Provided by: ocaml-man_4.14.1-1ubuntu1_all 
NAME
ListLabels - List operations.
Module
Module ListLabels
Documentation
Module ListLabels
: 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.
The labeled version of this module can be used as described in the StdLabels module.
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 4.05.0
val compare_length_with : 'a list -> len: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 4.05.0
val cons : 'a -> 'a list -> 'a list
cons x xs is x :: xs
Since 4.05.0
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.
Since 4.05
Raises Invalid_argument if n is negative.
val rev : 'a list -> 'a list
List reversal.
val init : len:int -> f:(int -> 'a) -> 'a list
init ~len ~f is f 0; f 1; ...; f (len-1) , evaluated left to right.
Since 4.06.0
Raises Invalid_argument if len < 0 .
val append : 'a list -> 'a list -> 'a list
Concatenate two lists. Same function as the infix operator @ . Not tail-recursive (length
of the first argument). The @ operator is not tail-recursive either.
val rev_append : 'a list -> 'a list -> 'a list
rev_append l1 l2 reverses l1 and concatenates it with l2 . This is equivalent to (
ListLabels.rev l1) @ l2 , but rev_append is tail-recursive and more efficient.
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 ListLabels.concat . Not tail-recursive (length of the argument + length of the
longest sub-list).
Comparison
val equal : eq:('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 ListLabels.compare_lengths first.
Since 4.12.0
val compare : cmp:('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 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 4.12.0
Iterators
val iter : f:('a -> unit) -> 'a list -> unit
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 : f:(int -> 'a -> unit) -> 'a list -> unit
Same as ListLabels.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 map : f:('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 . Not tail-recursive.
val mapi : f:(int -> 'a -> 'b) -> 'a list -> 'b list
Same as ListLabels.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.
Since 4.00.0
val rev_map : f:('a -> 'b) -> 'a list -> 'b list
rev_map ~f l gives the same result as ListLabels.rev ( ListLabels.map f l) , but is
tail-recursive and more efficient.
val filter_map : f:('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 4.08.0
val concat_map : f:('a -> 'b list) -> 'a list -> 'b list
concat_map ~f l gives the same result as ListLabels.concat ( ListLabels.map f l) .
Tail-recursive.
Since 4.10.0
val fold_left_map : f:('a -> 'b -> 'a * 'c) -> init:'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 : f:('a -> 'b -> 'a) -> init:'a -> 'b list -> 'a
fold_left ~f ~init [b1; ...; bn] is f (... (f (f init b1) b2) ...) bn .
val fold_right : f:('a -> 'b -> 'b) -> 'a list -> init:'b -> 'b
fold_right ~f [a1; ...; an] ~init is f a1 (f a2 (... (f an init) ...)) . Not
tail-recursive.
Iterators on two lists
val iter2 : f:('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 : f:('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. Not
tail-recursive.
val rev_map2 : f:('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
rev_map2 ~f l1 l2 gives the same result as ListLabels.rev ( ListLabels.map2 f l1 l2) , but
is tail-recursive and more efficient.
val fold_left2 : f:('a -> 'b -> 'c -> 'a) -> init:'a -> 'b list -> 'c list -> 'a
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 : f:('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> init:'c -> 'c
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 : f:('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 : f:('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 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool
Same as ListLabels.for_all , but for a two-argument predicate.
Raises Invalid_argument if the two lists are determined to have different lengths.
val exists2 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool
Same as ListLabels.exists , but for a two-argument predicate.
Raises Invalid_argument if the two lists are determined to have different lengths.
val mem : 'a -> set:'a list -> bool
mem a ~set is true if and only if a is equal to an element of set .
val memq : 'a -> set:'a list -> bool
Same as ListLabels.mem , but uses physical equality instead of structural equality to
compare list elements.
List searching
val find : f:('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 : f:('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_map : f:('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 : f:('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 : f:('a -> bool) -> 'a list -> 'a list
find_all is another name for ListLabels.filter .
val filteri : f:(int -> 'a -> bool) -> 'a list -> 'a list
Same as ListLabels.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 : f:('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 : f:('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 4.12.0
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 ListLabels.assoc , but uses physical equality instead of structural equality to
compare keys.
val assq_opt : 'a -> ('a * 'b) list -> 'b option
Same as ListLabels.assoc_opt , but uses physical equality instead of structural equality
to compare keys.
Since 4.05.0
val mem_assoc : 'a -> map:('a * 'b) list -> bool
Same as ListLabels.assoc , but simply return true if a binding exists, and false if no
bindings exist for the given key.
val mem_assq : 'a -> map:('a * 'b) list -> bool
Same as ListLabels.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 ListLabels.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 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 : cmp:('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, compare is a suitable comparison function. The resulting
list is sorted in increasing order. ListLabels.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 : cmp:('a -> 'a -> int) -> 'a list -> 'a list
Same as ListLabels.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 : cmp:('a -> 'a -> int) -> 'a list -> 'a list
Same as ListLabels.sort or ListLabels.stable_sort , whichever is faster on typical input.
val sort_uniq : cmp:('a -> 'a -> int) -> 'a list -> 'a list
Same as ListLabels.sort , but also remove duplicates.
Since 4.03.0
val merge : cmp:('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