l returns the value associated with key a in the list of
pairs l. That is,
assoc_opt a [ ...; (a,b); ...] = 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.
val assq : 'a -> ('a * 'b) list -> 'bSame as List.assoc, but uses physical equality instead of structural
equality to compare keys.
val assq_opt : 'a -> ('a * 'b) list -> 'b optionSame as List.assoc_opt, but uses physical equality instead of structural
equality to compare keys.
val mem_assoc : 'a -> ('a * 'b) list -> boolSame 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 -> boolSame as List.mem_assoc, but uses physical equality instead of
structural equality to compare keys.
val remove_assoc : 'a -> ('a * 'b) list -> ('a * 'b) listremove_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) listSame as List.remove_assoc, but uses physical equality instead
of structural equality to compare keys. Not tail-recursive.
val split : ('a * 'b) list -> 'a list * 'b listTransform 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) listTransform a pair of lists into a list of pairs:
combine [a1; ...; an] [b1; ...; bn] is
[(a1,b1); ...; (an,bn)].
Invalid_argument if the two lists
have different lengths. Not tail-recursive.val sort : ('a -> 'a -> int) -> 'a list -> 'a listSort 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,
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 listSame 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 listSame as List.sort or List.stable_sort, whichever is faster
on typical input.
val sort_uniq : ('a -> 'a -> int) -> 'a list -> 'a listSame as List.sort, but also remove duplicates.
val merge : ('a -> 'a -> int) -> 'a list -> 'a list -> 'a listMerge 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).
val to_seq : 'a list -> 'a Seq.tIterate on the list
val of_seq : 'a Seq.t -> 'a listCreate a list from the iterator