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.
val length : 'a list -> int
Return the length (number of elements) of the given list.
val hd : 'a list -> 'a
Return the first element of the given list. Raise
Failure "hd" if the list is empty.
val tl : 'a list -> 'a list
Return the given list without its first element. Raise
Failure "tl" 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.
Raise Failure "nth" if the list is too short.
Raise Invalid_argument "List.nth" if n is negative.
val rev : 'a list -> 'a list
List reversal.
val append : 'a list -> 'a list -> 'a list
Catenate 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
List.rev_append l1 l2 reverses
l1 and concatenates it to
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 concat. Not tail-recursive
(length of the argument + length of the longest sub-list).
Iterators
val iter : f:('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 : f:(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 map : f:('a -> 'b) -> 'a list -> 'b list
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
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.
Since 4.00.0
val rev_map : f:('a -> 'b) -> 'a list -> 'b list
val fold_left : f:('a -> 'b -> 'a) -> init:'a -> 'b list -> 'a
List.fold_left f a [b1; ...; bn] is
f (... (f (f a b1) b2) ...) bn.
val fold_right : f:('a -> 'b -> 'b) -> 'a list -> init:'b -> 'b
List.fold_right f [a1; ...; an] b is
f a1 (f a2 (... (f an b) ...)). Not tail-recursive.
Iterators on two lists
val iter2 : f:('a -> 'b -> unit) -> 'a list -> 'b list -> unit
List.iter2 f [a1; ...; an] [b1; ...; bn] calls in turn
f a1 b1; ...; f an bn.
Raise Invalid_argument if the two lists have
different lengths.
val map2 : f:('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
List.map2 f [a1; ...; an] [b1; ...; bn] is
[f a1 b1; ...; f an bn].
Raise Invalid_argument if the two lists have
different lengths. Not tail-recursive.
val rev_map2 : f:('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
val fold_left2 : f:('a -> 'b -> 'c -> 'a) -> init:'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.
Raise Invalid_argument if the two lists have
different lengths.
val fold_right2 : f:('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> init:'c -> 'c
List.fold_right2 f [a1; ...; an] [b1; ...; bn] c is
f a1 b1 (f a2 b2 (... (f an bn c) ...)).
Raise Invalid_argument if the two lists have
different lengths. Not tail-recursive.
List scanning
val for_all : f:('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).
val exists : f:('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).
val for_all2 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool
Same as
ListLabels.for_all, but for a two-argument predicate.
Raise
Invalid_argument if the two lists have
different lengths.
val exists2 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool
Same as
ListLabels.exists, but for a two-argument predicate.
Raise
Invalid_argument if the two lists have
different lengths.
val mem : 'a -> set:'a list -> bool
mem a l is true if and only if a is equal
to an element of l.
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 p l returns the first element of the list l
that satisfies the predicate p.
Raise Not_found if there is no value that satisfies p in the
list l.
val filter : f:('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 : f:('a -> bool) -> 'a list -> 'a list
val partition : f:('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.
Raise Not_found if there is no value associated with a in the
list l.
val assq : 'a -> ('a * 'b) list -> 'b
Same as
ListLabels.assoc, but uses physical equality instead of
structural equality to compare keys.
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)].
Raise 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,
Pervasives.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 : 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
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 containting 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).