module List: sig end
Some functions are flagged as not tailrecursive. A tailrecursive function uses constant stack space, while a nontailrecursive 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
val hd : 'a list > 'a
Failure "hd"
if the list is empty.val tl : 'a list > 'a list
Failure "tl"
if the list is empty.val nth : 'a list > int > 'a
Failure "nth"
if the list is too short.val rev : 'a list > 'a list
val append : 'a list > 'a list > 'a list
@
.
Not tailrecursive (length of the first argument). The @
operator is not tailrecursive 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 List.rev
l1 @ l2
, but rev_append
is
tailrecursive and more efficient.val concat : 'a list list > 'a list
val flatten : 'a list list > 'a list
concat
. Not tailrecursive
(length of the argument + length of the longest sublist).
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 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 tailrecursive.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 tailrecursive 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 tailrecursive.
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 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 have
different lengths. Not tailrecursive.val rev_map2 : ('a > 'b > 'c) > 'a list > 'b list > 'c list
List.rev_map2 f l
gives the same result as
List.rev
(
List.map2
f l)
, but is tailrecursive 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 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 have
different lengths. Not tailrecursive.
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
List.for_all
, but for a twoargument predicate.
Raise Invalid_argument
if the two lists have
different lengths.val exists2 : ('a > 'b > bool) > 'a list > 'b list > bool
List.exists
, but for a twoargument predicate.
Raise Invalid_argument
if the two lists 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
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 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
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 assq : 'a > ('a * 'b) list > 'b
List.assoc
, but uses physical equality instead of structural
equality to compare keys.val mem_assoc : 'a > ('a * 'b) list > bool
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
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 tailrecursive.val remove_assq : 'a > ('a * 'b) list > ('a * 'b) list
List.remove_assoc
, but uses physical equality instead
of structural equality to compare keys. Not tailrecursive.
Lists of pairs

val split : ('a * 'b) list > 'a list * 'b list
split [(a1,b1); ...; (an,bn)]
is ([a1; ...; an], [b1; ...; bn])
.
Not tailrecursive.val combine : 'a list > 'b list > ('a * 'b) list
combine [a1; ...; an] [b1; ...; bn]
is
[(a1,b1); ...; (an,bn)]
.
Raise Invalid_argument
if the two lists
have different lengths. Not tailrecursive.
Sorting

val sort : ('a > 'a > int) > 'a list > 'a list
Pervasives.compare
is a suitable comparison function, provided
there are no floatingpoint NaN values in the data.
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
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
val merge : ('a > 'a > int) > 'a list > 'a list > 'a list
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 tailrecursive (sum of the lengths of the arguments).