ListLabels(3) OCaml library ListLabels(3)NAMEListLabels - List operations.
Module
Module ListLabelsDocumentation
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 con‐
catenated 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 ele‐
ment 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
List.rev_map f l gives the same result as ListLabels.rev ( ListLa‐
bels.map f l) , but is tail-recursive and more efficient.
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
List.rev_map2 f l1 l2 gives the same result as ListLabels.rev ( ListLa‐
bels.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
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 sat‐
isfies 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 struc‐
tural 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 pre‐
served.
val find_all : f:('a -> bool) -> 'a list -> 'a list
find_all is another name for ListLabels.filter .
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 associ‐
ated with a in the list l .
val assq : 'a -> ('a * 'b) list -> 'b
Same as ListLabels.assoc , but uses physical equality instead of struc‐
tural 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 inte‐
ger if the first is smaller (see Array.sort for a complete specifica‐
tion). For example, Pervasives.compare is a suitable comparison func‐
tion. 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
Same as List.sort or List.stable_sort , whichever is faster on typical
input.
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 com‐
pare equal, the elements of l1 will be before the elements of l2 . Not
tail-recursive (sum of the lengths of the arguments).
OCamldoc 2013-10-24 ListLabels(3)
