Provided by: ocaml-nox_4.05.0-10ubuntu1_amd64 
NAME
List - List operations.
Module
Module List
Documentation
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.
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. 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 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. Raise Invalid_argument List.nth if n
is negative.
Since 4.05
val rev : 'a list -> 'a list
List reversal.
val append : 'a list -> 'a list -> 'a list
Concatenate two lists. Same as the infix operator @ . Not tail-recursive (length of the
first argument).
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.
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
An alias for concat .
=== 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 map : ('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 : (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. Not
tail-recursive.
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 : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a
List.fold_left f a [b1; ...; bn] is f (... (f (f a b1) b2) ...) bn .
val fold_right : ('a -> 'b -> 'b) -> 'a list -> '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 : ('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 are determined to have different lengths.
val map2 : ('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 are determined to have different lengths. Not
tail-recursive.
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
. Raise 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)
...)) . Raise 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) .
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) .
val for_all2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool
Same as List.for_all , but for a two-argument predicate. Raise 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. Raise 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 . Raise
Not_found if there is no value that satisfies p in the list l .
val find_opt : ('a -> bool) -> 'a list -> 'a option
find_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 .
Since 4.05
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 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 . Raise
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); ...] = 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 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.
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 List.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 : ('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 : ('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
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 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).