module Enum:Enumeration over abstract collection of elements.`sig`

..`end`

Enumerations are entirely functional and most of the operations do not
actually require the allocation of data structures. Using enumerations
to manipulate data is therefore efficient and simple. All data structures in
ExtLib such as lists, arrays, etc. have support to convert from and to
enumerations.

`type ``'a`

t

These functions consume the enumeration until
it ends or an exception is raised by the first
argument function.

`val iter : ``('a -> unit) -> 'a t -> unit`

`iter f e`

calls the function `f`

with each elements of `e`

in turn.`val iter2 : ``('a -> 'b -> unit) -> 'a t -> 'b t -> unit`

`iter2 f e1 e2`

calls the function `f`

with the next elements of `e`

and
`e2`

repeatedly until one of the two enumerations ends.`val fold : ``('a -> 'b -> 'b) -> 'b -> 'a t -> 'b`

`fold f v e`

returns v if e is empty,
otherwise `f (... (f (f v a1) a2) ...) aN`

where a1..N are
the elements of `e`

.`val fold2 : ``('a -> 'b -> 'c -> 'c) -> 'c -> 'a t -> 'b t -> 'c`

`fold2`

is similar to `fold`

but will fold over two enumerations at the
same time until one of the two enumerations ends.Indexed functions : these functions are similar to previous ones except that they call the function with one additional argument which is an index starting at 0 and incremented after each call to the function.

`val iteri : ``(int -> 'a -> unit) -> 'a t -> unit`

`val iter2i : ``(int -> 'a -> 'b -> unit) -> 'a t -> 'b t -> unit`

`val foldi : ``(int -> 'a -> 'b -> 'b) -> 'b -> 'a t -> 'b`

`val fold2i : ``(int -> 'a -> 'b -> 'c -> 'c) -> 'c -> 'a t -> 'b t -> 'c`

`val find : ``('a -> bool) -> 'a t -> 'a`

`find f e`

returns the first element `x`

of `e`

such that `f x`

returns
`true`

, consuming the enumeration up to and including the
found element, or, raises `Not_found`

if no such element exists
in the enumeration, consuming the whole enumeration in the search.
Since `find`

consumes a prefix of the enumeration, it can be used several
times on the same enumeration to find the next element.

`val is_empty : ``'a t -> bool`

`is_empty e`

returns true if `e`

does not contains any element.`val peek : ``'a t -> 'a option`

`peek e`

returns `None`

if `e`

is empty or `Some x`

where `x`

is
the next element of `e`

. The element is not removed from the enumeration.`val get : ``'a t -> 'a option`

`get e`

returns `None`

if `e`

is empty or `Some x`

where `x`

is
the next element of `e`

, in which case the element is removed from the enumeration.`val push : ``'a t -> 'a -> unit`

`push e x`

will add `x`

at the beginning of `e`

.`val junk : ``'a t -> unit`

`junk e`

removes the first element from the enumeration, if any.`val clone : ``'a t -> 'a t`

`clone e`

creates a new enumeration that is copy of `e`

. If `e`

is consumed by later operations, the clone will not get affected.`val force : ``'a t -> unit`

`force e`

forces the application of all lazy functions and the
enumeration of all elements, exhausting the enumeration.
An efficient intermediate data structure
of enumerated elements is constructed and `e`

will now enumerate over
that data structure.

These functions are lazy which means that they will create a new modified enumeration without actually enumerating any element until they are asked to do so by the programmer (using one of the functions above).

When the resulting enumerations of these functions are consumed, the
underlying enumerations they were created from are also consumed.

`val map : ``('a -> 'b) -> 'a t -> 'b t`

`map f e`

returns an enumeration over `(f a1, f a2, ... , f aN)`

where
a1...N are the elements of `e`

.`val mapi : ``(int -> 'a -> 'b) -> 'a t -> 'b t`

`mapi`

is similar to `map`

except that `f`

is passed one extra argument
which is the index of the element in the enumeration, starting from 0.`val filter : ``('a -> bool) -> 'a t -> 'a t`

`filter f e`

returns an enumeration over all elements `x`

of `e`

such
as `f x`

returns `true`

.`val filter_map : ``('a -> 'b option) -> 'a t -> 'b t`

`filter_map f e`

returns an enumeration over all elements `x`

such as
`f y`

returns `Some x`

, where `y`

is an element of `e`

.`val append : ``'a t -> 'a t -> 'a t`

`append e1 e2`

returns an enumeration that will enumerate over all
elements of `e1`

followed by all elements of `e2`

.`val concat : ``'a t t -> 'a t`

`concat e`

returns an enumeration over all elements of all enumerations
of `e`

.
In this section the word *shall* denotes a semantic
requirement. The correct operation
of the functions in this interface are conditional
on the client meeting these requirements.

`exception No_more_elements`

This exception *shall* be raised by the *shall not*
be raised by any function which is an argument to any
other function specified in the interface.

`next`

function of `make`

or `from`

when no more elements can be enumerated, it `val empty : ``unit -> 'a t`

The empty enumeration : contains no element

`val make : ``next:(unit -> 'a) ->`

count:(unit -> int) -> clone:(unit -> 'a t) -> 'a t

This function creates a fully defined enumeration.

- the
`next`

function*shall*return the next element of the enumeration or raise`No_more_elements`

if the underlying data structure does not have any more elements to enumerate. - the
`count`

function*shall*return the actual number of remaining elements in the enumeration. - the
`clone`

function*shall*create a clone of the enumeration such as operations on the original enumeration will not affect the clone.

For some samples on how to correctly use `make`

, you can have a look
at implementation of `ExtList.enum`

.

`val from : ``(unit -> 'a) -> 'a t`

`from next`

creates an enumeration from the `next`

function.
`next`

`No_more_elements`

when no more elements can be enumerated. Since the
enumeration definition is incomplete, a call to `clone`

or `count`

will
result in a call to `force`

that will enumerate all elements in order to
return a correct value.`val init : ``int -> (int -> 'a) -> 'a t`

`init n f`

creates a new enumeration over elements
`f 0, f 1, ..., f (n-1)`

`val count : ``'a t -> int`

`count e`

returns the number of remaining elements in `e`

without
consuming the enumeration.
Depending of the underlying data structure that is implementing the
enumeration functions, the count operation can be costly, and even sometimes
can cause a call to `force`

.

`val fast_count : ``'a t -> bool`

For users worried about the speed of

`count`

you can call the `fast_count`

function that will give an hint about `count`

implementation. Basically, if
the enumeration has been created with `make`

or `init`

or if `force`

has
been called on it, then `fast_count`

will return true.